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LECTURE NOTES

THE SAFETY ASPECTS IN THE INDUSTRIAL APPLICATIONS OF RADIATION SOURCES

PART I

Division of Radiological ProtectionBhabha Atomic Research Centre

Trombay, Botnbay-400035.

CON T E NT S.

Chapter.

I Basic Mathematics

II Elementary Nuclear Physics

III Interaction of radiation with matter

IT Interaction of radiation with living cells

V Biological effects of ionizing radiations

VI Units of measurement of radiation and radioactivity

VII Maximum permissible levels of radiation

VTII Radiation detectors and instruments

IX Kroduction and processing of radioisotopes

Bibliography

I . BASIC MATHEMATICS

1. ALGEBRA ' . ... . ,, \. _, . ,,..,.-.. • /•,.-. . ." ;Algebra may be thought of as a continuation of arithmetic in

which letters and symbols are used to represent definite quantitieswhose actual values may;or may not be known."' The signs of operation+,-, X ana j have the same meanings as. in arithmetic.

1.1 Example: (x + y)- + (2x - 3y)

x + y + 2x - 3y

= x + 2x + y - 3y

3x - 2y

1.2 Sxaiaples To fina the value of XYZ

if x = 5J y = 8 and z = 9xyz = 5 x 8x9 = 360

1.3 Example; (x + y) (x + y)

(x + y) (x + y) = (x + y)x + (x + y)y

2 2= x + 2xy + y

1.4 Examples (aX + bY) (cX + dY)

(aX + bY) (cX + dY) = aX(cX + dY) + bY(cX + dY)

= abX2 + adXY + bcXY + bdY2

= acX2 + (ad + bc)XY + bdY2

1.5 Example5 x^ (x raised to the power y) if x = 5 and y = 8

5 x 5 x 5 x 5 x 5 x 5 x 5 x 5

390625'

GTO:loo.31.8.76

1.6 Example:

1.7 Example: (xm)(xn)

1.8 Example: (x )m

1.9 Example: —•

(xm) (x"n)

1.10 = X °

1.11 nl or*

•5 I

31 = 1

1.12 Exponential

XCř —

1 IT may be any number

is called as n factorial

2 . 3 . . . . . . . .

1.2.3.4.5.

function

2.7183 . . . .

O.36788

(n-1)n.

'•-• • ' - . 1 - 3 . ".. ••-• - : • . ' • . • ' - : ; .

" •" -; '••'. = 2 3 - >• 4'v . ' 5 ••+ x ) = ^ ^ - ^ — - ^ - y - ^ - , . .

„(for a l l values of x£>i)

f or x = 1

log; « 1 —- + ' 3 ' - . ~ 4 ~ +

1.14 Solve x2 - 3xy - 2y2 . 4 (a)

4x + U = 5 (b)

irom (b) y = 5 - 4 x . . . . . . . .

Substituting this value of y in - ' , Jä.QpV

x2 - 3x (5 - 4x) - 2(5 - 4x)2 «• 4. ,

x2 - 15X + 12x2 - 50 + 80x - 32x2 - 4 + 0

• - 54 + 65x - 19x2 = 0

i .e . 1?x2 - 65x + 54' = 0

i 9x2 - 27x - 38x' + 54 = 0

19x2 - 38x - 27x + 54 = 0

19x (x - 2) - 27(x - 2) = 0

(x - 2) (19X - 27) = 0

. *. x = 2 or | ^

Irpm y = 5 - 4x

y = -3 i f x = 2

and = -13/19 if x = 27/19

2. LOGAMTEIIS . •

By the use of logarithms multiplication is reduced toaddition! division is reduced to subtraction, raising to a power iš 'reduced to one multiplication and extracting a root is reduced tö onedivision. ' ....''• '•.

•10°1Ö1

10,000

log 10,000-

log 1000

log 100

log 10

logO.1

log 0.01

log 0.001

= 4= 3= 2

and so on.

If = K

then b = log Na.

(logarithm of IT to the base a)

i . e . (Base) ° e = number

If xm = A

nx" • = B

(xm) (xn) = xffi + n

log (A.B) = m + n

= log x A + logx B

logx(A.B)

4 = log1 0 10,000 or 104 10,000

log (A.B.CD.) = logaA + lognB + lognC + lognD

, . .1-5

.1-5,;

I f -x m = A and ; x n = B

m: _2r_n

m - . n = logx(A/B)

log„A - log^B logx(A/B)

10000100

100 and 4 log 1 0 10,000

log x = log 1 0 ( i0 4 ) - l o g 1 0 ( i 0 2 ) ' - "log 4 ^

log , . ( 10* ) = 2

•f-x

If xm "=

logxA.

= antilog 2

l ü g x A

T /il/n

l o g / 7

. .1/n= log A '

2.9 log 2207 = log(i000) (2.207) = log 1000 + log 2.207

= 3 + 0.3438 (see tables)

2.10 Examples log 0.02207 = log j j ^ = log 2-207 - log 100-

= + 0.3438 - 2

i.e. = - 2 + 0.3438

2,11 To evaluate; 14.65(0.00362 x 8767)

U.630.00362 x 876?

log 14.63

log O.OO362

log 8767

14.63 x.

X say.

0.00362 8767

= log 14.63 - log O..OO362 - log 8767

= 1.1652

» 3.5587

= 3-9428

log O.OÖ362 + log 8767 = I.5OI5

log x = log 14.63 - (log O.OO362 + log.6767) = 1.6637.

or X = antilog (T-6637) = O.46I (from tables)

2.12 Example say N = a

log = b (1)

Mult ip ly

& (1) (log/)

(logjja) b x

. . . 1 - 7

Change of Base

2.3O26 logj i

log 1 Q e x log JT

0.4343-

Given x = log 48

loge48 =

= 2.3026 Iog1048

= (2.3026) (1,6312)

.*. x •= 3.871 .

2.15 Logarithms to the base 10 are knoiroi as common logarithmsand log to the bass ' o ' 2x3 knorra as natural logarithms.

.*. 2.14.can be evaluated directly by referring the naturallogarithm tables.

2.17Example:

log 10 = 2.302C & log 101

log 102 = 4 . 0 0 %s log 1ÖÄ

= 3.6974

= 5.3948 e tc .

log 684,7 •- log (6.847.x 10 )s s

= 1.9238 + 4.6052 (from tables)

= 6.52SO

2.18 (i) Activity of a radioactive material fa l l s exponentiallyand the mathematical equation is given belows

A = io ě

Where Åo is the activity at time t = 0- A is the activity after time t ?;and \ is the decay constant : L with;half .life: as.T 1/2 = 0.693/Xpf,T1/2 = 5.2 years and 7io s ;1000 curies, what" will-be the activity, after1 0 y e a r s , y , ; . , ^ , -.: ; 1 O t O : ' • • • „ • ••'"'.. :•',•:•>• •'•''. \, _ :\ \, •;•-'; •

A «=1000 ě II

.695a 1000 ě .5.2,

= 1000 é 5.2

• x 10

Taking logs

Log A * log 1000 6.95" 5.2 log e

5.000 - 1.53 x .4343

3.0000 - .5786 .

2.4214

Taking anti logs

A = 263.9 = 264,curies"-' ' *(ii) In case Ao = 1000 f^i.T1/2 =,5.2 year find-the required

time to get the final activity reduced by half.

5001000

-.693t/T 1/2

-—.693VT.1/2

Taking logs .

log .5 *.695t

T.6990

i 693t• 5

5.2 x• 4343

5_.2 *. .

6990693

• -inaes

.4343 x .693

= 5*2 years.

3 . TRIGONOMETRY:

If there is a horizontal l ine A.B and another l ine CD.s tandson i t ve r t i ca l ly , then angle BCD = ACD. each i s equal to one r ightangle . Each r ight angle i s divided in to90 equal parts each par t i s called a 1 - pdegree. Each degree i s sub-divided into60 equal parts each par t i s called aminute. Finally, each minute" i sdivided into 0 equal par ts and eachpar t i s calle^d a seconds 'Thissystem of division i s knom as sexagesimal system. .

1 rt =

60'(minute)

^' = 60" (seconds)

Circular system;

Draw a circle with radium equal to r.to the radius r. Join 0A + 0B.Then angle A-Q-B is called asone radian. In sexagesimalsystem one radian is nearly equal57 degrees and 18 minutes.

Cut in arc,-AB, equal

- ' .-.";-• _ /-:1,-'-" i - l o - • • • z - , : - - :, /[/•':. -'•'-. :í-.- " •••••-.

Angles are measured either in degrees;or in radians

2 right angles - 180 degrees = "ífradians . .

where 7 T « ".—-: =, 3-14159

For.cpnversionpetweeri degrees and radians ,: ' • " ' - ' • . " • " • " . • - ''-••-'.': • - • • • . " • - ' " • - " • . ' • . - - " ' - . V . - . . ' • - " • '

1 degree « 0.017453 : radian (i.e. 180 =3.14159

1° = 0.017453

1 radian 57.296« 3.141.59

: 18Ö •3.14159

1° = 60 minutes (601*) '

1' = 60 seconds (60")

3.3 A.B.C. i s a r i g h t ángíéáand angle B.A.C., i s equal to 0.and anglo A.C.B. is equal to 90*- L ,

- Now,

(1) (BC^ -opposite side() hyAB) hypotenuse

AOVAB)

,= ~- , , -^- is called the sine of the angle

(2) fAOVádnacent side(AB) hypotenuse

(BO) Opposite side(x\ (BO) OPPV} (ACTadj(AC) adjacent side

-z i s called the cosine of. the angle €.Cos ft

— is called the Tangent of the anglek - '•'•• .,.' Tan;©-

(4) AC_. "-'.: AB •:

is balled the Contangent fr of the"Cot %

i s called the Secants- -r : • Sec -0

is called Cosecant O ' " Cosce &

It may be pointed out that for a given angle such ratiosare fixed, whatever may be the size of the right angled triangle

3-4 Values of some common trigonometric functionss

STC/CEKKilco. 4 ix 76

ingles

Quadrant

trigonometric

functions

in different quadrants

Sec Cosec

f All +

¥ Sin +

' • ' " " ) " ', }"-~i"\

Sin (90-

Cos (90 -

tan (90 -

Sin (90 +

Cos (90 +

tan (90 +

Tan-©—

cot-e-

SinV +2

tan^- +

• • * ) =

» ) =

Cot2«

Cot-fr

Cos -e-

Sin-e-

-cot-e-

Cos^9*

Cps-9-

sin-e-

= Sec2«-

2>- = Cosec ©-

-.«);.-

-e) ,-

- e-) =

+ o) =

+ +) =

Sin;»';

tan ©•

-Sin".©-

-Cos •©-

tan -Ö-

Functions of sums and differences

Sin (A + B) = Sin A Cos B + Cos Sin B

Sin (A - B) = Sin A Cos B - Cos A Sin B

Cos (A + BJ = Sos A Cos B - Sin A Sin B

Cos (A - B) = Cos A Cos B + Sin A Sin B

t a n ( A + B)

tan .A - B)

1 - tan A tan B

tan A T tan B1 + tan A tan B

!lC0/4 ,1-13

Addition theorems;

Sin A + Sin B = 2 Sin

Sin A - Sin B ~ 2 Cos

Cos A + Cos B = 2 Cos

Cos A n Cos B = 2 Sin

Multiple angles;

Sin 2A = 2 Sin A Cos Å

Cos 2A

t a n 2A ••

A + B.2

A + B2

Cos2A -Sin2A

2 tan A„1 -• tán A

Complex exponential function

I = 1-1i 2 . -1

Cos A + t Sin A .

Cos A - Sin A+CA

Cos A - -§—_-±-

t/\.. -CA-§__

2 ~ ' •''

X «•'

A - B2 ,

,A - B2

A - B2

= e ( Cosy + i Sin y)

= e Cosy + e t S i n y

CVR;lco/4 ix 76,1-14

4. DIFEERMÉTIATION;

Let y be a function of a variable, x.: Let. A y andsmall increments in y and x respectively then the l imi t whichapproaches scro i s isritten as l imi t "£*—> ©«'and i s denotedby

A**- i e . derivative of y with respect to x. The process of findingthe derivat ive of a function i s called 'differentiations;.

f(x +& x)

f (x + A x) - y

f(x +A x) - f(x)

f(x + A x) - fix)—a _ —

I t - f(x)

Lt f(x +Ax) - f(x)dy.

4.2 Examples i) Find the derivative of the function of x

y +A (x + Air-

x + 2 x «-a

T 4- ? "V / ^ V

x + 2 x^nx

2x 2 S X

Lt 4udx 2 x

GTO:lco/4 ix 76

i i ) Differentiate y = Sin x.

y = Sin x

y + A y = si» (x -tJ&x)

y K Sin (x +A x) - Sin x.

Sin (x +J±.x) - Sin x.

2 Cos x_+A.x + _? Sin x +jQ_ x -_x

2 Cos(x + Ax)~ 2

Cos Sin A x2_

this becomes

dxCos x

d (sin x)dx Cos x .

The following table gives the derivative of some of thecommon functions: *

ilmction. ydx

axaeax

GVRslco/4 ix 76.1-16

1 •••<» •-? c"í .7.r- .-?

Function y

Cosec x

- Sin x2sec x

- Cosec x Cot x

Sec x tan x2

- Cosec xa* log a

4.4 Eotes; 1. •. If a function has an added constant, that does notappear in the derivative. „ .

2; If a function has a raultiplied constant, that constantmultiplies the derivative. •

Examples y = 2x + C where C is a constant

find 4xdx dx - ' • « •3. The derivative of a sum (or difference), is the sum

(or difference) of the derivatives.l ^

Example: y = —x— ~ —I— find - rx x5

- ex"5

4. If y is a function of V^and (A-is a function of xdy dy dudx = du dx "

Examples y .= sin(6 + 29*+ 7) find - ^

Let u - Oh + 26

then y = Sin u

dy = Cos u.du

29 + 2

dy dude-

Cos u (2Ö•'+ 2)

Cos(9- 2)

1) cosCe- + 2« + 7)

4 .5 . •

Differential calculus i s a very useful tool when the rate of»hange of a variable quantity, i s to be determined. For example, if anobject is moving, i t s speed is given by the f i r s t derivative and theacceleration by the second derivative. The slope of a certain curvedefined by an equation i s given by the f i rs t derivative. . Biffereritialcalculus is also employed to find the maximum and minimum in a varyingquantity. THe examples given below will i l ias trate some uses.

Examples! T. If tfee height of a ball a t any1 time t i s givenby the equation h = 72t - 16t , find the velocity and acceleration at anytime.

h = 72t - 16t

The rate of change of height is called velocity ie. dhdt

||. = 72 - 1.6 x 2t

ix 76.

The rate of change of velocity is called acceleration.

acceleration » rdh.dt

*. Velocity at any time« 72 - 32 t

A solenoid has a fixed internal diameter D and has alaminated core of the form shown in figure. Determine the dimensionss and t of the core so tha t the cross-sectional area of t h e core wil l bea maximum

Consider the t r i ang le A B. C.

AC = •£= D Sin I?'

BC, = s = DG'osM' . . , '

Area of the core i s given by

A = s- x t + 2 x t .. x -fs - t,,2 ' '

st + t ( s - t ) 2 • • • " • .

D Sin Ö-D Cos'4-' + D Sin •©• (D COS-©-- D Sin

A = D2 Sin %• Cos -e- + D2(Sinö- ;,Cos«) - D2

GVR:lco/6 ix 76. . . . 1 - 1 9

A i s maximum if •

1 - 1 9

is zero and

Sinoe A = D2(2 Sin©-Cose- - Sin2-©>

dA _2ď©- • D d (Sin2Ö-) Ji_ Sin

D (2Cos 29-- 2Sin9-Cos©^Q

D ( 2Cos 2©- - Sin20-)

= 0 (say)

Since 3 ) ^

i s a - ve

2Cos 2©- = Sin2©* = 0

2 = tan29-'

= 63.5 degrees (from the tables)

-e- = 31.75

ån- - Sin2©-)

— ^ . ~ m D ^ ( _ 2 S in 29-2 - 2 Cos2.©-)

= - D 2 (4 Sin2& + 2

.*• A i s naximum v h e n * - = 31 «75

AC =.D S i n 31.75 = (D) (0 .5262)

BC = D Cos 31.75 = (D) (O.85O3)

-v . • t *

. , - , - - \ - -T

_ ' — . . . C ~1-20

5. INTEGRATION;

Consider "the equat ion ,

y =?\,t(. - - * i i s rb ' im.rmixr.oi v i k , ' .

where C vis'"å-constant-"*". ••" • .• ;; '•

(fe.o) (a) -•dy = 30x dx

.TÍ: B op 'i Í= pa

OS-I . . If we are given the eqn

;v ' cdy = 30x dx' "

then y must bé given by the eqn

2 - 'y = 15x-,.,+.. some constant C

i e . 30x dx has now been integrated

The symbol.which demands the process of intearation iswritten as . : . - ,. . v

I . r , • 2 : • • - ' • ' •

i . e . J30x dx = I5x '+ some constant.

I t i s easy to see that intej^ation is the reverse processof differentiation... . .6 . . .

5.2 The following table "gives tfie integráteďvalues of certaincommon

Integral .function,. - r •• - fat.ggrated value

log x + c

:/6 ÍX 76

Integral function.

10. J5-2

I Cos x

Sin x dx

Seccx dx

Cos ax dx

Definite int

Integrated value

e x + G

- Cos x + C

Sin x + C

tanx + C

Sin ax + C• a

A log (x - r) + C

log a+ C

Definite integral as the limit of a sum

Let w&en. be a curve y = f(x). We are interested in finding the areabetween the x axis and the curve y = f(x) and between the lines x = aand x = b ie . area ABCD

We can devide the area into strips of finite width. The areaof each strip is approximately the area of a rectangle f (x. ) units inf t and t^x units in width. •-

. . The area under the curve i s approximately the sum of theareas of these rectangles. The more rectangles we have, the olosenthe approximation.

The area of one of these elemental rectangles i s

f (xi) dx in general

. . The sum of al l the-_e elemental rectangles betweena and x = b can be written

ie. = f(x.j) dx + f(x_) 4 x + f (x ) q x. to n terms

f(x) dx = Limit f (

Find by integration, the area of a circle of radius 10 cm.0

let us first find the area of the quadrant (see fig.)

Say, area of-the quadrant = ^ y dx

The limits between which we shall integrate are

x 3ST 0 and x = 10cm and

< 2 210 - x (from r t angle triangle OAB)

TrTOilco/6 ix 76 ,..1-23

How in

area of the quadrant =

(100 - x ) dx

Substitute 10 Sin©- for x

102 - x 2 dx

, ' . 100 - 100 - 100 Sin2O

y 100 - x2

100 (1 - Sin20)

100 0os20

10 CosO

Sin"1 -X-S m 1 p

10 SinO

10 CosO dO

-j10 Cos9- dx = 10 Cose-d©"

100 Cos2-© dB-(

50 2 Cos % dö-

f50 f ( i + Cos e-) dö-

50 Sin"

50 S p

T7T + 50 "

- X 2 / 1 0 0

1-24 jö

X\ dx 5G 10

50 Sin | | + 50 Sin1 + 50 f

+ 50 101 - 0/100

-150 Sin (1) + 0 + 0 + 0

= 25 I T

50 ~g- ( = radians)

, " . Area of the circle = 4 x 25 l|

= 100"TT ( ="TTr2 where r = 10 cm)

5.5 Example: To find the rate of disintegration.of a radioactivenuclide.

The disintegrations, from a radioactive nuclide are purelyrandom. Suppose there are N- atoms present at zero, time ie. when t = 0,then the change in-this number K in a short interval of time

^AC" V • » . cJí^X^^/ will "be proportional to the totalnumber present.

i.e The probability that a radionuclide will decayÍT

ie . .The probability that a radionuclide will decay = —z, / dtper see

For a particular radionuclide this is found to be aconstant. dH_-/ dt • \

GW:lco6 ix 76

( > •

'the constant of proportionality is called the trans-fornnation,constant. Since the no. of atomsicontinuously decreasing - vesign is introduced) K

Say at time t let then be N atoms left

.'. on integration

ie. log

ft • ť

_ _ X dit"

log IT -

Example:

g .=O"

, To find average life time of a radioactive nucleus.

lT is a small group of nucleus which decay during a timebetween t and t + ^.t, the coinbinded life time of this groupinterval

Adding a l l these life times for the groups of nucleur the decay during theentire time interval from t = 0 to t = COwe get

T = • dl = t dg

.". Dividing this by all nucliithe average life time ( =» TA say)v

initially present we get

dN Koe" ^ dt

GVR:lco/6 ix

A = _/V I t e

i d / e- >*

_ 1 _ ě X t at 1

I I ELEMENTS OF MIGIMK PHYSICS

History of the atomic concept:

The idea of atoms as the fundamental building blocks of ,matter was postulated by John Daltoa in the beginning of the, l a s tcentury. According to him, a l l matter was bui l t of componentscalled element's,: of which there were a large but limited number.The ultimate particle of the elements were atoms whicn were thoughtto be indivisible and unalterable. Atoms of.a particular element wereexactly alike but different from atoms of a l l other elements.

After the discovery of radioactivity by Becqueřel in .1896,and the electron as a constituent of matter:.bý' J . J . Thomson in 1897,the picture of the atom as hitherto supposed had undergone a completemodification. The atom as pictured by Eutherford and Bohr in 1913consists essentially of a central nucleus carrying most of the atomicmass and.a positive charge; t h i s . i s surrounded by a system of electronswith a negative charge, so that the atom as a whole i s e lectr ical lyneutral. The electrons move in orbits around the nucleus like the . .planets around the sun and thus the atom i s described as a miniatuřesolar system. - .

The electrons of the atomic structure f a l l into certainstable configurations or shells according to a sequence ofincreasing atomic 'number, e.g. the f i r s t of K shel l i s completedin Helium'with two electrons; the second or' 1 shel l i n Neon witheight additional electrons; and the third or M shel l "in Argon withanother eight electrons. All the. shells except the K shell, can beconsidered to be made'up of subshells. The outermost electrons i nuncompleted shells are óalled valence electrons and they directlygovern the phenomenon of chemical bonds. Elements whose atoms havegot ful l complement of electrons in their outermost shells arechemically i n e r t . The noble gases like Helium, Neon, Argon,Krypton and Xenon belong to t h i s group.

The Huclear structure: . ,

The atomic nucleus i s bui l t up primarily of protons(which:are positively oharged particles) and of neutrons- (whichcarry no eleotr ic charge but have almost the same mass.as theprotons). The electron i s a part icle which has a negative charge.The proton has a positive charge equal in magnitude to the chargeof the electron.- The mass ofan electron i s about 20ÖÖ times. . '''-smaller than that of a proton or a neutron andi s ' therefore negli-gible compared with the mass of fthe l a t t e r . The nimber of electronsorbiting around the nucleus i s always equal to the number of protonsi n the central positive nicleiis ,the atom is electrically, neutral .

cpd/mlp/31.8.76

II - r

Masses of nuclei lor of atomic components are specified interms of mass un i t s . One mass unit i s equal to 1.6598 x 10~24 gram.

1 Proton has 1.00759-,mass units = 1.6723 x 1O~ gm. „' - ' . ' - " . ' . • ' ' ' - " • " • '-' . • " • • * - '" "• — 2 4 - ' ' "

1 Neutron has,.1.00398 mass units = 1.6747; x 10 gm .* •••PS '

1' Electron has Ö.OOO549 mass units = 9.108 x 10 . gm . .

The number of protons in a nucleus equal to the atomic •number of an element, 2LdetenBines'its place in the periodictable . The to ta l number of protons and neutrons in^the nucleusconstitutes cthe mass numberfof the atom and'approximates »its atomic weight.

Hydrogen i s built up of one proton in i t s nucleus and asingle orbital electron. Helium comes next with two protone andtwo neutrons in the nucleus and two orbital electrons. Thestructures of some simple atoms are shown in Pig. 1.1.

Isotopest -

Considerably before the discovery of the neutron i t hadbeen observed that .there exist several species of nuclei of the sameelement. These atoms.are.chemically identical but baye differentmasses. The' term ^''isotopes" was suggested for such atoms.. • AÍL1isotopes of one element have nuclei of the; same nuclear charge, .because i f is íthé nuclear charge which determines the chemicalproperties of an element. The isotopes-, however,; differ in theiratomic weight. According'to our present ideas, a l l isotopes have .the sane number of protons.in the nucleus, but the number of neutronsis different for different1 isotopes. The structures of some isotopesare also shown in Fig^ Í..1-» . r . . ,,

The discovery of the isotopes gave the explanation why certainchemical elements have atomic weights which are not. integers. /Eov Iexample, the element chlorine was found to consist of two isotopesof atomic weights 35 and 37, present in the ratio of about:;3, to 1 i nnatural chlorine. This makes the atomic weight of naüural^chlorine 35.5.

Almost every element was found to .consist .of several .isotopes» liydrogen for instance has three isotopes., with atomic weights1, 2 and 3». However, the isotope with atomic weight 2,, called heavy -hydrogen or deuterium is. present.in bn3y.minute quantities, name3yonly about 1 part in 5000 of natural hydrogen.' -.Some elements havelarge number of isotopes; t in for instanos has 10. When.the.weights-of the individual, isotopes were determined, they were found to be muchcloser to integers than iiie ordinary chemical atomic weights had beenbut'even then they were not exact integers.'. ' • - . . .

opd/mlp/31876

^"™ «C^

!«"•

I I - 4

I t i s evident that ah atom.cannot be fully identifiedby. the respective chemical symboly but; the mmber and the_,type of thenuclear components should also be specified« Therefore a.common notationhas been .adopted for the atom. The chemical symbol carries a subscriptdenoting. the number of nuclear protons (or of orbital electrons).This i s called the atomic number and.chemically" identifies the element.There i s only one atomic number for. each element from 1 to 102 includingthe tränsuränic elements. The chemical symbol also carries- a super-script denoting1 the total nulnber of the. nucleons ( i . e . protons plusneutrons)» This'is the mass number and physically characterises theparticular isotope'. .

Isotopic masses are specified i n terms of the mass of 8atom whose mass i s taken as 16.000. The values thus expressed ares l ight ly dif ferent from chemical atomic weights which are based onthe t o t a l i sn topic msxture of oxygen (containing small amounts of

8 and 8 ) . The physical un i t i s about 0.02% le s s than thechemical one. Atomic mass u n i t therefore i s 1/16 of the mass

0 1 6 -24of 8 or 1.6598 x 10 gm. Table 1.1 gives a consolidated information

of what has been discussed so f a r ' i n tabular form. .

Z to K r a t i o sI t may be noted tha t i n the l igh t s table nucle i , number

of neutrons ;(N) i s nearly the .same SB the number of protons ( z ) .As Z increases , .N increases a t á fas ter ra te so tha t above Z = 20there are more number of neutrons i n the nuclei than, protons.Graph 1 represents- th i s v a r i a t i o n . This ¥/Z r a t i o roughlyindicates the s t a b i l i t y of the nucleus.

Dimensions of atoms and nuc le i :

The atomic and nuclear dimensions are exceedingly small .The diameter of the outermost electron o rb i t of the atom i s ofthe order of 10"8 cm and the diameter of "the nieleus i s of the

^-13order of 10~1 2

to 10 cm.

Haclear forces:

The neutrons and the prctons ore held together in ifaerucleus by some strong forces, the nature of which has beenthe subject of investigation. I t may be expected that theprotons would repel each other according to classical electro-static behaviour of charged particles. I t i s evident that thenuclear forces are neither electrical nor gravitational. Thepresently accepted idea is that there exist sc called

S.T.C./Ccpd/mlp/1.9.76

A./r-'

• f * .

"iff *

I ta feö To 9° Jelo i/o JXö

2 VoSc?, N . T U ^5^ L e . - * . te*

II - 6

exchange forces. I t i s assumed that a number of small sub-atomicparticles called 'mesons' exist within the nucleus which play animportant part in the exchange of forces.

I A B I I E - 1 . 1

Nuclear Nomenclature

Name Symbol What it means Examples

1 • AtomicNumber

NeutronNumber

Number of protons inthe nucleus, which is9.1s o the number oforbital electrons.

Number of neutrons inthe nucleus.

For hydrogen

For stable nitrogenN =-7

For deuteriumN = 1

3* MassNumber

4« Isotops

5.. Isobars

6. Isotunes

Number of nucleoné . .in the nucleus(protons andNeutrons)

Note that A = N + Z»

Nuclides h-iving thesame number of protonsbut different numbersof neutrons in theirnuclei

Elements having the samenumber ci nuclaons (pro-tons + neutrons) butdif fere nt numbers uineutr Abs and protc-nsin their nuclei, i . e .elements having thesame A but differentvalues of Z and N.

Elements having the samenumber of neutrons, butdifferent number of p r j -t->ns in their nuclei i . e .elements with the same N' sbut different Z's and A'si . e . (A-Z) = constant ina l l such eltaents.

For stable nitrogenA = 14

For deuterium•!--. A = 2 ,

o12 c13 u6° 6° ; 92U

92Jü".238

»40 ,41

all having 12neutrons•

S.T.C./C.cp.l/mlp/1.9.76

II - 7

Table 1.1 Ccmtd.

Name Symbol What i t means Examples

7. Isomers Niiclides of sane, elementhaving the same mmnerof protons and neutronsbut in different energystates.

Radioactivity;

Closely associated with the discovery of X-rays in 1895 byWilhelm Conrad.Roentgen is the discovery :f radioactivity byHenri Becquerel. \7hile investigating certain substances whichomit fluorescence ;n exposure to sun light, he accidentally discoveredthat a compound of uranium emitted some invisible radiation even withoutexposure to sunlight and that fluorescence had nothing to do with thephenomenon. 5he study of a large number of such substances was pursuedby Madame Curie and the term "radioactivity" was given to thisphenomenon. She investigated systematically the known elements andcompounds and i'.yand that al l compounds of Uranium and Thorium, and noother substance possessed this property. Birthermcre, she f jund outthat et-.iae of the natural ores nf uranium were much more active thanthe eleaent itself and therefore concluded that they must contain ahitherto iM&nowa radioactive eLvaent. iChis led to the subsequentdiscovery of the two elements, radiura and polonium.

£hus t»he phen-aonan of 'tiadioaetzttiCii*" can be describedas a spontaneous end self čAan;p?^v€ýactivity exhibited by several'ofthe heavy clensnt^ •:.•£ atimia vteigí5& greater than 20c, occurriEg innature. iChe result of..ttis is the.breaking up. of the nucleus itselfi»a.: an irreversible .«if disintegration». The aft^ivity is spontaneousin the G6E39 that Ac arises aoltly from'the intrinsic natural causes,unaffected by a^T external, agent, physical.or chemical» Theactivity consists in "tiie emissi m of complex type of radiations.

All these radiati>ns were thought to be alike, differingon^- in penetrating power and l i t t l e was kn-jwn of their individualnetitre. Eut later researches ly.Becciiierel, Pierre Curie and Villardproved the existence <f three quite distinct types of rays. Thiscan be demonstrated by a simple experiment, illustrated in i lg . 1.2

y.c/o.:,/inlp/i.9.76

..-•/,--^-.-.i-p ,-

%\ \-X

O ' \ fc

X C Í I Á O

II - 9

A radium preparation is kept in. a lead block wherein a small hole. Í8drilled to allow a collimated beam of the rays and the whole thing i senclosed in an air tight container which carries ä photographic plateat the topi If a magnetic-field is applied at right angles to theplanes of thy figure and directed away from -the reader, then there willbe a Mackening at three places, on the photo£raphic film afterdeveloping) thereby proving_the existence of three different types ofradiations« The one on the left lyin& on thfc arc of a circle oflarge, radius must have been made by one group containing positivelychstrgedpsrticles^Df^cp.mparativeQy heavy mass» "This heavier, componentwascalled the alpha (oC)^raUiátionf~orlm;jíe,properlyparticles»The- one on the. right situated also on the arc of ärcirele'-af-a^iauch ..smaller radiusj ..must have been trade by a second feroup, of particlescalled beta raysy^of negative charge and of very light mass t Thethird central trace must have been produced by rays which, areuncharged and hence undeviated by the magnetic field» These rayswere identical with those emitted by an X-ray tube and were calledgamma ( Y ) rays •

Modes of Radioactive Decay:

Radioactive decay, whether natural •_£• ar t i f ic ial , can occur \only in a limited lumber of ways (1) Alpha decay (2) Beta decay(3) K-electron capture or (4) Positron emission» However the f i rs ttwo nudes :,f decay are the ones trust commonly observed» I t mayalso be noted that in a number of cases the decay process i sfollowed by £ amma ray emission.

Acc-jrdirg t.. the Buhr1 s liquid drop m^del, the nuclfco' .TVSart distributed inihe nuclear volume just as the atumsof aliquid arc. únif-'roly distributed in a drop of liquid. Thesenucleons are in a. constant state ,t motion insider the. ňucle.trs(within -üie radius of the nucleus), and keep »acolliding; witheach :ther. In the stable (ncn-radijactive nucleus), a l l those havetht same energy. Radioactive nuclei however,, have; a certain excessof energy, which a nicleon or gruup of mclec-né occasic.rialtysucceeds in capturing, and thereby escapes frrm the nicieus thusresulting in radioactive decay. If all the extra energy is not utilizedby the escaping particle, the nucleus mqy. be left in an excited statefrom which i t will recover by the emission of a gauma ray, returningto thej ground ...r the most stable condition.

S.T.G./C.cp«3/mlp/i.9.76

I I - 10

1• Alpha Decay: >

Án alpha particle i s the nucleus of a Helium atom and consistsof 2 protons, and 2 neutrons» Disintegration by alpha emission occursonly among the heavy, nucliděs:which are naturally radioactive (z^83).There, are. also a few artificially produced "alpha emitters with eithervery lorig er short half lives i The atomic numbers of these artificialalpha/eraitters lie between 60 and 85«

, ' The resulting daughter rucleus after alpha decay, has an atomicnimber less by two and a mass number less .by "foiir than the parentnucleus. As stated before alpha emission i s usually followed bygamma emission. ••,•>•••!

Alpha, particles from a particular isotope have a l l the sameenergy or.energies distributed in discrete monoenergetic groups»Since particular groups of alpha particles are monoenergetic,members of the same group willJSayg...the same range, in-air or in anymedium. The range of an alpha particle depends,on i t s energy andit, is given by the empirical relation, R = b E3/2, (where b is a

' constant). . . •.•.-••

Alpha rays :

1. These are positively cherged par t ic les each haying a massabout .four times, that of the hydrogen atom and carrying two unitsof positive charge. They are identified with the nuclei, of Helium ,atoms stripped off t h e i r orbital electrons, and represented as „He

2. . They produce fluorescence when they strike certain: substances»When the fluorescence i s examin&d with a" low-power microscopé, i t.will be seen that i t consists of á ser ies of scinti l lations» whichshows that' th'e alpha rays consist of discrete particles»,

4* • When alpha p a r t i c l e s pass through matter, they causeionization (process of removing or adding electron to neutral atom).

