KCN

AE-127

A Gas Target with a Tritium Gas Handling

System

B. Holmqvist and T. Wiedling

AKTIEBOLAGET ATOMENERGI

STOCKHOLM, SWEDEN 1963

AE-127

A GAS TARGET WITH A TRITIUM GAS HANDLING SYSTEM

B. Holmqvist and T. Wiedling

Summary:

A detailed description is given of a simple tritium gas target

and its tritium gas filling system, and how to put it into operation.

By using the T(p,n)He reaction the gas target has been employed

for production of monoenergetic fast neutrons of well defined energy

and high intensity. The target has been operated successfully

for a long time.

Printed and distributed in December 1963.

LIST OF CONTENTS

Page

1. Introduction 3

2. Description of gas cell and filling system 3

References 9

Figures 11

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1. Introduction

A large number of methods for preparing absorbed tritium

targets may be found in the literature . But there seem to be

few descriptions of tritium gas targets, including the technique(2)

of handling the gas oxitside the target cell. Nobles has given

a short description of the Los Alamos high current target.'' Kond-(3)

rashev et al, have described a target used in connection with(4)

a cyclotron. Schwarz ' has recently described in some detail a

new gas target and Coan has surveyed problems related to

gas targets.

We shall present a complete description of our tritium gas

target and itd gas handling system, as well as how to handle the(4)

entire apparatus which is a modification of Schwarz gas

target.

2, Description of gas cell and filling system

Apart from the high cost of tritium, there is no reason to make

the tritium gas filling system extremely small since it can quite

easily be rendered completely gastight. It is much more important

to have a limited gas volume just outside the target cell and accord-

ingly to reduce as far as possible the amount of gas which is let

into the drift tube and vacuum system of the accelerator if the tar-

get window foil becomes punctured. In our target system the total

volume is about 15 cm and the volume containing tritium during

an experiment is about 7 cm' . This last volume can be made even

smaller.

Fig. 1 a.nd 2. show the target assembly and its parts:

A_ gas target cell

B_ manometer measuring the gas pressure *'

C target valve

D_ Vacuum gauge tube with metal shield

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E vacuum pumping valve v

_F_ flange of the vacuum pump

G filling valve

H crusher for tritium gas glabs bulbs

I_ uranium oven valve

J uranium oven

K cooling flanges

_L_ steel projectile

M baseplate

N glass wooJ

The uranium oven J is made of stainless steel. All parts are

connected by copper tubes which are silver-brazed to the different

components,

Fig, 3 shows a detailed drawing of the tritium gas target cell

and its parts:

ja. target cell of 0. Z mm brass

b gold 0. 07 mm thick

c front of target cell of 0. 1 mm gold~ _4 (Q)

_d window of nickel 10 inches thick v ;

e inner 0-ring o.f Viton

i_ outer 0-ring of Viton

_g insulator

h collimator of tantalum

i_ part of the drift tube

j_ tritium gas input tube

The tritium gas cell has been made with a minimum of

scattering material. The entrance hole in the target cell is 6 mm

in diameter. To avoid disturbing reactions resulting from ion bom-

bardment of brass, a tantalum collimator h. was inserted in front

of the entrance hole and the target cylinder was lined with a gold

foil. One of the technical problems was to fit the nickel window

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(5)vacuum-tight to the target eel] v . Many authors (i. e. reference 4)

prefer to soft solder the nickel window in order to get good conduc-

tion. But this can readily lead to contamination of solder of the foil.

With two 0-rings _e and f_ for sealing, there are no problems at

all in mounting the nickel window. A nickel window was cut out

with a diameter a little larger than the outer diameter of the inner

0-ring j£. Before mounting the nickel window it was carefully

cleaned in acetone. The inner 0-ring seals off the gas cell from

the target tube, and the outer 0~ring seals off the ambient air from

the accelerator vacuum. The arrangement has to be carefully

tested with a helium leak detector.

The shape and size of the beam spot can be checked on a

viewer placed 22 cm in front of the nickel window of the ceJl. In

order to keep the current density low on the nickel window, the

beam spot has been maintained as large as possible without loss

of current to the collimator h.

