Design, testing and optimization of a neutron radiography system based on a Deuterium–Deuterium...

Design, testing and optimization of a neutron radiography systembased on a Deuterium–Deuterium (D–D) neutron generator

K. Bergaoui • N. Reguigui • C. K. Gary •

J. T. Cremer • J. H. Vainionpaa • M. A. Piestrup

Received: 6 March 2013 / Published online: 15 September 2013

� Akademiai Kiado, Budapest, Hungary 2013

Abstract Simulations show that significant improvement

in imaging performance can be achieved through colli-

mator design for thermal and fast neutron radiography with

a laboratory neutron generator. The radiography facility

used in the measurements and simulations employs a fully

high-voltage-shielded, axial D–D neutron generator with a

radio frequency driven ion source. The maximum yield of

such generators is about 1010 fast neutrons per seconds

(E = 2.45 MeV). Both fast and thermal neutron images

were acquired with the generator and a Charge Coupled

Devices camera. To shorten the imaging time and decrease

the noise from gamma radiation, various collimator designs

were proposed and simulated using Monte Carlo N-Particle

Transport Code (MCNPX 2.7.0). Design considerations

included the choice of material, thickness, position and

aperture for the collimator. The simulation results and

optimal configurations are presented.

Keywords Thermal neutron radiography � Fast

neutron radiography � D–D Neutron generator �Monte Carlo simulation (MCNPX) � Collimator �CCD camera

Introduction

Neutron radiography (NR) is an important tool in non-

destructive examination, which has been adopted in

industrial, medical, metallurgical, nuclear and explosive

inspections [1]. From the 1990s to the present day, neutron

radiography imaging systems and the methods used to

analyse the images have continued to advance [2]. It offers

some very explicit advantages over c-ray (or X-ray)

imaging.

Neutron cross-sections, being almost independent of the

atomic number (Z) of the material, result in neutron

imaging being capable of discerning materials of similar Z

and/or low Z materials even when they are present inside

high Z surroundings. Also, hydrogen, which is a very

important element in determining the properties of mate-

rials, can be imaged even if present in minute quantities

due to its significant neutron scattering and absorption

cross sections. Neutrons also offer the advantage of being

able to differentiate between isotopes of an element. Fur-

thermore, radioactive materials which cannot be imaged

using photons due to fogging of the detector can be imaged

with neutrons using the transfer technique [3].

The neutron radiography facility discussed consists of

three major components: a neutron source, neutron colli-

mator and image processing system (Fig. 1). The neutron

collimator is a critical component in neutron radiography

because it affects directly the characteristics of the neutron

beam and the quality of the radiographic image [4, 5].

Thermal and fast neutron images were acquired using a D–D

neutron generator and image intensified Charge Coupled

Devices (CCD) camera focused on a neutron sensitive

scintillator. While these images demonstrate the ability of

laboratory based neutron radiography, they could benefit

from decreased imaging time and reduced background. The

K. Bergaoui (&) � N. Reguigui

Unite de Recherche ‘‘Maıtrise et Developpement des Techniques

Nucleaires a Caractere Pacifique’’, National Center of Nuclear

Sciences and Technologies, Technopole Sidi Thabet, BP 72,

2020 Tunis, Tunisia

e-mail: [email protected];

[email protected]

C. K. Gary � J. T. Cremer � J. H. Vainionpaa � M. A. Piestrup

Adelphi Technology Inc., 2003 East Bayshore Road, Redwood

City, CA 94063, USA

123

J Radioanal Nucl Chem (2014) 299:41–51

DOI 10.1007/s10967-013-2729-y

neutron flux, spatial collimation and neutron to gamma

ration (neutron/gamma) can be improved through collima-

tion. A range of collimator designs were considered and

modelled using Monte Carlo code Version MCNP 2.7.0 [6].

Materials and methods

Neutron generator D–D

The deuterium–deuterium 2.5 MeV neutron generator

developed by Adelphi Technology Inc. [7], uses a deuteron

beam produced with radio frequency (RF) plasma and

acceleration voltage in the range from 100 to 140 keV

(Fig. 2). The deuterium ion beam was directed at the tita-

nium-covered cathode, which adsorbs deuterons and works

as a deuterium target [8]. The neutron source operates in

continuous mode, producing up to 1010 neutrons per sec-

ond, though an intensity of 109 n/s was used in the mea-

surements presented. Due to the physics of D–D reaction,

the generated neutrons have a well-defined energy maxi-

mum close to 2.5 MeV, slightly dependent on the emission

angle. The energy and this anisotropy were included in the

MCNP simulations for the moderator design. The effective

fast neutron source size is 2–3 cm [9].