5« Alpha part ic les are unpenetrating and they cah be stoppedeven by a thin sheet of-paper.

S.T.C./G.cpd/ialp/2.9.76

II - 11

2. Beta decay and positron decay:

As electrons are not Gonstitttents of the nucleus, i t isassumed that electrons are created and ejected in a radioactivetranaformation. Negative, and positive electrons are believed tobe created by the following transformations.

n-~—7? p +p (neutron-proton ratio high)

p •__»y n +/%(neutron-proton ratio low)

B emission is not as common as B™ decay; i t occurs mainly inelements of low atomic number, ana is not found above the atomicnumber 79» Some nuclei which are close to thefistability lineshown in graph 1 decay in.both ways (e.g. 29<*i * ) , The productnuclei from fit" or /^disintegration have the same mass numberbut different atomic numbers.

The. energies of the emitted beta rays from a given radio-active isotope are not the same but are distributed over a continuousenergy spec-trun as shown in fig. 1.3» There is a definite majcimumenergy associated with each beta emitting isotope and is denotedby 53 • But in dosage calculations i t is the average energy E

maxthat trust be used. E •enipirically is taken as E

av • max

avTable 1.3

shows a list of the most comnonly used isotopes in medicine withtheir maximum and average energies-

Energy, " (MeY)

1 . 0 •,..

S.T.C./C.cpd/mlp/2.9.76

Typical Ranges .:

Ii E 1.2

Ln Air and Water of Alphaparticles and Electrons

Alpha .particleIn air .. '•

(centimetersj

' . : • . " • - " • .

Range . :

In Water, .-_"(mi'cr.ons)

. Electron Range'; In Air '

(meters)

' 10.0

In Water(centimeters)

II - 12

Isotope

6cu •

Cs-137

Au-198

1-131 ,

Sr-90Y-90

T A B I

Some; 'beta-emitters ,

• •Half.'life:/

5600 yeara-

30 years

5.3 years

2.7 years

8 days

2.33 hours

20 years

14.3 days

&, the ;_Wüa particle energies

Percentagedisintegration

855 •92$

18$2A362 3 ^20JŽ15JÍ

" '100%100$

• :• -max-,MeV

Ö.155

1.170.51

1.370.96

0.6070.3290.255

2.121.531.160.900.73

0.532.25

E•'MeV

0.200.93

The fact that a l l ' the beta particles from a given isotope do notposses the same energy indicates that anointr^particle mustbeinvolVBdih. the ertergy exchange. :;,Ťhis particle was called the, neutrljajand'was shown theoretically to be a particle wi.th. practically zeroaäss..arid no-charge. I t could.not- however, be'detected experimentally

_on .account of the fact, that i t rarely undergoes a nuclear interaction»I t was only in 1958 that-i t was detected for.! the f i r s t "time byelaborate techniques with large scinti l lat ion detectors.

Beta rays:

1. The beta rays are negatively charged particle's and areidentified-with electrons. •

2. Their velocities are of the order of 90 - 95$ of thevelocity of light.

S.T.G./C.cpd/mlp/2.9.76

II - 15

3. The beta rays have a range of few meters in air (Table 1.2)«

4- These also ionize gases asdooalpha particles but, the ioniza-tion is less intense compared to that of the latter. This is becauseof the fact that the beta particles are lighter. Ťheyare easily-deflected in a magnatic field.

5. Beta rays are comparatively easily absorbed in matter,their penetrating power depending mainly on their energy and onthe density of the absorber.

Th&. emission of a beta part5.cle may or may not be accompaniedby gamma rays. If the electron and the neutrino together utilizeall the disintegration energy, gamma rays will not accompany the betarays. If the nucleus retains some excess energy, it will be emittedalmost immediately,in the form of gamma rays.

3« K-electron capture: • '

This is an alternative to positron emission. In this modeof decay, the nuclear proton is' changed into a neutron by capturingan electron from the k- . orbit. The condition, that the nucleus hassufficient excess energy so that the criterion that the mass of theproduct nucleus is less than that of the original nucleus and tj eelectron is fulfilled. Here the atomicnumber of the compoundnucleus is less .by one than that of the parent as it will have thecorrect number of orbital electrons with one missing in the k-orbit. An electron from the outer orbit will subsequently fallinto the k-'... orbit with the emission of k characteristic X-raysof the new atom. . 'Internal Conversion:

This.is a type of internal photoelectric phenomenon.When, the gemma, energies associated with beta or alpha.decay arerelatively low the decay is accompanied by)internal conversion.The gamma ray ejects one of the orbital electrons of the atom, with.,an energy equal to the difference between the gamma energy and thebinding energy of the electron. When the vacancy left in the atomicshell is filled by all electron from another shell' X-rays are emitted.It is obvious that when internal conversion takes place, the number ofprotons and neutrons in the nucleus remain the same.

S.T.C./CCopied:mlp«2.9.76 ... 11

„X...

I I - 14

Muclear isomers t

In some-cases, the excited state of a nucleus persists,for an appreciable time;.; From,'this métástable state,, i t ,can eithergo to ..the 'ground state of ;energy or decay into, some other, nucleus,ihere is :i f inite half l i fe (.fraction of a second to several-months)associated with this" decay. The nucleus :in metaštable state is anisomer of the ground state nucleus. The energy may be completelytake-up by the gamma, rays, or part, of i t may undergo internalconversion with emission of conversion electrons. . " , ••'•;-':

. Some of the typical beta and gamma decay schemes are:indicated, in,fig.1.4. Some typical älphä,dec&y schemeda£e. showni r r f i g . i . Š i ^ " ; : ^ * W - • * '•" . , . '••'-'] _ i f \)_ - '"/'; > : . " • _ ; •

• B a á i o a c t i v e

Prom a. s ta t is t ical study of radioactive decay,' rfc hasbeen shown that the number of disintegrations occurring in.unittime is proportional to the total number of radioactive-atoms1

present and i s given by . . . •

... ä F ; ' 1V

Oh integration, this gives

. . . (1.1)

(1 Í2 )

where N represents the ini t ia l number of atoms of a-radioisotope;andlíT represents the number of atoms present at any time t . . The .constant of proportionality ( ) is called the radioactive decayconstant of the isotope. Equation (1.2-) is often called.the,exponential decay law. If this value is substituted'bäbk into '•__Eq..- (1.1),,the number,-of; disintegrations per unit time becomes

. . . (1.3),

This quantity dN/dt is called 'act ivi ty ' (A) . -AS could be seen if romeq.uation 1.3» activity decreases-exponentially and this decreaseis represented by. . . ' \ ' '

Since the activity of a radioisotope includes-factorsother than the quantity and nature of the isotope present, we shallfind i t more satisfactory for quantitative work to deal with the actualnumber of radioactive atoms present and the rate at which decay takesplace.

S.T.C./C. . . . 12Copied»mlp:2.9.76

H II -.16.

Half Lifet

In actual practice, the decay.of a radioisotope is usuallygiven in terras of its half life, the time required for one-half theatoms originally present to decay. Setting N : W o / 1 and t = tt in Eq.(i.2)

« •

This important relationship correlates the half life and decayconstant of a radioisotope. Note that in a tine equal to one half-life, the number of atoms and the original activity will he reducedby a factor of 2, at the. end of a second half life the number ofatoms and original activity will be reduced by a factor of 4« theore-tically, it requires infinite time for the complete decay of aradioisotopem, although in most cases» a time of about 10 half liveswill reduce the "activity to a negligible value.

Average life:

. The average life of a radiqisotope is larger than thehalf life because the average life takes into consideration thoseatoms living through several half lives» The average life may bedetermined by summing the time of decay of each radioactive atomand dividing by the number of radioactive atoms originally present.Thus

. No NoThis can be integrated by parts* to give

— j >Thus the average life is greater than the half l i fe toy a factorof I/O.693 = I.44. .

T=Ut _. • ••• \1•&)

Hote that in a time intervalTt radioisotope will decay toi/e of i t s original activity.

*"ote that in substituting the upper limit, the indeterminste

is obtained. ^"roa elementary calculus, i t can he shown thatthis quantity approaches zero as á l imi t . . .

S.T.C./C.Copiedsmlp:3.9«76

. . .13

X,iii\

— 1 —t!i V*

. - --

• • : " . ' • : • -

II .- 10?

Example *

Hadon gas has a half life of 3.82 days. What is itsradioactive decay constant? lhat percentage of the radon atomBoriginally present will decay in a period of 30 days?

Solution From equation (i«5)» m Tto " •18"' day"'

99*562 pér cent of the atoms originally present will decay ina period of 30 days. . -Chain decay:

• ; In many cases, the decay product of a radioisotope isitself radioactive. Is the parent isotope decays, the daughterstarts contributing to the activity and, depending on their decayschemes and half lives, there may lean increase in the totalactivity. Bat eman has developed equations for solving the activitiesofL •• ^j ä a radioactive-chain of"anylength, provided that at zero J

. . only the" parent'lisotope is present. Thus if we consider thechain \

then the number of atomstime is

of the nth member as a function of

-Ue ; •+ . . . . (1.8)

where C =

of parent radioisotope present at zero time.If some of the daughter products are present at zero time, thegeneral solution can be obtained by summing Bateman solutionsfor an n-nembered chain, an (n - 1) - nembered chain using the•second radioisotope as parent, etc .

S.T.C./C. .14

II - 19

For example, if we consider the case of a chain of tworadioisotopes decaying to a stable product, for. the first memberwe have simple exponential decay

and for the seoond member

....(1.9)

. . . (I .IO)

Transient and secular equilibrium t

The relative amounts of a radioactive-parent • anddaughter preset depend on their relative half lives. If theparent has a longer half life than the daughter ( T ř Jo. O* i-CAi. )after a certain period of time gT^'s-*:" ^s negligible in comparisonwith ~)Mt and Eq.(1.10) reduces to

....(1.11)

substituting the value of Wo from Eq.(i .2). This is known as transientequilibrium. Since the ratio of the amount of daughter to the amountof parent present is a constant, although the absolute quantities ofthe two .radioisotopes present are continuously decreasing with timeat a rate detennined by the decay constant of the parent. Pig. 1.7»i l lustrates graphically a case of transient equilibrium.

• ' ' • • ' • . • ' • " • ' - • • " : • ' . " • ' , ' ' • . " - . . ' • • • .

If the half life of. the parent is very long, as in thecase of the naturally occurring radioisotopes which are members ofuranium and thorium, series then is negligible in comparison with thedecay, constants of all the descendants, and,

/1,1V, ' - ^ N ^ . (1.12)

This is known as secular equilibrium or radioactive equilibrium,and it is illustrated graphically in fig. 1.8. In secular equilibrium,the amounts of all radioactive products present are, inversely propor-tional to their decay constants or directly proportional to their halflives. Since" V\ is very smajl> |v« is essentially constant and theamount of any daughter present per unit weight of the parent willalways be a constant at equilibrium.

S.T.C./C.Copied imlp13.9.16 ... 15

i * if

o-. v>

< x •

': '""'",

- • -

i • '

Ví - y

..v...,

I I > 22

If the half l i fe of the daughter is longer than that ofthe parent (\ j > ýx /, no equilibrium is attained, and as an in i t ia l lypure parent fraction decays, the. amount of the daughter r i ses, passesthrough a maximum, and then decay? according to the half l i fe of thedaughter» •

In some cases-.we are interested in the time tff i re uired forthe daughter to attain its''maximum activity in a. freshly preparedparent fraction. '- his can be found by differentiating Eq.(i.1O)and setting the differential equal to zero to give.

)(1.13)

Radioactive Series? ' -, • •" \

Badioact.ive substances can be divided into two groups.1) Eaturally. occurring radioactive,substances 2) -Artificiallyproduced radio-isotopes. The ; naturally occurring radio elementsof high atomic weights at the end pf the periodic jtabie fallinto three distinct groups. These are known as the ThoriumSeries, the Uranium Series and the Actinium Series* The massnumbers of the individual elements.in each' of these series can berepresented by 4n, 4 n + 2 and 4n + 5 respectively, ň being an integer.The three series are named after the longest lived members in eachof them. Figure 1.9 shows'one such series.

It will be seen that there is. no natural radioactiveseries of elements whose atomic weights are represented by 4n + 1 .However recently a number of elements belonging to this serieswere produced artificially. The fact that they do not exist innature is explained when one considers^the relative half lives ofthe various elements in this series.•. This artificially produced4n + 1 series has been called the Neptunium aeries.

Miclear Reactions8

The principle of radioactive isotope production is basedon the interactions between nuclear particles and the^stable nucleiof the elements. These interactions or nuclear reactions are similarto the ordinary chemical reactions in that they have a heat ofreaction (mass change) and an energy of activation. The completeequation for Butherford's first nuclear reaction may be written as

»1+ 2 Q

S.T.C./CCopied:; 16

P a '•

i t * — ~ " * % < i ?

\t-Tl Sil &

: ... -

- • '

/t'ř9r

• •" Ah.

\7H-« s .

1 1 - 2 4

where Q represents the energy change. If Q is positive, energy isreleased, and if Q is negative, energy is absorbed. The f i r s t type,of reaction is called exeergic and the second type is called endoergic.This energy change is based on Einstein's mass and energy relationship.

E = Me2

where s is the energy in ergs equivalent to a mass of M grams,c being the velocity of light ^2.9976 x 101"cm/sec).

A nuclear reaction proceeds in two stages. In" the firststage an unstable compound nucleus containing both the target andbombarded particle is--formed and this is followed, very promptly by arearrangement to a more stable.state, with the emission of'energy.It is convenient in writing nuclear reactions to use an. abbreviatedform in which the target .nucleus is indicated first, followed byparentheses containing the bombarding particle, the expelledparticle next and finally outside the parentheses the product nucleus.Thus Rutherford's first, transmutation reaction can be represented as

Mechanism of nuolear-rXeaptionst

The nature of nuclear reactions has been elucidated byProfessor ^iels Bohr. The target nucleus constitutes a systemlike a drop of liquid, since it contains many particles, (protonsand neutrons) among.which the total energy, is distributed more or lessequally and among which there is a constant interaction. Theimpinging particle, on such a system, distributes its' kinetic energyand binding energy equally among all the nuclear particles so thatthe compound, nucleus is raised in energy content. The stage of thecompound nucleus is no longer dependent oii, the way it is formed andcould: have been produced by any other particle, with correspondingenergy incident on a suitable nucleus. Its decay into, an emit tedparticle and a residual nucleus is thus independent of what happenedbefore.

Yield of a nuclear reaction: ,

. . . The yield in.a particular bombardment depends on the numberof bombarding particles and the number of nuclei,and on some factor /targethaving to do with the probability of a collision. -A target area orcross' section is assigned to each nucleus for each type of reactim.The cross section , of a nuclear process is the portion of thebeam area of the bombarding particles which is removed by the process

S.T.C./C. . . . 1 7

II - 25

i n question vflien the beam is incident on. a single target nucleus.If a very thin, element of .target, dx cms thick, isexposed to abeam of partioles with intensity I , where I i s the number cfparticles tfer,unit area of beam, the diminution inbeamintensityai -brought about by the process with cross section Q""" i s given by

:: a i > CT"-M,I dx where N is the number of target nucleiper unit volume ;(1 cc) "and the cross section in sq^ ems.(The cross section i s sometimes measured in barns, one barn being

equal to 10~ sq« ems.)« This expression can be integrated in thesame manner as that for radioactive decay and yieldsj

J-0 ' *

If I is the number of particles passing completely through thetarget, the no. of particles absorbed and used up in producingthe nuclear reactions i s

- N— e

Muclear reactions are commonly produced by. various types ofbombarding particles like the neutron, neutron, proton and so on.Huclear reactions are usually denoted by (n,p), (n,*O, (« .»p)?(d,n>, (d,cO, (p,n), (p,o() etc, .

Artificial Radioactivity} .

Many elements which .disintegrated under álpfia particlebombardment, gave rise to stable products, .fy'nee the bombar dingparticle s.ourbe was removed, no. further particles .or' radiations wereobserved. vHowevtr, bombarding aluminium^ With alpha particles Gurie-Jo'liot observed that .even-after the".alpha, source was'removed, theirradiated aluminium^foil continued to emit some kind of radiation,which decreased exp6nentiailyi,;with time« Apparently as radio activesubstance had'-'-been.-created. '•••.,... ''.

,2713 + 2

This announcement was followed by a search for other isotopes whichbe produced art if icial ly. ; . ' .;

* A STAR indicated the product i s radioactive«.

S.T.C./G.cpd/mlp/6.9.76 .26

I I - 26

Energy considerations;

Por any of the nuclear reactions to take place certainconditions oust exis t . ' The mass of the two reacting particles plusthe mass equivalent of tht kinetic energy of the bombarding particleraist exceed the mass of the resulting products. All bombardingpart i ©lea mist have sufficient energy to surmount or penetrate thepotential barrier. The higher the atomic number of the target thegreater, is the potential barrier. For instance, the bombardment of

,,A1 by energetic neutrons may result in any one of the following

reactions. ' ' '

(n, r ) i 3A:

,2711Na

3 4 127

(n,2n) 13A 126

In general the simpler reactions s tar t at lower bombarding entrgiesand produce better yields. . .

Huclear fissiom

We have seen that in order that an atomic nucleus shouldbe stable, the rat io of neutrons to protons must-lie within certainlimits. For l ighter nuclei this rat io i s nearly unity and i t goes

._ on increasing slightly with the atomic number of the nucleus, ibrUranium this ra t io i s about 1.6. If the ratio pf neutronsto protonsi s very much different from the rat io for s tabi l i ty , the nucleusis . unstable an'! has a tendency to approach the stability, ratio •I t can do this i n one or two, -way a»J?irstly,; i t .nay emit alpha or betaparticles or undergo K-electron capture, thus exhibiting radioactivity.

In certain other cases a new. phenomenon known as nuclearfission might take place. For instance when a uranium nucleus capturesa neutron, i t sp l i t s into two almost equal,fragments, which flyapart with tremendous energy. This ^splitting of a nucleus into twoor more nearly equal fragments has been termed fission. I t wassoon found out tliat the nucleus which underwent fission was mostly the235 isotope of uranium and that slqw neutrons were more effective incausing fission of Ü-235 than fast: onešv- íur/ther, besides the twofission .fragments^ 2 to 2. fast" neutrons were álao released in.thepracess. Neutrons above thermal energies also .ta^ed'|íis,Í3Íoii /in.U*235, but the probability for this process i s ""email.' .

S.T.C./C.

cpd/ialp/6.9.76 .27

I I - 27

Slow neutrons are readily: absorbedin U-238, but those are incapableof causing fission. This slow neutron absorption produces the unstableisotope 239 of Uranium and we shall have occasion to study i t s lifehistory later. Past neutrons cause fission in U-238, though the•probability for this reaction is small.

• -' Since fission-is caused by neutrons and the process i t se l fgives rise to 2 to 3 neutrons,, which may again cause-fission in uranium,the question arises as to whether a mass, of natural uranium can main-tain a self-sustained chain reaction. The answer is no. Because ofthe presence of" about 99.3$-'jf U-238 isotope, in .natural uranium, whichabsorbs neutrons but does not necessarily undergo fission, too manyneutrons are removed from the system without creating- new-ones. Huwever,if one' could separate U-235, a chain reaction could be obtained. Ifthe mass is too small, a large fractijn of the neutrons may escape outcf the system and few may.be lfcft'-f.T absorption in uranium* Since onemay expect the fraction cf neutrons absorbed to be roughly proportionalt ! the volume of the.systen and the fraction leaking out, to the surfacearea, we can increase the relative absorption by increasing the massof the material. The volume that wiil just" maintain a chain reaction isreferred to as critical volume and the corresponding mass of U-235as the cr i t ic? ! massi

Slow neutrons are highly effective in causing'.'fission i'nU-235. In oase one wanted to establish a chain reaction using naturaluranium, the only possibility is to increase the relative effectivenessaf U-235 by slowirg down the fast neutrons emitted in fission. When ahigh energy neutron collides with any nucleus, i t loses-some energywhich is inversely proportional to the nuclear mass. A neutron, therefore,may be rapidly slowed down by collisions: with, nuclei of. low atomicweight like H,D, Be or 0. Foť :example, a neutron, on the; average losesabout j^' of i t s energy in a single collision with H; while in the case ofC, the energy of the neutrons. gpe,s down by the same factor of e(e=2.7183),in about 6.3 oollisiqns. The medium which is used for slowing down,theneutrons i s nailed the moderator. When a neutron has attained thermalequilibrium with the: atoms of the. moderator, i t is referred to as athermal, or slow neutron. It3 most prqbable energy is kT ergs., wherek i s the Boltsman Constant and T is the temperature of the moderator,on the absolute scale. . . '

Thus to get a self-sustain<g chain-reaotion with naturaluranium, one mist háve, in addition to. the fissile material (or fuel)uranium, some, material for slowing down the neutrons,, i .e . a moderator.Any assembly of fuel and moderator or pure fuel (as.in the case ofa mass of pure U-235 isotope) whioh is capable bf -maintaining acontrolled self-sustained chain reaction i s called a reactor or a pile.I t turns cut that a homogeneous misture of

STC/CCopied:mlpi6.9.76 . . . 2 0

1 1 - 2 8

ria"€ural uranium and graphite,;will nut sustain a chain reaction,while a heterogeneous assembly willeustairi one. Such, an assembly*i s realised ,tý..having uranium, rods or .blocks;embedded itt„á graphiteb l o c k . '"• ' • ••- • -••'• : •'•' • . • ' • ' ; - " •"-•"-•.' :.•• \ . V ' w . i W . _ V . : . ^ ; , ' - :

Reactors can in general be divided into various categories..A) Thermal reactors, B) East reactors, o) Power reactors. .We shallnow deseribe a few reactors inorder to i l lustrate the principles onwhich Their construction i s based. Apsara, India 's f±rst;reaetor i sa reactor of the thermal type. I t makes use of enriched uranium asthe fuel. Water which is used as the moderator/for.thermalisinM fastneutrons,."produced in the fission of U—235,: also „serves*"as''-a coolant and iálšb^asa radiation shield. The thermal "neutrpri f lux at the edge of thecore is about"3'X'1Oi3 neutrons per square cm. "per seeond.when the operatingpower i s ÍOO kw. This reactor i s rbeing used for research in íundámantalnuclear physics and also for the production of radioisotopes for industrial,agricultural and medical applications. .-.-_;•->• . '.•-.'•

Another reactor known as' . Zerlina i s designed;tuoperate at a maxinum power leyei of 100 watts.. / I t Till>be usedto carry out studies relating to new fuel configurations.'. Herenatural uranium i s used as fuel and heavy water as the/moderator.

The thi rd reactor i s the Canada India Reactor. Herethe maximum heat out put i s 40 mega watts. I t makes use of naturaluranium as fuel and heavy water as the moderator. I t s ..principalu t i l i t y will be the large soale production of rädioisptöpes.

üast-3y before constructing a power reactor, the design should be such "that maximum.beat....transfer takes

place frqm the fuel elements-to theheat'exahangers.

Production of. Radio active Isotopes;

Radioactive isotopes became 'available as a result ofthe development of maij*ÍEtn. reactors • In: the niclear reactor orpile,"the :fuel rods of a fissilie material, -for exam- pie. U-235 areirradiated with neutrons. A U-235 nucleus on capturing a. neutronbecoiaes so unstable that i t disintegrates forthwith .giving two"fission fragmente together'with two or three more neutrons whichmay be captured by other U-235 ruclei so that the process continuesand a chain reaction i s set up.. At the same time a considerableamount of .energy i s produced..- Any neutrons over and;-, above thoseused up .in.maintaining the chain-reaction are available\for otherpurposes-, suoli as" the production of radidisotopes by neutronirradiatian.

STC/C0opied:mlp:6.9.76

. . .29

I I - 29

The fragments resulting; ířpis the. fission process occurringin a reactor consist, of the nuclei.of 'elements occupying;"the;.-middleportion of the periodic system. They are highly radioactive, and.since they are'.formed in the urenium or other nuclear ..fuel elementsthey can be extracted chemically in the "carrier, free" stalle.

Most.of the fission fragments decay to form daughterprpducts*which are thec'aelves radioactive and these in turn decay bybeta emission •'. _ t i l l "She final stable element is'reached«The fission products include some. 200 radioisotopes* with half, livesranging from' a fraction of a second bo reveral years. .

I-Í31 which is probably ike most widelyussd radioisotope inclinical work i s derived from i'o-131 which i s a fission product. The"two noble .gas isotoper Kr-85 and Xe-133 may easily be separated from thefission product mixtuve and thus be readily available«

There are three main ruolear. reactions for the -production,of isotopes, i n a reactor« ' . '

i ) Tiie simplest one i s the (n,Y) pron^ss where a neutronis captured by the target nucleus to form Em isotope of the sameelement and at the.same time a 'Y 1 rev ic etnitted. Ha-24 i s normallyprepared in this mannsr by irradiating the naturally occurringNa-23 thus:

- 2411r,£ n 11

The cross section for the reao'jion Is iaiTlr high. As the productnucleus i s an isotope of tha target nucleus, i t cannot be. generallyseparated oheoicallý. f?he specific activity obtainable by the(n,V ) reao.tion :'.s

2) (n,p) and (r..,c<.) recotfoua:

• 2hei"9 are booe u.i.clear reactions where the neutron i scaptured followed by the emiccion of á proton_oi an glpha part ic le .The target nucleus therefore loses one "oř "two units of electrioal oharge,thereby altering the atomic numoer so that the product i s a differentohemical.elemen-j!. Shis can be íreparcited by chemical methods from thetarget material to yield a product yiihieh i s effectively carrier free.Some 'isotopes which are require«! fpr»clinical use with a highspecific activity are thus prepared . ' " .

116 + 1

S.T.C./C.Oopiedsmlp s6 c9»76

I I - 30

The same isotope is forned, through with a much smaller yiedl, by an(n»(X ) reaction involving «hlorine. .

Buildup of-aotiviV»

1) If the activity induced i s very short lived l i t t l e or noactivity will be built up since i t decays, almost immediately.2) If the induced activity has a lore half life than theproduction rate; i s constant-and the amount of new activity: inducedwill be proportional to the time of irradiation.

3) If the induced activity has a half l i fe of the order ofthe length of irradiation time, the buildup i s quite distinctlyexponential. -.After 4 or. 5. half lives f the rate of production comesnearly equal to the rate of decay (saturation.condition)9 so that

: any iurther irradiation i s of no use.The equation governing the buildup of specific activity

with tide in a reactor i s given by ' , • ,.

s - 3.7 3C 1O1O( 1 - e —== )

whereS = Activity in ouries/gm

CO = neutron flux per cm /sec.

A = Atomic weight of target element.

0 = Activation cross-section of target element in barns.

( 1 barn = 1n cm) . ::

t /% = irradiation time/half l i fe of the isotope.

I I . Accelerator produced Isotones:

: ~ There are a number of isotopes useful in clinical-research-.notably Ha-22, Co-56, #n-65 which,cannot be produced in a r^a»tor, or

whose specific activity when obtained by neutron irradiation i s nothigh enough. In these, cases, other nuclear reactions are employed wherer"putrnns and nmtnns are used as bombarding part icles. As theseparticles are positively charged in order to overcome the consequentelectrostatic repulsive^ forces, they oust be accelerated to very highvelocities corresponding tó energies^of several million electronvol ts . Various -types of high energy maöhihes, known as acceleratorsare generally used for th is purpose«\ , . . .

31Copied:mlpig.9.76

I I - 31

An an example the production of Na-22 by bombarding amagnesium, target with 15 - 20 MeV deu trons may be given

,Na'22

In this reaction the isotope produced differschemically from the target element and can therefore be separatedin the carr/.er free state.

S.T.C./CCopied:mlpi6.9-70

•V.-'

• . III IJSEEERACTIOir OF RADIATION WICH MA7TER :

H. the end of the last ec-ntuVi, X-rays werei discovered byRoentgen, while studying the passage, of electricity through gases.There wáš no appreciable time lag in harnessing the property ofX-rays to penetrate through opaque biological material for the use„ofmedical diagnosis, Almost simultaneously radioactivity was' discoveredby Beequere!.

The irony of the discovery was that no r. ncr than a quarterof a year of these radiations being put into use, its harmful effectssuch as skin erythema posed a new problem. With the passage of timeharmful effects began to pile upj to mention a few:

i^ Leukaemiaill) Smarting of eyes

These were the side effects which paved the way for subjectswith prefixes "of thé Vř1^ "Hádio", "Radiation" or "Radiological". ..Decay oř disintegration of a radioisotope gives rise'"to radiationswhich are particulate in.nature such asjrays. and/or electromagnetic t Rradiations viz gamma rays» Gamma rays "are essentially of the same ' *nature as 3C*-rays and are found to be equally' harmful to human beings. ,It. WPS also observed that particulate radiations are also capable ofproducing similar effects. Thus the new subject' callsd "RadiologicalPhysics", had to embrsce the nature and hazard of Radioisotopes inaddition to the effects of X-rays.

The effects of these radiations being undesirable thefirst logical step 4s to s-tudy the means of detecting them by evaluatingand controlling the hazard arising from them. For all the above threephases the importance of a study of the interaction of radiation; withmatter becomes evident, in which one comes to know about the eventstaking place on passage of radiation through matter.

Having established the necessity for the study, the nextstep is to get introduced to thp two entities involved in such astudy.

I) MatterRadiation

Matter can simply be deecribed in terms of the atomic numberof the constituent elements. The interaction i s almost unaffected bythe chemical or physical state of the elements.

:Radiation for the purpose of studying the interaction canbe divided into electromagnetic'*md particulate, aid pártičulatě canbe further subdivided into charged and uncharged particles»

EKECTROMJGHEDIC RÅTH-gPIONS:

These are wave l i k e dis turbances which a r i s e i n assoc ia t ionwith v ib ra t ing e l e c t r i c cha iges . Radiowaves, infrared' r a d i a t i o n s ,v i s i b l e - l i g h t , u l t r a vo i l e t r a d i a t ^ n , X-rays and gemma r ays , a r e a l lelectromagnetic rad ia t ion . The oníy difference e x i s t s in t h e i r wavelengthor in t h e i r frequencies. Wavelength arid frequency- . a re . re la ted wi theach o ther by the mathematical r e l a t i o n as fol lows:

10where is the wavelength in cms and in

cycles/sec, C = 3 x 10 cms/sec.

In.vacuum all electromagnetic radiations have the samevelocity which is nearly equal to 3 x 1010 cms/sec.

Generally, radiations are characterized by the energy theycarry which is commonly expressed in terms of electron volts (kč-Yand'W). *

Electromagnetic radiation get attenuated while traversingthrough matter. Thickness required to reduce the intensity to half theincident intensity is known as the half y&lue layer (uvil). Electro-magnetic radiations are also cherecterised by WL (mm of Cu or Ål).

In esse of electromagnetic radiation the absorption ofradiation follows an exponential low (Pig.i ) , which when writtenmathematically i s

- T ; ra.I = I&e

where Io is the intensity of the incident beam, I is the intensityemerging out after traversing thickness x of the material and u isknown as linear energy absorption coefficient. This is defined as thefractional decrease in intensity per unit length of the material.

Sometimes it is convenient to use mass absorptioncoefficient defined as the fractional decrease in intensity per unittraversed. It is usually denoted by mU is equal to u/ whereis the density of the material. In such cases the thickness x isexpressed in gms/cra2 and in cm2/gm.

..Ill- 3.

Similarly electronic absorption coefficient is thefractional decrease in intensity per electron is üsuaiiy denoted bye u and is equal, to (v/p) (i/do). where Ho" is equal to the number of electronsé(v/p)

Similarly the atomic absorption coefficient is defined as thefractional decrease in intensity per atom and is equal to e jLWzswhere z is the.atomic number of the material. . i '/V

During the passage of radiation through matter radiationcan be either scattered o™ absorbed. The mechanisms of absorptionand scatter of radietion-. are of fundace ntal interest in the field ofradiological health primarily because of the following.reasons«

1i Physiological injury2. Beteet;..|n of .radiation3. Shielding requirements

In general all types of radiations are either absorbed orscattered while traversing through matter, the specific mechanismswhich are responsible for either absorption or scatter vary with type,of radiation. -

Basically there are three main process which describe theinteraction of X and gamma rays through matter. They are

i) photoelectric effect i i ) compton process andi i i ) pair production*

Photoelectric process:

In the photoelectric process, the photo.n imparts all i t senergy to an orbital electron of an atom of the medium & the.ejectedelectron is known" as a photoelectron..

A photon of energy htywill release an electron withkinetic energy (KE) = hY-^Ty wteref-is the binding "energy of theelectron in that particular orbit* ** "

The probability of occurrence of the photoelectric processas a function of the photon energy is as given in f ig . i /

1« Photoelectric process involves bound electrons.2. The probability of-ejection of an electron is maximum

when the photon energy "is just higher than the binding' " eneigy of the electron.3. The .photoelectric örbss-section varies with'eneigy

approximately as i/B^.' " ;4. Maes absorption coefficient varies approximf* ely as 7?,

..III-4

-...->„.

Compton processi

Compton process involves transfer of a pert of the energyof the incoming photon to a "free electron". The outermost electronsof an atom which have very low binding energies are considered freeelectrons, since the compton process ihvolvesthese free electrons, theprocess is - independent of the atomic number of the medium in whichthe interaction takes place. Since, most of the materials havepractically equal number of electrons per gram. ( Z/A), it followsthat absorption by this process is nearly equal for all materials.The photon trsnsfeis. only a part of its energy to the electron andgets scattered.

The ene jgy given to t he eompton electron is ultimat elyabsorbed in the medium.

1. The compton effect involves &n interaction between aphoton ard'a free electron.

2. Is independent of Z ° .3. Decreases with increase in energy of the 'incident photon4. In such collision some energy is sbosrbed and the rest

scattered depending upon the angle of scattering.5. On the average, .the fraction of the energy absorbed in

a collision increases with increase in energy of theincident photon.

6. On the average, the fraction of the energy scattered islarge for lov/ energy photons aid very low ior highenergy photons. '

7. In soft tissue the range of 100 keV/ to 10MeV fcompton absorption is much more r".;>. -\ './than ^ pphotoelectric or pair production process. ^

8i /is the energy of the incident photon is increased, theelectron will be ejected in more and more in theforward direction at which time the electrons, carry thenieximum enexgy.