A nickel window can withstand several hundreds of pressure

changes from 1 kp/cm to vacuum. The same foil can be used for

several hundred hours at a tritium gas pressure of about 1 kp/cm ,

a mean pulsed proton current of about 1 jxA, and in the proton

energy region of 1-5 MeV, To be able to work with much higher

beam currents ^ ' it is necessary to cool the nickel window. Many

authors (see i. e. references 2, and 4) use two nickel windows and

circulate helium gas between the windows. Another way to cool the

window is to circulate the tritium gas with a small pump. Introduc-

tion of a pump does not need to increase the volume of the system

by more than a few cubic centimeters. There is no large difference

between the two methods of cooling since the helium gas will very

soon be contaminated by tritium b<

nickel window next to the gas cell.

(5)soon be contaminated by tritium because of diffusion v ' throw the

The gas handling system and the gas ceil are insulated from

ground with plexi-glass insulators inserted between the baseplate M

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and ground and between the gas cell <x and ground. The screws

connecting the gas cell and the target tube are insulated from the

gas cell by tubular insulators made of Teflon. Accordingly the

ion current can easily be measured.

After careful cleaning in alcohol, acetone, and ether the

whole system was tested for vacuum-tightness with a helium

leak detector.

The uranium oven was filled with 8 grams of small flakes of

uranium metal which had been washed in dilute nitric acid and

acetone. Before filling the oven with tritium gas, the uranium

metal was activated with hydrogen gas in the following way.

First it was heated to about 600 C under continuous pumping in

order to pump off gas impurities. After that the oven was allowed

to cool to room temperature and hydrogen gas was let in. In the

first absorption of hydrogen it was only possible to absorb about

50 cm at a pressure of 1 kp/cm . It was also noticed that the

absorption proceeded very slowly. The oven was again heated to

600 C and the hydrogen was pumped off. New hydrogen was let

in after cooling and so on. When the activation process had been

repeated some 25 times, it was possible to let in a volume of3 2

about 1000 cm of hydrogen at a pressure of 1 kp/cm . During

absorption it was found, by closing the valve _E_, that the ura-

nium could absorb in about two seconds 10 cm hydrogen at

1 kp/cm , contained in the gas handling system. On measure-

ment of the final pressure after absorption the vacuum in the

system was 2 microns, which, because of the getter action of

the uranium, was a factor of ten lower than was possible to achieve

with the standard fore vacuum pump.

After the activation of the uranium metal in the oven, all hydro-

gen was pumped off by heating to 600 C for several hours. When

the uranium gave off no more hydrogen, it was ready for absorp-

tion of tritium gas. This procedure was performed in a fuming

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hood to avoid health hazards. The tritium gas ' was contstined

in small glass vessels, containing 10 cm at NTP corresponding

to 20 Curies. The tritium gas absorption was accomplished in the

following manner. First the valve I and C were closed to prevent

air entering into contact with the uranium metal, because it has

been found that air diminishes the capacity for fast hydrogen absorp-

tion. The gas vessel has a tube of the same diameter as the crusher,

and a vacuum-tight connection between the two tubes can be effected

with a polyethylene tube. The small amount of air is then pumped off after

opening of the valve G_. When the vacuum is good, valve I_ is opened

and valve jE_ closed and, with the help of the small steel projectile

K , the thin output tube in the vessel can be crushed. The tritium

gas absorption was controlled with the vacuum gauge and a final

pressure of about 5 mm Hg was reached. The residual pressure is

probably caused by impurities in the tritium gas. The impurities

were pumped off and the process was repeated until 120 Curies

were absorbed in the uranium.

Filling of the target cell is done as follows (Fig. 1 and 2),

The valves C_, _E_, and I_ are opened and valve G_ closed. By

closing valve E it can be checked that no leaks exist. E being

closed the uranium oven is heated and the gas pressure is read

with the vacuum gauge and the manometer. If the pressure rises

immediately after heating is started, the oven should be cooled

again because it has been found that impurities absorbed in the

uranium are given off before the tritium gas; and knowing that

tritium gas is absorbed very quickly, it is possible to decide from

the absorption whether tha gas causing the pressure is an impurity

or not. If it is decided that the first pressure rise is caused by

impurities, valve E_ is opened and the gas is pumped off. (Im-

purities are given off by the uranium below about 200 C. ) The

oven is heated again and, when the temperature has reached about

500 C, the tritium gas starts filling the system. When the mano-

meter shows the desired pressure, valve C_ is closed and the

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heating is stopped. The gas in the handling system is quickly

absorbed in the uranium when the oven is cooled down, and after

that valve _E_ is opened to the vacuum pump.