The CCD detector

A camera box allows the Stanford Photonics CCD camera

and its electronics to be placed outside the direct neutron

beam exposure. A scintillator is mounted on the inner

surface of the 3 mm wall of the box. A mirror reflects light

from the scintillator out of the neutron/gamma path to a

5 cm diameter lens with f-stop equal to 1.0. The lens

focuses the light onto the dual microchannel plate (MCP).

The dual MCP light amplifier and a coupled CCD chip are

thermoelectrically cooled to -20 �C. A tapered fiber optic

directs the amplified light to the CCD sensor. The dual

MCP amplifier produces high photon gains up to 106 at a

very low dark count levels of 1 or 2 electron counts per

frame at 15 frames per second. In our experiments the dual

MCP amplifier was set to an overall photon amplification

gain of 5 9 105. The Stanford Photonics CCD camera uses

a Sony XX285 scientific grade image sensor, which has a

full frame pixel count of 1,380 by 1,024 K, where the

pixels are 6.47 microns square. The 1.6–1 reducing fiber

optic taper creates an effective square pixel with 10.35-lm

sides at the input image plane. The dual MCP image

intensifier has a 50 line-pairs/mm resolution, which cor-

responds to the effective pixel size. An image is created by

summing multiple frames. The short 15-s frame times

reduce the dark count accumulation to 1 or 2 dark counts

per frame, and the data acquisition software further reduces

Fig. 1 The principle of a

neutron radiographic facility (D:

diameter of the aperture next the

neutron generator and D0:

diameter of the aperture next to

the image plane)

Fig. 2 The D–D-110 neutron generator

42 J Radioanal Nucl Chem (2014) 299:41–51

123

noise by filtering out cosmic ray noise and spot noise from

each of the incoming frames.

The radiography system

The design of the collimator will directly affect funda-

mental properties of the resulting neutron beam. The design

choices that are made must recognize the relationship

between all of the various components and features. The

key issues in the design of any facility for neutron imaging

include the neutron flux and L/D ratio [10].

Collimator parameters

The parameters most important to the quality of the image

data are the ratio of the collimator length to diameter of the

aperture (Collimation Ratio (L/D)) [11], Beam Divergence

[11], Gamma content [12] and the thermal neutron content

(TNC) [10].

Collimator design

Geometric Shape of the Collimator: The divergent beam

collimator is commonly used after the conclusion of Barton

in 1967 that divergent beam collimators produce highest

resolution [13]. Among them the most commonly used

physical form is a truncated cone or pyramid [11]. In this

study, we used a divergent beam collimator.

Materials of the Walls and their lining: The most

important item of each collimator is its lining. Unlike

charged particles, neutrons cannot be focused [11]. Hence

the neutron beam must be collimated by suitable lining in

the collimator. To prevent stray neutrons from reaching the

radiographed object and to reduce the scattering of neu-

trons within the collimator, the lining must be made with

neutron absorbing material. Some materials suitable for

this purpose are: boron, cadmium, dysprosium, europium,

gadolinium and indium [11]. The effectiveness of these

materials varies with the neutron energy spectrum. The use

of boron is recommended because it gets less activated,

which facilitates maintenance of the collimator [11].

Generally boron in the form of Boral (B4C) is used in the

collimator [13]. Borated Polyethylene (PE-B) (2.5 cm) and

Lead (1 cm) are chosen as our collimator wall material.

Gamma and Neutron Filters: To filter out the gamma

rays from the beam, Lead (Pb) and Bismuth (Bi) filters are

used [11]. Neutron filters are also required to filter out the

fast neutrons from the beam. Single crystal sapphire

(Al2O3), silicon, quartz and Bismuth act as fast neutron

filters [14, 15]. Sapphire (Al2O3) is an effective fast-

neutron filter because its transmission for neutrons of

wavelengths less than 0.04-nm (500 MeV) is less than 3 %

for a filter thickness of 100-mm [14]. For gamma filter we

used Lead for its effectiveness in attenuating the gamma

and its durability. Bismuth may be used as the gamma

filter; it is usually more expensive than Lead.

Experimental neutron radiography configuration

In this experimental step, a D–D neutron generator was

used to illuminate a set of objects, and a scintillator cou-

pled to a CCD camera was used to record thermal and fast

neutron images. The generator was housed in a polyeth-

ylene block 61 cm high and 61 cm deep. A 15-cm 9 10-

cm square opening extended from the wall of the generator

to the edge of the polyethylene block with a length of

20 cm. This opening served as the collimation for the

experiment.