Pair production process! • • .

Pair production is the conversion of a photon into'a pairof positive and negative electrons in the nuclear field. Since thecreation of the pair requires a minimum energy of 1.02 HoV,- (which istwice the rest mass energy according to the mess energy relationship£-s YY\&3~ ) unless the photon possesses at least 1.02 Mev,: the

process will not take place. Energy in excess of 1.02.Mev is sharedequally in the form of kinetic energy by the pair formed> The positiveelectron having lost its kinetic energy combined with a negativeelectron giving rise to'annihilation ratfietion normally in the form oftwo photons each with 0.51 Mev moving in opposite .directions.

YaflUY\Q-7uL

....III-5

Reviewi

2.3.4.

It involves an interaction between a photon aid thenuclear field. • .Threshold energy i s 1.02 MeY. . 2

I t increase rapidly with atomic number as Z , per atom.The absorption per gram varies directly as 2

Thus while traversing through matter, radiation undergoesa l l the three processes in varying degrees, eech process predominantlyoccuring depending on the energy of the radiation and the nature of themedium to'.Cach process is attributed a probability of occurrence •*" iwis refered to as photo-electric, compton and pair pioduction absorptioncoefficients. *^he total attenuation coeffici ait i s the sum of all thethree coefficients. For monochromatic radiation., the absorption ofradiation follows an exponential lifcy which when written mathematically is

Charged particles; * * *=

Charged particle lose energy in medium by ionizing andexciting the atomic electrons of the medium. If the energy trsnsferredto an electron in the medium is sufficient to remove i t complectctä^out ofthe atom, the process is referred to as ionization if the electron isjust raised to higher energy state, the process is called 'excitation1.Thus ionization and excitation occur along the path of a chargedparticle in a medium ana the rate at which the ion. pair^are formeddepends utjon the charge arů energy of the incident particle and the atomicnumber of the medium.

The number of ion pairs produced per unit path length ofcharged particle is called specific ionization and fig... shows theBragg curve which :rives the variation of the specific ionization with thedistance travellejj^by the particle in the medium. The distance which aparticle travells before i t comes to a stop is called i ts range.

Br ii. tive collision:

$hen a fast moving charged particle passes close to a nucleus,i t undergoes a deflection in which i t los es energy in the form ofelectromagnetic radiation. Eadiation thus emitted is known as 'brems-strahlung1. The intensity of bremsstrahlung radiation increases with theatomic «umber of the medium, and decreases with an increase in the massof the particle. For this reason energy loss by radiation is moreimportant in heevy elements than in light elements, aid for lightparticles sucb. as electrons then for heavy particles such as protons andalphas.

...III-6

Sineeo(-xeys'"from a friven radioíiuclidé ere all emitted withwith the same energy, those emitted from a given'source will haveapproximately the saae range in a Riven material. The range of anslpha particle is usually expressed in cms of eir . The relationshipbetween the range and the energy has been expressed empirically asfollows:

3/2 . - .Ra = 0.318 E where Ra is the range in cms of air at one

atmospheric pressure at 1 1 E i s -fclle ene:r.Sy ^ ^ev. /•A r*

Range i-, solid media can also be calculated by the followingapproximate relationship.

T> R T Density áf air fit solidsolid ~ air Density of the solid A air

Where A solid and A air are the mass numbers of the solid and airrespectively.

Electrong;

Electrons by virtue of their small mass, experience frequentmultiple scattering and consequently have a very tortuous winding pathinside the nedium.

An empirical relation between the range and energyof electrons with energies more than 6 MeV. in gms/cm? is given by

O.53E = .1.06 fe

Eowever^rays from a rasioisotope do not all have the semeenergy but ÍÍXQ emitter as a spectrum with an E^av. The relationshipbetween E and range i s given by

maxmax

= (Empy/2 • / •? where P is the density of the medium.mac'

Neutrons:

. Neutrons being uncharged p a r t i c l e s do not produce any d i r ec tionization or excitation, but take part in .nuclear reactions.

Heutrons a- e usuaXLy c lass i f ied according to t h e i r energiesand the following groups are in use .

1. Thermal 0 - 0.5 eV2 . Slow • 0;5 - 100 eV3. Intermediate4. Fas! t5. Very fe si t

100 - 20 KeV20 Kev - 10 MeS/10 Mev - 500 MeV

is^c^Ä "•'V.Cl.'::. iUiÄ«'JJJS'ÄSE

Capture phenomenon:

When a neutron gets absorbed by a nucleus, the resultantnucleus i s excited and can emit alpha particles or protons or/andgamma rays.

Examples are given below

li7B 1 0 C 'V

Co59 (n f r > Co60

The above reactions are most common when the neutrons ha-vethermal energies.

j neutrons undergo elastic and in elastic scattering withnucl.*ii In tissue, the elastic scattering of neutrons with hydrogennuclc.ij releases proton which account for the biological effects offast neutrons.

INTERACTION OĚ RADIATION WITH SITING CSKES

Introduction ; .

Cell being the fundamental un i t of which a l l l i v ing organisms are made,i t i s generally accepted that radiat ion damage ar ises from e i t h e r an impairedfunction ;pr the death of individual c e l l s . To understard the biologicaleffects produced by r a d i a t i o n , the effects on isolated c e l l s end ce l lcolonies should therefore be studied. Thi e i n turn requires a basic knowledgeof the structure and function of c e l l and c e l l const i tuents .

The Cel l i

A l iving organism i s made up of a ^number of t issue-such as braint i s s u e and muscle t issue/give r i se to dif ferent organs of the body. Theset i s s u e s are in t h e i r . t u r n made up of raillionsof individual u n i t s , the

. nature of which determines the entire propert ies of. the t i s s u e . Theseindividual uni t s are, cal led l iving c e l l s . Cells of di f ferent t i ssue aredi f ferent .in shape and properties» St ructura l ly , however, they a H havea c e l l membrane? a cjrtoplasm containing various organelles and a centralnucleus. Such a composite c e l l i s shown i n f i g . 1 , based on vvhst i s seeni n e lect ron micrographs.

. The various organelles found i n the cytoplasm namely the mitochondriaribosomes,. golgi.-bodies and lysosbo.es have specific functions. Themitochondria for.example, const i tute the power-house of the c e l l wher a l lthe metabolites get converted into energy and.stored in the form of ATP(adenosine triphosphate) molecules which have high energy phosphate bonds.

Cel lular const i tuents '. 1 •

. About 70$ of human body is water. The remaining 30$ is made..up byraacromolecules such as nucleic acids, fats, carbohydrates, proteins andinorganic, sa l ts . .• Proteins are the most important'component of the cel l s ,since' the enzymes without which l i fe cannot exist have, been'identified to beproteins.- In addition to the enzymatic function, proteins are also found tofunction as antibodies, hormones and structural,units that make up theorganelles.

The other mac romolecule of great importance i s the nucleic acid.There are two types of nucleic' acids namely DNA (deoxy ribonucleic acid)and E P (ribonucleic acid). The ENA i s present in-the .form of anet likestructure called the 'Chroma!xn1 material inside the nucleus of the ce l l .

Cell Division:

l i fe i s perpetui* ed by the proliferation and growth of individual •cel l s . All growth is determined by an increase in -ftie number &f cells,

C ELL.

brought a lout by the division, of each cell into two identical"_ units., Incomplex organisms cell division is not confined to. growth and reproduction,but is necessary for the maintenance piff the adult. .Damaged cells have tobe replaced, and many specialized cells such as those making up the outerlayers of the skin, or lining of the stomach and intestine, "as well asthe cells which iaácé up the blood, have only.a short life and must bereplaced continually. In general,'once cells become highly specialized whichis known as differentiation,, they do not.reproduce by cell division. Examplesof types of highly.differentiated cells are ,those which.make up musclesand nerves.

The period between, divisions is called the 'resting.stage' aid isfollowed by the process known as mitosis, in which the nucleus duplicatesitself ana: the cytoplasQ:cleaves into two parts. VQien 'mitosis' is completedtwo cells each identical with the original one are formed.

Mitosis8 ...

Each mitosis is.a continuous process, one stage merging imperceptiblyinto the next. However for descriptive purposes mitosis has been dividedinto four steges namely i) prophase. 2) metaphase 3) anaphsse aiodAJ Jelophase... _lr. : / .

Prophase 1), In the:prophase.'--the chromatini.material in Ihe nucleus beginsto condense and form 'chromosomes', appear^'a^ a tangled mass of threadswithin the nucleus. Each chromosome has'previously undergone an autocetalysisand the synthesis of an exact replica has been achieved;

üs this procesis develops it becomes apparent that these chromosomethreads are composed of two filaments, known as chromatids.

2}- Sintilteneously the nuclear membrane, contracts and finally disappears.

3) -At this time a gel-like structure known, as the spindle vstretchingout from the center) appeers in the cytoplasm. In human cells prophase lastsfrom 30 to 60 minutes." Í. T "V" ".

Metaphase'- ' " . - ".. " •" ' | -ý;\ \ '• •

The spindle becomes attached to -the chrpmbsomes, ..which now arrangethemselves in an orderly manner across-the equitoriaí Opiáte of the spindle.In human cells the netaphase lasts fiom 2'to 6 minutes. 'The times v&ry fordifferent tissues and dtifferent species.

imaphase•

1. The doubled chromosomes begija to separate«

2. The spindle pulls the two sets of ehromatids to the opposite endsof the. cells.

• • > .4-

The events fron the time when the ehromatids first bqgin to move apart untilthey reach the pol^s constitute the sosphase, e period of three to fifteen :

minutes«

Telophsse:

The telophsse begins when the ehromstids reach the poles. This isa period equal in duration-to prophase (3O-6O minutes). In telophase,s

1. the cytoplasm cleaves into two approximately equal masses dividedby a new cellular membrane,

2. the nuclear mambrance reforms, and

3. the chronosomes in the daughter nuclei swell until they can nolonger bo seen as threads end the nucleus assumes the aprie ranee of theresting cell .

Resting stase':

MEPj'.PHASB (SIDE YIEW) ÅIUVSÅSE TEEOPHÍÍSE

Figure 2: The mitot ic cycle of c e l l s from vicia faba (been shoots)

• . . . .5

Duplication of the chromosome material namely DNA aid synthesis ofproteins take place during the intermitotic period. . The DM. moleculeconsists of O a sugar molecule (deoxyribose' 2/ phosphabe groups and3) nitrogenous bases (adenine, guanine, thymine ani cytosine).'

The Waston and Crick model for a DNA molecule i s a double strandedhelical structure. Each strand is made up of alternate sugar and phosphategroups and the strands are cross-connected by "adenosine-thymine" and"guanine oytosine" pairs. The specificity in the pairing of the bases andthe endless possibility of varying the sequence of the bases are made useof in the coding model proposed for the synthesis of proteins In the cel l .These features explain

1) the formation of an ENA molecule with the same sequence of bases (uraciltaking the place of thymine in KJii)

2) the functioning of the ENA molecule as the messenger of the code forthe synthesis of proteins.

-Having studied the cel l division procese and knowing the functionsand structure of the cell constituents, the effects of radiation at thecellular and sub-cellular levels can be examined.

Direct action;

In general, when radiation strikes biological material two types ofeffects take place. Firs t ly, the complex molecules present in the cellsmay themselves be ionised or ^excited. In this case, the action i s said tobe direct, . ' . - . . ' ' . ' ' " ' > - : , .

; On the.ptherhanä,. i f the, radiation primarily affects the watermolecules of the tissues, thus giving rise to free: radicals, H Og e tc . ,which subsequently affect the complex molecule, the action i s saxd to beindirecti ' • . : ; _ . - .

Target-

••"..- The direct action of radiation is explained by the- theory known asTarget Theory. According ;tq .-this theory, every,,living cell-..OK organism issupposed to contain one or more radio-sensitive molecules or structureswithin the molecules'. The sensitive volume i s teimed as the ' target1 and theproduction' of ionisation'-in th is voliicie as. the ' h i t l i Ionisation, whichoccurs within the cellj but outside the volume of sensitivity i s consideredto be ineffective. If a single target.is.assumed,, the theory is.known as thesingle target theory, (single-hit theory) while if more, than one target isassumed i t i s known as multiple target theory (multi-hit theory).

• •a • « 0

- •'"-••,-In theí case of the single. ta iget - theory : theV^umber of' organisms 'n 'surviving a dose- 'D v is,.related; t o . \ ^ .•'»* bythe- re la t ion , ' •-,'-'' . ' ; . ' • , '•}•'•• '• ". i:/£;VU':^^--'?,£ >:^\" -

. . . n = no e - 0 ^ 0 where Do i s the • constant-:of';proportionality.The relation signifxes^that the number of .cells surviving;, should decreaseexponentially1; éís,the..račlietion;dO3e increase's- (FÍg.3). : ; ,'-!

DOSE . ,

I t can be shown.; t h a t Do i i s t h e d o s e rieoessöxy t o p r o d u c e on f a n avera./as onehit per organisni'.-(because some organisms äéy:receive^^ isbře .thsn-örie h i t , andsome' no. hit at a l l ) ani heöcé i s ''r^ferTed":^ö'v-_es;"th^''^aa;!t"^thiai dose. I tcan also be seen from the relation thai; when D = Do ;^ n = .37 np • HenceDo i s also referred to as "the37% dose. " V;.-." J.... ..;

;The target thep iý.demands'tltiati(i); the. effect'produced should, beindependent "of ..the dose?řs|e ](2)^different ra'diationg;: shpuldLíháve -differentefficiencies in^proaucing^hersame'ieffects.!. ^ d ; i f ?.thefsiigle).Mt theorywere to' hold gopd,Jdehseiy;-ionising vraåiatiph" should :!bétié.ss;ieff ective,becauset when,they.pass.through""tjiř;^target, a number-of iönisåtions willoccur, a l l but oné of which; are; wasted.".'-' _-.'_ ' • " ,

I n d i r e c t sct ion ' : - . '. ..'..'"'''"•'''. ' '' " • :'sr.,r~~ v^-y-,'fi!—:'-

iiccording to the accepted -theory of the inechánióia/by which the free^radicals are producedV the. fbilowing reactions afe:äiciOlyed;« ;i .

ILO' . r a d i a t i o n ^ .2

• + • : •-•,'. e

The electron i s then captured, by, a.no.therCwater/^molecule tö give a negativeion (HgO • + e~ H^O-) to, complete -thef r o t a t i o n of;• an' ion pair. The twoions are very" unstable, and decompose as follows * - •

••+ 0H°

OH a0thus giving - rise to two free radicals.

• * • « * /

<*••• ť. . - s r . i -

The two stable ions H and OH~ recombine to form E^O.

Reaction (a)«fnr the free H atom (H°): (t) Being a reducing agent, thefree hyttiogeš oai react with oxidising agents (2)., In the presence ofdissolved ,oxygen, .

•H + O r

w(Perhydroxyl radical)

(b) for the OH redioal1

This may react with reducing agents. Hydrogen peroxide, if formed withinthe nucleus} will produce seiious damage«

0 0The extent of biological damage ceused by the action of H , OH.,

H.O and "HO will depend upon (i) the rate at which the HP OH0 ^ 3 ^ ^get separated fron the place of formation and (2) the availability ofdissolved oxygen.

Effects :on cells; . •

The various conseguences due to incidence of radiation at thecellular; level are (1) Inhibition of mitosis (2) Chromosome breakages andabenetions. (3) Death of. cell ani (4) Sene mutations..

Inhibition of mitosis i This in other waords is a temporary arrest of thesubdividing process. . . .

With small doses of the order of 50 r, no appreciable reduction inthe mitosis rate is observed.

II(t EB

K"cr ĚH E»-S

- I í%

•«oS-s-s.0

202 3 4 5

f i g . 4DÜR/.TIOI OP INCUBATION(IN HOURS) MTEEL IERADIiMION

is the dose i s increased^ a sharp minimum ia noticed, in about an hour or two.This tame delay shows'that the cells affected are not those that are actuallyin' division, but rsther those that are s t i l l in the resting period, forotherwise, an immediate fa l l should have been recorded. The-fact that thenumber of dividing cells increases afterwards indicates that the inhibition ofmitosis i s only a temporary phenomenon. A stage will bé reached when therate of division is greater than even that in controls (unirradiated cells) ,because the cel ls undergoing mitosis now include not only those affected byradiation, but also those unaffected. The extent to which the mitotic rateis lowered by a given amount of radiation depends not only, on the total dose,but also on the rate at which i t i s given.

Chromosome breaks end- aberrations: • •

A serious consequence of the action radiation on living cel ls i s theinduction of chromosome changes. * Often these changes are permanent, andcannot be repaired,, and may lead- to the death of a number of daughter cells .Since the ce l l i s most sensitive in. the resting.stage, i t must be concludedthat chromosome changes are results of some processes taking place in theresting stage. ' ( * ' • ' • ' • ' - . • > ' ' - . • . -

Chromosome changes are believed to be caused, by the. breaking ofchromosomes due to radiation. The broken chromosomes ..may .reunite in thesame way as before irradiation or in a variety of. other fashions.- In theformer case, no injury would be caused. However, the second type of unioncan give r ise to a number of abnormalities. If breaks, take place in somaticcells , considerable functional disturbances resul t , the: cells affected areweakened, snö may be even ki l led. On the other hand, i f the 'cel l with thebroken chromosomes were.to be germ cells and undergo fer t i l isat ion, a l l thecells in the embryo vsould be sbnormal, and would be expected to'die in theuterus at an early stage leading to malformations and abortions.

The number of chromosome abnormalities depends on the dose as well asthe dose ra te . Further, the depends on the dose varies.with the nature ofchromosome abnormality. In the case of simple freaks, the proportionalitylaw holds i .e. . if 100 r produces 6 breaks per hundred cel ls , 200 r willproduce 12 breaks per hundred cel ls . ,

Death of Cell: Both the inhibition of mitosis ani the breaking of chromo-somes, sometimes result in: the death of the ce l l . . However, i t i s s t i l l notclear, why some cells are killed by a few hundred reentgens, whereas, most cellsrequire a few thousand roentgens. In general, i t hese been found' that sellsare sensitive to radiation in proportion to thei r proliferative activity and ininverse proportion to their degree of differentiation.

EFFECTS OF MDI/TION

Biological effects of radiation are the effects produced byradiation on biological systems. • Broadly speaking, this-can be dividedinto tvjo classes- . ( i) Somatic effects: relate to.injuries to cells whichere concerned with the maintenance of body functions, such as cel ls inblood and bone marrow. :These effects are rnanifested during the lifetime ofthe individual. (2) Genetic effects5 re late to injuries to1 ce l l s in thegonadg which are responsible for the propagation of genetic '.characteristicsto' subsequent generations. ' . , .

Somatic effects .are of two kinds ( i) Somatic effects after acuteirradiat ion (large exposure. In a short time^ (2)- Somatic effects due tochronic irradiation (exposure spread over a long" period)* :

The severity of radiation injury in any particular instance i sdetermined by.several factors 5 (i) the nature, energy, to ta l dose and doserate of radiation received, (2) the extent and part, of.the body which hasbeen irradiated, (3) the age of the person exposed, (4) radio sensitivityof the organs involved, and (5) .whether the source i s internal :or externalto the body. The effects produced ;ařé,also dependent, upon factors,..wich as(w) the degree of oxygenation iaaď hence temperature .of the part of the bodywhich has been irradiated, (2) metabolic stáje and hence on diet, (3) sex,and (4) body colour. ! • ;• _.

Lethal doset In evaluating the effects of radiation i t has to beborne in mind, that there i s enormous variation in the rad-iosensitivity ofdifferent typeso? species. An idea of ;the extent; of variation may beobtained by comparing the lethal'döse required to k i l l 50^ of the exposedanimals in thirty days. (üD 50/30). ;

MammalsFrogSnailFruit-flyAnoeba -

. Pařamecia

200-1000700

1000060000

100000 r3OOOOÖ r

The ID. 50/30 for mäi is,estimated to be in the range".4.ÓÓ-5Wr of X-rays. N.The lethal dosé of ^radiation for man i s about 600r,which corresponds to anabsorption of roughly 6 x 1o4, e r g s , The total energy putput.of the metabolicprocesses in a human body i s of the order of -200 watis, "which corresponds to2 x 1O9 exgs per second. Thus the aiabunt of energy,of:the ionising radiationwMch i s sufficient to k i l l a man, i s about o.vbnndred: thousand times smallerthan the amount of energy liberated.in the body, in one second. The mainsite of acute'radiation injury in animals and man'is the: haembpoietic systemof the bone marrow and the lymphatic tissue. The only way of recovery is tbereplacement of damaged cells.

k • t a *C.

Specific Somatic Effects:

' Skin:, Ionising radiations from external sources f i rs t pass throughthe skin. . Erythema of, the skin, following external;. irrad iät ion, by X-rayswas for. long jtaken as the. basis of the biologic al unit of dose i With laigerdoses the erythema changes tö pigmentation, and after s t i l l greater dosesvarious typeV.0f radiodermatitis appear which may finally become.malignant

. g r o w t h s . . ' . '. '"' . .'' ]. ' ••_"•'••', ' "' " " -".' . : '--••'

Blood: A dose level of about 25 to 75 r will affect the differenttypes of white cells and a reduction in the blood count may be observed.The normalcy will be restored in a few days. Red blood cells are more radio-re sist ant., and cooperatively higher doses are necessary;tö produce areduction in the number of red blond' cells. P ls t le t count slso; drops downmaking, the individual tiusceptible to .haerao riia/=;e. .

Sonáds: The.sex glands are very sensitive to radiation and loss offer t i l i ty 'may be produced. Experimental'results suggest that recoverysimng germ cel ls in the tes t i s may be expected even after exposure to severalhundred rads, whereas recovery of damaged germ cei ls in the ovary i suncertain and errat ic . If a pregnant .'woman i s irradiated, depending on thedose level and the stage of" pregnancy, the child may die in the embryo orabortion may take place or abnormalities may bé observed in the offspring»

Eye: Radiations may produce opaque cells in the eye lens and thiswill impair the eyesight. This is'called cataract formation.

Other effects such'as leuckäemia-overproduction of immature whiteblood cells may also.be manifested a number of years after the. dose i sreceived. " ' •'.': . .

Shortening, of l ife span: Experiments on. animals suggest thatexposure to ionising radiations may lead to reduction in the expectationof l i f e .

Genetic effects of radiations:

Gene mutations: Irradiation of the germ tissues may cause mutations whichappear in la ter generations. . These ,are sudden permanent.: changes which maycause some alterations in the, hereditary t r a i t s carried iby'^the'.genes. Thealtered genes are called mutagenes. Once a.mutation hasiOccurred, gehe i sreproduced and passed on in the new form in a l l subsequent''c e l l divisions*The mutant genes, in the vast majority of cases, and infall the, species sof&r studied, lead to some kind of harmful effect.. In extreme .cases theharmful effect i s death i tself , or loss of abil i ty to produce offspring,or some serious abnormality.

Spontaneous mutations: Occasionally in nature, mutations do occurspontaneously, although the frequency of .their.occurrence is small.

These so ceiled spontaneous mutations of genes appear to result fromrare ultramicroscopic accidents thst occur in. the course of.thermal agitationof the molepules of which they are composed.. The various factors contri-buting to the spontaneous mutations are (i) temperature.(2) chemicals(3) natural radiation»

Mutations and natural selection* The frequency of spontaneousmutation is about 1 in 20 cells per generation, ana as the body contains atleast a thousand billion.cells, the frequency is appreciable indeed. About99"? of the mutations lead to harmful effects, and it is only in eirtremelyrare esses, that a beneficial mutation occurs. .Among the harmful ones,apain, there are those that sre lethal and those that lead to various typesof hereditary ailments and weaknesses. Individuals bearing harmful mutationsare handicapped relative to the rest of the population in the following ways:they tend to have fewer children, or die earlier. -And,hence such genes areeventually aliminated soon if they dp: great hana, more slowly if onlyslightly harmful. Ä mildly deleterious feene may [eventually do just as muchtotal damage as a. grossly anä abruptly-hamful one, since the milder mutantpersists longer and has a chance to harm more people. • Asa result ofsimultaneous elimination and generation of. gene muta.tioňs a stat e ofequillibrium called genetic equillibrium will be reached when the rete ofproduction of harmful mutations becomes equal to the rate at which they areeliminated from the population.

This however is not the case with useful mutations. Even though -..their occurrence is low they are not eliminated from the population at all«Por this reason the,number of useful mutations would have reached; nearlythe saturation value in the course,of several millions of years. Occasionally,however, a useful:mutation may occur, which may improve the :species. Thisprocess by which the evolution of living creatures proceeds step by steptowards perfection is celled natural selection.

Unlike somatic effects, it is believed that there is no thresholdfor the induction of gene mutations, and any, radiation, above backgroundis undesirable. However, recent experiments suggest that in human beings,radiation given at low dose rates is less effective than at higher ratesin producing mutations. ,

To make a quantitative assessment of the genetic effects of radiation,the term doubling dose macle use of. Each individual, on the averageinevitably experiences, during his reproductive, life-time a certain1 numberof harmful spontaneous mutations from \atursl causes. He would, experience anadditional equal number of harmful mutations ifhe received a certain doseof .radťLstion during-thft same period. This is known as the "doubling dose".Its value isestimeted to-be between 30r ard ÓOrfoř. man. Thus, somethinglike 30r to 80r would <jt£'mankind twice the harm it is. now experiencing fromspontaneous mutations. ; :

Taking'various factors into consideration, i t has been stated,according to one. estimate" that 1 in 5.deaths i s due tö genetic causes.Doubling 'the mutation rete would naturally increase this to 2 in. 5;.Further,, since infeetion,: nutritional diseases, climatic and oühertypes of diseases, are rapidly being overcome due to" the •feremend'ousadvanceraaxfc in medical science, genetic affects will be „the cause for agreater end greater fraction of the total death in the wrid*

. . . . 5

THE BIOLOGICAL EJECTS OF RADIATION

Acute Doses0-25

25-5050-100

t00-200200-400400

remsremaremsremsremsrems

600 or more rems

Probable effect

Ho obvious injuryPossible blood changes but no serious injuryBlood-cell changes, some injury, no disabilityInjury, possible disabilityInjury and disability certain, death possibleFatal to 50 per centFatal.

SUMMtY OF EFFECTS RESULT IflG- FROM WHOSE BODY EXPOSURE TO

Mild Dose Moderate Dose Semi-lethal Dose

0r25 rema

BTo detectableclinicaleffects.Probably nodelayedeffects.

50 remsSlight tran-sient bloodchanges»No otherclinicallydetectableeffects.

Delayed.effectspossible,but seriouseffect cm .a-verage indi-vidual- veryimprobable.

100 rems •Sauséa andfatigue withpossiblevomiting above125 r

Marked chpngesin bloodpicture withdelayedrecovery.

Shortening oflife expect-ancy.

MM/9.9.76

200 rems

Nausea and Vomitingwithin 24,hours

Following latentperiod of about oneweek epilation, lossof appetite, generalweakness and othersymptoms such assore throat anddiarrhoea.Possible death in2 to 6 weeks in.asmall fraction ofthe individualsexposed. Recoverylikely unless com-plicated by poorprevious health,superimposedinjuries orinfections.

400 rems

Nausea an3 vomitingin 1 to 2 hours.

lethal Dose

600 rems

ifter a lat ent periodof about 1 week, begin-ning of epilation, lossof soetite and generalweakness accompanied byfever. Severe inflamm-ation of mouth and- throatin the third week.

Symptoms such as pallordiarrhoea, nosebleeding &rapid emaciation inabout the fourth week.

Some deaths in 2 to 6weeks. Possible eventualdeath to 50 per cent ofthe exposed individuals*

Mausea and vomitingin 1 to 2 hours

Short latent periodfollowing initialnausea. '.•Diarrho ea,vomiting,inflammation ofmouth e nä throattowaiäs end of thefirst week.

Fever, rapid emaci-ation and- death asearly äs secondweek with possibleeventual death ofall exposed indi-viduals.

TI - 1

Units of measurement of radiation and radioactivity.

Introduction;

With the discovery of radioactivity, the need for a unit forspecifying quantities of radioactive substances arose» Since the firstradioactive element to be discovered was xadium the unit of radioactivity,namely ourie, was defined as the activity of one gram of radium«Subsequently it was defined as the quantity of radon in equilibrium withone gram of radium. /When equilibrium is reached, the number of radonatoms disintegrating per second is equal to the number of radium., atomsdisintegrating per second. This number was found to be 3«7 x 10 .Later, when more and more radioisotopes came into use the curie wasredefined as that amount-of any radioactive substance which disintegratesat the rate of 2*7 x 10 disintegrations per second. The millicurie(10~pcurie) and the microcuxie (10 curie) are alBo in use. Thecurie unit is applied to any radioisotope regardless of its mode ofdecay, and is denoted as 'Ci'.

Interpretation of the unit 'Curie1;

Tery often radioactive substances decay with the emission ofmore than one type of radiation. In such cases it is customary to use'gamma curie' and 'beta curie.' By gamma curie is meant that the numberof •..gamma quanta emitted by the substance is 3*7 x 10 per second.Similarly, by one beta curie is mea.n±othat the number of beta particlesemitted by the substance is 3.7 x 10 per second.

Example; Given below i s the decay scheme of C0-6O

.33 MeV

' it-Vi- '."£,."';..

Yl : 2 s

-In the case of Cobaít-60 one curie means .actually the "emission of

1) 3.7 x1010beta particles (of maximum energy 0,31 MeV), per second

2) 3.7 x 10 gamma* rays (of 1.33 MeV) per .second";and

3) 3«7 x 10 1 0 gamma rays (of 1.17 MeV) per second, ,

Total curie ana Parent curie; .:. ' ', ,

,,, , These units are used in cases of radioactive substances,such as radium and strontium which decay giving rise to radioactivedaughter produots. The decay of Sr-90 is given below:'

38k„90

(0.545 Mev)

•90A0* (2.26 Mev)

„90From the above it can be seen that one curio of freshly prepared Sigive 3»7 x 10 beta particles (with a maximum.energy.of 0.545 Mev)per second. Bat one curie of Sr-90 in equilibrium; with-Y-90 on theother hand will give: • ' . -J.' . : •

3*7 x 10 beta particles (with a maximum energy of 0-545 Mev)per second and . ;

3«7 x 10 beta particles (with a maximum energy of 2.26 Mev)p e r s e c o n d . ; •' ' ••'• ••- . 'Í v v i .„...-•<••

This is referred to as 1 parent curie or 2 total curies.

Electron Volt; is the energy acquired by an electron when it fallsthrough a potential difference of 1 volt.

The quality of the radiations, emitted by the radioactivesubstancesT nameljr alpha, beta gamma and neutrons, which is given bythe energy associated with them and is expressed in terms of electronvolts (eV). j , ' ;

1 eY <= 1.6 x 1C"q ergs1 keV ,= : 1.6 x 10"?- ergs ,

1 erg1.6 x 10'

6.25 x 101

,-6ergs

VI s 3 :

Units for measurement *f radiation; The need for the quantitativemeasurement of the radiations emanating from an X-ray tube /was feltafter its use in medical field started. X-rays being electromagneticin character the most obvious way of assigning a quantitative, meaningto an X-ray team was to refer to the intensity at a point which wasconventionally defined as the radiation energy in ergs flowing per secondper square centimeter »f an area placed perpendicular to the direction«f propagation. la other words, since the energy flowing per squarecentimeter is known as the energy flux» the intensity is just the fluxper second.

The intensity at a point is not adequate for the measurement-»f X-ray doses in relation to their physical and biological effects fortwo reasons. Firstly, the concept ni the.intensity at á point is ratherdifficult to maintain under coi.ditiwis such as å radiation field due toa complicated and unknown distributira of sources in space. In orderto take this into acount, the intensity «*f radiation at a point isscmetimes [defined as the energy per,unit time entering a small sphereof unit ci'JSS sectienal area Centred at that point. Secondly, radiationcan Tiring about a physical nr biological change in a medium only byvirtue of the energy actually abs afiied and this depends not only on theintensity but alst on the absorption coefficient, «»f the absorbingmedium.. This absorption coefficient is, in its turn, a function of thephoton energy of the incident beam.

As soon as these difficulties were pointed out, the searchfor some method of determining the energy absorbed per unit mass ofsome standard substance became necessary. The methed thought "if wascalorimetric determination of the energy absorbed. In 1«*>97 a measurementwas made of. the heat produced by "the complete absorption of an X-raybeam in á metal. In view of the great difficulties involved in measuringsmall increments of energy by thermal means, the calorimetric method *was not pursued further".

Js s o w as it was realised that all the physical and biclogicaleffects of X-rjys are essentially due to their ionizing properties, itwas. suggested that the energy absorbed per unit mass *if a standardsubstance could perhaps be measure! by estimating the degree rf ionizationcaused in it. The measurement of i^nization can most conveniently becarried out in gases of which air is the most suitable partly because «fV.ve practical,advantages involved as well; as the fact.that the energyabsorption in air closely approximates that in.tissue, the two beingnearly *f the same atomic composition. Air was hence chosen as thestandard substance for defining and measuring; x-ray exposures. Asthe energy absorbed per gram was known to be "directly proportionalto the degree «f ionization, the unit of measurement called the r^entgenwas defined directly in terms of an amount of ienization .in air. Theoriginal definition *f the roentgen was subsequently extended to crverthe gamma raý region alBO and the definition, ae accepted to-day byICEtJ, the International Ommissiin on Radiftlogieal Units & Measurementsreads as follows:

KGVtvkki31viii76. 4/-

VI Í 4 i

"The roentgen shall be tht quantity of X or gamma radiationsuch that, the associated corpuscular emission per 0.001293 gram ofaii (i.e., 1 co of air at NTP) produces, in air, ions caixying 1 e.s.u.

IMÖ1TPD QUANTITIES FROM THE BOEMTGEW

1. Energy absorption in air;

By definition one roentgen gives .eise to 1 esu of quantity ofelectricity of either sign in air.

1 roentgen = 1 esu of electricity of either sign

4-8 x 10'

4.8 x 10"

,-10ion pairs (4,8 x 10

-10being the charge ofan electron in esu)

. 4-8 x 10'

x ¥ (W being the energy required ön theaverage for the production of anion pair in air). n

x 34 e7.(J4 eV being the value of W for air)

nr 1 roentgen

4-8 x 10'

x 34x1.6x10"12 ergs (1 10~12erg)

34 -c 1.6 x 10"' ergs per gm of air0,001295 '•• . •

('.' density of air.oai-293 g/cc

Thus the amount if energy deposited."by one roehtgen in one gram ofair B 87.7 ergs.

2. Energy.Fluxa . . " "

At a given point in a radiation field where, the-exposure is1 roentgen^pér second, let the corresponding intensity "be"Io ergs/cm /sec.