During all experiments the amount of tritium gas in ambient

air was checked with tritium gas monitors. It has been found that,

when the oven is hot, small amounts of tritium gas diffus\e through

the walls of the oven. Measurements of the tritium content in the

mercury of the high vacuum pumps of the target tube show a conta-

mination of tritium because; nickel becomes increasingly trans-

parent to hydrogen with the increase in temperature caused by

proton bombardment. Therefore all the outputs of the vacuum

pumps connected to the tritium gas system and the target tube are

connected to a ventilation system.

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References

1. EVANS CPreparation of thick zirconium-tritium and zirconium-deuterium targets.1955. AERE-I/M-38.

MASSEY B JPreparation of thin tritium-zirconium targets.1957. ORNL-2237.

WILSON E JDeuterium and tritium targets for neutron sources.Atomics and Nuclear Energy 9 (1958) p. 238.

SCOTT V D and OWEN L WDeposition by thermal evaporation of thin films of titaniumand zirconium for tritium targets.Brit. J. Appl. Phys. 10 (1959) p. 91.

MASSEY B J5th National Symposium on Vacuum Technology 1958.Transactions, London 1959, p. 72.

McCORMICK R D and McCORMACK J DHydrogen and carbon target preparation for a positive ionaccelerator.I960. HW-67797.

PETROV V ICirkonievye mixeni na podloschach tz medi i serebra.Pribore i Tekh. Ekspt, 6:2 (1961) p. 174.

McCORMICK R D and McCORMACK J DHydrogen and carbon target preparation for a positive ionaccelerator.Nuclear Instr. and Methods 13 (1961) p. 147.

2. NOBLES RHigh-current gas target.Rev. Sci. Inst. 28 (1957) p. 962.

3. KONDRASHEV L F, RYBIN S N, SOKOLOV N Iand KHALDIN N NThin vacuum-dense walls.Instr. and Exp. Techn. 4 (i960) p. 625.

4. SCH WAR Z SA versatile gas-target for neutron-producing reactions.1963. FOA 4 Report A 4291-4262.

10 -

5. COAN J MChapter IV D of Fast Neutron Physics, Vol. I, ed. by Marionand Fowler.New York, Interscience I960.

6. Manometer type 41M -1+1 from Ing. firma Stig Wahlström,Stockholm, Farsta, Sweden.

7. Vacuum valves, sealless type Sylphon No. 96415 from Robert-shaw-Fulton, Controls Company, International Division,1701 Byrd Avenue, Richmond 26, Virginia, USA.

8. Autovac Gauge Tube, No. 3591, from LKB-Produkter AB,Stockholm 12, Sweden.

9. Nickel foils from Chromium Corporation of America,Waterbury, Connecticut, USA.

10. Nuclear Data Tables, Part 3.Wash. D. C. I960 p, 125.

11. Tritium, gas of 98 % purity from The Radiochemical Centre,Amersham, Bucks, England.

5 cmi i t i i t i

FIG.3

LIST OF PUBLISHED AE-REPORTS

1—50. (See the back cover earlier reports.)

51. Aclivation analysis of tiluminium. By D. Brune. 1961. 8 p. Sw. cr. 6:—.

52. Thermo-technical data for D2O. By E. Axblom. 1961. 14 p. Sw. cr. 6:—.

53. Neutron damage in steels containing small amounts of boron. By H. P.Myers. 1961. 23 p. Sw. cr. 6:—.

54. A chemical eight group separation method for routine use in gammaspectrometric analysis. I. Ion exchange experiments. By K. Samsahl.1961. 13 p. Sw. cr. 6 r - .

55. The Swedish zero power reactor R0. By Olof Landergård, Kaj Cavallinond Georg Jonsson. 1961. 31 p. Sw. cr. 6:—.

56. A chemical eight group separation method for routine use in gammaspectrometric analysis. I I . Detailed analytical schema. By K. Samsahl.18 p. 1961. Sw. cr. 6:—.