The set of objects that were imaged is shown in Fig. 3.

The objects were chosen to provide varying contrast for

fast and thermal neutrons as well as gammas and X-rays. A

4-step lead phantom was used to provide contrast for

X-rays and gammas. Polyethylene blocks (2.5 and 1.3 cm

thick) provide contrast for fast and thermal neutrons.

Beryllium, in the form of a biconcave lens, has a cross

section that is relatively larger for fast neutrons. Electrical

tape, due to the presence of hydrogen as well as higher Z

materials has good contrast for both thermal neutrons and

gammas. The smaller 6.25 and 12.5-mm steps of the lead

were eclipsed the bottom half of roll of black electrical tape

The 2.5 cm and 5 cm thick portion of the 4-step lead

phantom covers a 1.25 cm thick polyethylene plate. On top

of the lead phantom and eclipsing the 1.25 cm thick

polyethylene is a 2.5 cm thickness of the 4-step silicon

stacked-chip phantom. Silicon has a low cross section for

all the radiation measured, but is significantly more sen-

sitive to photons than neutrons. This variety of materials,

and the use of know thicknesses provides qualitative

information similar to that from more expensive calibrated

beam purity and sensitivity indicators.

In the fast neutron radiography we placed the object at a

distance of 1.52 meter from the D–D generator. A 4-cm

thick BC-408 plastic scintillator was placed immediately

behind the objects to convert the fast neutron signal to

visible light imaged by the CCD camera. For the thermal

neutron radiography we placed 2.5 cm of polyethylene

before the object to moderate the fast neutrons and the

10 cm 9 10 cm by 5 mm thick plastic scintillator on the

inner wall of the camera box was replaced by a

10 cm 9 10 cm by 100 micron thick gadolinium-based,

thermal neutron phosphor, Gd2O2S:Tb, which produced

light upon thermal neutron capture by the gadolinium.

J Radioanal Nucl Chem (2014) 299:41–51 43

123

Simulation model

Thermal neutron radiography

Simulations of the thermal neutron radiography facility

were implemented in four stages: In the first stage (1), we

tested the best position of the divergent collimator (the

length of the collimator L = 50 cm, diameter of the

aperture D = 1 cm and the aperture next to the image

plane D0 = 12 cm), from the neutron generator with a

variable thickness of polyethylene, between the neutron

generator and the aperture of the collimator (Fig. 4).

In the second stage (2), different configurations were

considered to obtain the maximum thermal neutron flux

(fth) at the image plane (Fig. 5), the first configuration was

composed of a divergent collimator (L = 50 cm,

D = 1 cm and D0 = 24 cm) and walls made of 2.5-cm

deep (PE-B) covered by 1 cm of lead. The walls started

15 cm from the neutron generator. The second configura-

tion was similar as in the first with walls starting 40.35 cm

from the neutron generator. The third configuration was

composed of a divergent collimator (L = 50 cm,

D = 1 cm and D0 = 12 cm), 2 cm of Polyethylene

between the aperture of collimator and the neutron gener-

ator and the walls made of (PE-B) with depth 2.5 cm

covered by 1 cm of Lead. The fourth configuration inclu-

ded two collimators. The first was a conic collimator with a

length of 13 and radii 4 and 0.5 cm [16]. The larger radii

was close to the source, with 2 cm of Polyethylene between

the aperture of collimator and the neutron generator. The

second was a divergent collimator (L = 50 cm, D = 1 cm

and D0 = 12 cm). The walls were made of (PE-B) with

depth 2.5 cm covered by 1 cm of Lead.

In the third stage (3), we studied the influence of gamma

and neutron filters on the parameters associated with neu-

tron radiography. In our study, we tested sapphire (Al2O3)

for fast neutron filtering and lead for gamma filtering

(Figs. 6, 7).

In the fourth stage (4), we fixed the best configuration

from the last stages and we calculated fth, TNC and (n/c)

parameter with a variable collimator length (L), diameter

of the aperture (D) and diameter of the aperture next to the

image plan (D0).

Fast neutron radiography

In the fast neutron radiography facility the quality of the

NR image is determined by the collimator ratio (L/D) in a

similar way as in the case of thermal neutron flux. The

imaging quality of a fast neutron radiography facility

would be further characterized by the beam quality profile,

described by the number of uncollided fast neutrons that

reach the detector position within the neutron beam [16].