'.. . 4n eii- film of thickness t cms'and area of cross-sectionone sq.. centimeter perpendicular to the direction of incidence of theradiation will have a mass of air equal'tó f t grams. '( P being thedensity of air at BTP). The energy absorbed in this film will be87.7 t p ergs per second.

... 5/-

VI i 5

The reduction in the intensity dl = Io-I due to absorptionis therefore 87.7 tp ergs/cm2/sec. „But, the intensity I after passingthrough the film is given by I = Io ejja t where \*-& is the true linearabsorption coefficient for sir in cm" .

dl - Io - I

= In (1-eTa *)

Therefore.Io dl 87.7 t ° 87-7 ? m

where«(fa/p) is the true mass absorption coefficient of air expressedin cm/gm. " »» * .« +

J% (1 -e ' °" ' ** f a for small values of a -/

In general, the value of-'fa/ of the X or gamma rayphotons/varies (in a manner shown in fig.). In the region_from about Cto 2 Mev, a/p is practically constant & is about 0.028 cm /gm.

Using this value we get,

3132 ergs/cm/sec.Io = 8]0.028

Thus 1 roentgen/se«. «= 3132 ergs/cm-/sec.or 1 roeritgen = 3132 ergs/cm

In other words one.roentgen corresponds to an energy^fluxof about 3132 ergs/cm within "the energy range 0.1 to 2 Mev.

3« Energy absorption in other media;

Let B be the energy absorbed per gram per- roentgen in a givenmedium of true mass absorption coefficient, (u/p) med.bin /gm andIo be the intensity of th& radiation beam corresponding to an exposure of1 r.

Then Io = ormed

Since depends on the energy of the incident beam, E,the energy absorbed per gram, per roentgen in a given material will varywith the photon energy. On the other hand,; by definition, the energyabsorbed per gram of air per roentgen is always 87.7 ergs whatever maybe the photon energy. In other words, whenever an energy absorption of87.7 ergs/gm. in air takes place, the radiation exposure is one roentgen.

GVH:vkk:2ix76. 6/-

VI : 6 :

Inadequacies- of the zbentgen: . ; ;. ,

. By the very definition of the unit röentgen, it^is applicableto eleotromagnetio radiation only viz. X-rays and gamma rays. It is ameasure of exposure only. ,/ \.

Iii. order to evolve a measure, of all types of radiationsas well, as to include the energy .that is; absorbed "by. a medium,.introduction:of other units was: inevitable. These had to,bequantitative.measures of absorbed energy in any medium.(including air).These will be called by the term «absorbed dose1.?, ,

Eept . To - include other types of radiations a new unit of absorbed dosewas introduced by Parker in 1948 • This new unit, wbich can be, usedfor all types of radiations, electromagnetic as well as corpuscular,was called the 'Rep' (roentgen equivalent physical) defined as thatdose óf ionising radiation which produces.an energy absorption of94 e*gs per gm. of tissue (HT =52.5 eV)'« .. - .

Radt 'All- the difficulties involved in the rise("a£ the. roentgen willalso be inherent in the use of the rep, because, essentially the twounits are of the same character, the only difference being that thestandard substance in the case of the.roentgen is air,v whereas in thecase of the rep, it is soft tissue. These difficulties led to theevolution of a new, unit called the 'raď (the first three letters ofthe word 'radiation') which is equal to an energy .absorption of-100 ergsper unit mass of the irradiated material at the place of interest.If 300 ergs are absorb?^ ner gram of bone, the döse is 3 rads in bone.If the, dose is such tha-t- T'- same 3°°. ergs are absorbed per gram oftissue, the dose is 3 -rad1, in tissue. When the dose is specified inrads, the absorbing medium must be mentioned.

Energy flux per rad: , • " " "

Consider ra thin film'--of. a medium of thickness.-t cms with-.unitcross sectional area. Let the absorbed dose at the. film be trad. Letthis correspond to a flux of Io ergs/sq,. cm.

Since I -• Io

Io -I-».lo (

-or the energy absorbed in the layer is Io (1 -e"

GVR:vkk:2976OR merely 'dose« according to ICRU, 1.962. .... 7/-'

VI s 7

But the energy absorbed .in the layer = 100 x t.p ergs where p:is thedensity of the medium . -

' " " Z' '" • """""• -: ' •••'•' r, T TOO

100 t p ergs cr\ ±o -or Id (i-e~ra -)

• ' • > - ' '

r J22 m2erga/cm2 whereas 1 r ; - 87.7/(.

med ergs/cm fmed

REE_! The biological damage produced by the same rad dose ofdifferent types of radiations is, not the same. In order to accountfor this a factor hasT been introduced known-äs" the Helative BiologicalEffectiveness. (ĚBE). HBE of a given radiation was defined as theratio of the dose required oy irradiation with .250 k7 X-raýš to producea certain biological effect to the dose required by irradiation withthe radiation under consideration to produce the same biological effect.The EBE values for different types of radiation, to be used:for protectionpurposes is given in the following table.

Radiation

X-rays, Gamma rays,electrons and betarays

Fast neutrons andprotons

BEE and type of radiation

Biological effect

Hiole body irradiation(blo-.d forming organs)

Cataract formation 10

Alpha particles

Heavy reooil nuclei

Carcinogenesis

Catarcäct formal'ion

EBE is a function of linear energy transfer (IET) whichis the energy transferred by the radiation per unit distance in themedium.

CTH:vkks2976. 8 / -

VI í 8 i

EEE is expressed in terms of the pertinent Diologioaleffectiveness of ordinary X-xays taken ås unity (average specificionization of 100 ion pairs per micron of water, or linear energytransfer of 3.5 keV per micron of water). In cases where, sufficientexperimental data are not available, an HUE value based on the LEI1

of the; radiation considered, may he taken. The relation between IEDand RBB is given in the following table. (1 micron = 10 7 cm).

REE and

Average specificionization

(ion pairs per micronof water)

100 or less100-200200 - 65065O - I5OO1500 - 5OOO

Specific Ionization

Average linearenergy transfer

(KeV per micron in water)

5*5 or less

5.5 - 7.OO

7 - 2 5

25 - 55

55 - 175

11 - 2

2 - 55 - 10-1 0 - 2 0

Ultimately to express the dose incorporating the HEB.valuea new unit 'rem'(roentgen equivalent man or mammal) has been definedand is as follows:

Hem is that amount of any radiation which produces the same•biological damage as one roentgen of X or gamma radiation.

Dose in rem = Dose in rads x HHBi

.... 9/-

VI - 9

Current Trends; ICBU 1962

Even in its 1959 report, the Commission expressed misgivingsover the utilization of the same term "EBE" in both radiobiology andradiation protection. Many factors, apart from LET, affect "the EBBof two radiations vizj-

(i) the biological effect considered,

(ii) the nature and condition of the biological material(including physiological state, temperature, oxygenconcentxation etc.

(iii) the dose,

(iv) the dose-rate and fractionation,

(v) the dose distribution within the irradiated materials.This means that one must not speak of the EBB of two radiations

without also defining the exposure conditions and the biological end-point . The Commission recommends that the term EBB be used in radiobiologyonly and that another name be used for the IET dependent factor by whichabsorbed doses are to be multiplied to obtain for purposes of radiationprotection, a quantity that expresses on a common scale the effect of a l lionizing radiations. The name recommended for this factor i s the qualityfactor (OF). Provisions for other factors are also made. Thus aDF for

change in biological effect due to non-uniform distribution of internally depositedisotopes. The product of absorbed dose and modifying factors i s termedthe dose equivalent, (EE). ÅS a result of discussions between ICRTT andICHP the following formulation has been agreed upon:

The dose equivalentt1. For protection purposes i t is useful to define a quantitywhich will be termed the "dose equivalent" ( )2. (EE)- is defined as the product of absorbed dose D» Qualityfactor (OF), dose distribution factor, (BF), and other necessarymodifying factors.

(IE) « D (OF) (BF) rems

5» The unit of dose equivalent is the rem. The dose equivalentis numerically equal to the dose in rads multiplied by the appropriatemodifying factors.

Integral Dose: (or Integral Absorbed Jose) : Integral absorbed dose isdefined as the energy imparted to matter by ionising, particles throughouta given region of interest and is expressed in gram-rads. It is numericalyequal to the dose in rads multiplied by the mass in gms of the areairradiated. The unit of integral absorbed dose is gram-rad «=100 ergs.

GVR:vkks3976 10/-

Yl - 10

MEAS0HEř"E8T OF RAJIATIOF

The method to measure the exposure in roentgens in accordancewith definition is to measure the charge collected in a given volumeof air, under known conditions of temperature and pressure.

Free air ionisation chamber;

S = Area of the Diaphragm -ABCD = Volume under considerationP,R = Parallel plates to collect the charges, G = Guard ringsš = Distance of diaphragm from source

A = distance of collecting plate from the sourceL - Length of the collecting plate.

The radiation passes through a small dia.phragm S into a shieldedbox which has two parallel plates maintained at a high potentialdifference. The volume under consideration for collecting the ion pairsliberated, is ABCD. If q. is the' charge collected, I the length of thecollecting plate and A the area of cross section at the point of interest,from the definition of roentgen, it followss

Exposure in roentgens = q/l A

Applying corrections for volume to get the exposure atNTP we have

Exposure in roentgens = q/l A (76O/p) x (275 + t/273).

where p and t are the actual pressure and temperature.

(NB. i vfck i4,9.76

VI - 11

Thus in the formula above the measurement of exposure involvesonly the measurement of q, L and S. The above setup should be sodesigned that the volume ABCD is at the required distance from thediaphragm for electronic equilibrium to be established. At the Bametime this distance should not be too large so as to cause any attenuationof the beam. Further, the beam should have a uniform intensity atthe volume under consideration.

In case of high energy electromagnetic radiations the rangeof the secondary electrons becomes very large and hence the dimensionsof the chamber have to be increased enormously. This problem hasbeen solved to a certain extent by increasing the pressure of airinside the chamber. Even under a pressure of 10 atmospheres, forradium gamma rays, the plate separation has to be 30 cms. Insteadof increasing the pressure we can have a solid material, of higherdensity but equivalent, tc air in nature, with an air cavity inside.In this case the charge collected within the cavity can be taken forcalculating the exposure.

Measurement of Poses

• To measure the dose to a given medium the gas in the ionisationchamber should ideally have identical radio-physical characteristics arthose of the medium, so that the replacement of the medium by the gasat the point of measurement does not alter the energy absorbed at thepoint. This would mean that the chamber gas must vary from medium tomedium which is unpractical.

Principle s

Bragg-Gray principle states that the ratio of the energyabsorbed per unit mass of the medium and the energy absorbed per unitmass of the gas enclosed in a small cavity in the medium is equal tothe ratio of the mass stopping powers of the medium and the gas

Energy absorbed perunit mass in medium

Energy absorbed Mass stopping power of mediumper unit mase in gas Mass stopping power of gas

E'med (S

(S oed/S ) x J x W ergs.gcL5

(where J is the number of ion pairs, and W the energy ( Ut.ergs)required to produce one ion pair in the gas).

GVE:vKk:4976 12/-

VI - 12

Conditions for validity of the -Gray principlei

1. The cavity dimension should "be such that only a very smallfraction of the particle energy is dissipated in the cavity.

2. Attenuation of the primary beam over the cavity dimensionshould "be negligible.

3. Divergence of the beam should be avoided. The chamber shouldbe kept in a field of uniform flux, which can be achieved by keepingthe source at a fairly long distanoe.

4. The cavity should be surrounded by an equilibrium thicknessof the solid medium. No particles created outside the chamber shouldreach the cavity. The wall thickness should be equal to the range ofthe maximumenergy secondary electron. In practice however, pathobliquity leads to the approximate establishment of electronic equilib-rium at a wall thickness considerably less than the maximum range.

Discussion of Bragg-Gray principle;

med ~ gas x med'S gas

The ionization J thus depends on

1 • The fraction of primary photon energy that is given tothe secondary electrons per electron encountered in the medium,8lven / ^ J " ^ hst)) '

cavity

2. The relative stopping power per electron e _/e

For a chamber with an air equivalent wall and air filled

so that the chamber is capable of giving readings inroentgens.

GVR;vkk;4ix76

Measurement of dose under equilibrium conditions;

In a Bragg-Gray Chamber, . •. •• «; _

If the charge collected" i s Q. esu in a volume V cc,

(Q/v)34 x 1 .6 x 1 0 ' 1 2 _ e

'4.8x10' x. 001293

r a d S » r a d

The absorbed dose D in any other medium, i s given bym

D" • D T , xm wall

rads .

This is a general formula from which the various methods of

measuring dose and the conditions for which they will apply can te

deduced.

When a chainber csliTsrated in roentgens reads 'r' roentgens . :

) • 7 x_. axr __/

0.877 ( l / P ) «- 1 /( H ř ) • 'is''called the f value of the medium'- • • • • | ' I VV"tf>-<3!- a i r . i •• • ... . i. ..iD = f x r where r is the reading in roentgens.. .

For example the f value for tone falls from 4>3 to 1.1 as theHV1 of the X-rays is increased~from 0.01 to 4 : mm of copper.

In practice the chambers are provided, with proper tiuild-upcaps to obtain anďequilitarium wall thickness. ' ^

The simplest method'of obtaining the absorbed dose to different) media, from photon energies uptp 3.Mey»,~is to use a-calibrated Bragg-Graychamber al«>ng with the expression D .= 0.877 x (LlIP) a/('uJ.P)' • x r =f. x r rads. • •• '

Measurement of dose when electronic equilibrium is not-attained;'

The dose near a tissue-air interface or.at any, point in^a mediumexposed to radiation of energy greater.than 3 MeV, cannot be deduced -•with the above formula as the roéntgen has not been defineď fbr these .regions. The absorbed dose may however.be measured by placérig a verythin walled ion chamber at the point «f interest.

GVH:vkk:6ix76 14/-

1. Interface:

Consider the ease of an interface for example a'tone-tissueinterface. Because of the higher absorption coefficient of tone,there is a greater"electron-flux in bone than in soft tissue ." Thusthe absorbed dose will change rapidly from a higher value in the ,bone to a low value in soft tissue. The change in the absorbed dosewill occur even a distance equal to the;range of the electrons«Since the oonversidin factor"f « (.877 xÍK. ,/A^L-n i B applicable,only

under equilibrium conditions, the absorbed dose in the medium can bemeasured, only when the ionization produced in the. Cavity is byelectrons which come from the medium, and when practically no ionizationis produced in the csfrity by electrons which are set in motion in thewalls of the chamber. This is possible only if the walls of the ohamberare made extremely thin. Since it is difficult to make the walls thinenough, it is advisable to make them of a jmatérial which closelyresembles the medium, in which case the walls are essentially part ofthe medium and would introduce, the least amount of, perturbation inthe ionization. If with such a chamber of volume V co the "chargecollected is Q esu, the dose to the medium is given by

2. High energy radiation: •With photons of energy above 3 MeY» nuclear absorption processes

assume greater significance. Further, the range of the ionizingsecondaryelectrons greatly increases-; Because of- fcheir greater energies theelectrons are slowed down in radiative collisions es Hrell, andthebremsstrahlung thus generated combined with jcomptoh scatter and-annihilationradiation increases the ionisation" in an air' cavity by an additional, butnot easily déteřminabie amount. However j thes£ Ipomplicntioris mainlyaffect the deduction of the energy-flux from ibrií-zation measurements,but cavity ionization is still proportional to the energy deposition inthe medium at the point rif measurement; in this, situation also, a thin-walled chamber of a known volume can be used to obtain the energyabsorption in the medium.

Summary of methods to determine absorbed dose í

0.877 x r rads. This may be usedtd calculate D

absorbed dose in air at a place where the exposure is j : roentgensi

2. 0.877 x r xmedThis may be used to calculate the

a point where the exposure is r roeritgens.

air J rads = f x r raäs.

•«sorbed dose in the medium at

G7E:vkk:6ix76 . . . 15'

3x Q/V. This relates the absorbed

dose to the ionization Q (esu) in an air filled cavity of volume Vccat the point of interest in the medium. The walls of the cavity are ofthe same medium. This relation may be used for any type of ionizingradiation whether electronic equilibrium is attained or not. -;•

D.med0.877 x

In this expression Q is the ionization (esu) in an air filled cavityof Vcc inside á chamber of some wall material; This chamber is placed atthe point of interest in the medium/: This relation may be used for anytype of ionizing radiation regardless of considerations of electronicequilibrium. , .'','-. •

5• Energies upto 5 MeV (x and gamma rays): A chamber calibrated inroentgens can be used with the expression mentioned in (2).

6. Energies above 5 MeV s A chamber of known volume:and compositionshould be used with the expression in (4). This method can also be usedfor energies from 1-3 MeV.

Beta radiation8

Å small cavity of low atomic number and having a very thinfront wall can be used to measure the dose in j:ads from an externalsource of beta rays. If the walls of the chamber are approximatelytissue-equivalent and^fii is the mean stopping power.ratio of the walland air for the beta ray energies present, the Bragg-Gray relationgives the beta ray energy absorption, E in tissue as

Such a chamber can be calibrated by converting it to a thick-walled chamber and measuring its response J to a gamma ray source wlichproduces a known energy absorption. E , in1- the wall material. Then

s T/ "V

If the gamma ray source produces secondary electrons of approximately thesame energy distribution as that of the beta rays to be measured.

Ts/Fv - / . - -If a known concentration of an isotope is emitting

particles per gram of wall material, then..

.... 16/-

71 -• 16

" Though the, ionization chamber" is generally moře convenientlyapplicable to, electron; beam intensity measurements, the scattering andappreciable energy loss,in the. wall of the chamber coöstitutei more 'serious problems, witK'telectrons.thanjiiith.X-raysj.;, Electrons above1 MeV in energy, lose ;&p^b:B^ material.Electrons below 1 üeY iia „energy.: lose^;oénergý,.evěn/moř^±ápidly,> Thisrelatively large energy löss >;by eiéctrönaj places, ;a/severe iimitationof the* thickness óf the ibriization chamber walls in vorder that thechamber *iir riot seriously perturb the beam intensity..,'

! ;í ' 'Y'\'

VI - 17UNITS OF RADIATION ARD RADIOACTIVITY

UNITS OF ACTIVITYRadioactive transformations or disintegrationper unit time is the criterion.

' 101 Curie = 3.7 x 10 dps of any radiqnulide

This is equivalent to the activity ofa gm oi* radium

SingleEádionuclide

Exposure doseox

EXPOSUREt

Roentgen(R) definedfor" air at N.T.P.

along with 'radioactivedaughters.

to 87.7'ergs absorbed per

of a i r .

}Total curie 1 One curie., may bemaybe 3.7 x 10 dps1 c u r i e . because of the

occurence as aminxture of manyradioisotopescf the element.

.. , '•.• •' - I - • ••'..

UMTS,' OF RADIATIONtAbscrbed dose

', . • ' ' or"' ' •

Energy absorbedin.one gm ofmedium.

Bioldgical

DOSE ::: EC OTAEENT

•l.l ř--: .Effect produced1KX i i l 5 ^ 1-Xl£!) IH8<"fc u©3?bj- 1 rad of the

,-:. radiation

Hem =(Ead)x(QP)

for radiation protection

RH5." for radiobiological purposes

vkk:7976 .... 18/-

VI - 18

MEASUREMENT OF RADIATION

EXPOSURE (HOENTGEN R) DOSE (RAD)

Free-air ox Standardionisation chamber

Aix equivalentchamber

Bcagg-Gray oxThimble chamber

Tissue-eqn ivalentand 'HEM* chambers

Measurement of chargepeür untt volume ofair.(corrected forH.T.P.) !•

Faergy absorbed, pergm of wall whichis air-equivalent^then 1 r =87.7 ergs/gm

Jlfeasurement ofabsorbed energyper go of wallmaterial.

Measurement ofrads in tissueor rems directly»

MAXIMUM PERMISSIBLE lEVfLS OF RADIATION'

Soon after the discovery of X-rays fy Roentgen in 1895 and 4fradioactivity by Becquerrel in 189*, it was recognised that exposure tointense beams of radiations can cause a variety pf injuries.to the humanbody, such as dermatitis, smarting of eyes, epilation of hair, inhibitionof bone growth et*.f It was in 1902 that, the first case of radiation inducedcancer was reported. By about i£Öt it was-established that almost all 4rgansof the human body are sensitive to radiation.

Sffeots of radiation:

Ever since the* early "days of X-rays and radioactivity it has beenthe aim of scientists to arrive at a value for the maximum dose of radiationexposure that could T»e tolerated without experiencing any deleterious effects.The most important effects are summarised in chart 1. Any of the effectsmentioned in this chart is undesirable and is to be avoided.

Heed for maximum permissible levels;

Radiation exposure due to beams of radiation and radioactivity oaneccur as?given in chart 2. The ideal condition to avoid any of the. effectsgiven in chart .1, would be not t« have any radiation exposure at all. However,anyjtxse» peaceful or otherwise, of atomic energy will not be feasible withoutgiving rise to some exposure. Yet, these, exposures must be.made as small- aspossible, consistent with the feasibility of operations and requirements »f thejob.

Chart 2

Due to "radiation", .

IEXTERNAL EXPOSÖRE due todifferent kinds of radiationssuch as alpha rays or betarays and beams of X-rays of*neutrons.

iiation exposure

Due t« "radioactivity"

HTTERÍÍAL..EXPOSURE due toradioactive materialswithin the Vtdy.

Apart from the exposure arising from the man-ma4e sources ofradiation, nature contains in itself radioactivity. Radiation such,as cosmicrays also forms part of nature. This is called environmental radioaetivitygiving rise to 'natural radiation' or 'natural background radiation.'

cpd:vcs3-9-76.

Chart 1

VII - 2

Eaäiatibn

Exposure,

Absorbed dose in ma».

Biol«gi«al

Somatio feffects*i

Examples:

A» Ihoidenee of leukaemia2. Carcinogenesis3. Skin erythema4« Shortening of l i f e span.

Äenetio effleots**»•

Gene imitations• • ' ' "• • 1

PossiVLe effects onprogeny.

* deleterious effects manifsstable in the lifetime of the individual.**. Injurieus effects transmitted to future generation. -

•3/-

cpd:vcs5-9-7«.

VII -.3

Natural background radiation

The components of the natural background radiation a--j given inchart 3 and in table 1.' The table" gives the average yearly gonadal. doseto population inmrems due to natural background radiation. The total, yearlydose to every individual averages to 125 mrems.

Variations in background:

The doses given in table 1 are only average. Variations in thesevalues exist, from place to place.. Some of the factors responsible for thevariations are;

i) the latitude and the longitude of the place; :

ii.) thě,.actiyity,..conteiit.ofithé earth;.'.:_iii; the activity contained in the atmosphere;iv) the radioactivity in food and water taken by the inhabitants.

An example of the variation in cosmic ray intensity (and hence dose dueto cosmic rays) can be seen in table 2.

Variations in terrestrial radiation:

Variations in natural background are also due to terrestrialcomponents of a place. In areas where high concentrations of.radioactiveelements are found in the earth, natural background is naturally higher thanin other areas. Some values of concentration'of radioactivity in rockp,,soil,water etc. can be seen in (14) & (17)*« Apart from mines of radioactive öres,two areas of very high background are well known viz. Brazil and Kerala inIndia. The average dose rates in these areas are given.in table 3^

PERMISSIBLE DOSE: '

"Any significant departure from the environmental conditions in whioh man hasevolved may entail a risk of possible deleterious effects. Strictly it mustbe assumed that long continued exposure to ionizing radiation at a dose ratehigher than that due to natural radioactivity, involves some risk" (3)»Therefore it becomes necessary to choose a practical level such that, in thelight of the present knowledge,, involves a negligible risk; This can be calledpermissibledose* This was defined as (3) "that dose of ionising radiation whichin thelight of the present knowledge is not expected to, cause appreciablebodily injury to a person at any time during his lifetime."

* See list of references at the end.

Chart 5

VII - 4

Natural Bafliaticn

a) EXTERNAL DOSE: due to i) cosmic rays and ii) radiation from the earth andt h e a t m o s p h e r e . '"'•.;'.' - ' -. ' ;- . . '- ~";;: -•,:;- -.',/ :,\_]i . V ' 1 " , .,:.'•'.":. '.';

L) IHTEHffAI: BÖSE: due to trace quantities of radioactive materials in theh u m a n v - a " " " " • ' - " ' : ' : •• '•''•• • ' - • . • ' • - • • • '• ••-'• - • - ••.••••. '"• --••••'' - • - • - • -

Tahle 1 . ' •.• .' . .

YBÄÜLY DOSES TO POPULATION BPE BAGgGEOUMB'R-ADIATIQN (t)*

Source of Irradiaticn Gonadal dosemrems/Year. .;

External dose:

Cosmic rays .• •

Terrestrial radiation

• 50

Internal dose:"

Potassium (Z7 )

Hadium:

, . Carton (C 14) .

Hadon:' (Prom air tostream)

' - ' •

* Numbers in brackets

it6-9-76.

: 'blood

Total'.

rafer to

i • • • - ; - •

.' • • 1 '/ . - .

•': " • • " ' - • 3 • • - ' • • -

" .• . y':./} ylist of references given at the end.

v i l - 5

Annual doses (in mrads) from cosmic radiation at different altitudes andgeomagnetic latitmdes (2):

Geomag-netic . álatitude.

•Altitude

(metres)

6pd:vcs:6-9-76.

r i,'.

VII - 6

Tafele

Some very

Brazil:EspiritoSanto;Rio åeJaneiro

Brazil:Goins;Mina aGersis

India:Kerlla

hip;h natural

Affectedpopulation

50,000'

100,000

background areas of the world

Deposits ofthorium"bearing-mineral

Volcanicintrusives

Thoriumsands

; Approximateyearly dose

O.5-Ir/year

12-rads/yr.

iomparison- with normal

average

5 to 10times

120times

25times

cpdwcs6-9-76.

i • • • ml/—

vil - 7

A more specific and currently applicable definition *f permissibledose has been given as (4.) (for an individual) "that dose, accumulated over along period of time, or resulting from a single exposure which,, in the light ofpresent knowledges carries a negligible probability of severe somatic orgenetic injuries" (abbreviated as MPD)* It was also hoped that any effects, ifat all, will be of such minor nature that would not .be consideredunacceptable by the individual and the competent medical authorities«

History of

In the initial ůuys --íf medical use of radiation, when only X-rays-were being used, no ooncept of permissible dose existed. The reason was thatX-rays were put into use even before their effects were completely known.Chart 4 indicates the recognition "f ill effects of X-rays in the very earlydays of their usage.

The first observable effect of radiation was e>n skin, i large dose(of the order of 600 radtí (or r^entgeni) of X-rays) produced intensereddening of skin called skin erythema. It was suggested around 1925 thatI/IOO of akin erythema dose in 30 days could be tolerated. This amounted ťs1.5 r/week.

Later, as other ill effects of radiation became well known, theMPD was also accordingly changed. Tahle 4 gives the development of MPD values.

ICKP BEOOMIiENDATIONS, 195S U)?

In settiaig jip the MPD* 3, certain long term effects due even tochronic lew level exp«, «o radiation such as incidence of leukaemia &shortening of life span and the genetic effect considerations, have given thefollowing broad MPD values (7):

(l) For occupational workers, si accumulated dose of 5(N-1/l)per person whenthe person is K years of r.gc; sz-i. lior.ee* an average rate of 5 rems per yeartaken as a practical working faide.

(ii) A total dose of 5 reits in 30 years, per individual of the population,,. when,considerably large fractions of the population are exposed.

Detailed recommendations have been made (4,0) which will conform tothis general basis, These will he seen presently (Tables 5, ,7 & Charts 5,6)

Categories of Exposure;

The ICHP has considered radiation exposure as consisting of fourcategories as given in chart 5. The nature of recommendations with respect t*these classes is outlined in chart 6. Values of MPD'S are given in table 5.

epd:vcs6-9-76.

C h a r t 4 .._ „ v :-v " V .•. .. .;- .. ... -•. ..-. . ••.• .. , A - - > . . > , . \ -

."'-':" .'-'.--. '•'-."-;' Recognition of radiation injuries^' in the early days

1895- Discovery of X-rays by Hoentgen ,, . . •'/. ._

1896 Dermatitis of hands; / :' : /

Smarting of eyes and Epilation

1897 ' Constitutional symptoms

1899 Degeneration of vascular éndothelium

1902 Sterilization due to radiation

1904 Leukopenia due to radiation

I9O6 Bone marrow changes due to radiation

1912 Anaemia among X-ray workers.

cpd:vcs8-9-1976

vil - 9

Table 4' " - , • . . •• - - - : - . ' - ' - • - • "" . " • • • - • , .

Historical development »f MED f*»r

i : 1a.

- , _ - - • - • - -t

Year and authority ,

1954» reooinmended ly ICHP*

1934» reconikěnded ty NGBP* ,

'••' . 1 '-

mäiåtiori

••• ,•. ! . 1 ;

.• :' , ; Ö.

w^rkers-^

2 r/day

/«'V ' •

r/week

ir/day

2i 1950, recommended Tny ICEP

3* 195$, reooznmended "by ICHP

0.5 r/week

0«3 rem/wk.

5 rera . ju"

0 . 1 rem/wk» •

* ICBP - Bitefrugtional Commission oni Eadi«logical Protection

** NCHP - National Committee *n Radiation Protection. \

.10//-

Chart 5/MPL VII - 10

f!n,tRßories of Exposure

Category name Referred

to as .

3)efinition Gomments

Ccvupationalexposure' <

Exposure of ..''!special groups

Exposure of ari individualwho normally .works in <?.controlled a sea* • -

I B(a) Adults who work in thevicinity of controlledareas'*' • ; '

; Adult's who enter controlledareas, occasionally.

B ( O ) Members of the public living; in' the neighbourhood of: controlled area»

normally adults more than18 years of age; only asmall fraction of thetotal population.

Constitutes a small fractionof population, but larger thanA. These are not themselvesradiation workers.

Exposure of the j ipopulation ať large, C*!

Th'e population .ás a whole,or a considerable fraction,thereof;. .. I

Exposure may be due toenvironmental contamination,TV sets, watches & ths generalexpansion of the use of atomicenergy.

ópd;ves

Chart 6/MELVII - 11

outline of ttrV» * to the categories of-expoBure

Category Considerations Nature of recommendations.

A general reduction in oldMPD's. Considering "bothgenetic & long term latentsomatic effects!

D » 5(N-18) as guide line;Weekly, 13 weekly doses;Recommendations for planning foremergency;

iv) Guide for internal, limited todyexposures etc«individual personnel monitoring isimportant.

Bfa) ... Limiting exposures with a&(l) view tčv reducing average

dose to per capita popula-tion. • - • •

í/5 the MPD for A category, general guidanceSome cases, 1/iOthf"these 3 r e t o b e taken '"for guidance in planning of design and work:in controlled area.

B(c) The radiosensitivy ofpregnant women & childrenconsidered o

(Stiide line for environmental tjontaminationin the neighbourhood of controlled areas.-

The genetic effect considered Very low levels (i/iOOth of values allowed forCat.. A when gonads or total fcpdy is exposed)of environmental contamination recommended•

D The danger of; contribution of theexposed patients to averagegenetic dose to populationemphasised. '

All unwanted exposures to he ;avoidedj Coirrectlyestimated doses to desarving cases recommendedto the medical profession. (

Natural background; Ns recommendations; the IPD's given areover and a^ove the dose due to naturalbackground,, ,

~1Tahle 5/MPL

V H - 12

FAXMÖM PEHMISSIBIE JOSES (rems)

Organ exposed

Total Vody; orBlood- formingorgans, lenses ofthe,,éýes, Gonad.s".

Bone, SkLn orThyroid

Extremities., (Hands, foreärms,feet & ankles)

Any ether singleo r g a n . ' ' -"'•'••

Category A

13 week dose

yearly dose

{Annual doses .

Category B(a) & B(t>;

1.5 ..

Category' B(o)

Individualsin category

ópd:vos9-9-76.

v i l - 13

Table 6/WL

Emergency, exposures of Occupational Workers

Exposure,category.

Application Criteria Doses.

Emergency

exposure or

planned

emergency

exposure.

1) Applicable ; only, .to

occupational workers

(Cat. A)

• A.:maximum dose cf

12 rems.

2)2) Kot applicable to women to

reproductive age even if

belonging to category A..

iXlTsea for. flexibili ty of: operation.-3)'" in case rof important work. .

4). Future control of exposure to

personnel involved must be possible

and exercised.

Can be done even if

formula 5(N-18) is7

exceeded;.. .

íhé exaess must Tse

adjusted within the

next five years.

Accidental 1) Cases of very high

exposure envisaged}

2) Not more than 'once in a l ife

time- of ah ihdiv' dual is •

.. expected, to happen...

Maximum limitof 25 rems;

Any excess over

formula 5 (N418)

written off..

cpd:Vcs20 .9.-76.

rYII - 14

Table 7/WPL

Special cases.of exposure

Exposure type Criteria

Occupational workers,whose previous radiationhistory is unknown.

It will be assumed,that theINDIVIDUAL has received1thelull allowable dose accordingto the formula, D=5(N-18).Personnel ..monitoring service willbe started & future ±eoordsmaintained. *

Occupational,exposure. of non-adults.

Normally h« person under age.18 is.employed in radiation work.In any"case, minimum age,limit forsuch work.will be 16. The dose tosuch persons should not exceed 5rems until age 18, and 60 rems at age30.= .-.

Exposure to population. An example of apportionment ofmaximum permissible population doseof 5,rems per individual, is given as:

Gat.Gat.Cat.

A ••'. B • -. c'.,-'"

Reserve '

'otals-"

1.00.52.0,1i55-0

rem.it

cpd s vos:' 10-9-76. .15/-

vil - 15

Internal exposure of occupational workersI

The maximum permissible doses given in table 5 represent totaldoses to whole body or individual organs or extremities, from all types ofsources and radiations.

These total doses may consist of totally external» totally internal'or a mixture of both. Chart 7 gives the differences between internal andexternal exposures.

It can be seen from chart 7 (adapted from ref.9) that there areimportant distinctions which differentiate the problems óf internal andexternal exposure.

It is also clear that internal exposure due t* radioisotopes fixed inorgans is much more dangerous than external exposure. Considering.these,ICRP has given detailed recommendations regarding internal exposure. Thegeneral features of these are outlined in chart P.

The radiation protection measures thi are made feasible Tiy acombination of the abovementioned KPL's for external and internal exposureswill be seen presently.(table 10).

Classification of MPL's '.