57. Heterogeneous two-group diffusion theory for a finite cylindrical reactor.By Alf Jonsson and Göran Näslund. 1961. 20 p. Sw. cr. 6:—.

58. Q-values for (n, p) and (n, a) reactions. By J. Konijn. 1961. 29 p. Sw. cr.

59. Studies of the effective total and resonance absorption cross section forzircaloy 2 and zirconium. By E. Hellstrand, G. Lindahl and G. Lundgren.1961. 26 p. Sw. cr. 6:—.

60. Determination of elements in normal and leukemic human whole bloodby neutron activation analysis. By D. Brune, B. Frykberg, K. Samsahl andP. O. Wester. 1961. 16 p. Sw. cr. 6.—.

61. Comparative and absolute measurements of 11 inorganic constituents of38 human tooth samples with gamma-ray spectrometry. By K. Samsahland R. Söremark. 19 p. 1961. Sw. cr. 6:—.

62. A Monte Carlo sampling technique for multi-phonon processes. By ThureHögberg. 10 p. 1961. Sw. cr. 6:—.

63. Numerical integration of the transport equation for infinite homogeneousmedia. By Rune Håkansson. 1962. 15 p. Sw. cr. 6:—.

64. Modified Sucksmith balances for ferromagnetic and paramagnetic mea-surements. By N. Lundquist and H. P. Myers. 1962. 9 p. Sw. cr. 6;—.

65. Irradiation effects in strain aged pressure vessel steel. By M. Grounesand H. P. Myers. 1962. 8 p. Sw. cr. 6:—.

66. Critical and exponential experiments on 19-rod clusters (R3-fuel) in heavywater. By R. Persson, C-E. Wikdahl and Z. Zadwörski. 1962. 34 p. Sw. cr.6;~~.

67. On the calibration and accuracy of the Guinier camera for the deter-mination of interplanar spacings. By M. Möller. 1962. 21 p. Sw. cr. 6:—.

68. Quantitative determination of pole figures with a texture goniometer bythe reflection method. By M. Möller. 1962. 16 p. Sw. cr. 6:—.

69. An experimental study of pressure gradients for flow of boiling water ina vertical round duct. Part I. By K. M. Becker, G. Hernborg and M.Bode. 1962. 46 p. Sw. cr. 6:—.

70. An experimental study of pressure gradients for flow of boiling water ina vertical round duct. Part I I . By K. M. Becker, G. Hernborg and M.Bode. 1962. 32 p. Sw. cr. 6:—.

71. The space-, time- and energy-distribution of neutrons from a pulsedplane source. By A. Claesson. 1962. 16 p. Sw. cr. 6:—.

72. One-group perturbation theory applied to substitution measurementswith void. By R. Persson. 1962. 21 p. Sw. cr. 6:—.

73. Conversion factors. By A. Amberntson and S-E. Larsson. 1962. 15 p. Sw.cr. 10:—.

74. Burnout conditions for flow of boiling water in vertical rod clusters.By Kurt M. Becker. 1962. 44 p. Sw. cr. 6:—.

75. Two-group current-equivalent parameters for control rod cells. Autocodeprogramme CRCC. By O. Norinder and K. Nyman. 1962. 18 p. Sw. cr.

76. On the electronic structure of MnB. By N. Lundquist. 1962. 16 p. Sw. cr.6:~~*.

77. The resonance absorption of uranium metal and oxide. By E. Hellstrandand G. Landgren. 1962. 17 p. Sw. cr. 6:—.

78. Half-life measurements of «He, « N , «O , »F, »A I , "Sem and "°Ag. By J.Konijn and S. Malmskog. 1962. 34 p. Sw. cr. 6:—.

79. Progress report for period ending December 1961. Department for Reac-tor Physics. 1962. 53 p. Sw. cr 6:—.

80. Investigation of the 800 keV peak in the gamma spectrum of SwedishLaplanders. By I. O. Andersson, I. Nilsson and K. Eckerstig. 1962. 8 p.Sw. cr. 6,:—.