The fast neutron radiography facility was examined in two

stages: In the first stage (1), different configurations are

considered to obtain the maximum fast neutron flux at the

image plane (Fig. 7). The configurations of the collimator

are shown in the Fig. 8. The first configuration was com-

posed by divergent collimator (L = 50 cm, D = 1 cm and

D0 = 12 cm). The second configuration was composed by

divergent collimator (L = 50 cm, D = 1 cm and

D0 = 12 cm) and the walls were made of (PE-B) with

depth of 3 cm covered by 1 cm of lead. Configuration # 3

we used divergent collimator and the walls are made of

iron with depth 3 cm covered by 1 cm of Lead. In the

second stage (2), we calculated fast neutron flux, and un-

collided fast neutrons parameters with a variable collimator

length, diameter of the aperture D and diameter with

D0 = 24 cm.

Results and discussion

A thermal neutron image of the assorted objects was

acquired with a 17 min exposure using an intensity of 109

n/s, and is shown in Fig. 9a. The fast neutron image shown

in Fig. 9b was acquired in a longer 67 min exposure. The

relatively long image times can be shortened by using the

full output of the generator (which requires greater

shielding for personnel safety), but improvements to the

geometry can reduce exposure times without increasing

radiation dose. Importantly, significant degradation of the

image quality was observed due to gamma radiation

Fig. 3 Set of objects that are imaged by thermal and fast neutron

radiography. Assorted objects were 4-step lead and silicon-chip Rose

phantoms, beryllium biconcave neutron lens, black electrical tape,

1.25 and 2.5 cm polyethylene blocks


123

background [17]. The thermal neutron image shows

absorption of some of the signal by the lead, and the

contrast for the tape, which contains higher Z elements in

addition to hydrogen is equal to or greater than that for the

polyethylene, while one would expect the polyethylene to

have greater contrast for a pure thermal beam. Significant

neutron radiation is present as can be seen from the contrast

from the polyethylene and beryllium, both of which have

very small gamma absorption, especially in comparison to

the lead. Similarly, in the fast neutron image, gammas are

indicated by lead contrast, but the presence of fast neutrons

can be seen from the beryllium and especially silicon

contrast. Some of the contrast from the polyethylene and

tape could be due to thermal neutrons.

A better collimator system would reduce the background

noise and improve the Single/Noise radio (SNR) and

thereby improve resolution and contrast. Thus, the mod-

eling effort concentrated on increasing the neutron flux and

improving the n/c ratio to reduce quantum noise and

gamma background.

The goals of the computer modeling of the fast and

thermal neutron radiography system were to optimized

useful neutron flux for a given source intensity, provide a

large L/D for good resolution, and minimize the stray

neutron and gamma background, while providing sufficient

shielding for radiation protection. Polyethylene and paraf-

fin were used for neutron shielding and lead for gamma

shielding. For the setup shown in Fig. 4 the neutron flux at

the image plane in the case (L = 50 cm, D = 1 cm and

D0 = 22 cm) as a function of collimator position is given

in Fig. 10. The maximum fth occurs for a (0 cm) of poly-

ethylene between the aperture and the neutron generator.

Fig. 4 MCNP model of the D–D generator with moderator, shielding and collimator for various polyethylene thicknesses between the collimator

and the generator


123

This position (0 cm) was used in all successive designs

presented. The neutron flux at the image plane for different

configurations of the collimator, as shown in Fig. 5, was

calculated. These results are given in Fig. 11. The best

configuration is number # 2 corresponding to maximum fthat the image plane. Neutron energy spectrum calculated at

aperture and image plane for the configuration # 2 of

neutron generator based thermal neutron radiography

facility is shown in (Fig. 12).

For the configuration # 2 we fixed (L = 50 cm and

D = 1 cm) and we varied the value of D0 (see Table 1).

We choose the value of D0 = 26 cm as the optimal con-

dition since it yields the maximum TNC and (n/c)

parameter while maintaining a large neutron flux. We also

calculated the fth, (n/c) parameter and TNC at the image

plane with neutron fast filer sapphire (Al2O3) (see Table 2).

The presence of the sapphire filter decreases the thermal

neutron flux fth, and the (n/c) parameter, but increases the

TNC. The same result was reported by Fantidis [18].

Fig. 5 MCNP model of the thermal neutron radiography facility with different types of collimators

Fig. 6 MCNP model of the thermal neutron radiography facility with

the sapphire fast neutron filterFig. 7 MCNP model of the thermal neutron radiography facility with

the Lead gamma filter


123

For the presence of lead as a gamma filter at the colli-

mator, the thermal neutron flux (fth), TNC and the (n/c)

parameter decrease (Table 3), except in the case where the

thickness of lead was equal to 5 cm, which resulted in a

slight increase in (n/c) parameter.