In the course of setting up of MPL's, values for the follrwingquantities have been set up:

1. Maximum permissible ,individual dos.es.

2. Maximum permissible tody ÍUrdens

3» Maximum; permissible concentration in air and water.

In an attempt to conform to these levels in actual practice of radiation work,it becomes essential to control • ." the. field (i.8, dose rate in r/hr) ist tkeworking, place, the contamination on the working surfaces etc. ;. Considering'these, a classification can be made of MPL*s as'given in chart 5.

MPSC; • " . ' ' :

Chart 9 indicates th.% to control the internal exposure ofoccupational workers, the auxiliary methods (viz* Secondary and tertiary sstandards) are helpful. The considerations leading to a set of MPSC (feximumpermissible, surface contamination) values (inltcVam^) are given in «hart 10.A set of .MPSC values is given in table 9, | . *

cpdtycs10-9-76 .16/-

A comparison of external & internal exposures

Maximum permissibleindividual L exposure.'

Exposure, peripd. ',.'

Cumulative dose to theindividual is the controllingfactor - j . .In administrative-practiceweekly, 1$iweekly & yearlydoses' cari "be -stipulated.

The exposure-ceases assöon äs the řádiajtionwork is terminated;

Internal Exposure .

Maximum• permissible tody turden of eachisotope is given -. Flexibility of control,rendered difficult by the retention &elimination: properties of he isotopes.

P.M.* has to be done by excretion analysisor whole-body iuOnitorá. :

Because of the retention of radionucliäe..in the tody» the exposure.continues evenafter radiation'work is discontinued,Xtorev!hazardou.B. . • -

MPli in the -workingareas

Bosé-rates iň woríkingareas .& other places _aredefined; Occasional orperiodical or continuousmonitoring:of these oah be donei

MPC's.in environs are listed; These teingvery low for working areas, and extremelysmall'for othor environs, monitoring andchecking become/difficult.

• Control i): Laying off from radiationwork will do.

ii) Proper shielding willreduce the hazard.

i) Uiscbntinuipg radiation work will nots u f f i c e . ; . . . '••

ii)íbctřéiae čare in design of work,handling & ventilation systemsnecessary.

• n • -- • i

* P'.M. - Péiřscinň^l monitoringů

** MPO - máxlimim."permissible cohcentřation.

VII - 17M«des of Entry »f Isotopes* into the Body.

IIngestion

Soluble

Absorbed ingastibintes-

"tinal. tract»

ÍCertain frac-tion intoblood.

Inscluble

Not absorbedin gastrcintes-tinal .tract >aidse laayés the

organism with <the fetes«

Critical Organ

rest .is excrečed in. urine j feees or throughthe ir.ngs.

Inhalation

Soluble

25$ exhaled, '•.50^ depositedin upper»espiratorypassages andsubsequentlyswallowed.llo

de25$ depositedin the leverrespiratory'passages.- -

ainCertain frac-tion into:blood.

Critical OrganThe rest isexcreted inurine, feces orthrough the~lungs.

Insoluble

2596 exhaled'50$ depositedin upperrespiratorypassages and.subsequentlyswallowed•

Injection andthrough s H n

Soluble

IDissolvesíá the -••blood

OriticalOrgan

depositedin i the lowerrespiratoryjasságe,. out. cf .

: which -1 al^is, 'eliminated fromlungs.;- Thus tctalswallowed amount is

•, .-;••;••,.•-y

: Passing; throughgastrointestinaltract leaves'theorganism with thefeces.

Insoluble. • I _

Partly carried-away fcy the fclocd] Btreåmi; Partlyretained in álocalized region.The second partgives rise tclocal irradiation.Jlrst-parteventually appearsin the critioai

, :/(irgan.,~ •'- -i:. •

opdrycs...18/-

VII - 16

Ohart -6/to. .... (in conjunction with 8(a) to 8(f) )

Internal Dose forOccupational Workers

Internal: exposure "by

.. Inhalation

Iiireot experience J

/ ' " • ( " : • ' • • - • ^ ' : ^ ' • • • • • •

In case of radium, J.1) luminous dial.painters2; Patients treated with'• E s •.'•.'" y-.-h' ,-3) Users'.of .'public water

supplies relatively richin Ea-;

q. = 0.1 b- gra (or

Ingestion Absorption through skinf' ,or wound.

HPBB** (q ) is set on the basis- oft1

Comparison with:radium + •*•

For bönéséeking isotope andemitter,

Permissible dose Other Considerationsrate to the i . VV. . ,critical- organ*** e.g. chemical

I .toxicity; in' case •"••Will be given ty q, of Uranium: ,.•••--•.• .

t is that amount of this radio-. (jx-C*.) in the , . ...... ,:isotope:which will deliver the body. isame dose, in reins to thecritical organ as 0.1l*-gmof Ea. (& itä daughter products)

* for Criteria for critical organ see chart 8 (a)

** MPBB (maximum permissible body burden) is that activity (in the total body) ofa radionuclide wMcti can be accumulated by a radiation w»rker.

*** These dose-rates are given in table 6 (t)

cpdtrcs13-9-76.

VÍI -

Chart 8(a)Choice of the Critical Organ

definition; The. organthat is subjected to the highest jäose-ratefor the lowest concentration in air and water, or for the lowest "bodyTrarden in the whole body, is selected as the critical orga». •?

• This is governed i. Vyt * • | 4^ ^. - ** ~

1) Ťbe MgaJa of. greatest concentration of raäioéctive material*,

2) The éssentialness «f the <»rgah to'the well being -«fthe entire -iiody;

5) The damage to the organ in the route of entry of the řaů*«miblide

4) The radiosensitivity of the organ.'-

5) Other factors such as chemical toxicity of the radionucíide specifié, • . : v l | • • " • » • • • • • - • • . • - " - • v .

to the orgán. ;

* ''Except-for a few radionüclides, this becomes the determining factor 1»choosing the critical liody organ." j

~ ? —i

is.,-'",;•-:, •" ' . - " - - i i '.:

cpdrvcs . . .ti .-.. rriři.

VII -"20 •'>•

-Table

Maxiinum permissible dose ra tes to5 organs

Orgäna;, remsi/weék

1. Total.boäy

Gonada;

.•Blood forming organs.

2 . Bone V-

3 . Skin;

.Thyroid •

4 . Any,oth|;r orgán

• \ . 'V'*-:-: • >

opd:vo813-9-7« . 2 1 / -

Chart 8(c)/MPL

VII.- 21

Maximum Permissible concentration (MFC V_ _ _ - - -That concentration in air or water-jwill give rise to UPBB in a standard man*during the period of his i radiation work(viz,'50 years). :

A standard man with some average characteristicsis assumed for purposes of calculation.

. : ; , y - ' - . - ; \ r - • • • • • • • " . ' • ' • • '

MPG defined for: ." • • • • • - t • - • . ' - •• ' '• .

IFor radiation workersWorking hours considered; ,Inhalation of contaminatedair during working hoursenvisaged,

others

, Safety factorsare assumed; .suitable to thecategory and•ritical organ.

" . ' I -

* For some characteristics of. standard man see table 8(d)

** for radiation workers and others» the trend now is to haveone limiting (MPC),in water for all (15). ."

cpdivcs13-9-76

VII •- 22

Certain characteristics of the; STJßTMKD 14AN(applicable to woman also)-

Weight

Period of radiation work-

Aix^-íntake per day.

•fiir-intake during work-hours

Water-intake per day.

50 Years

20,000 Utře»

10,000 l i t r e s

2.2 l i t r e s

Water-intake during work-hours 1.1» l i t r e s .

cpd:vcs13-9-76

"?**.&,•«•. I f ' l » " ' V

VII - 23

Some special oasest affecting internal exposure

Oase Remarks

1.. Eadionuclide with áchain of daughters.

energy «ontrilniting to dose,of.all the daughters with appropriatefractions »f the parent activity andwith proper BBS values is used»

2. Known mixtures ofradionuclides.

Weightage is given to ttífe actualconcentration and (llPC) of eachradionuólide. to determine theoverall (MPC) thAt.can he. permitted»

3. Unknown mixtures ofradionuclides

A/broad classification of radio-nuclides , into groups.is.medeí The(MPC) of the most hazardous r.ií* ineach group is taken as the (MPC) forthat group.

4. Submersion exposure. This is a case of exposure due to acloud of radioactive gas. The dose tothe skin of the whole body or thetotal hody itself due to penetratingradiation will,decide the (MPC). Thisis applicable to certain gaseous r.i.

* Toy the ICHP in ( G ) .

** r.i. - radioisotope.

cpd: vcs13-9-7Í.

VII - 24

Modification

Category

of (MPC) values

Persons

for other than radiation

Modification

workers

factor

B (a) " Non-radiation workersin the,yicihity ofcontrolled areas»

B 00 Adults enteringcontrolled areasoccasionally.

10 t . A

B(c) Individuals livingnear, controlledareas

Populationto

Ci) 1100

(if total body or.gonads istie critical organ).

(for other organs)

cpdivcs15-9-76

vn - 25

Chart 9/MPL

Classification of Maximum Permissible levels*

Primary standards

Laying down ofMaximum Permissible(individual) Doses

(s)(a)

Individual personnelmonitoring necessary

Secondary standards

Setting up of limitst? the contaminationof the environment

(MFC's) " •in air & water(b) *

IEnvironmental (or area),monitoring as to ensure;

), envisaged.

Tertiary standards

Limiting contaminationof working areas(MPSC's**) , y

Checking ofmonitoring forspread of radioactivity.

* These are mainly for occupational workers

•** MPSC - Maximum Permissible Surface Contamination

a) These are rems

b) These are microcuries/c.c.

c) These are microcuries/sq.cm.

opd:vcs13-9-76 c..i,.*.26/-

YII - 2É.

Chart IQ/MEL.

A. in controlled areas

Basis Í B the moreStringent ef:

Irradiation of handInhalation cfactivity.

Maximum Permissible Surfaoe Contamination

B. In general areas

Basis is Ingestion*f actiyity "by anon-radiation worker^

C« On skin.

Basis is possiblecontamination ofthe hands ofradiation workers.

MPSC in^o/cm or dpm/cm in general will bs the MPSC for A,B,above of the most hazardous'radionuclide in each group of*

(a) OC emitters;

Alpha-emitter«:

Beta emitters :

Controlled areas

-A / 810 *kc/om

10t:>/kc/cm

adapted from (10) & 0 0

-9-76.

General areas

1O"7-5

10 j/cm

.«•--•

vir - 27.

Methods .»f Control:

Realising these MPL's in practice is the crux.of any radiationprotection measure to. toe -taken-'by: the worker and the management; includingthe Health Physics personnel and the'Radiological Safety Officer; 7Thequantities and methods toy which they are either measured ,5,r controlled aregiven ih Tahle 10 i" ' ""

> ' • • ' - • • . • • - . • • • . - : ' • ' ; •• '

MPL for neutrons; . •

The MPD's in rems mentioned are equally appjlicabletf,neutrons. Butneutron fields are normally expressed in terms of intensity'otf>flux-(vizn/cm /sec etc.) Because of- the peculiar nature of interaction and energytransfer of neutrons with matter (for that matter, cells of the tissue)special calculations become necessary to.find out the dos.e in rads.. So itis Convenient to express MPD for neutrons in terms of their intensity. Thevalues of ( M P F ) Maximum pérmisnible flux, for thermal and fast neutrons aregiven in table 11 and charts 1 t & 12,

Current trends: " • , .

The International Commission on Radiological Protection, just as theICRTJ, meets from time to time tó review the knowledge in.radiatiqn Effect B andt« use the'experience"gained in radiation protection, and t« accordingly makesuitable recommendations* . ' • •

• In | recent publication (ICRP publication no.. 6, 19^4-), the ICRPmakes additional reöqmmgndations (to those of 1958) mainiy with respect to,

: 1) Exposure of women, "•_ ••"•-

2) Combined exp. to internal and external radiation; and

3) Exposure categories. " -•'":

With regard to. exposure of women of reproductive age, the commission reoommendsthat the. abdominal exposure of such women should be limited to 1.3 rems/13 wksfd i order to reduce exposure during "possible undiagnosed pregnancy. This d«sé-icate corresponds to a yearly dose rate of 5'rems", hut taken at an even rateV

. :••:• With regard tb radiation exposure of pregnant women, the -• co .urecommendation is ás follows: . . • • - . • * • - . -,

After the diagnosis of pregnancy, the foetal döse during theremainder of the pregnancy should toe limited to T irem.

cpdivcs13-9-76 .2«/-

Table IP/MELQuantities and their1control

Quantity

Maximum permissible dose. Individual personnel monitoring; ,The film badge, Meásúríág - -"•"••• /instruments like pocket dosimeter

Cumulativeindividualdose«

Keeping of records of a l l perso»nelmonitoring results; Yearly additionof weekly (or periodic) drtses.

Emergencydoses. .

Secorďs of ylanning; the doserate .monitoring data; and proper Creditingof doses. . ' • • • ' . • " ' • ; •

Maximumpermissiblebody burden.

Periodic urine analysis (or otherexcreta analysis); or whole bodymonitoring. , -.

Maximumpermissibleconcentration

(a) In air;. Continuous aij; monitorsin neoessary areas; Por environs,sampling air (oocasipnal)

(b) I* water: Pe»L«ďi« sampling of water& «ounting metfiods; Similar; pro»eäurås forfood and food articles.

Maximumpermissiblesurfacecontamination*

(a) In high aative areas; : .Oheoking •ontamination;

J TJsě of glove >pxes fc fume hoods.(bY Of working areas t v: •: : í. .Methods such as swipe testing.:

(•) >f hand's etol Geiger :founter; »rhand and foot monitors.

CBBivcs10-9-76. .29/-

.. - i

711-29

' " • ' • ' - ' • ' ' " • - ' • • • - . " '

C h a r t I l / M B L * * . •..;•; • . . . y : 1 ; --;.,:, • ';< ý i v . r - , -•..- ^ - l : - . , . , J ; . . v / '

Calculation pf. MPF \of, Thermal neutrons

41 • Neutron absorption by hydrogen & nitrogen

' ' ' in'.tissue i . '"' '•' - •

i ) H(ňi. | ) D - with 2.2 Mev "gamma.

ii);IT1 4(n,p)Ö1 4 - with 0.6 Mev P. ' »

Using appropriate cross-section and EBĚvalues^ that flux which delivers a döserate of tyr>0 mrem/wk to the total body iscalciilatedw : - ; *;: •

Chart 12/MPL**

Caleulation of ffl^í1 of Past:Neütrona " ! '

Elastic seattéring5by; elements in tissue

Energy impařteattelg óf-tissue is given by*v

TJsé"1.proper BÄE- values - j;or f^ind'äoseVin'rainsjtp total '•»ody

epd:vcs.10-9-76.

f: w h e r e »>':•.'.; £%.';, : !;,' :.;,' •.. 'c,:. ..&;•: v:iv{ •-.

. B. ;ř'. energý^in; .ey,: of incident neutrons' M' -' mass :no.~«f":ěíeméhťi'V., .*. '••-. '"•';

N. - atoms :ř«f. the element/g: of "tissue«<$"* - oross-section i n Tiarns. Í .

^ »ruf

r ís vá

K -JÍ

l - 30 ...;

"• ' 1 - - - -

Table- *-"-. *- rt-^i^t.- Fliixés &

energy

ThenfiJÍ y

0 . 1 3&T{ř-c:

0 . 5 KbT

0.02 MEV. '

0 .10 MeT "

2Í5" 570

dose »f

-. TíiŠRl B? :: Vä r.i .->: » S.,' :'Ji>íf;/ . V-;. S C l ; í * 4 Sť]^; f. i

cpdjvos. ? " . - ; :;••-!o

,-• if.-", "i ••Ir: 1 , .K-

''<z"\ví i.1-"•i'VJT'-'

TEE - 31

This can be achieved by applying the control limit of 1.5 rems/yr.appropriate to non-occupational exposure.

Cb).If the foetal dose will be considerably less than that received by'the -woman, e.g. due to soft X-rays, than continuing ocopational exposure ata rate of 1.3 rems/13 wks is acceptable.

In respect of the additional dose due to external radiation, to thedose from long-lived bone-seekers,v it is recommended that any curtailing ofthe external dose is not necessary if the estimated ,>ody burden of theindividual is less than, one-half the maximum periniseirLe ¥ody burden. Noradiation exposure will 'Jbe allowod if the estimated BB reaches the M

As regards the exposure categories, the commission has recommended Gu-that the category B^s) (see chart 5) detailed in1958 Recommendations needno more be considered. Since this category^ consisting of members of thepublic living in,the Jieighbourhood of controlled areas, includes pregnantwomen and children, it will be appropriate to consider these persons also asmembers of the general population (i.e. category c ) .

cpd:vcs1Ö-9-76".

rVIII RADIÄPIQK DETECTORS AMD INSTRUMENTS

Principles of Radiat ion Detection;'- The fundamental mechanism underlyingthe operation of a l l nuclear rad iå t ibn detectors i s the diss ipat ion ofenergy by a charged par t ic le in a su i tab le medium and the d i s t r ibu t ion oft h i s energy among excited s ta tes in the detecting m a t e r i a l . Thus in placeof a single charged par t ic le which provides the energy, there are "producedmany ions, or l i gh t quanta emitted from excited centers in phosphors asthese . re turn t o the ground s t a t e . The ions can be seperated and the t o t a lquantity of e l e c t r i c i t y measured'. Light quanta may be absorbed in a photoe l ec t r i c surface causing emission of photo e lec t rons which,can a l s D becollected af ter proper mul t ip l ica t ion , and measured. :

One or other.of these two processes i s employed in the de tec torsmost widely used v i z . ionisation-chambers,-proportional and Geiger counters,and s c i n t i l l a t i o n counters. In a l l these , -a part of the'energy of thecharged pa r t i c l e s is used up in the ultimate"production of a pulBe-Df. '.e l ec t r i c charge. Ailarge proportion of energy diss ipated in matter appearsas heat and therefore i t i s possible t o detect a high energy flux by someform of, thermally seas i t ive device, such as thermo couple a l s o . - • • ; . . :

Other pr inciples of detec t ion invplve the. i n i t i a t i o n of chemicalreac t ions due t o passage of. a charged par t ic le or a^permanat a l t e r a t i on .o fthe s ta te of m a t e r i a l as in case of passive detectors l ike films which goan storing up information un t i l they. are examined but do not of themselvesproduce a s i g n a l . ' .

: "v. . Tne líásic pr inc ip le of detection of nuclear r a d i a t i o n -s l i e s in measuring the charged p a r t i c l e s / i n an ionis ing medium, Bie produceddetect ion of electromagnetic through,the /process.of interact ions r e s u l t in-the t ransfer of jan appreciable, part o r - a í l , *oY, the energy to one or a few.charged p a r t i c l e s . Elas t ic co l l i s ions of fa'a^neutrons in the hydrogen;nucleus, compton sca t te r ing of a gamma photon-ani t ransfer of.energy t oelectrons are examples. Thus the primary energy i s dis t r ibuted through, theoetíiun óf secondary charged p a r t i c l e s , leading t o the .above mentionedprocess of de tec t ion . , . . .

•' The in terac t ion medium where the charged , or uncharged p a r t i c l eor photon in t e r ac t s and. produces, secondary charged par t ic les .sand the .detection medium in. which,; the^/chargéd: par t ic les , d i s s ipa te the i r energy may/secondaryoccupy the same space .or they-may. be. d i s t i n c t as. in case of ionišat ion- ' .chamber type instruments and neutron de tec tors . . . . .

In the latter» neutrons interact with hydrogenous foils and ejectprotons which dissipate their energy in ionising gas in a spaceabove the foil. The amplest kind of instruments viz. ionisationchambers and .conduction counters use gas as interaction as well asdetection medium. This is because the seperated charo^s &novlr- hemobile under the influens of an electric field applied to theelectrodes in contact with the detection medium, if the result beeto be of use for measurement.

Ionisation Chambers*- Ionisation chamber consists of an outercylinder coated inside with graphite, to make it conducting and *a central olectrode insulated from the chamber wall. The cylinderis. filled either with air or with a suitable gas acting as aninteraction as well as detection medium. When the chamber isexposed to radiation,ion pairs are farmed and are collected bythe electrodes. These ions are allowed to flow through an externalcircuit giving rise to a-more or less"continuous.current if the '",radiation intensity is sufficient. Thus an average, rate of energydissipation in the chamber is measured. Such a measurement is oftencalled a "dose-rate" measurement. -The minimum current that Can beconveniently measured is about 10™ amps. The ionisation .currentis a measure.of intensity of radiation. For á cylindrical chamberthe approximate relation between current and intensity of radiation

.where

10,-16

• V = Volume of the chamber in oo.R = Döserate in mr/hr.I = Current measured in Amp.

For example a chamber having a volume V = 500 cc and for a doserateof 1r/hr will give a current

500 x 1 x.1000 x 10,

•LÖS "~

= 5 x 10,-11

Such a, feeble current cannot be measured even by a highly sensitivemeter. Normally the current is amplified seyeral times• beforeit, can be measured by a meter.;. Lower rate of charge accumulation ismeasured by corivertingthefeeble d.c. into a.c.: by vibrating reed . ' •' electrometer and then amplifying the a.c. signal. The amplifieda.c. signal is then rectified to yield, de. : ' -

Lower rate of charge accumulation can also be measured. by measuring the time taken from a known value of electrical capacityto .be dåcharged over a specific voltage range so that

• 3/-

The surrent collected-from an ionisation chamber exposedto a constant radiation intensitymincr'eases.as the voltage appliedto the collectiig electrodes is increased from zero. Above a certainvoltage ho increase in current is observed because all théílibéráted.charge is collected. This voltage is called Saturation voltage andion chambers are operated^above this voltage. As the. .doserateincreases,' the voltage at which the chamber.saturates increasessince the electrons and positive ions tend to reoombine unlessthe electric field is strong enough to force the partiales to theelectrodes. Pig. 1 shows the saturation curves for a .-typical ;ionisation chamber. , . • .

Almost all applications of.ibnisation chambers requirethe saturation of the chamber. Some' applications sucn:äs ppcfcei;dosimeters and thimble chamberä which operate over a ratige of : ?voltages must have the chamber saturated at the3Sw«*t. vbltagé;"these chambers measure theaccumläted dose r a maximum value:,of jrate must be stated for .saturated 'operation.;; ' '•;.>..'::••;'>•'.';,':-:'.í--ť':'.'.

pVIII - 4 -

Proportional .Countersi- To make possible the detection of" a singleparticle whifah dissipates less .energy in the medium, it is necessaryto multiply "the .secondary ionisation by a constant factor M on itsway to the oallecting electrode, and no signal should be producedin the absence, of ionising radiation. . Suhh a process is found inthe gas amplification phenomena and the .counter making use of. this iscalled a proportional counter.

Thus in a proportional eounter the number of events isdetected. Theoretically ionisation chamber itself can be used asa proportional counter and a Geiger counter depending on theoperating voltage. But practical design considerations aliter thesituation. Pig. (2) illustrates the charge collected per primaryion pair in the counter for an idealised cylindrical counter

^ ó0 3

±_^/r. • ! . .

/ ' ; t' ! !.,:

• * >

x ; - !i " i i1 i i! i »

) i. :

•4QO

GVIhpp s:4.9.76

VIII - 5-

IT the voltage of an ionisation chamber is increased beyondsaturation region the number ofu. electrons, collected per event .."increases. This is due to the higher electric field in which the;secondary electron is accelerated toward the anode and the increase 'in its kinetic energy reaches the ionising energy of the atoms ' .of the gas filling the chamber. It encounters collisions in its':path and creates another ion pair. If the process repeats beforeactual collection takes' place, the, resulting number .of. ion pairsis much greater than, but proportional to the original number*••

This amplification effect is called ga.s multiplicationand the ratio between the original and collected charges is:thegas amplification factor M. If M is to be independent of the positionin the chamber at which the'primary ionsatiori occurs a suitablegeometry is cylindrical, on». The anode, is'mafie: isf, very thin tungstenenabling the production of an intense field át the' center over a .desired number of mean free 'pathawhiie the"field-,is less. over, the»nainder of the portion. Gas multiplication takes place very closeto the anode and hence M remains, constant irrespective.of the pathof primary event. . . .

The phenomena stated above is used for counting/photonsor particles. A single event entering the counter,thus.résults.in 10 times as many electrons as it originally .produced and if thischarge.is collected over á short time a pulse, results.. The: amplitudeof the pulse however depends on' the• specific ionisat'ion of: theentering: event. .., " : . , . , •/',-' ••'.'''•

-•-•': -After the negative ions are collected,- a sheath, of''. -positively charged .ions^surrounds =the electrode.'; This, shéathmoves more slowly towards1 the, cathode, than, the electrons move,towards the anode. • .-•. "••" . , _ : !.:;...;

.;' . Therefore a volume, in the vicinity of the anode :istemporarily dead and other:events occuring in this yblüme;duringthfe collection time will not be counted because:the:.späperQharge ;f;reduces the :éffective field strengthi. „-':í*ř:-;í^J/:-'-\$?:

:": "?'':''/"'. "t

Counters operating:in proportional región are made far;.:,seperatipn of pulses, produced.by mixed type of 'radiation., Differenttypes of radiations"are^ having:different specific-•ion'iBa

!tipns-?ian'ä•'-. ; 'hence produce pulses'of different heights^ which can', be' sep'e'ra.ted.' : : .electronically. * If the amount of primarjr .ionisat£pni:is proportionai-..to the energy of the| radiati 6n;'-' the:^Biiribu'tioiisofe^iöebÄäi^ts:^from a proportional counter gives.anKeriergy distributionipfíthe •••.;,• •p r i m a r y r a d i a t d m . ' . . . . :,, '.'-/• /' ,' •,?;• ... ;;> .

VIII - 6 -

The. construction of .proportional counters mainly dependson tlietype of applications. Large number of applications:involve• 2nor 4J|counters with the.gas flowing through the sensitive volume.Such 4ííčíounters enable, an absolute measurement of activity ofvarious samples with case of replacement of the' source of activity.

Geifer Counters*- If the voltage applied to a proportional- counteris raised "the electric field inside the counter increases and so doesthe gas amplification. The .proportionality between the originalnumber of ion pairs; and the pulse height np longer exists'in a region,which is called the region of limited proportionality. If the voltageis further increased all the pulses, become'the same height regardlessof the original number of ion pairs in the counter. The relation betweenthe pulse height and vfoltage ahows4 that t the pulse height attainsmaximum and remains!constant over a region. The voltage at which thisstarts is'called threshold voltage and' the region of constant heightis caled as Geiger region or G-.M. platesni Increase in voltage beyondthis region produces spurious co unts in the counter and it goes in tocontinuous discharge.

The pulse height observed in case of G.M. oounters islarge (upto 2 volts) and hence preamplifiers are not essential .»for the recordingsdevices to be triggered.

Pulses in G.M. counters are formed by the collection ofelectrons by the anode and positive ions by the cathode. The latterupon reaching the cathode, pull electrons from the.metal and combinewith them. Sometimes the difference of energies between the ionisationpotential of the ion and work function of; the cathode is .radiated as a.photon which releases an electron by photoelectric absorption ofcathode. This.additional electron results in another discharge. Toquench' this multiple discharge one of the following methods can beused. -' ' •" . ' •'"• "'.'.'': I' :'- '.''•-'•''

1. External quenching;- The negative pulse from ,G.M. counteractuates an electronic circuit which will, reduce, the potential onthe wire for a.fixed interval of timev During this period the lowpotential "gradient stops further avalanche formation.;

2. Internal: quenching!-(PoLv-atdmic) vapour molecules.alcohol, otheror acetone-;, and halogen vapours filled in the counter along with thefilling gas .also stop the secondary avalanche formation. In thesecounters áhe positive ions of the filling gas which travel "i;owprds thecathode

GTRjpps «6.9.76 • -4 . . • * 7/~

. vin - 7 -

collide with the quenching gas molecules and their chargeis transferred to the latter, which move further towards the cathode.Energy released during the.process of transfer of charge (Ionisationpotential of argon = 15.7 V that of .alcohol 1..+ .W); goes intodissociating alcohol molecules rather than producing ä photoelectron.Thus multiple avalanches are stopped. In case of halogen «quenchingthere is an additional advantage as the halogen gas raol-oculesafter dissociation, recombiné to replenish the supply of quenbhinggas. This extends the life of the counter indefinitely.

t n e discharge of counter, the electric.ow normal afie to the presence or. a posi

fieldtive inj.1. n TÍ J?QHwTÚt}&,tne discharge of counter, the electric. fiel

the G.M. tube is^ielow normal afie to the presence or. a positiveion sheath.- During. initial .stages therefore the counter reipainsinoperative. This interval is called.as dead time of'the counter.The time required for the complete recovery of the pulse size afterthe end of the dead time interval» is known as recovery time (fig.3/Typical value lies between 100 and 200ij&ees. . This uncertainitycan be avoided by fixing "the in-operative period of detectionsystem .electronically, a value slightly higher than the dead time.G.M. 8oun.ters can be built in a variety of geometry and. sizesdepending-oh. the applications..Beta counters, gamma counters,liquid ountěrs-are the common types. ..-•'

The efficiency of G.M. counters is defined as. fractionof particles which upon entering the senstive volume of the tubeproduce discharges. Efficiency in case of counters is unitywhile for gamma, rays it is dependent on energy of incident ray,and is verylow, of the order of 0.01.

Sen» i

VIII - 8 -

Precautions»-' Geiger counter operations can be drastically affectedby applying too high a voltage and allowing it to go into. "Continuousdischarge. Hence the upper end of the plateau should, not be .investigated when studying a counter. , ' . ,'"'•''

flETECTOHS •

Principlei- A scinti l lat iondetector consists of the. following1) a lumihesoent material, fe) an optical device to faci l i tate, thecollection of. l ight, (3) an optical joint between .the luminescentmaterial and "the photomultiplier, (4; thf P.M. tube, and an (5)electrical circuit to record the, pulses appearing at the output ..ofthe photo multiplier tube. The performance of this detector systemmay be explained in the following consecutive stages. • ...

The incident particle impinges 1 on the phosphor, where, i t •dissipates.its energy in the Ionisation,;and excitation;of ,ittie. . .,,.,molecules. , A fraction of this energy: i s converted into photonswhich are radiated in all- directions.. ;Some; of these photons, fäl l ..on the photocath 5de of the. multiplier tube .and eject, a „number;, of •photoelectrons. These photo electrons are;accelerated?.by thepotential applied between the cathode and the f i rs t dyňode of thetube. On striking the f i rs t dynode .each photo electron ejectsseveral electrons by secoÄdary emission. "•'•;.••.

This electron multiplication-process is repeated.at.subsequent dynodes,: each of which is at a, higher potential .thanthe qpfceedíníi one.. Finally after a multiplication of-.about10^ to 10 the 'electron avalanche arrives at the collector-'Jplate*It produces, a voltage pulse in the output:cbnďenáer whiéh, is;

coupied.to an external äulse amplifying circuits 'Thus the'initialenergy of a single ionising particle is transformed into a -single;voltage pulse. The whole system, is enclosed in a light tight boxto eliminate effects.other than;those due to incident lionising ' 'radiation. ' . - . ••-•." : -'-, .••-,:'=-•. :

1. Absorption of incident radiation by the phosphor'- A chargedparticle dissipates its energy through the luminesent materialthe amount of .energy dissipated depends on the; dimension;: of thephosphor and the maximum range of the particle in the.material ifthe later is large compared with the dimension ;6f the phosphor.

uncharged"ra diatioňs ionise *. the.medium indirectly.The fraction of incident .quanta of ionising,the medium is

G¥R»pps:6.9.76 •9/-

VIII -. 9 -

where K,, i s absorption coefficignt..;óf the^phosphor for theradiation and • , , •..- . •-• , : '"."' '•'.'•''•' .

where Kph

Kph +-EQ--+ Kpp V ;' <v. • ; . \ - '

Coeff for photoelectric: process

" " compton process •

" " pair production process

The energy-transfer by the incident quantum'to the secondary-electrons depends on which of the three absorption processes iso p e r a t i v e . •'.••' .- . . ., ""-._.-' .' "; ' • - ' . . • "

2. Photon emission from the phosphort- . The. energy "i ~st by eithercharged or unhharged particle inside a luminescent.material is•partly converted into photons of wavelength corresprmding to thedirect energy transitions from an; excited^electronic level to-ground state. >In condensed systems the emitted rádiátion1 is .distributed over an emission band due. jbo yipratidhai broadeningof. electronic energy levels. However, this banciofRemission ;Isindependent of inöiäent, radiation, and its energy. ;The conversionis dependent on the,absorbed energy.. " : : ' :

The photon emission.Sue to the- transition: from; 1;he excitedstate of the molecule to.the groimd state, in" most of; the cases..(fluorescent materials) takes pjace within- an interval of 10~ • to10 sees.. The rate'of "emission iis-usually-vexpptential«. Howeverin some luminescent materials there, is :anrafterglow; existing becauseof the metastable states of ...excited- mbjucules". This phenomenais, called phosphore-sence. Emission occurs qnl r when; the excitedmolecule has received the small additional energy: hépessary tom a k e t h e t r a n s i t i o n . ' •'•.".'•'" . ..- . . •' ;,. '•:';•'/;!'', •'•••_-"•• •>'•'_.

The major luminescent process úl-the scintillation ,; ,c o u n t i n g s y s t e m s i s f l u o r e s c e n c e . . V • .. '•':'-.-•'.-''•-'.;.• ._•.:' "'••-'-' •

Conversion into photo electrons:- Hiotbris incident on.the photo- .cathode of P.M. tube are converted into photoelectrons.. Efficiencyof this conversion depends on the properties of bathpde maierial/'T;.;. ;.and on; its optical rbsorption for the incident rsdiåiion.- Normallyffb-Cs surfaces deposited, on nickel are ,used as photocathojles. / . 'This has been found to have high photoelectric and secondary ...emission-factors with a low tiérmioniö emission. : . ,

VIII - 10 -

The thermionic emission of electrons from photoöäthödésprovides the main background of dark-noise pulses against which thesignal pulse i s to be detected; .

The thermionic emission depends on,the work function of .cathode and is proportional to the area of the cathode. (This emissionis reduced, biy:1 operating the tuba at a low temperature). Othersources of dark current are .ohmic leakage in the tube, and the 'incidence of penetrating radiations on the subsequent dyňqdesgiving rise t? secondary electrons. The l a t e r can be avoided vby screening and by suitable geometrical arrangement of the system...