81. The resonance integral of niobium. By E. Hellstrand and G. Lundgren.1962. 14 p. Sw. cr. 6:—.

82. Some chemical group separations of radioactive trace elements. By K.Samsahl. 1962. 18 p. Sw. cr. 6:—.

83. Void measurement by the (y, n) reactions. By S. Z. Rouhani. 1962. 17 p.Sw. cr. 6,:—. '

84. Investigation of the pulse height distribution of boron trifluoride pro-portional counters. By I. O. Andersson and S. Malmskog. 1962. 16 p.Sw. cr. 6,:—.

85. An experimental study of pressure gradients for flow of boiling waterin vertical round ducts. (Part 3). By K. M. Becker, G. Hernborg and M.Bode. 1962. 29 p. Sw. cr. 6:—.

86. An experimental study of pressure gradients for flow of boiling waterin vertical round ducts. (Part 4). By K. M. Becker, G. Hernborg and M.Bode. 1962. 19 p. Sw. cr 6:—.

87. Measurements of burnout conditions for flow of boiling water in verticalround ducts. By K. M. Becker. 1962. 38 p. Sw. cr. 6:—.

88. Cross sections for neutron inelastic scattering and (n, 2n) processes. ByM. Leimdörfer, E. Bock and L. Arkeryd. 1962. 225 p. Sw. cr. 10:—.

J59. On the solution of the neutron transport equation. By S. Depken. 1962.43 p. Sw. cr. 6:—.

90. Swedish studies on irradiation effects in structural materials. By M.Grounes and H. P. Myers. 1962. 11 p. Sw. cr. 6:—.

91. The energy variation of the sensitivity of a polyethylene moderated BFjproportional counter. By R. Fräki, M. Leimdörfer and S. Malmskog. 1962.12. Sw. cr. 6:—.

92. The backscattering of gamma radiation from plane concrete walls. ByM. Leimdörfer. 1962. 20 p. Sw. cr. 6:—.

93. The backscattering of gamma radiation from spherical concrete walls.By M. Leimdörfer. 1962. 16 p. Sw. cr. 6:—.

94. Multiple scattering of gamma radiation in a spherical concrete wallroom. By m. Leimdörfer. 1962. 18 p. Sw. cr. 6:—.

95. The paramagnetism of Mn dissolved in n and fi brasses. By H. P. Myersand R. Westin. 1962. 13 p. Sw. cr. 6:—. H

96. Isomorphic substitutions of calcium by strontium in calcium hydroxy-apatite. By H. Christensen. 1962. 9 p. Sw. cr. 6:—.

97. A fast time-to-pulse height converter. By O. Aspelund. 1962. 21 p. Sw. cr.6:—.

98. Neutron streaming in D2O pipes. By J. Braun and K. Randen. 196241 p. Sw. cr. 6:—.

99. The effective resonance integral of thorium oxide rods. By J. Weitman.1962. 41 p. Sw. cr. 6:—.

100. Measurements of burnout conditions for flow of boiling water in verticalannuli. By K. M. Becker and G. Hernborg. 1962. 41 p. Sw. cr. 6:—.

101. Solid angle computations for a circular radiator and a circular detector.By J. Konijn and B. Tollander. 1963. 6 p. Sw. cr. 8:—.

102. A selective neutron detector in the keV region utilizing the »F(n, y)«Freaction. By J. Konijn. 1963. 21 p. Sw. cr. 8:—.

103. Anion-exchange studies of radioactive trace elements in sulphuric acidsolutions. By K. Samsahl. 1963. 12 p. Sw. cr. 8:—.

104. Problems in pressure vessel design and manufacture. By O. Hellströmand R. Nilson. 1963. 44 p. Sw. cr. 8 : - .

105. Flame photometric determination of lithium contents down to 10-3 ppmin water samples. By G. Jönsson. 1963. 9 p. Sw. cr. 8:—.

106. Measurements of void fractions for flow of boiling heavy water in avertical round duct. By S. Z. Rouhani and K. M. Becker. 1963. 2nd rev.ed. 32 p. Sw. cr. 8:—.

107. Measurements of convective heat transfer from a horizontal cylinderrotating in a pool of water. K. M. Becker. 1963. 20 p. Sw. cr. 8:—.