Electron multiplication:- Eiotö electrons produced at thie- cathode :

are multiplied at the subsequent dynode, by secondary,emission.If there are m dynodes with the multiplication f actor7 R, the total;

g a i n ' : . " G « ' c r - , , _' " V ' - ' " . ' " : • ~ :-'' '•'•• .'-'••'.•••'•"•"'• '•'•'• :'\- •

where C 44 * col lect ion efficiency faotor of photo electrons1,bythe dynodes. ;Contribution tc the noise iá also made byv subsequentdynods but l i t t l e . The over a l l gain i s nearly 10? to ; 10 .and: .thus the output pulses can be direct ly .'-recorded' by bráinaryH,pulse measuring c i r c u i t s . ,The t r a ň s i š t time of, P.Mi tube i ö 1

generally 10 sees, hence fast, counting can.be achieved. without the use of a fa s t j broad band amplifier.. .; ;"'-.• ?

" CÓHSOáuáTIONAL FEATURES-OF P;M. TUBE

S....11/-

vru - 11 -.' • i Survey Meters

1. Gun Monitor» ' " ' - l • . "•'• :: .This type of detector consists of an^ionisan.chamber of ',••

cylindrioal geometry with a coaxial electrode and á volumetric gammaradiation ring at ground potential to. keep leakage to minimum. Thewall of Jhe chamber is of Backc-lite with a nylon window approximately.85 rag/cm at the end of the chamber-to permit very low energy B radiations.Å semicircular movable ahulter is provided to protect •. this windowduring the measurement of gamma,radiation fields. The instrumentthen reads only the gamma dose incident on it. The difference of read-ings with the window opened and closed gives a,measure of B dose. Theinside of the cylinder is made conducting with a coating of aquadag.The chamber volume is selected to give adequate Ionisation current forthe range of intensities of radiatirm to be measured.

The current is given by P = ^ | Q 1 0 K / O " 3

I = Current in amperesV = volume of chamber in c c ..

• . H = Dose levelin tí/hr\ } £ft.Thus a chamber of volume 1ß00 cc exposed to a dose level of 10 mr/hrgives a current about 10 amperes.

The electronic circuit (fig. 6) employes an electrometer tubeCK 5886 with negative feed back which permits extremely stable, operationand a reduction of time constant. The output voltage appears in seriesopposition to the signal voltage developed across the input resistor.

• ^ '

i ' L " t 1

F^.l• .... k12/—

YIII - 12 -

If the gain.be large,.the output voltage will be very nearlyequal to. the signál voltage while the grid excursion of the first tubewill be relatively small. A yolteeter M may be employed to read thisvoltage. -..itom-'ELg. (7) '.' .'... ' "

. Al E'in = Eo + E Sig • • '

-Eg.. ,Hit E S I A + Eo =»

Ij A 771- Eo == E- gig.

Effective capacitanceA

is also reduced and hence the timeconstant is also reduced gréately.

The amplifier consists of a voltage amplifier CK 5886 and acathode follower power output tube connected to provide drive, for a50 / A m meter. The ionisation current flows through one, of the in putresistor selected by range switch suitably developing a_signal;voltageacross it. The suitableijs a very "high resistance type leading to ..negligible leakage. £1 zero position a iďresistqr is useds so thatnegligible signal voltage is developed witfc even the maximum amountof ion current expected from the chamber. .

The signal is amplified by ck 5986 whose platě is coupled tothe grid of the cathode follower and whose plate supply is derived fromthe screen vitsige of the second tube7. Positive feed back is obtainedsince the variable plate supply is in phase with the plate itself.Regeneration is limited and hence the system .;remains stable with greatergain. • ' ; '' V " '• • . ;. :•"" •- / . . ; :." \

A battery is provided to bring the.DC level of the, signal onthe filament of the cathode follower back tó zero.and thence to thebase of the input resistor thereby completing: the negative.fééd back100$ ..Bias and screen voltages fór ck 5886 ;are obtained "from a bleederresistor across the plate supply battery of second tube. Zero.adjust-ment is made by varying the screen potential by'means of a. potentiometer.

The amplifier receives a negative signal from the ion chamberand produces a positive output which is impressed in series with thesignal. Since the output, is positive the power tube can be operatedat law quiscent. drain on batteries resulting in an increase in batteryl i f e . ' '••• • ; ; ' '.__. .-•_;.; .• •-. ; •••; •••:; '•:' . •• , :, v > . ; .: - • ' !"

.. The acuracy of such monitors" can be v/ith + 10JŽ for gamma rays._.. ' They.are being used for^.area ;mbhitoring- of X-ray.;.installations.

2. G.M.typer survey mfetérsi (Contamination Monitors) : '- The.electronic amplification nécěssaryVinTcase of ionisation

chamber type of• instruments is;;limited uptoHfO" /7.amperes.

GVH:ppsi6.9.76 ' • '.•' : ' I3/-

VIII - 13 -

Since Seiger counters produce a pulse of every ionising event in the tube,these can be used where ion chamber instruments fail due to drift. Gridcurrent troubles encountered-with . do amplifiers can be avoided by usingsmaller load resistors and vacuum tubes as the pulses from G.M. tubě yieldrelatively large currents. Such instruments can be mainly used fordetection of radiation rather than measurement. Quantitative measurementsare difficult since the energy response of the detectors is not flat. Buttheir use in contamination monitor or low level detectors is unique.

In order to achieve higher sensitivity at lower counting rateseach pulse has to be stretched to present more energy per pulse. Whileat higher count rates the pulses should be shortened in order to avoidlosses due to coincidences These considerations have lead to the develop-ment of following circuit coimnily used the basic circtit shown in fig. fe).

The negative pulse arriving at the grid of HL due to drop in voltageocurring across EL when a pulse occursin the G.M. tube, tube Ť. which isbased fór conduction in quiescent state, stops conducting. A positivepulse appears in its plate circuit which .produces a large plate: currentin tube T2 which is normály biased to cut off. Hence the meter respondswith a kick every time a pulse octurs in, the G.M. tube. The,time, constantof the ratemeter is increased by the condenser across. the meter makingthe deflections steadier.

The modification to strectch the pulses when the count rateis low is seen in fig. (9).

r FVIII - 14 -

The positive pulse from the plate is fed back to the grid through the .capaoitance and after .the original pulse has passed, the grid will be heldnegative until C has discharged.. The diode prevents the grid from goingpositive on the pulse overshoot. The,length of the pulse is dependent onthe value.of 0;which thus controls the sensitivity of the instrument•

Normally the tube is conducting and the plate voltage is below iiheignition voltage of the neon lamp. If a pulse causesi .the.tube to cut off,the plate voltage increases, the neon lamp conducts and a current is •indicated on the meter. . . :, ,

Sich instruments .can be used in a range between ;0;'2 -to 20 mr/hrdose level. They are calibrated in terms of mr/hr with the help of radiumgammas. The maximum limit of such instruments is due to the blocking of ,G.M. counters and in such conditions the meter reads zero. -L ,<r

. A variety of counters are available for such purposes of^whichportable equipments are two type. Thin walled G.M. counters are used for

contamination monitoring purpose. Thin end window G.M. counters hxpused for detection of alpha and low energy beta particles. The former^3>ade of 2& window: of 40 mg/cm glass while the latter are ha2 mg/cm . .

Beta gamma scintillation counters». .

having window of

surveyE.lphacommon

Scintillation counters are used for special purposes where G.M.meters cannot be used with certainity. Some of these uses includedetection, neutron detection and very low avel gamma detection. Acircuit is shown in Fig. (io).

The power source has to supply a very large "current, for thevoltage divider compared to that in G.M. tubes., The resistance of thedivider, should hot be greater than. 20<$ .M.ohms, otherwise the time constantassociated with the voltage divider resistors and "the. dynode capacitiesbecomes too large..

Increased sensitivity is achieved with the help of such detectors.Aerial prospecting for uranium aňdwell. logging are their immediate applica-tions. The circuit, shows a logarithmic response as the relation betweenplatecurrent and grid current i$ logarithmic .over a limited range. Use ofHal (TI ) crystal of, one inch size enable?s the instrument to bé used forbeta and gamma detection. " • ..

rvin -15

Alpha survey, instruments:^ o f t n e alpha survějymeteis are mains: .operated units as süoh

surveys; .'axö, done in laboratories. Scintillation counters .offex; /greateradvanta^íďue t o higher; sensitiyity. "But light t ight windows ^an, not bethin enough' to admit the alpha particles. These are replaced \by\;proportionalcounters with air' as médium of defection. Since in such oases-also thewindows have to "be thin »gas flow types of .counters are preferred to thegas enolosed type. Air'does not exhibit, as liighva,gas multiplication as •methane,; or.vbutane and -that f i l led contfrs have, t ö he bpeřa-béďat very highvoltages* Hence methane i s used as ionising medium. '

", Such counters are useful in the detection of heavy tcharged partic-les evenin the presence 6f a high baol^raund of.weakly^iipnisirLradiations.Proportional cquntérs can also he made sensitive to beta- and;.Gfeinma: raysbut provision of sliding shields can help asoertain tlie contribution ófalpha !beta and gamma seperateiyk.. "",'•". . . . . ; ; .

Scintil lation counters for alpha particles.on the,orther hand,have "been made "by UBing a photossjltiplier optic&l^y-coupled to 'a base sheetof'clear-plastic covered with. Zm S (Ag) phosphor powder^in, a very thinlayer. Thin aluminum fpil;, i s rolled over vttó_ 2S&s to make "fche assemblylight tight .A simple icircúit fór detection óf alpha particler^iä showni n f i g . . ' - ( i t ) . . . - „ . . , - , • , ; . •.. "•; -•'••'•• •-•• / V ; ' . V ; : . ; y - ' - '

Many special monitoring purposes enplóy either cone'or more of the.above types of contamination monitors. Hand and shoe monitors, fioor'monitors1, laundry monitors are employed in laboratories, where radioisotope^.are handled. The choice cf'monitor "depends on theftype radiation expected.Beta and gamma monitoring needs proportional or scintil lation counters.

Contamination Monitors: ' . . .•'. '" .•"" 'Monitprs for hands, shoes, floors are used;in laboratories where

radioactive .materials are ftandled. f :.In addition ip these iaunďry monitorsand special ;monitors for specific materials are also^'used where routinechecks on specific materials are desired". These ňphitórsiia: the -rapidcheck of workers for contamination. '_'•':. "''".'.'•-:"' :' ;"J ".'" .

. . . 16/-

VTÍI - 16

Monitors are classified as beta^^ammi-ray type and X^ray typedepending on the type of radiation. Beta gamma ray mp.aitoriňg íš; done byusing G.M. counting •set.up with a thin: walle^ G.M.Cpuiiiter. ;:The>±ecordof counts is made either by a rate meter or sealer! •••• , Since the ti«e . ->constant of rate metess has to be large^-for; ayeraging ť » ;ň*ter fluolaia+.ionsa sealer is always preferred with a fixed couňtii^g time jsf't^secs.

. ••;- , A handland shoe monitor oonsists of twelve ?thin irailrorganicquenohedG.M,; counters, trith two för each side of .each hand .two*£ox eachshoe and two each for, hands; Glow transfer tubes "are^usědvťo record.the --counts over a fixed time. The counts are recbrded1into thVje iohsimelsone -for eábfc hand- and; one; for -the feet.,, .The npraaljbáiplqsround is nearly•15 to: 20 counts'•;;pér channel jsit since only .tte,i^sttw6ig?.ow tubes aredisplayed on the front, panel i only one or two.background counts are seen-.

For alpha monitoring large" area proportional counters were beingused. Zns (Ag) phosphors along with phbtompltii/Jir and counting system \have replaced the.proportional counters. .

. . . Laundry fmonitors;ar^ iipěd;in laundries;for 'contaminated garments

to-determine the dtmt bf cbntaminatibn in clothing; "^fore, .and;, after \washing.-Manual operation of a G.M V counter is feasible: for: small number ofclotheB. For á large number 'of clothes smiautbmatic monitor with motordriven rollers feed the garment past G.M. counters. 'Thin walled ionchambers of large window diameter, along with an electrometer amplifier can-also bei used for rapid monitpring. r

Floor monitors present the samé problems aspabove. They aremounted in wheels so that the;detector is very near the floor.Photographic films- Dosimeters: -

: Photographic-film is in wide use for monitoring personnel forthe radiatiort dose dueto X, gamma & B radiation. A need for good,permanaht records of personal exposures fpr legal purpose as well as expo-sure statistics is met with by films. Additional advantages of film araits small size, ruggedness small cost, simultaneous recording of'•• more thanone •type of radiation and measurement' over a wide range of total exposures.The response to X a id gamma radiation is independent of rate for intensities"of ät-least T to

silverhalide crystals in gelatine ±n the^/orm of thin.layers, špieád on cellulose•acetate films. .The thickness of emulsion .ranges from a few: microns toseveral hundred microns, with most commeh emulsions between about 10 to 25microns.. Over the emulsion surface there is'a, yery:-thinrprotectiyegelatine:layer of 'thiötoess of 'about O^Tvďéioněi'1^ gelatine supports thegrains pefinaipantly. still;-p^n^ts ready access; of .processing chemicals to thegrains,.;. ttyalso .ploys "áníaótive part in the photographic rprocess as i t scompositionüiflueices the"^^^sensitivity of the gráiňs.5anď:it takés part is.the energy transfer between radiation: aňáigraixiB. 7

... 17/-

yip. -17 .The grain size influences the film sensitivity. : Average diameteróf the grain varies from 0.3-microns to 2 microns.\:for neutrons andx or.r ray detection respectively, ^ •)•••

Latent image formation; .-.:,••

Under the action of radiation a latent image 'is', formed in thegrains such that they can he reduced to metallic;silver by.thedevelopment1 process. The exposing agent transfers aome of its energyto the silver-bromide crystal ^ tiieréhy. ráisirigrthe energy of one ormore electrons into the conduction energy hand of (the C2ystalf> Theseelectrons travel through the crystal until trapped ih the impuritycenters or crystal deformities in the lattice. The eléötroÉtatiepotential set up about these centres attracts the very eaall fractionof silver ions in the crystal, which ;axe free to migratei Under continuingexposure .these two processes will continue until;a group, of"silver clumpscontaining several silver atoms each, are,distribut-d.throughoutthesurface of the crystal* These are called latent images. During thedevelopment process these clumps catalyse 'the: chemical reduction of theremainder of ionic silver 'in:ihe grain \

Chemical processing . ';-..-.:

During development: each grain is reduced as a unit to metallicsilver, the. developer Be^å^.^iaé^:.^'tbB>.xed^±^':s^^t\.y-^!hB:reducing agent is generally^ an aromatic organic compound. The fewsilver atoms^ which constitute the latent image; iare, multiplied by afactor of 10 until the fiill,;grain is convergedßxAo elemental silver.

, After development the film is rinsed in the stop bath for ashort time. A dilute ascetic acid solution stops the developnehtquickly by lowering the -pH« ^ ! . - , , ' > [:"'•'-.",

•hypo'The underdeveloped silver haíide is then dissolved in the

The characteristic »urve, of ahenailsioh whiih is the relationbetween the ppti»al density and the logarithm^ of exposure is known asD-LogE»urve _ . ( f ig . 12.).

. . 18/-

....... . • • j , \ . v i i i - , 1 8 .. ' ; ' _,.,- .- •.;.,; ,;:-. •• •

The optical density is'-jraasured'.after the processing of the film isdone. The dansity i s "^measure, of; the logEtrithm, of: opacity aridallows .the. dose to which the ,:.f ilm:;is ^exposed to Ъе,estimated. Eheestimation is done with the help ef calibration curve sdrwm /by usingknown exposures of different types of radiations.,. •

•Йзе response of the film, varies with the enexgies'.bf.X andganuna radiations as shown int figure 15> •, ; . / ; . , . ; . , '•

In partiwilar i t r ises.as the photon energy de*re;as,es helow150 keT.-- 1% asudLtalDie. chpiee of. absorlDers so chpseri^hat1'theirabsorption. Ys energy response." matshe^'. the''film 'derisl-fcy ^ energjr':'characteristic1,-the film dosimeter can^be; made .aikb'st energy':i.№

;.; Phptographic film can. ^ 1;'.wprn•aff, •a'-;• gё•\ ••yhё" •'form.;of a fingerring. 1_ typical ;h'adge f*rm is-'shown ;in. fijg. Ji!^sl^--'№e/Jilm;V^s^iii1saaiiyahout 1-1/2 Ъу 2 inches. I t i s wrapped in a thin, -light, .tight paper

help improviiig'the energy, response, discrimiriate.he.twe.en .betas,. ••GaEpias and thermal^ijeutrons.r. Щ.^.bpenwindow. helps in. ''conjunction with other .data, . the ^estimation''djlieta dp^se.Д..The,filtersdifferentially ahsorh x and :gamma rays and the densityepatterns ;under

, these f i l ters give an Indication' bf'^the ..energy, of incident' pho-bbns also.

JL...'..'..•:.: ; : л

, . . 19/-

•-Ф--

Vlll-19

, ... .. Measurement of neutron dosage by film method isdone by comparingfilm densities" under cadmium and copper filters» These filters are!. . that both attenuate gamma rays "by the same amounts Hpwěver, becauseof, (n,r) reactions induced in the cadmium by thermal neutrons, exposureproduced behind cadmium is higher than, that behind copper ,v.when

: thermalneutrons are present. Differential density measurements are calibrated'in.terms of thermal neutrons exposures. Alternatively the dose pan beestimated by counting the tracks, made in ar nuclear' ěimiísion, 'such asEastman Kodak HTA.. Fast neutrons produce tracks through; the scatteredprotons with which they share, their energy while slow neutrons interactwith, the emulsion by HI 4 (o, p) C14 reaction. After developing the filmtracks are counted under microscope and the number of tracks per-..unitarea is interpreted in terms; of flux of neutrons. Since cadmium filterlets only fast neutrons, a differential coiont allows one'to.distinguishbetween fast apd slow neutrons. ' •.'•'•.•' '

Pocket Dosimeter's; . . .

Pocket dosimeter shown in fig. (15) which have, the size andshape of a fountain pen..consists of, a.chamber with ä,collecting'volumeof approximately. 2 cc, a small quarta fibre electrometer*which is;alsrpart of the collecting electrode and a small compound microscope fórviewing the fibre. A separate battery charger places an. initial.elec-trical charge of a given amount on the system, as indicated by theelectrometer. Collected ions produced by the radiation in the collectingvolume decrease the total charge on the system thus.changing the positionof the quartz fiber as read on the Y that is calibrated in rfor mr .light for.viewing the filter through the microscope'comes through awindow either in theend or on the side of the.dásiméter.

C - 4-

- •-*»*•<-••

VIII - 20 -m

:."' , \i' Commonly available, ranges, are 100, 200 mr, i f 5» 1° and 50 r'full scale. ' With a collecting volume of ,2 ccjand. a. capacitance of3'pf, exposü^and ai Qhain e,;pf nearly 30 vplts. .I>oaiinetera; fior ÍB;for.-: abpv,é.:i döse :'•,:level usually contain a capacitor to maintain reasonable sizes andv o l t a g e ' r a n g e s ' . ' '• r •• : :

:"\ -: •.-.•• ' "' ' . >•'•••.':••:'• "• ;•' •• •" , " • _ - . : ; ' [ '_[

- ., The.resis.tance, of the.electrode, insulator and ciapacitor mustbe e3rtremely_hign, since any leakage of charge will produce a reading.Leakage that pan K<s .tolerated should be smaíl cömperefl with thecharge collected, in the chamber over the time of measurement, .ihe:insulators -must be kept clean and dry. A sealed diapb'agm containingan. electric »contact insulated, fronuthe chamber wall protects, the;. 'electrode f rom /external influences. Goraiexioň 'to the. collectingelectrode for charging i s ;made by, mechanical p r e s s u r e . ; ' ř : '•''

Pocket dosimeters are energy -dependent:due,:to the use.ofphosphor bronze for, collecting electrode. and aluminium for pocketchambers. The dependence i s about 10j& for ;energies : above 40, keÝ asshown In fig. 16. ;. • " . " . . -

•-••• • • y - : ' "•- • ' . - • ' " ' ' . ' • - - . : •••'. - V ' ; : . - . ' . x ; / - . - " • ' • . . " • : . ' , .

The shape of this curve depends on, tb.e..spectrum ofradiation.- Broadband radiation gives a f latter curve than monochromatic radiation.

Pocket-Dosimeter

A, charging unit is employed for charging the pocket dosimeters,so that they read z^ro initially. The principle employed is „thatvoltage from a variable voltage source is applied to the collectingelectrode. The,zero position of tbe fibre indicates the maximumcharge on the fibre i.e. the maximum voltage. Therefore beforeusing the. dosimeter for measurement, pf'radiaci on .dose, the dosimeteris charged to zero. ;, The circuit diagram of a,charger is showni n ' f i g . 1 7 . •-••;-.... •• .• '.' ' - : ^ . ' - / v . . . . , - - " ' .- .-; . / V . . - " ' -;'•••••. •.;•

GVR:pps:9.9.76 . . . . . 2 1 / -

VIII -21 -

-TTipfitrnm'calftvr'Unclear'Badiation ifeteotorB

Interaction: of nuclear,partic,le with the detector,can be, ._,considered i;o rěiasé; archaiř^etat ;\the input of succeeding electroiaic ,,,c

equipment. ^Since there occur, pulses öf different sizes atid .amplitude,i t i s necessary, to ©aplpy proper: combination of .suitable circuits :toobtain presentable data ábot ť the radiation quality and, intensity. :block diagram in fig. (18) shows the stages_.inj.whioh'^^,Éřulse;fpo(Bi-déVeotb^ iáisuitably moálfied^for'th'e.'jnirpose" la question.,

Small a ignalB- 'avîabie:^©^^^!^!^ '^?^©^!^; . 1 ^^ f i r s t amplifiedby a.cathode,follower in order ^to-,transfer:.them to, the "mkLn.ampl;ifi.eř;without attenuation. . These, pulses, éiřp 'furîiéť/aîiřiěiaî^â^stable';-''1'high gain amplifier.. .Noise. piilsieá.ánQ undesirable 'lowJeňergypulsěsyr'are discriminated by the discriminators ^tCT-;whfch\tóe;î?anabni^púlá0s_.of /different' shapesr are shápea;• ťp, actoáte;;,furthteri .countingííěquipšíent'."";

pulses from pulse sháper are-féd tó, pom1řing},cii;cuit;^hichmay be either a scale of two, or a scale',-pf--t'en 6T\a'"rate"netey'reirauiti.The .out put from these i s fed toi'-'a visuály.rauišl or. pen »recopding'system.In a few cases the pulses of different: amplitude or.Bhápé. are" šepératedby an analyser and recorded in sépérate :'chántiéís....,'. .. i •' '. •

If however the signal "is a die. signal pulse equipment-as' •;replaced by d.c. amplifiers and/recording»system., . The•requirements forthe study-of ;fi.c. signals and -that óf d.c>7 areÍ .differ eht.""''; - Í ' " ' ' ' '

.122/-

VIII - 22 -

High Tolta^e 'Shits .

Hadiation detectors n&inly G.M. counters and ..scintillationcounters are operated at voltages in the range of 5 0'*° 2000 volts.Portable survey instruments use circuits^lhieliuse low voltage, tiatteriesfor stepping up the voltage by a factor of 10 to 20. Following types ofoscillatior power supplies are in.common use. , :. . •

Glow láimp oscillation- H.H.T. . . .

High voltage is obtained from the inductive pulses appearingacross a highly inductive coil wound on ferrox-cube core, when its currentis rapidly interrupted. A neon lamp relaxation oscillator deyelbpes asaw tooth, wave with a rapid negative return. This is coupled to the gridof 1 V5(fig. 19) .

Glow lamp oscillator E.H.T. supply

This current, builds up. in the plate inductor during the "positive swingand is then interrupted when the. neon lamp fires and drives the controlgrid negative. The pláte of the tube then swings .positive byapproximately 1200 volts.. After the pentódfc; has been out off its platethen returns to the B plus value makinfe; thé: plate".of the. diode- negative-bythe voltage developed across the capacitor,C_. . . .;

ián RC filter (R-G4) filters the high voltage and the coronaregulator VR 900 limits tfleD.C voltág to 900 volts. This lis.applied'to the cathode of the CHi:. counter.1 . To avoid humidity^ effect the E.H.T.part 4s sealed in a tin box.

Transistorised Oscillator1 E.H.T. supply •', . • , . '•• : . .< ,., .

In order to supply E.H.T. £ÓT G.M. tube's and Ř.T.': för theoperation of countingratefneterSiiDiiG. converters are used. Theseemploy transistors which act as switches tö interrupt the D.C,: input.' The circuit in (fig.20) operates as a relaxation oscillator generating arectangular wave form. '•"-'' • ','•';. ,, • • • . ' • - . : • , . > . , .

).J6 • . ' - ...7." 23/-

VIII - 2J -

fig (20)

, • Transistorised oscillator E.H.T. supply

After the d.c*> voltage is connected a linearly riáirig current flows,through primary winding. The transistor i s "bottomed and a l l of the.input voltage i s applied across the • p r i m a ^ > v é é ; !negative voltage and current in base winding, -the collector'Currentr ises until i t reaohes the value of base.current. The. transistor thenmoves out of the bottomed state and switching^ off-begins. ...The .collectorvoltage rises and the voltage across the primary fallai The consequentfa^.1 in the base current reduces collector current and the voltages acrossthe windings. - . ' ' . ; . . . ' / . : ! . ;'

The reverse voltage rises rapidly: and cuts off thetransistor, but this reversed increase is arrested when secondary, voltage ,reaches the value V which already exists;across the f i l t e r capacitor.The diode then star ts conducting and out put capacitor i s charged witha linearly decaying current. When i t has fallen to aero the positivevoltage across the base windings disappears, the, transistor switches on

..».24/-

vin - 24

again and the cycle repeats. The. voltage obtained in 2.H.T. secondarywinding of the transformer is quadrupled to get voltage as high as 1200volts, å corona regulator V x R 100 limits the p.c. out put voltage to1000 volts. How voltage is taken from the other secondary winding.

• . Feeble signals from radiation detectors have to be amplifiedseveral times in order to study the nature and intensity of Radiation.These signals can be either d.o. or a.c, depending on the geometry andtype of detector and intensity of radiation. JD.C signals are amplifiedby 33.C. amplifiers without much difficulty upto a lower limit of 10~ 4

amperes» Signals beyond this level are first converted into a.C. andthen amplified by conventional p.ilse amplifiers. Small a.c« signalsare first amplified by a cathode follower preamplifier circuit and then bymeans of a pulse amplifier. Requirements of these various types ofamplifiers are different.

D»C. Amplifiers for Ion chamber instruments

The range of currents of interest in ionisation chambers is

Conventional—6 -16from as large as 10 aaips to as small as 10" amps.3) A rsonvai type neters can be used to measure currents upto 10"amperes. Below 10"° amperes indirect measurement only can be adopted.This .involves the use of an eleotromster tube to measure the voltagedrop across a high resistance.

Electrometers are vacua tates rith vary small grid currentseven less then 1P~V<- anpers which give a 1 volt input when used with agrid leak of 10" 4 aijjag, A schamatic diagram of a simple, electrometeramplifier is shown in fig. (21). .

fig. (21) Vacum tube electrometer circuit.25/-

This i s a balanced: p^cuAt in which thevoltage |årop ;fřbm theplate t&.the cathode óf the type^OC 5^'A-x7^^>íeí ' .6qi^M^th,^hs.t,across thej potentiometer í>. . lAny. imhaifficeis indicated í^ the jnicröameter

.ST.;',' In i t ia l ly *1*" input, c ircuit- is shortedlapdP, is• adáuflted^ so^that thenétěr ^eMá. zero; JVoltage "dr "theflow of ionisation búrrént cáaséa an itnhalárícé.of the circuixland: a.

" i i ďefléction^of the'méterillf- : •"'••'"!': '•'•>/ '• %'': t""r :'"ř'f-;"•'•-• ''

V Ťhé disadvantages • pf. such • tuběs>ařé their1 'dependence' on tubecharactěrisfips • áad1 power ;supply vpitagesífor linearity anď; stability.Feěd back amplifiers have "rei n f i g . - ( 2 2 > " '•• ." :" . ••' ;" r ;"' -*;"'v •• ' . -:,'.' .;:;'-' ! :' r

A 'high gain amplifier: is connected in'such a way that, theout put signal is fed back in äeries with the input signal.'Such anamplifier acts as "a current amplifier.-: -i'-'.'-'1-.'.-:-Vi j>":--';. ..>«,.

The instrument has a i u l l scale sensityivity of 10 " "Aand can "be used for a full ecal«? s»n3itivit;r of lO"''? amp. The negativefeed "back i s applied in aeries with the input resistors connected in thecathode circuit of T p . Transient negative, feed 'bsckpccurs through thecapacitor 25 uf,from :the,cathode, of T„ to .the screen of % ., Positivefeed Tsack from, the prcáte cf T_ to screan grid; of T/ i s used, to increasethe gain of the feed, oackloop „of improve the response of the.system.The power supply i s a regulated uait powered "by 230 voits/50 cps powerline which enables the warming up of the instrument and minimise thedrift in the zero

B.C. amplifier for portable survey instruments is shown infig.(T3) These are battery operated negative f,eed "back oircuits suitablyoperated which reduce the drain on the batteries and thus increase, theeffective battery life* •

| ...26/-

S ~ Ü = » " » «•<•-••

:.- VIII--:2é7

. Vibrating capacitance EÍectroÉeteř.r

i o f 1 ^ 3 "**'••C" isuffes vi ^^

-vól-isgeBrpróaabs-a ži&}éi:that!jíěX^ÍBÍln5|aÍBbá>íe:'l!cbinthécurrent being ňeasureďL This type of Adriftcanňotr;bél': eliminated, "by . . :•negative feed• "back. This theiefpre needs.;the}turning off- of 1;he radiationspuroe -to [ad-Just the .ze'xo of the i st uittnt.> i*i qdently.a!;\':&xó;dxiftiproblem Inas, ibeen,; s^cés;sfullý;solved r^i eoyeiifing the:; signal}4nip AX.and. ainplifing,ihist signal and then converting it, ihtp d,.c'. as.fin case ofvibrating reed electrometers. = , : , • • •-:,-...-,.-.. .i: .

; .; ... The vibrating Teed electrometer consists of á vibrating reed.which is a condenser, in,}vhich the lower, pláte is driven towards and ',away from the upper fixed plate by an .A.C. .magnet ät. a fairód frequency.Change in the capacitance value will result in > rise and. fall of" thevoltage with a frequency of that of_• the A.C. applied ibö the magnet.The amplitude of this voltage will depend'on the charge imposed on theviirating condenser. The A.G« signal is amplified by a:tuned A.C.amplifier having á gain of TOCO. The^^amplified signál isithen rectifiedyielding a D.C. voltage She circuit in fig. (23) illustrates the mode ofoperation of the instrument. •'.

=- . Vibrating ieeed Electrometer. .-. ; .. '". :-/••• •~i;.:

:\.'~'.

If a rectifier is ušed as shown in the circuit the; outputvoltage depends on1 the magnitude and iiot polarity of: the: iňpat voltage.This however leads to oscillations and therefore phase sensitiverectifiers are used so that the outimt voltage is no* made to dependon the phase of the input voltage' also. . ; "

... 27/-

vni - 27

Cathode follower

The cathode follower circuit is widely used in pulseamplifiers for nuclear detectors. Mainly it acts as an inpedencematching device where pulses with'fast rise time must be transferredthrough a coaxial cable from one part of the circuit to another. Italso produoes high input impedance and low input capacitance required forsmali pulse rise time. .The "basic circuit is shown in fig. (24)

:-/<£vň ;

The gain for such a circuit is given by G = VR4

+ gm+-. j.

TUhere rja. = ;dynamic plate resistance ofr,the. tube'

Thus,the gain is nearly unity. The output,.inpedence is

gm + 1 + iH4. - :

••. IP

while input inpedence is

Zin' - Z

Zgmrp; B4E4 +. ; rp

/ , • ^ • • • r p ' . '

Ifřheré 2 » input inpedence without freed back.

The application of a^positive step input to the grid causes the.plate current to rise quickly. This current goes to charge the capacityCK which shunts the cathode load E4 thus giving a very rapid rise ofoutput voltage. Mien the input pulse returns quickly to zero, .the: platecurrent is initially cut: off completely beeause of- positive potential of thecathode. It will therefore decay with time constant HK x GK. The outputfrom cathode follower is fed to ithemain amplifier.

• , \ ••-"-..'.•- ... 2 8 / -

VIII- 28

Pulse Amplifiers;

The requirements, of a,pulse amplifier are high,gain»stability,, linearityland polarity. ? . r v . .

Gain , Noise voltages that (^'never, be^iybided;: are of t%; order; of10/uv. The lower limit for the height pf useful signals isfthe^efore10uv. The output voltage required from an .amplifier';to~< operate ,,.a discriminator is minimum 10volts hence a gain of 10° is desirableof the amplifiers. Gain control is also essentially;to ije provided.

Output Since there is a large number of circuits which have to beaotuated by the output from an amplifier a cathode follower iircuit isalso incorporated in the pulse amplifier.

P o l a r i t y ; .»,' '.'•..""'•' ' '..-••• ,'>'-';- , , . i ' " " y - .

. The, input pulse may be positive ;or negative depending> on thetype of detector."/Whereas the output pulse is always positiye. '

Stability: / :"''- • '•' : j - -.'-. v '•-'.-- ".." ';'": :\'i ''} -VX-,'••'•;"•' /''X^'] •,•-.-In energy•measurements^ the^proportionality;/between pulse

height and particle; energy is constant while if:,-there is; a;cháněe; in gainin the amplifier, á shift in the fraction of pulses passing thě;discrimíňattv? occurs. This necessitates the stable operation of an amplifier i ti s achieved by negative feed back and .good regulation in the powers u p p l y . '" , •' _ • . ''".,. . ' : ".'" •.•/'-\'.:- '•". •'- v - 1 " ' - ' - ' '•'•/•\Xrr:'>"~:c'. : •

l i n e a r i t y between pulse input signál :and ou-tpiit; signals of0.5 per aent i s often necessary. This 'is obtained by a.choiile of properoperating points for the väecum tubes within their l inear ; range and bythe use of.negative feed baok. ^ : ;T 'f ; V : : v ; ' ;

- The block diagram in fig. (25) šhows.a pulse amplifier whichmeets the above requirements. \. ;. ;-'"-.'".'• ; :, , :

ÜTonöverload linear amplifier*

. . 29/-

VIII - 2 9 -

Ihvertert For either negative pr positive polarity input pulses thisstage introduces polarity reversal In such a manner that always positivepulses are obtained and fed to the suceedíng stages which accipt only-positive pulses. ;

Gain control is achieved by varying the attenuation of the signalswithout affecting the load of the inverter. Y '

Differentiators .

RC clipping is introduced in linear amplifiers to permit highrandom pulse repetition without ELleup. The differentiator also improvesthe signal to noise ratio. The differentiator is placed at the input ofthe main amplifier in order, to, obtain good overload charactristics.

Cathode coupled amplifiers •• •.\' .'',;• Loi^:tail pair. (L.T.P.) are employed to accept signals larger

than their quisentbias without drawing grid currents With positive feedback the loop gain is ß 0 with slight loss in' (gain stability. The' signalhandling capacity of '••;thisi loop'" is about 70 yolts. .: '•'••'• :: r-

The cathode follower is designed to deliver positive pulsesinto, a capäqitive, .load of as ouch as 60 pf representative of long cablesused in -connecting the counting circuit; with "the amplifier.

Such an, amplifier- provides a variable gain about 4ÖQO with agood stability, short rise time and' excellent overload characteristics.The rise time is nearly" 0.5'u Sees. ; > ' ' '; :

Triaker circuits and vibrators' ' ' ' • ' • • ' - ' • • . : • • ' " ' • , - , . - ' • > • • • ' • : • " ' ' - • " ' / ' • • ; ' • ' . • - ' , '

Trigger circuits find an application in the production,ofcertain desired discontinuous signals haying specifió periodicity. Suchcircuits are useful in counting equipmentsi; They'are classified incounting equipments. They are -'classified. ."' ' ,'

1) Relaxation oscillators •'-.''2) Circuits with single ;stable states:;•-J') Circuits that ,can be made to pass back

;two stable states. ; • ; .'';.;-between /forth

1) Relaxation oscillators». This is a convenient source of relatively,large signals.

It may be used either free running or synchronised with'some other,periodic signal, to serve as a source of signals "of. á desired form orfrequency. .Multivibrator, and free running: blocking oscillator areexamples of this type. . Jjhltivibrator ísusefúl where, similar'pulses ofopposite sign óccůring at same time or-at different .times are desired. ;;It can; be seen from the circuit in: fig. (26) that it -is an amplifier /.•'.-with;its input coupled to its output.•

VIII:-50 -

• .. - , fig (26) ' . ... .;

The frequency of jthe symmetric multivibrator-is determinedby. IL & C1 and is inversely proportional to the product of the two iif

frequencies frpm .10 to. 10 cps can be secured conveniently.The pulse shapes obtained from such circuits are äs fjiowti in fig (27)

— nVeJk?.

For,frequencies above those handled by multivibrator ablocking ascillator -(fig.28) i s used i.e-. from ,1Kc/s6iC to.\1-•.•MJ/sec/.The frequency in such oscillatpřé can also'be varied and controlledeasily with the help of Cj-and R,

fig (28) BLocking oscillator.31/-

VIII - 31 -

fora given set up of transformer and. CL & IL, values, thefrequency varies linearly with R,.

Trigger circuit with a single Btable statel

This elass of circuits has one stable state and one quasistable state. It is most useful for obtaining pulses of desired shapeand magnitude, in response to triggers that may occur intermittentlyand of varying shape andaiágnitude. Under the influence of an appliedtrigger the circuit is passed from the first stable state tö the secondquasi stable state. It then returns to the original state after a timedetermined by the circuit parameters. Univibrator anä thyrateoncircuits are examples of this type.

Univibrators

—1—*Ca. f */

• 32/-

yiii - 32 -

Univibrator is á modifioatioň of multivibrator, used in delaycircuits in which an output is produced át some/controllable time afterthe occurence of .an initial trigger. It, as also .useful ,ás,;a source ofrectangular voltage pulses. Wé output frqiřthis circuit shown in fig (29)can'be taken from any of the several jointgapcordineto the need. TShenthe grid/of tube.T.. is at ground potential the/cireüit is in, stable state.The plate of 5L being ät .+, 10Ö volts. The grid, of Tg iš át'a negativepotential determined by, R, and Ru" and the ahqde of T„ is at positivesupply voltage. ," ^ ' ,' „ "''.-' .'_•.,-.•.•: ...

r Jf by a trigger mecahnism, the grid of T„ is. brought to within15 volts of ground the circuit becomes'regenerative'and quiokly transfereto a new state that is only temporarily stable. In this state the gridof Tg is' at ground its anode is at + 100 volts and 3L is cut off. Afteran interval of time when Pg/discharges through Hg the grid of .T^ reachesa potential within 15 volts oif ground. The cixcuit becomes regenerativeand changes its state to its original stable state. ; •

The wave forms.at the grids.and plates are as shown in fig (The square waves at the plate of T.. and at the grid öf ü?2 are .suitable foruse as gating pulses. When differentiated by means of an EC-cöuplingnetwork having a short time constant they provide delayed pulses fortriggering other circuits. ,

Trigger circuit with two stable statesx- • i

I - - • • • , ,

Two stable state circuits called also as flip flop circuitsare inäespensiblé parts of computing or tallying circuits. A synmetr'form of such a circuit is shown in fig (31).

fig (31)Eccles Jordan Circuit

•33/-

VIII - 33 -

Operation«

ÍB initially, conducting .g1 will be at ground potential100 volts. . . ' : . :;and plate at

Because of E ? t E-, gp will I» at 50 volts more than enough tooat off the tube current. Plate of .OL will be close- to + 3Q0 voits andg1 will üehd to be at + 30 volts. This state.is a.stable one. Since smallcnanges^plate potential of T. will not move the grid of 3L above put offand therefore no change in g 2 and hence at the plate of T7 will be produced.

If by means of á trigger djhe grid g^ is moved to,within 15 voltsof the ground, the circuit becomes regenerative and a rapid change to ásecond stable state occurs. The symmetry of the circuit shows that thesecond state is a mirror image' of • the first and that a suitable triggerwill return the circuit to its initial /státě. '-''••

Output of the circuit ban .be.taken from a number ofpoints from a flip flop circuit depending on the d.c. level desired ofthe signal.

Sealers .

The,function of a sealer is to--store'"-the number of pulses froma counter occuring during a measured length of -time in -a electroniccircuit and represent it in a readable form.: The pulses.'from amplifierscannot operate a mechanical' register; directly1because the; speed; of ,response, of the register alone is too slow- Hence the electronic, circuitstores a number of counts equal to „the1 scaling;, factor. .{The; mechanicalregister advances every time the scaling circuit, is filled.,. ., -

... Sealers generály consist of an input; circuit an; nplifier,, :a variable.high voltage supply and a scaling circuit;..• ,'.,, ''•' ,< ~

Two types óf scaling circuits, have been extensively used förcounting. The Ijitiary and the decade., . ; \,- : :•"••' '.,'•

The scaling stage of a binary sealer which,is: shown, in fig (32)has two stable conditions of equilibrium i The triWe is assumed to beconducting. :A negative input pulse is, applied to. the grids of bothA & B but, since B is not ondücting the. pulse has: no i.eff ect on B. The .negative pulse on the grid, of A momentarily stbpé.A from conducting,raiding thtreby the pláte voltage and the grid voltage';of B. TriodeB will start conducting which further reduces the grid voltage of A& firmly holds A; non-conducting. The indicator lights are neon glowtubes;connected across the plate.resistor. If a triode is non-conductingno potential drop occurs .'across the plats resistor and hence the necn

....33 A

vili - 35 A -

tube, while if a triode is conducting the drop across the resistbr.lightsthe glow tube. One negative pulse makes the neon lamp go on while .the second pul3e extenguish«s»it. The out put is taken from one of the •plates- of the triodes and. consists of a negative pulse for every W oappearing at the input; If n šucíí; circuits: are placed in series thes c a l i n g f a c t o r i s 2 ,.••'•••'.•• J -'•' , " ;• .•• ''••''• . ' •'•;• •' . • "• '"'.ř: '•••".' •, '-';' .

fig (32)

Scale of two circuit

-S-fcV\

Ilekatron drive circuit. . . . . 34/-

YIII - 34?-

, Resetting the --stages is done by raising the grid Voltage, ofone of the triodés by disconnecting, one'1 of .the grid resistors ifřóm.; ; .ground.. This, raises the grid to the potential of the plate of othertriode. In ascaler with many stages one of the grids of .each 4stage isreturned to ground through the reset switch. ., \ i;» v

Binary sealers can;handle high counting rates with goodresolution; as 7-Uort as 5 usecs.

Decade Sealer (See fig.33)

The second type of sealer,a glow transfer counter is simple,consisting of an entire sealer in a cold cathode tubei This has relativelypooi?. resolution and hence low maximum counting rates can. be, handled with ,this' but useful in health physic s applications where high resolution,isn o t i m p o r t a n t . ; ./• ..'•/•••'•-". '' , - > ; - -. ••• •.._'..••;•. . : ' - ' V * - -.',.'.'.•'..''•'' V " ••'""•'•"• •

. - . The'tube is a gas filled glowtube,with 10 cathodes^ in. a.rihgaround the anöde. Between, each of'-.; the., cathopLes are. two, guide . electröjäeswhich are normally held at .about^ 5Q Jvbltši. 'in input-pulse first drbpsthe potential of guide 1 below the.cathode:and:the. glow transfer to!it.The driving tubel'then drops- the potential, of guide; 2.and rai&e.s .that ofguide 1 causing the glow to transfer to guide. '••• Finally ;boi;h-guidesreturn to their quisent state and the gloW:is;transferred to the hextca'chode. The !Zero* cathode is brought;!out,of;:the-glass envelope andwhen the glow, is "transferred to. it positive pulse is developed which isused to drive the next decade. % V

Di soriminatbra * . . . : • , ' .

A studyi^pf pulse height distribution of pul ses if rom tf- '.'..' ;-proportional or scintillaition counters, is, nácesěiaý to.;dé^eimíne: the.distribution, of: the, energy absorbed byjthe .detedtar. -This- informationenables the study of energy-fl-istřibuti!>n-;bf; ^ original rääia,tioxjt ; ;

.Biscriminätor is..the' simplest type of .óircuitřtn: 8ěperate,,cj)ulseš.v;'it" ;•passes" any pulses higher, than gome/pireäeteimiiiéä; voltage • andyipjects-J:

all lower. The diáoriminat.or determines the base /line" or. lower •! \a c c e p t a b l e v o l t a g e . , . ".r < - " ! ; '-r- '.';"' "" „••,-"' ''.:'/'(.• -','•• '•';"•!. v'-•'••,-'-^'.".V-•.'•/-.•••.. -

Discriminators as well,as pulse-^height analysers, employ';"'•'•.,-,"pulse shaping circuits tr stanďárdisé,the ou^^t'pulse. -3í.;:éhe:.iňput .pulse is of acceptable height it; triggers .this „circuit ;,áhď á ,relativelylarge,: square ;pulso results. If;

;the input^ ;pul:se is of..-na* •.sufficient;height no .pulse appears' ať the óutpu t. '_-,:EL.ihgrji,a chEtidt^trigger-^circuit;

or a Univibrator can be used. ; -These :vToéxic&:.a,-vconstant aaplitude-and '^^•••constant length: pulse w;hen triggered. -":;;, :=;;•-•-';'•/".,, ''; ..:/.;',: ;? -'.-.'.' .'

VIII - 35 -

Schmidt trigger circuit

fig (34) .

fig (35)

VIII'-. 36 -

In the circuit shown in fig 34 the steady voltage.-of the.grid, of T .-depends on the setting of potentiometer R' '' • The'tube T. is':

triggered to a new state when the voltage at g.goes above ä critical'value set by R1 and returns t.-- its original state when the voltagedrops below the critical.valu^- If R1 is adjusted to give a biasvoltage of 50 volts the circuit will be ..triggered when input •signal75O T and remains in this state till the signal voltage is 75P-.••••• Thispotentiometer E. is supplied with a dial that reads from 0 to 100 andhence the discriminator level is adjustable.

The pulse shape of the output signal depends mainly on R, and straycapacitance. If the output signal has to reach its maximum value the.'input signal has to remain.above bias voltage for a sufficient lengthof time hence the heed of pulse shaping of the input; pulses.

When it is desired to use discriminator for pulses that arefairly uniform in amplitude trigger circuits as.shown in fig (35) canbe used suitably. This circuit operates' diřeptly from 'G.M. tube andtriggers reliably on -ve pulLses .of 1; volt. It:is á cathode cpupledUnivibrator; When it is triggered it remains in a second state; fora few- hundred micro seconds. The recovery times ;of G.M. counters ishigher, than this and hence the. dead time of discriminator is anadvantage as it provides multiple counting of individual pulses havingminor oscillations superposed on them. ': .

.Count rate meters

For many purposes "when high dBgree bf. accuracy, is not.,7required,. the rate meter-is an:useful, instrument, Presence of;;l;-rand gamma

radiatån can be indicated by means of a, flashing neon; bulb and by .the deflection of the pointer, of a micro ammeter. , Thepřinciple of .a •

count; rate meter is as folloT»rš. . •, • .'. •••/..'"-- ,"i. \-.'-ýr.-'-- .

The pulses from Geiger counter, which;are.of same.size arefed into a resistor'ca.pacitor circuit; so arranged tha^ each pulse givesa constant charge to the condenser.^ This charge is: allowed to leak; .away through a resistor with &• microanmetér in -series with it.- If thereare is pulses per second and each gives a charge"q^ to the condenser, a 'steady condition can be obtained.in v;hich the charge .leaking; throughthe resistor Is equal to.xq. This.current i=xq is proportional to x,the rate at which the pulses" are'received., However he microameterii opindioation reaches, a steady state only'after a.. time=RC sees.; VR is ih-ohms. andC in farads.'"; - • : "

Vlil - 37 -

Fluctuations of the pointer is another source.of error thereason being the random nature of radioactive disintegrations. Thisis more obvious at lower count rates. In practice it is usual withratemeters. to allow five times the time."RC" to elapse before'takinga reading, • •• , . . . ' . . ' ' •• •

In most cases the indication given by the meter is linear overthe first half of the scale, thereafter, it is usually less than alinesr relation. Several circuits are used to give á good approxi-mation to a linear scal-a1 over the entire ranges

; The simplest possible ratemeter circuit is shown in Fig.(36)

Fig.(36)

High current GM tubes are however quite cosily.

'• Ratemeters with transistor amplifiers using p-n-p junctiontransistors as current amplifiers es. shown in fig. (37.) are nestsuitable. The transistor is used in earthed emitter connection,the anode of GM tube "being connected to the base of transistorthrough a high resistor- In.the absence of radioactivity nocurrent flows through the resistance when.the switches. are..closed.

iOOůikf

S-.J8 -

A single dry cell is required in t h e • ^instrument is shunted by á 1000 pf capacitor to"reduce hightions. Thi.s forms; a basic ratemetér circuit .with transistor ; ;.a m p l i f i e r s . -•• ;.'" " " . '\ • ,:':\ • , .• '"' ' '.:C'.l. . , ..-V'.'-C-.r •': . •'

D i o d e p u m p r a t e m e t e r t ' •'• ... , ••

Another common circuit for .feeding the charge ] in the taiikcapacitor is the diode-pump circuit-• shown in fig.jéí. ; Rectángiiiar:pulses of duration T and height IT are deyelopéd: across a xßsisíkanceRf. The oapábltpr Of. is charged, ' . . . \ ,::. •"; V... •.•;...,:.., •

. ~ through] the resistance Rf: in.series with ML'.•',• •.1iiptb,;-néarly;the pulse yoltagě Ť, .provided the ptíláe;duration, T is.;greater than5 Rf Of. TShen the input pulse returns to zero.i Of: discharges hroughT, placing a fixed charge "Vg for pulse" on the capacitor Of provided

The first two conditions.ensure that negligiblěíicharge. Remainson Cf in equilibrium. . The thirdcondition^/éháůfeš;tha;t:;,siiff-icient: v ;,./time ^lapses for equilibrium '-to.-'.he nearly.'reached-fbéforeith- -~^---»'>~~

' o c c u r » . ' •-.;'"'. '' r ','"':•[• i ' ' : " '•.'.:'£',-']•. '"',1:"._; '. ^ ' • ' • • ' k p ^ ' - : . . , , ~ :-••*'.'--s;'--pulse:-

If i T i s n o t <C<C Y, the. charge per -ptilse becomes < (V-Ý) Pf..' •'therefore the equilbriura valueVof • the voltage -v- 'becomes1'''!' '''.'•'• '•

Hence by proper choice öf åxqi±i cpmpohénté relatiorishíp;. betweenvoltage and counting rate other"-than! linear' can beobtaiiied. ^

.....59/-

T«ísi?ím™^^**^at-^~*"-i--'r-'>í*3ř«-'i7*-«"ftlí

•,yiiĎr.'-'

tiinear Counting Bate Meter i

••r .Linearity in doling rate meters can be achieved with the helpof a diode-pump circuit and a feed back amplifier. The block diagramin fig» 39 illustrates the comitrate meter. . .... ;"'„.. . .'.,-.

Diode pump circuit vrith feedback amplifier:".

,- Ells circuit in' řig^^4.0 satisfies; ine.cpndition" ^as Of and >;H. aře^made, the ,f eedback;; elements -of the d. c ."•; 'amplifier. , •Capacitor Cf disoharges into Cf :,thrpugh_-.ÍT^-however because, of the :.feedback practicállý' all the resultant;.voltage change appears;on theouibput terminal side of •p.^^sllš^ljecausyi.^né.^fee^back^^ťhe- 1 '.circuit consisting of T3 and Tf kěěps ihe poťénÚal of grid of Tnearly constant. The voltage change appearing ag g 'léfl&äe'•: than /that:across Ct,by ;a: factor; G whefe GVis^^.^f e e d b a c k . '..'. '.-.::' '-,'••'•'..,i ',. i-,-,':'-'.'.•' [::.::'ř'l- :^:'V.-:"-•'•"•'.:• „•«'•••'.U..'--'.'.£•;':• '•''-. •'."': •?*•<' •

GVEsppsrt5.-9.76

IX - mOOTCTIOK AND BSOCESSING OF RADIOISOTOPES

Introduction:-

Mature has provided a v a r i e t y of radioactive ispecieš. Some radioisotópesare "being continuously formed in pur upper atmosphere while some have existedpresumably since the earth was created. In recent years, however, man-maďeradioisotópes have Exceeded nature in variety» Man:\'hås used high-ybltagemachines to induce, the necessary nuclear reactions for , the production of manyspecies , but the foremost achievement in th is d i rec t ion has\ come from thevuseof natural ly occurring radioactive isotopes. Special ly , t t é é ^ c l e a r chain-reac tor , in which the fission of a heavy isotope sue b äs U^- produces a neutronr i c h envoronment, i s used to carry out many neutron in i t i a ted nuclear react ions.The greatest quant i t i es of radioisotópes arise1 as f i ss ion products which occuras a mixture of isotopes representing a l l elements of „atomic^r&mbers roughlyfrom 30 to 66. ' • ' ] ' ' : ' :, •• . / . . . . , ;.••

Separation of a par t icular radioisotope and the ] purif ication tthereof,therefore assumes importance. The following pages give áií account of theseaspects , v i z . , production, separation,purification- and preparation in the •required form of radioisotópes. . ; .

Sources of Radioisotopes

Naturallyoccurring

iclaiArtificially produced

Reactor-producedisotopes

Neutron activation methodsn, i reactionsn, Vf reactions

3) n, ^ . r eac t ions

Fisåionproducts

Ac celerator-producedisotopes .-:••'•'.,-,1);yan-de-Graaf;generators2) Linear accelerators

Na Naturally occurring radioisotópes;

Most of the naturally occurring radibisotppes cah'be grouped into fpurseries viz. , the Uranium Series, the Thorium Series, the'Actinium Seriesand the Neptunium Series. Other naturally: occurring, isotopes;'-of interest are

4U tritium and Garbon-14: :. j. :

The primary radionuclides which have, survived thei-age}of'earth and areat present;..naturally available are Uranium--238, thbriuia-232lan(ä a smallfraction;' of Uranium-235 and á series of daughter .products of these) nuclides.

GVRslco

Artif icial radioactivity: isotopes that are produced ar t i f ic ia l ly are calleda r t i f i c i a l radioisotopesi , . . • •

There are three methods of producing, ar t i f icial radioisotópes.

1. By activating elements with slow neutrons in a reactor. -2. By processing the fission products from a spent uranium fuel

rod of a reactor. •,5. By 'bombarding elements'with charged particles from a cyclotron or

similar accelerators. . . . . ; . .

Reactor Produced Isotopes ... .

Neutron Activation Method; \ . . • ' • . ' • • •When almost any material i s placed in a nuclear reactor, i t may become

activated by the bombardment of the neutrons in the reactor. This is theprinciple underlying, t h i s method.. Most neutron activation reactions are dueto the (n, ) reaction. .

The following are some examples:-

g 125 .,50 S n +

The fast neutrons present in a pile ..can also bring about nuclearreactions of the type (n,p), (n,Ot) e t c .The following indicate, some examples;:- •- .•" . - , ' " • "

1 3 A 1

s 5 2S

GVSslco15ÍX76

"* °n

'•' 1+ no

> 16"335

. . . • i i i.3

: i x - 3 • . " - . • • ;

. The neutron, addition reactions may be» implemented with, ease in anuclear reactor since, the material tö be activated' or irradiated maybe encapsulated in pure form, placed in a reactor and removed from thereactor after a suitable time* . ' " '' "1 • " ' • . . - .

Method of irradiation in the reactor:1 . ( a V C o n t a i n e r s ; • ./.... .. •- .' • • ••'•.,:%'•.;, • ' > . : - • V Y - :• •. .

For irx.elating in reactors the target material, i s usually enclosedin suitable containers. 'The material with which tfie container i s made.should not have a large neutron cross.section and i t should nöt reactrwiththe contents at the temperature and the neutron flux present in the reactor.Aluminium i s of ten. used for this purpose. Specially pure, gráde 2S aluminiumshould be used since commercial grade aluminium contains chromium arid ironfor which the neutron cross section i s highj: Where the sample; cannot beplaced directly inside the aluminium container as:;for instance'•.when it'..is aliquid, gas or a porder that i s likely to react;^tö;å3i™iniumi -an.innercontainer of glass or quartz, must, bé used.\\ Glass contains. Caarid Ha andhence is likely to.become active; Tifhen i t i s desired to transport theisotope alongwith the container quartz i s preferred. Gaseous material orsamples with a high vapour pressure may be loaded into,such containers asshown in the figure. ' \,'n

:.'A. •* '^ ; ? : 1 8 . 0 cm-

SealedT*after.loading

Naturally the amount of smaple that can be irradiated in.this type ofcontainer is limited bý the. expected increase in pressure duringi r r a d i a t i o n . ' ••". ••_.'• r -. .- • •' . v . ';•••'••'"•?•• ' • '.••.;, •

1.(b) Target; . >

Iti chbsihg the target material certain charác:térist.ids should beconsidered, namelyt-' ; . ; : ' . . .' : . ••'•-"• • : '

i) The temperature in-the core of the reactor will be. high and thereforethe target material should have,:high thermal stability,; V

i i ) Forms of element which do hot iroiatalise'arid attack the material of

GVP.rlco

• K . - . 4

i i i ) The target material should be.one which does not give rise to any-undesirable nuclear ot. chemi'cal reactions. -' ' . -

. iv) The metál itself is ttie ideal sample» Incases where theavailability of pure metál becomes difficult, the tiext preferable sample willbe i t s oxide, for the interaction cross section for oxygen- is small while aoarbpnate is the next preferable form. Sometimes pure oxides and carbonatesare either very eostly or not easily available and then other compounds such aschlorides are to be chosen. ' \ .; J ; ; ,

Sulphur.:35; isi prepared by irradiating* potassium chloride (containingchlorine-35) with neutrons . i ;

.17 .; '?,35 j .

But some atoms' after capturing neutrons emit 6< particles: instead of protonsthereby resulting in; P-32- . •; : ' I ' .-

17 C 1 ~ 5 + n V17 /• + Qn ^

The reaction

17,cr35

i s also possible. Further since potassium chloride is used as the targetmaterial, the K-4Í atoms get "activated to K-42. "

In selecting the target material one.should avoid, a sample in whicheven traces of nitrogen or: nitrogen compounds "are present ow,ihg .to possibilityof the formation of C-14. Once the target materiál if selected.,it can beintroduced into the reactor enclosing, i t in'proper containers and activated.As illustrated above the resulting sample will not;be: pure and•;as such somemethods of purification are to be,adopted. . , ,: . :. , . •'_; • :

The space available is.^also;another considerations Where^ neutron •absorption cross section i s very high, only\,very small quantities of thetarget can be handled. . ' ' • ' • - ' •• ; ' . • .I . e . Specific Activity ' , . •

The calculation of the specific activity of' the radioisotope obtainedby neutron activation method: may'be calcúlátod by. using, the. follpwing 'expression. ' . •-. ' '•'-'/ ' : ':

GVR;lco/i5ix76

IX - 5

W h e r e . . . -• :.••-.•.: 2 3 ,

N is the Avogadro number. (- 6 i 02 x 1 0 ) ' . .

0T is the thermal neutron cross-section of the target material in cm .

^ is the neutron flux in neutrohs/xm. /sec

W is the mass no. of the target-element1 •

A is the decay constant of the radioactive product.

The specific activity calculated'from the above equation must becorrected for several sources of error. The actual activity produced isusually less than:the calculated one. The ratio of actual to calculatedactivity is called the irradiation efficiency. Eráctical irradiationefficiencies may;be as low as 20% or as-high as 80$. • '•'•'•'

The main factor tending to reduce the irradiation efficiency is"self-shielding" in the target material. If' the target is of considerablethickness, the neutron flux is attenuated as it passes through the targetand the affective flux or the average flux throughout5 thetarget may^be; lessthan the ambient flux. Calculations of the effective flux within the targetis in general very difficult, as this depends on the geometéry of the target.Some idea" of the ei'fects of self shielding may.be obtained, by consideringthe greatly simplified case of a parallel beam of thermal, neutrons incidentat right angles on a slab target. Calculations are easy in this case andyields results which are shown for various target elements' in the figure.

4»ofr—-^ """ 3*,.

Irradiation efficiency cannot in general be predicated, by theoreticalmeans. Tn practice"predictionsTare based'on empirical'factorö derived fromresults of past irradiations. These include certain factors which do not,strictly speaking,, belong under the heading irradiation efficiency. They are;

a) Bay to day. variations in, the neutron flux, due to shielding by othertarget materials in adjacent reactor positions and to unscheduled variationsin the reactor power level. - „., " . •";"

" " ' • • " . • " • • " ".". 6

15 ix 76

, E t - 6

b) Impurities in the targets The effects of, impurities can usuallybe made negligible by taking care to see that no, impurities are presentthat will give rise to unwanted radioisotopes or that will absorb a largenumber of neutrons. , ,.-. .. ._.,,,-..;... .

The equation mentioned above is á greaüly simplified one and isapplicable only to certain irradiations. One important factor that isnot allowed for is "burn up". Äs the irradiation progresses, the availableamount of target material gradually decreases, due to oorivérsioň. of targetatoms to the radioactive product, which in time are converted to othernuclides by exposure to the neutron flux.. ;. '•••.••,-•• Í

i. .. Because of burn up of target and,product, the rate of curie productiongradually, decreases with time. If;the irřadiation is continued long enoughthe production rate i s eventually equalled and then surpassed, by decay andburn up of the product» The time at which decay plus product burn up equalsproduction i s called; saturation point of irradiation.

The relative importance of burn up depends on the fliix, the neutroncross sections of the target element and the radioactive product and the rateof decay, of the product.

Wherever burn up i s significant the above equation cannot be applied.

G"7R:lco/i5ix76.

•v . r&Fi*

. • • X ü - 7 . - . - •

The n u c l e a r r e a c t o r i š t h e most important source of r a d i o a c t i v em a t e r i a l s . .Most i s o t o p e s oan b e produced möre^eaeiily;. i n a r e a c t o r t h a ii n a c y c l o t r o n o r i n any other high-energy., dev ice . . .,, ,,..! ,,.., ,,;,.-. l t .

• • ' " - •''••"-" V ' " - • • • • . i ' - - — • ,• ' " ; ,•.••.••; . ••. , : • . ' - : • - ' , ! v - . . . : - - , . ' . i r ' ' ; . - . ; . - . ' ' - " ' - . - . • ' • • ; • • , • ! ( * ' ' • • ( • : ' ' ' ' • ' • •

Ina,reactor, the uranium\atpm.fissionsijato.two;pap-bs.with therelease of neutrons and an enormous amount of energy. Ali" the" elementsnear the centre of the periodic table can appear as fission fragments"but, in particular, elements with mass "numbers in the region pť I40 and -90 appear most often. . ": . .. v.

Figure belov; shows the fission yield of U-235 by slow neutronsplotted against the mass number .... .v ,

^ ^ i j j r ; -.^•-xr.-..i--.•:>

I t may be seen ,th,at Caesium .137» • : i??požífcsúit: souroe, Inteletherápyunits,.appears.at the u p p e r ^ p e a k , Ä d ^ s ^fission yield.,.. SiDilOTly,i.Örr90^appears ;in the- peak^region. J. ^ ,rt_.. ;/''.:^':;"'v:'v:'v; "!ij\[,"' ' '.'f"''^.'".",'^'"'-'-'

Some of. the important, isotopes ^ obtained äs řissibníproduiáts areincluded1 in the table given in1 the appendix.' " ';;-, . • ,.;' .

.'r-8'

A c c s l e r a t o r p r o d u c e d i s o t o p e s •••. \ '.-'•;' ./.'•'-• /•-.•'."•;' •,'^'^:,.^-'l'. ••'•'.-.'<;-' '•;• "••'•' / : ••

In the production;'óTisbtopes by accelerators, accelerated chargedparticles suqh as ' protons i; ideu teröns i alphas, electrons and' tr i tons aremade to bombard certain elements, to produce isotopes. In these cages,the resulting,isotppVwill- be of an element different frpm: that irradiated.

•ms.H 2

The aďyantage-bf, t h i s method, i s thatuisótbpeš of ä certain elementcan be/producedr from a t o t a l l y different .element. In other words, carrier-free isotopes can be obtained by this method. - '

Badioisotope Separation and. Purification -

In many, cases more; than one "species" of act iv i ty i s ^produced in atarget* Thus some chemical means are usually required to separate th;edesiřed..Jispeeies".'from other "contaminating" isotopes. p r i t may be thatsometimes npn-radioäcfive'components haye-to-be lemoved.

Separatipn procedures are numerous for.each element. The,basic!separation methods are given below: - ;, ; ;• ' ! '••

• • : 1 . ' v - ^ c i j i t a ^ i ö ^ ^ i h o i ' ä - ' - v . ' v . •'--.'• -.-. ' ; . / [ • - ••. ,"',... " .2 . I s p . t P p é ; C a j » i e r í M e í ; , h t í d

, „u_ _ „ . . , . . . M e t h o d . : •1 5ť* V p i á t á l i s a t i d r i í o r ? D i é t i l i a t i b n Methods

6. Blěctrp-depbsi t ion Method ,";•'/.•; •••">'7 . Method employing Szilárd Chalmer Erocestí

1 .'• Simple p r e c i p i t a t i o n meühod? V• " " , • '•!• '•' • '•,>.

someCl-3atoms .get abui.vateä-;the. chlorine must be TOp~araťp.ď;;t^'''^{^.spurcé» ,i;.Åbtiyated FeC1 -3'.is;;mádé to.íreatít]wittí NaÓHigiýingliNaCl • |, T

••- i

„ j-^^^^a^^-^rtj K^rsFÄr^rriW^Ji^^^

FeCl3 Fe(OH),i

The r e s u l t i n g NaCl i s mixed wi th chemicals suöbias AgNO, whiehp r e c i p i t a t e the c h l o r i d e , thereby s e p a r a t i i ^ , the: Cl-38 frean/the5Fe~55

NaCl AgNO, NaNO, + AgCl

2. Isotope c a r r i e r method

If a c a r r i e r i s present with the i sotope t the separat ion becaneseasy. As an example, Ba-140 can e>e cairriea from solut ion by adding anormal barium s a l t such as BáCl-, mixing to give a uniform so lu t ion andp r e c i p i t a t i n g BaSO. by the addit ion of a sulphate. ,• .

3» Solvent Extract ion method ' . . ' • • . .>. ! . ; , . r • : ,

.The different jpolubility.of substances in ^ a solvent i s jthe basicprinciple of thisjímethiad. .• ActivatedUranium; f^ms.thei; large: numperr-of;fuel

? =(thB irradia |ed lutc^coniäinä;)? is/éxtEacjfced b ^ this mejthodw- Pór

4« Chromatogräphy arid > Ion Exchange Method:.,'..

The separiation ofysubstancěs^bý selective ůistřibutiortí between aflowing,fluid and;, an insoluble substance:Jmown ;asVthe" suppo?:t;i.:is calledchromatográphy. This method^ ia employed ,iri processingKsioa 11."iamdunts of.material for prpparative; purposes. :Based, on. thesý^y^cóf^ro^sšl^hich,predominates,/this can be':classified; into ad^orptiön=c&cpmatograpfiy,i part i t iono h r o m a t o g r a p h y — * '—: ~'—•----—- •-• •« •-*--'"' -•-.•—-••.

Ion exchange chroinätography: itírv exchange is thié rev^rsib le interchangeof^ ions between a-:.liqúid'riphase..andi ;;a;;solid: ma^rialywhich/tidpea/iio-b-^--1-1

a. rsubstantial chaise, in the strub$ure of the fflli^.ví:";lj^geí'*,cattí:bóth'and catipnf exchangers.!. Invthe iabpřátořy:,-:i sepařatibn\<óI^Co:$ťfitéru.i s effected in. presence of .hydrochloric; ácid íby lon^exchänge^iiThe wash .liquid used, for NickeX is áui^hydroóhlóric-aoiav?^^ •,-'-' •" '

Adsorption .Chromatograph^:: Ther distribution; of'o the íconstijtueňts of asbiutibh in a scJ.id cijlum tovdifferent,,extents_ÍB.c^chromatográphy. ..IJsingíalumináy^AlJ)^):asi the; adsorbent. i^.láVpossíbre to;separate Ü-233'. frpm; Thorium after Th hajr been,/i-pradiåte^:Ao;;- gívé tbeNforniéfdmiěr

s^is^sr^^ í™ií-WJiíCí=os^r*;^|7--T.nr^~^

The solid chosen for) this purpose'-may be the usual alumina, s i l ica otc,or sometime a f i l t e r paper. When tellurium i s bombarded yLth neutrons,I-1J1 is producediiibut1 alongiwith: the I-131.which is present ás the iodide,iodate may also ;be! oře sent. :\- .Separation • of v the. former from;; t he la t ter, isdone by paper chromotography using. 75% methanol for the mobile. phase.