108. Two-group analysis of xenon stability in slab geometry by modal expan-sion. O. Norinder. 1963. 50 p. Sw. cr. 8:—.

109. The properties of CaSOiMn thermoluminescence dosimeters. B. Bjärn-gard. 1963. 27 p. Sw. cr. 8:—.

110. Semianalytical and seminumerical calculations of optimum materialdistributions. By C. I. G. Andersson. 1963. 26 p. Sw. er. 8:—.

111. The paramagnetism of small amounts of Mn dissolved in Cu-AI andCu-Ge alloys. By H. P. Myers and R. Westin. 1963. 7 p. Sw. cr. 8:—.

112. Determination of the absolute disintegration rate of Cs137-sources by thetracer method. S. Hellström and D. Brune. 1963. 17 p. Sw. cr. 8:—.

113. An analysis of burnout conditions for flow of boiling water in verticalround ducts. By K. M. Becker and P. Persson. 1963. 28 p. Sw. cr 8:—.

114. Measurements of burnout conditions for flow of boiling water in verticalround ducts (Part 2). By K. M. Becker, et al. 1963. 29 p. Sw. cr. 8:—.

115. Cross section measurements of the ^Nifn, p)5!Co and 2'Si(n, a)MMg reac-tions in the energy range 2.2 to 3.8 MeV. By J. Konijn and A. Lauber1963. 30 p. Sw. cr. 8:—.

116. Calculations of total and differential solid angles for a proton recoilsolid state detector. By J. Konijn, A. Lauber and B. Tollander. 1963. 31 p.Sw. cr. 8:—.

117. Neutron cross sections for aluminium. By L. Forsberg. 1963. 32 p.Sw. cr. 8:—.

118. Measurements of small exposures of gamma radiation with CaSO^Mnradiothermoluminescence. By B. Bjärngard. 1963. 18 p. Sw. cr. 8:—.

119. Measurement of gamma radioactivity in a group of control subjects fromthe Stockholm area during 1959—1963. By 1. O. Andersson, I. Nilssonand Eckerstig. 1963. 19 p. Sw. cr. 8:—.

120. The thermox process. By O. Tjälldin. 1963. 38 p. Sw. cr. 8:—.

121. The transistor as low level switch. By A. Lydén. 1963. 47 p. Sw. cr. 8:—.

122. The planning of a small pilot plant for development work on aqueousreprocessing of nuclear fuels. By T. U. Sjöborg, E. Haeffner and Hult-gren. 1963. 20 p. Sw. cr. 8:—.

123. The neutron spectrum in a uranium tube. By E. Johansson, E. Jonsson,M. Lindberg and J. Mednis. 1963. 36 p. Sw. cr. 8:—.

124. Simultaneous determination of 30 trace elements in cancerous and non-cancerous human tissue samples with gamma-ray spectrometry. K. Sam-sahl, D. Brune and P. O. Wester. 1963. 23 p. Sw. cr. 8:—.

125. Measurement of the slowing-down and thermalization time of neutronsin water. By E. Möller and N. G. Sjöstrand. 1963. 42 p. Sw. cr. 8:—.

126. Report on the personnel dosimetry at AB Atomenergi during 1962. ByK-A. Edvardsson and S. Hagsgård. 1963.

127. A gas target with a tritium gas handling system. By B. Holmqvist andT. Wiedling. 1963.

Förteckning över publicerade AES-rapporter

1. Analys medelst gamma-spektrometri. Av D. Brune. 1961. 10 s. Kr 6:—.2. Bestrålningsförändringar och neutronatmosfär i reaktortrycktankar —

några synpunkter. Av M. Grounes. 1962. 33 s. Kr 6:—.3. Studium av sträckgränsen i mjukt stål. G. Ostberg, R. Attermo. 1963. 17 s.

Kr 6:—.4. Teknisk upphandling inom reaktorområdet. Erik Jonson. 1963.64 s. Kr. 8:—.

Additional copies available at the library of AB Atomenergi, Studsvik, Nykö-ping, Sweden. Transport microcards of the reports are obtainable through,the International Documentation Center, Tumba, Sweden.

EOS-lryckerierna, Stockholm 1963