5. Methods of volatalisation and, distillation

Ioäiné-131 can be separated from;non-volatilé impurities by yolatalisingwithon sdme;

air , .nitrogen ror oxygen» This :can ;be made- to deposit as:; solid iodinei m e ' c o l d . f r e c e i v e r ; .- .- • ;; ;-':' ':\,'- ':'," '"'-.•••:' ~ ' - : i - ' : •' ' • •• '"''•''•

Isotopes of mercury may be' separated by d i s t i l l s i t ion fiombne-another.

6. Electro-deposition . iv:^^' ;;': ... .--•- -:• . ;'".;- v :

-.,- ;Electrolysis can „be: used for source přepař.ation?"and : ípr 'separation ofthe component&:of a miicture, .Either .;tte iiijpiiriiies^or the äeaireäsinäteriälcan,be electtořdépositéd.> „Thorium; čaníibe. dp . p ^ / / ^ ^ ii t s aqueous, solution by ělectrp-dépositibri on. the cäthode'of a suitable yolta-.meter. '- When the mixture .qontatns;'i;TO.-=9rjmo^

imeter.on the .same electrode, separation can often, be obtained Ibýbontroi:of theapplied potent ia l , : the ac idi ty , ionicícpnceňtrátioniof oîeêlement by means ofai.compléxingâgént," orva combination - off: a l l thesei '^ •'-:•::•.-' V} :combination - off: all thesei

" J i _ S z i l l a r d c h a l m a r s . p r o c e s s - -•"•': •'...,•••.-•::~ :• ' '• - ' . - - ' - - , .'--:."-•

. . • , For iaany of the compounds;'-ith'evmolecular;:bonds are.weakyjn.such casesthe recoil energy associated ..with 'á radioactive^^ .äiöm Is; l^gerVi;han thebondlenergy with, ishxchiir. is;attached;;to the „restiof rthe1"molěcxile.':;í Thus, the'bond i s rupturediand-l the ätöm!géts expelled. Obvioušlýithisrexrpuisioh^willtk ltake place only, a f te r ...the.- convereion,- of;;íxnactxvé |ätpm?'ihtp: :an act ive atom.Br*82 i s produced by i r rad ia t ing ethyl bromide;";/In thiscasefith^- bpnd;energy,of: t h e ' Br-82 atoms becomes lesser, and íithey.áre .expeíledfrómithejcompoúnd. .Thereafter Br-82 can be' chemically separated.!. ;;'. . ;:;:; v-:' -•%? = •• •*&:;-"

: . . . Sometimes solid; sources may,be reqi i i redi . .Ther.methpds available forthe. preparation, of solid sources are. suimnärised: below. : > , > ; ,-.-:•'',.'; , ;

; . , ' ; 1 . Evaporation ;qf: a solution containing t he .radi'«-áctiyě; isotope in anon v o l a t i l e form"andidepositing i t on á surface.- ;- ; " ; ' ; ; """'_.":-';"

,• ; 2 . Mounting the..aanple :tp be i r r a d i a t e d in :the. fbrm-pf a powders.

. A ,3.«..'«Mounting,.a. sample, prscipitating.i^' 5 by,sctó-chemical means. •and drying ;the précijpitatě'.'" f ' • • ' . . - /"*:*:'•'';;: P.;:'.'';': '*>&,'.:':' •X'-,-:

i •,.,;•„

4. Obtaining^ the sample'^n! theXfor^i of p l a t e s by,electro 'deposit ion.

EC. - 11 .. "

Important considerations in preparing the sample in the form of aplate are that i t should be uniformly, deposited and i t should be chemicallyand physically stable.

Comparison of_ accelerator produced and Reactor produced radioactive isotopes

In the production of radioisotopes, reactor and cyclotron areccni&enexitary , The pile cannot manufacture the extensive variety ofradioisotopes that could be produced with a cyclotron because ,in thel a t t e r , onecaan vary the type and energy of projectiles.

Many isotopes produced in the cyclotron cannot "be produced with thepi le ; for example: Be-7, C-11, F-1B, Ma-22, Y-48, V-49,.Mn-54, Mn-52,Co-56, Ni-57, As-74, Pe-59» -Ag-74» which are a l l positron emitters anduseful for biological and medical purposes.

I t i s normally not:possible to produce- carrier free isotopes in thepile wherea.s i t i s possible with t be cyclotrons but the cyclotron is onlya feeble source of isotopes. ,

Of course recent developments of the cyclotron have? opened up newpossibil i t ies. With the giant 184" cyclotron one i s able to produce deuteronsof energy 200 lev and alphas of energy 400 Ifev;. and therefore,.,a completerange of hew isotopes could be produced«-.' . -...

Production of tele therapy c >alt sources

The method followed by the Atomicas foilowss-

of Canada Ltd., is

The cobalt target material consists of 1 mm ,x 1 mm cobalt pel le ts .These are cut from a 1 mn diameter wire supplied by the manufacturers.

These pellets are degrsased and oat-gassed and coated with a thinlayer of graphite (Mckel plating is used in Germany). This coating i s toavoid oxide formation. These pellets-are put in capsules andijbhese.capsulesare arranged around a ring in an-irradiation can. if the capsule, iscompletely packed the cobalt material in the centre \iould. bérpract.icallýinactive owing to neutron'attenuation. With such, än arrangement a finalirradiation efficiency is only 5CfC . Each• irradiation capsule, contains :•-; 1 ,30 grams of pellets.., The capsules are 'irradiated in a flux of 3vto; 6 x 10neutrons/cm2/sec_; and. the specif ic activity, on an: average increases at therate' of about 2 curies/gramš/moňth. Théréf pre :> to; gěi .35 curie s/gm of materiali t -bakes 17 to 181 months ;in..t,Ke""HRX,;.'The;.seäliné, ofí"these;.ci'apsules is doneby the cold-weld pröcéss.>: There is.a-lipyan. t&e ,ená"bf the capöiile and analuminium lid is placed on this,end.: ^The' capsulC;isTput in ,a die thatexerts pressure to produce a cold weld sealingjLprocess between ;iihe twosurfaces. These capsules' will stand •internal.:pressures of uptó'50.psiát room temperatures^ .; ';•' ,_ • ' ' ' ' ! ' " '•,"<; • -jó

GVR;lco/i6ix76 •'''"•' • '": •"• '

IX - 12

The capsules are finally loaded in the international standard capsule.

The production figures for Co-60 for Canada are as follows:-

Production

Total curies

60,000 (MX)

70,000 (mx.)

60,000 (MX)

3,00,000 curies

in U.S.A.

Specificactivity

- 35 curies/gram.

curies/gram.

• Cobalt wafers of thickness 1 or 2 up thick and 1 or. 2 cm diameterare usedi ' These are nickel-plated. These are loaded, in'internationalstandard :čapšules. Production is estimated ät 3»00j000 curiés/year in •U.S.A. and specific activity i s oT the order of 40 to 50 cuřies/gram.

Production a t Harwell ,

die can either'get the disc sources or the pellets with maximum,specific activit ies of the order of 80 c/gm for, discs; and 120 čurie-s/gmfor peljets (reference ümersham I962 catalogue) loaded in International-Standard Capsules. , " ; . '-''.:••. ' ; ':.••'"-'•'••..

Even-though one goes on increasing: the "strength of the teletherapysources, the effective output of the'source in rhm may hot increase : ' -proportionally because of self absorption. The linear self absorptioncoefficient fór Co-60 fór i t s own gammas i s := O.245 cmT: --'for A .ÉÍC.L.cobalt pellets, (packing density 5-65 grams/cc) and =0-.JßcS'- for f ,,:

A.E.C.L. cobalt slugs? (pencil aaurces arranged, in.the form of a follow'cylindericál r ing). .. í / ; .. .'• • . „ . . .

Interhationai Standard Japsule, '•.••'.- -; ...v . . ' , . , ; •

This capsule is designed to faci l i tate interchange of sources from,one unit to another and from one, isotope productioii; faci l i ty to another andhas been agreed upon by TJ-S. and Canadian, producers. The- capsule is shownin figure.

GTR:lco/i6ix76

. .• \ - • . . - • • • . " • • . . ; I X , - , : 1 3 ' ':•':: "'•'• , ' : ' V - ' / " ' , " ' .' "..' -."-• '•

The outer cap is provided with 2holes; on the source-end of the capsule; into"which ä spec iat'wrench may';bé f itted to''."screw'..thěrspiroeyinto yfctíe'therapy'1unit.The' soúree; i s •placed '.rSHfH 'stäihless steel :feup whictíliscrews, down onto two 'lead wire- gaskets' to;ensure/ an absolute^ seal. The) plughas a square 'hole' hn- its- end • tQ;'tákélfa7sp'éoii .'VréÍ£BÍi« :i^cept;)f or; t te S ť •:

/stainless-steelcúpv'thě' spurcé ckpsulé"is"máS'e of;^.avy-^metaliân^ållöy^^pf'-.tungsten which i s durable and .has.jináensitý ;of;;ôut;î7jigäs/cb^;'fThiSřhigiádensity material supplies attenuation of the gamma ray beam in «Tl. directionsfrom' the source except in the direction of the beam (upward) where there i sonly ä thin"layer of stainless steel. The heavy metal plug i s actually made

. in..two parts (not shown in the figure) so that sources upto 3«5 cm in diameterand of different thicknesses maybe loaded into the capsule. Because of theleakage of active cobalt dust from some of the older sources the present prac-tice i s to replace the inner lead gasket seal by a weld. The outer dimensionsof the source have not been altered. -

,Preparation of Cs-137 sources.

Cs-137 is obtained as one of, the more abundant fission products ofuranium. In a nuclear reactor, the'spent fuel is periodically processed tosepaxajheLvthe fission products. Caesium i s extracted as CsCl or CS2SO 4 sincein i t s elementary form, i t has a high affinity for other metals. The sa l t ispulverised and then pressed into small tablets. These tablets are packedand/sealed'into a stainless steel container. The es-137 thus obtained i scontárairated with i t s isotopes, Cs-134 being the chief contaminant (3 todefending upon the t'ype of fission) Cs-134 gives out gamma rays of energyÖiÖ'Meyjand 1.34Mev necessitating a thicker shield (1-| times the thicknessrequired for Cs-137). The isotopic mixture has got an effective half l i feof 26 years.

; -Although radium was used in the early days as a telefcherapy source,since "it i s no longer favoured as a teletherapy source, i t will not bediscussed here.

Sources.for localised irradiation

Radioisotopes in the forn rf neodlos, p l^uas , tubes, soods and viresmay be used for localised irradiation. The isotope may be introduced intoone of the natural body;cavities:(intra>cavitary)>; siirgically^implänibediintotumour,TEÓass ( in ter s t i t ia l ) or plape'd in contact'iwithvä skin :lesion."^-The:i;: •;"c ö m m o n é s t f o r m s a r e ä s ; f ö l l ö w s v " ' ' ' ;-:-\.r.r'i-r;'.•':•'•/_••. f .:;':•'• .-/(•'••'.*•_ .•;•,&-, • ' ;'••'. :'•<•'

i . Handoň Sources1; \r ',',". '.';•"•'•'•'"•• .'-; ^'-'-y-'' ..<J-::\-''''''-:j • ;~ ;"•'•', •'•'•": -;"'; '"'-"•" :-?r^' .'-J "

The radiui i s a l t = is.dissolvedîErâ.••;iiqúidi-:;ômž;án ;aqu^<^s-.solution-=of-'a. radium hal ide , . á g a s i s eVdlveävwhich'r^ :,.a b o u t 5 , 0 0 , 0 0 0 naT-hss n f ' h t h f i V ' ^ r i a e a J ' ' K i i - ' , í - '. / .'::' ! ;;. .-'"--'••' ' 5 " -'•?<*•

GTii:ic.o/i6ix76

• IX - 14 '

This mixture is. successively passed.over red hotcupric, oxide, and pptassiiunhydroxide. By doing this, hydrogen», organic vapours, hydrogen;; cftLpridé. ;|-..-'and hydrogen bromide are removed., The mixture^^^^^;henJÓ^teä;.: ^^,liqjil,i'd.•,airwhen radon;and carbon-di-oxide» are solidified. The^solidVmixtur.e.is.thenwarmed and passed over potassium hydroxide when carbon-diTOxide i s absorbeda n d p u r e r a d o n i s g o t . . . .-"•• • _•••'.-... -' '• •• ,':.M;, • ; ; . > • / . . ' ; \;'-. .••'••„V ••. •'•:• i :''•"

For some applications, ,rit is convenient to seal radon gas onto a ,small hollow gold tube called a radon seed and to use i t instead: of radium.

2. Hadibcobait needles and ribbons .-.>.;.'

Eadiocobalt needles are, fixiding increasing uše in i n t e r s t i t i a l therapyin place of radium because of the following advantages i t has over radiums

1« Has essentially monochromatic radiation

2. Is corrosion resistant

3.....Can be handled with ease-before and after irradiation* , /

. 4« Gets excretedr/q.uicüy from the body in case of any absorption.

5. is cheaper than radium . . ; : .

These, needles are .prepared by hermetically sealing small segments,of Cq-60wire in.sfcainle.ssrsteel tubing. A more.flexible^ ty^e .of:,.,indiyiduaiised application"^ for implantation therapy^cóňsists of silk tubesloaded. with, radon seeds o? nylon tubes containing small; Co-60 sources.

3« Radium Sources ^

Radium in the ,form of BaCl-2 i s mixed with a f i l ler and.loaded into.,ce l l s of about 1 cm long, and 1 mm diameter and the cells are: sealeďi - ÍTÍiésesealed cells are then loaded in platinum" sheaths (Pt.- I r alloy &Monelmetal are also used) which are againasaled. This double sealtis;necessaryto, pceyen^ the oscape of active, deppsits of radium. These needles;havee y e l e t s . . . , • ' • ' , ' " "••'. • " / ' "'•'"",_,•"•" ' • • ' ' " . i ' ^ ~ ^ ' " " . ' : " - ' . ' " ' " , ' "

quantity of,radivun i» a.source i s always specified;ra terms pfmilligrams or grams of radium. The, f i r s t radium standards prepared byifine. Curie in the form of chemically pure «aits' are stored near Baris.

Because the gamma rays from'.a radi'jin source are mainly due to Ba-Band Ba-C, new preparations of radium must be stored long, enough (about 1 month)to estabiish equilibrium of. thes^ .daughter products before the comparison ofthe sources.with a standard can'be made. , . ., : -

GVS:lco/i6ix76

-^TK"^ 5T~',*i* íf- T 1 ^ V s -•rt-iT7:'™-. -»«irlKy T i d*

IX - 15

4. Gold Seeds

Gold 198 seeds are used extensively ..for implantation into tumourswithin the urinary bladder;and abdominal.and thoracic cavit ies. Radio-goldis prepared by neutron activation of inactive gold. The specifications ofstandard gold grains are:- .,

Overall .length . 2.5 mm-Overall diameter 0.8 mmPlatinum; coating 0.T2 mm. •

Ah implantation gun for use with these grains has been developed atthe Royal Marsden Hospital.

Gold grains are activated to. user ' s requirement and any activityupto 50 :mc per. grain can be produced. Used grains can be reactivated.

'Tantalum .182 and Iridium 19.2 grains also may be used instead of gold.

5. Tantalum 182 wire " . . . • • " - . r ^

Tantalum wire is . suppli.ed. ei ther bare or sheatted,with Oil mm,platinumwhich f i l te rs out a l l beta radiation. • .Wire.^diameters, of 0,4 rän Ta (0;'6 -mmsheathed) or 0.2 mm Ta (0.4 mm sheathed)| arefavailäble in lengths upto 50 cm.

vdLre|.. i s often used in the forin..,of hairpin iinplants.. .Whenhairpins are requested the i;ire~ i s supplied and bent to the form shown inthe figure. Each hairpin requires 12.5 cms. of wire. .. _,^ z;,'.-;

t 3mmm

ingûse i s also êîa. made - of -platinum-sheathed' tantalunr- ' :•^replace rádium in ' ir i t^^bit ial . armlications. 'The; imnlant.is btiilttesfbitial. applications. .The.implant;is bui l t

up with empty stainless steel; needles wh'ichiare then loaded mth.tantalumwire cut to length as required.^ in th is application, one me of: tantaluai s approximately äquivalent to 0.8 me of radium.

Beta "Bay Sources.. ..'.".-v- ; .•'".•' "•. '

J . í a J ? ^ ? E I ! 9 ] ? ^ ^ certain verysuperficial lesionsi*ésp|cialjy those of the eye. .'•:-"•.'

.16GVR:lcoI6ix76

IX - 16

The following table gives the four beta-ráy sources used forcl inical use with human subjects!- •

Radioisotope

Bi 2 1 0

• Half-life

(Ra D) 22- yr-s

(Ra E) 5.0' days

28.0 yes.

64.4 hrs.

1.0 yr .

0.5 min

280.0 days

17^0 min

Maximum energy '• .Whetherof n raý (Mev) gamma rays

T present

0.542.24

•;. 0.3

every week

gammas

Obtainedfrom

*Natural

FissionProduct

Fission

Product

FissionProduct

• 9 0 ' 9 0 ; . . . , ' • ' • ' ' c ;.:

Of these Sr - Y i s used most because of the. ease in get t ingi t long half-l ife and13the absence, of any gamma-rays,-

Beta ray sources for, c l in ica l u s e s : - ;" • , ,-.-• ;. ', ,

Sr-90, Y-90 plaques 2nd plates are.avai lable for nedical uses. Tn aplaque, j^ctive component consist^'tpf -a sheet ;óí,'silyer.. 0.7 mm thick conta i -•ning the'isdASisotope cqii^dund, -sbrênrd^yiOviîîö^ölg p q ^ , ^ y ^ i âgainst corrosion by a rolled gold .coating. This is mounted in an'aluminiumalloy case with guard ring: 1mm-deep.;:

GTOslco16ix76

In the case of plate there is a margin of 3 mm inactive material but noguard r ing. .

. . . . . . . 1 7

' K - 17: '

Flexible beta applicator sheeting \

Thé. flexible beta applicator sheeting contains .phosphorous or'Yttrium which i s activated by.-irradiation. ' The sheet i s supplied instandard rectangular, piecesJ 50 x. 70.mm. \ Surface dose rates are checkedagainst a standard extrapolation chamber., . . . '

Beta ray opthalmic applicators.

They have the general shape shown in the figure. Applicators, ofRa-D + Bfjxshå for a long time for superficial conditions. At present^pereSr-90 + Y-90 sources-are used extensively.; 'Sr-90 foi l bonded in silver; iscovered with .-'polythene plastic to a thickness o f0 .5 min. (to .stop low energybetas) i s used. The back of the foi l ťs usually covered with.a layer ofsilver to;absorb al l , radiation. Some applicators .are".shown in the figure.

Strontium applicators give an absorbed dose rate" oř-about 100rads/minute at the surface. .

Yttrium 9p.'rodsj-

These are beta emitters and the available size i s 1.3 mm dia., 4 mmlength. They are used for pituitary implantation.. :; , ,:

OnrriTna ray sources for Industrial Radiography: \

Gamma rav sourims for^tofinsti^fcl-^fadiograTJhv are availably inStandard British Capsules,' the source, material ;0ccupyifig a'.cylindricalcavity of length equal, to^diameter. . The Tc_apsulés/ arg• se.aled.by .welding,or brazing. The following radioisotopes are available.

C0-6OCs-137

Ir-192Thulium 170

5.3 Years30 Years

74 days127 days

Encapsulation.

Stainless steel.'Stainless steel or

nel metal..

GVRslco

Allpminium alloy.Thulium dioxide.powděri s prééáed,; sintered andencapsulated in aluminiumalloy. ;.

Most widely used flanana ray sources in Industrial Radiography

Source

•J05.,

Trn170

Half life'1' ray energy used for

1,590 Y r s .

3.8. days

15.0 hours

4P,0: hours

Spectrum o£ energiesbetween .0.24 &.2.2 MeVwhich srong lines at ;0.6,1.12,1.76 MeV,

• ' _ " _ • '

33' Yrs.

120 days

2.75 &-ik38.'.MeV incascade

Sroin 0.093:strongest

5.2 Yrs.

/fl 7 days ,

1.17 & 1.33 Merlin cascadgl

1,22.MeV-ánď,many softer Il ines . , .v'..' * • ".'• '~''.~,\''"y~?.^J-

• V '" *- '-! "- . '. 'I''-' A

0.61 Mev and manj'' l ines, rdown t o O.X37 MsV , ' :

O.667 MeV. ;

84 & 53 KeV.

Por steelfron i4'tl-upwards

Por steel2i' to 6"thiók

For steel>é" to 2&'

Por Al•1/8 .to. 2"

•k . b

IX - 19

Neutron Sources

Neutron sources can be conveniently classified as follows:-

1) laboratory ne tron Sources.2) Accelerator produced neutron Sources. ;: ,3) The nuclear reaotor ( i tself as a source of neutrons). .

Of these the Laboratory neutron sources ape dealt here. These are sourcesof neutrons made up of a target material mixed or alloyed with a naturallydecaying radioactive component i«hich supplies the bombarding radiation forthe'release of neutrons. The reaction involved is the (0C>n) type, thoughCy ,n) reaction also i s possible. The important sources.belonging to theformer type are Ra-Be, Po-Be, Pa-Be and An-Be •flhile for t he latter "type themost important example is Sb-Be source; • /

"0 Ra-Be Source This i s the most widely used of a l l neutron sources.A solution or suspension of a radium ?salt, together with a suspension ofberyllium powder, is evaporatee to dryness, and the can carefully sealed.Radium in equilibrium with i t s daughter products, emits four alpha particles,of which one has an energy of about 8 Mev, which by virtue of i t s highpenetrating power has a high neutron yield. -

The Ra-Be source has a hi^h gamma ray output. I t s neutron spectrum hasa peak at about 5 Eev, with a maximum neutron energy of 13 Mev.2 ) Po-Be. Pa-Be & Am-Be Sources

Polonium-beryllium sources are often used, because gamma rays emittedare negligible, and the source size i s small. They can be prepared.as.above or by deposition of polonium on a very thin disc of silver or nickelpressed between trvo beryllium discs.. The chief disadvantage,is the relativelyshort half l ife of PO(140 days). " ' . ' -:' ,

vPa Jy has a half-life of .25,000. years and because; of the fact that the

energy of the alpha particles is only.5*35:lfev as:compared!.withgthe;i8 Mevfor oneof the alpha particles of radiunu the yield is about 10 n/secper curie as compared to the yield of 10 n/séc pér curie in ,-t he, case ofRa-Be source. A Pu-Be soiirce i s almost gamma free*

2 4 . 1 • ' " ": - ' ''•-•-

Am has a half-life of about 470 years and decays by emitting, alpharays of about 5.4 Mev and followed by gamma rays in the range öf 4Ö-6O Kev.Sb-Be Source i - Sb ^ has a half-life of 60 days and emits gamma rays of1.67 Mev and is a source of neutrons of energy about 25 Kév.

GVR:lco/i7ix76

rix - 20; . • -

FBEPAHATION OF M B , LLED COMPOUKDS : ."'"/'"•.!'

GENERAL PRINCIPLES "'/ '.'''' "•>'.'.. ;, , ,

Many tracer experiments require the syntheses of, molecules which are.'tagged' with a radioisotope in an appropriate position, jhešecompoundsare generally synthesised by either one of .the .'three., methods::V;Í), Laboratorysynthesis 2) Biosynthesis and j) Synthesis by;a nuclear reaction, ^g shallconsider here some of the more important labelled compounds. ;_ ;'•'•

1, Laboratory Synthesis;

In.this method the ordinary chemical synthetic methods, are followed,with some modifications so as to preserve, the more costly-radioisotope.As an example, we may cite the synthesis; of acetic acid which-is preparedby treating the Grignard reagent with C'4°2. v . '

CHj Mg Br

CILC^OOH

C%2 4 0 0 life Br ^

(OH)Br

Normally, in th i s reaction, . C02 w i l l be used in. excess, in order, to-ensurethe complete conversion of the Grignard reagent. V7tién the "active carbon. ,dioxide i s used,, howeverV the other reactänt i s used Jin excess. !

Similarly, when the synthesis of á labelled cqmpound, involves manys t eps , i t i s desirable to 'pick á troute :;t'hat';-wiii inc'prpprate :t,hé. radioisotope,element toward the end. This-will ensure mininum.loss as # l t as decay..Generally methods that m i l result in a higher yield!', and specific activityand minimum transfer of the solution should be preferred!'; ': :

- . ; . ' - ' " ; ' • ' • ' . - • • : : : . .'•'*•• '•••• :: ' • • • • " / • ' - • • ; . . • ' • ' ? : , f . I ..-. '• '• :

2 . B i o s y n t h e s i s : •' / - . ' ' ' " / - ' ' •"-• .. ' •••••:•-.'• •:•']'-' '.•:"'; ':'

This i s important in obtaining labelled compounds which;are. difficultor impossible to synthesise in the laboratory. This involves thev administra-tion of''a'radioictive conversion of this into the destbed .compound;,by theörgahi sm" and isolation of t he 'compound." Proteins, c ompléx, öarbohydi ate s,complex lipids^ nucleic acids and antibiotics, are mostly prepared by.thismethod. Sometimes the plants are grown or kept for;sometime in a radioactivecompound (such as CO,,, ILO, sulphate, and phosphate) after which labelled'sugars e tc . are isolated from''the plantsi Animals 'are,, used; for similarpurpose, "especially when the tagging.element i s sulphur,."iodine, iron.arid ,carbon.' * , • - . . • ' ' . , • ' • . ' • " . . . ;'. ''.-"' '.'.•• - - • ' " ' • • :

3» Synthesis by nuclear . r eac t ion : '-''-•.- '-•„ •'.'•.

A normal compound can be theore t ica l ly converted into a rááioactiyeone by i r radia t ing i t with neutrons inra reac tor . ;

GV£:ico/i7/ix76

EC - 21 _ .; / ,.:- . i •-. •

However the energy released during the reaction is sufficient to break, thechemical bonds and hence the lable is haphazard as a result ofintra-radicalreactions; hence this method is of limited use. One exceptional success wasvitamin B12 which, when irradiated resulted in a product which had .80$ ofthe activity in the cobalt atom* The biological activity of the. sample wasretained. Similar efforts to produce cysteine labelled with S*5 railed.Only O.O75Ž of the s55 was in the cysteine molecule even after one month'sirradiation, \In this, method, processing-of the target'salt is necessaryto aemovs other radioactive impurities formed as ä result of(n, ~Y)t (n,p)reactions. : , ": -A f

PREPARATION OP RADIOCOTLOIDS

1. Radiogoldt

The metallic; gold,foil which has been irradiated, in a reactor is,.converted by aqaa.řegia to gold chloride and then dispersed into, colloidalform by reduction with ascorbic acid in the presence of gelatin,, The' goldis now present as a stable suspension1 of colloidal Articles.of size 3 to 7m LA.

2, Silver coated Rafliogólds

This is prepared,by adding a fraction of-a milli l itre of metallic goldcolloid to a solution containing 5Qjgrams,of silver; in the form.of the nitr-ate and which already contains an excess of ascorbic :acid. ;. This resulted Lnthe immediate;dispersal of some silver. Anadditional three drops ofi40?S HaOH .and 1 ml of 6$ geletin were added, followed by á solution of ciyatemic acid

3« Chromic phosphate: ' -' . , . :/ , , : ,;! • . ' , ' . . . ,':,'•.

This i s prepared by adding 2 Ť 1,0"4 molesi'of 0.1 'M chrjomic nitrateto 0.1 M phosphoric.acid pontaining 1.95X 10"4' M of radioactive phosphate.'The suspension which is. now coarse is dried by infra-red and iileft overnightat SOO i After i t has colled, -|"; steel,balls are .added, the!, bottle is .stoppered and the whole rotated for| several days. .The. improvised ball millproduces particles smaller than 1 i n a.day and after; 2*4 days less than,0.01 |>^ize making tne suspension stable. The activity, is separated fromthe free phosphate by dialysis. ' !- ' , ' "• :

4. Yttrium - 90 v

Radioactive yttrium chloride forms some, compounds with-peritoneal andal fluids (probably with proteins)..to form colloidal substances. I t s

in-vivo hehaviour is very similar to Au-" and Crp52 .> colloids. ••plearal fluids

GVR:lco/i7ix76

IX - 23

Isotope

Aluminium-26

Antiinony-122

Antimony-124

Antimony-125

Argon-37

Arsenic-76

Arsenic-77

Barium-131

Barium-153

Barium-140

Beryllium-7

Bismuth-210

Bromine-82

Cadmitun-109

•Cadmium-1i5m

Cadmitun-115

G"VE;1CO/17/ÍX76

A TABLE OF

Half l i f e

1O5 Yrs. •

2.8 d.

61.0 d

2.0 Yřs

55.0 d

26.4 tarsr

38.7 hrs.

11.5 d

9.5 Yrs.

12.8 d

55-5 d

35.9 hrs.

470.0 d

55.0 hrs.

45.0 d

APPEEDIX

TJSEMJL RADIOISOTOEES

Beta-ray energies.(Mev). '

1.94, 1.46

2.32, 1.60, O.97O.6t,O»24

0.616,0.444,0.2990.128

2.97,2.41,1.76

1.02, 0.48

Li , 0.58

1.16,0.7,0.3

Gamma-ray energies(lev)

0.68, O.56

1.692,. O.725,0.646, 0.605

O.64, 0.60,0.46,0.45, O.I75

X-rays

1%210,0.648,O.555

0.5,0.57,0.045and others. ,

0.557, 0.3,0.082O.O57

0.557, Q.050

0.478, X-rays

1.475,1.317,1.0440.828,0.777,0.6980.619,0.554

0.087, X-rays

0.55,0.5,0.56,0.34

1.5,0.93,0.49

IX - 24

Calciura-45

Garbon-14

Ceritun-139

Cerium-141

Cerlum-144

Praseodymium-144 '

Caesium-134

Caesiuin-137

Barium-137^

Chlorine-36

Ghromiuin-51

Cobalt-57

Cobalt-58

Cobait-60

Coppeř-64 •

Europium-152

Europium-154

G-allitun-72

I64.O d •

5568.O Yrs.

140.0 d

33.1 a

285.0 d

37.3 "m

2.07 Yrs.

26.6 Yrs.

3 X 105 Yrs.

.27.8 d

27O.O d

. 72.O d

5.24 Yrs.

12.8 hrs.

13.0 Yrs.

16.0 Y-s

14.3 hrs.

0.155-

o.*518,0.442

0.309,0.175

0.083,0.683:

1.17, 0.51

O.57 (/O.65 (J31

11.7,0.9

1.84, 0.83,0.25,0.12

3.17,2.53,10.96,0.6.4

,0.655

O.O.55

•51,

Gold-195 180.0 d

0.133,0,081,0.540.042,0,033

0.802^0.797,0.6060.570,0.565

O.325, X-rays;

0.511,0.133,0.119,O.OI4

1.332, 1.172

noneX-rays

.1.227,1.007,0.9980.875,0.725,0.123

2.203,1.859,1.595,1.050,0.894,0.834,0.630,0.601

G7E;1CO/17ÍX76

IX - 25

Goia-198

CrOlŮ-199

Hafnium-181

Hydrogen-3

Indium-114m

Indiura-114

Iodine-129

Iodine-130

Iodine-131

Iriöium-192

Irldivü-194

Iron-55

Iron-59

Krypton-85

Manganese-54

Mercury-197m

Mercury-197

Meroury-203

Mo oybäenum-9i«

Keoåymium-147

Rromethium-147

: 107Yra.

2.6 Yrs.

O.29O, O.97 .;

0.46,0.302,0.251

-.O.4O8 . -;

, 0.018

I.T. ., .{' .-

I.03, 0.61-

0.608,0.335

Ö.46, O.27

O.695, O.I5 c t .

O.OO54

1.18,0.41

0.8,0.6,0.4

0.412, 0.7, 0.1

0.208,0', 158,0.050

0.482,0.133,0.004

• : .. - ''

0.04 .

, 0.744,0.667,0.537O.42O

"0.637,0.364,0.284

0.613,0.605,0.588,0.468,0.317,0.309,O.296.

' 1.2,1.1,0.9,0.64,0.6,0.47^0.33,0.3-

. X-rays

1.289, 1.098

0.54 •

0 . 8 4 ' / -

O.28,O.-19,O.16,0J3

0.19, 0.08

0.850,0.780^0.745,0.140

0.5,0.4,0.3,0.09

IX -.26

Hickel-64

Niöbium-95

Osraiuia-191

Palladium-109

Phosphorus-321

Potaslum-42

Praseodymium

Prbmethium-147

Rhenium-186

Rubidium-86

Ruthenium-97

Ruthenium-103.

Řuthenium-106

Rhodiua-106

Samarium-153 .

Sc.anäium-46

Selenium-75

Silver-11Cm

Silver-111

85«0 Yrs

35.0 a

14,0 hrs.

13.6 hrs.

14.3 a

12.5 hrs.

19.2 hrs.

13.7 a

2.64 Trs.

18.7 d

1.00 Yr;

84.O d

I27.O d

253.O d

7.6 ď

2.0,3.6

2.2,0.6

1.072, 0.954

1.78, 0.71

0.7, 0.22

• 3.53,5.1,2.44 •

•6.80,0.69,0.26

0.530,0.087

110, 0.8, O.7

1.045,

O.,83,C

0.14,O.O7

1.504,0.884,0.705:0.446

O.7Š5

0.624,0.

). 72,0.65

0.10,0.08,

,1.384,0.,0.817,0.,0.677,0.

.764,• 657,

GVEMco/17ix76

Sodium-22

Sodium-24

Strontium-85

Strontium-89

Strontium-90

Yttroim-90

Sulphur-35

Tantalum-182

Technitium-99

Thallium-204

Tin-113

Tungsten-185

TPungsten-187

Vanadium-49

Xenon-133

Yttrium-88

Yttrium-90

Yttrium-91

Zirib-65

Zirconium-95

3X-'-, 27

2,6 Yrs. 0,54 ( ß .-)

15.0 hrs.

65.O d

5O.5 d

27.7 Yrs.

64.2 hrs.

84.O d

115.0 d

0.514,0.44,0.36

2.1 x 1O3 Yrs. 0.29

3.56 Yrs. O.764

78.5 a

16.0 d

330.0 d

IO5.O d

57.5 d

245.O d

65,0 å

1.3,0.63

0.33 ( B ),0.33

0.40, O.36

2.75, 1 - 37

1.122,0.264,0.229,0.222,0.179,0.156,0.100,0.068

0.395,0.260

0.8,0.7,0.6,0.5,0.130.07.

1.314,0.986, X-rays

0.119,0.081

1.83, 0.91

0.75,0.72

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