In the optimization process of the collimator, the colli-

mator length (L) and the inlet aperture (D) were varied in

order to attain the values for which the maximum thermal

flux is obtained in the image plane. These results are given

in Table 4. The object to detector distance was considered

to be 0.5 cm. An energy boundary of 0.01–0.3 eV was used

to define the thermal neutron flux.

The fth would vary from 2.38 9 102 up to 3.29 9 104

n cm-2 s-1 for a maximum neutron yield by the generator

3 cm B-PE + 1cm of lead 3 cm of iron+ 1cm of lead

(a) Configuration 1 (b) Configuration 2 (c) Configuration 3

6 cm of iron + 1cm of lead 8 cm of iron + 1cm of lead 8 cm of iron + 3 cm B-PE+ 1cm of lead

(d) Configuration 4 (e) Configuration 5 (f)

(g) (h) (i)

Configuration 6

8 cm of Tungsten + 3 cm B-PE 6 cm of iron + 3 cm B-PE 6 cm of iron + 3 cm B-PE+ 1cm of lead 1cm of lead + 1cm of lead

Configuration 7 Configuration 8 Configuration 9

Fig. 8 MCNP model of the fast neutron radiography facility with different types of collimators


123

of 1010 ns-1. The TNC varies from 8 to 33 %. The fth is

comparable with fluxes from low power research reactors

[19, 20]. These values are higher in comparison to those

calculated assuming a yield of 1011 ns-1 by Fantidis [16].

In this work we used a different collimator configuration.

For all the values of L and D considered, the ratio (n/c) was

higher than 106 (n/cm2 mR).

The values for neutron flux; the ratio (n/c), and TNC are

higher than another study by Fantidis et al. [2] that used a

50 mg 252Cf source for neutron radiography system and

achieved fh equal to 1.57 9 104 ncm-2 s-1, the ratio (n/c) =

9.71 9 103 ncm-2 mSv-1 and the TNC = 0.51 % in the case

of (L/D = 50 cm). The present results are also higher than

those from a SbBe neutron source (fth = 6.13 9 102 ncm-2

s-1, TNC = 21.2 % and (n/c) = 51.0 cm-2 Sv-1 in the case

of (L/D = 50 cm) reported by Fantidis et al. [21], and those

reported for an 241Am–Be neutron source (fth equal to 7

.83 9 103 cm-2 s-1 with (n/c) ratio of 5.72 9 1012 cm-2

mSv-1) reported by Jafari and Feghhi [22].

In the case of the fast neutron radiography facility, we

present in Table 5 the value of fast neutron flux for each

of the collimator configurations. The best configuration is

number 6 corresponding to the maximum fast neutron

flux, equal to 1.08 9 105 ncm-2 s-1. The fast neutron

flux at the image plane varies from 4.76 9 102 to 1.83 9

105 ncm-2 s-1 (Table 6). These values are comparable

with low power research reactors [23], and are some

were higher in comparison to those found for a neutron

generator with a yield of 1011 ns-1 according to Fantidis

et al. [16].

Fig. 9 Radiographs of the

objects taken using D–D

neutron generator based thermal

neutron (a) and fast neutron

(b) radiography facility

1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0,01 0,1 0,5 1 2 5

102

103

104

105

Neu

tron

Flu

x (n

cm-2s-1

)

Neutron Energy (MeV)

0 cm of Polyethylene 2 cm of Polyethylene 4 cm of Polyethylene 6cm of Polyethylene

Fig. 10 The Neutron flux at the image plane in the case of

L/D = 50 cm for various polyethylene thicknesses

1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0,01 0,1 0,5 1 2 5

102

103

104

105

Neu

tron

Flu

x (n

cm-2s-1

)


Configuration 1 Configuration 2 Configuration 3 Configuration 4

Fig. 11 The Neutron flux at the image plate in the case L/D = 50 cm

for different configurations of the collimator


123

Tables 4 and 6 also include a comparison of the

arrangement used in the experimental images with a similar

setup (same L/D) using an optimized collimator. As can be

seen from the first two rows Table 4, the collimator slightly

increases the thermal neutron flux and TNC, while greatly

reducing the gamma background. From Table 6, it can be

seen that the collimator increases the uncollided neutron

flux. Greater gains in image quality can be anticipated from

changing to other L/D ratios as evident from the results in

the tables.

1E-81E-7 1E-6 1E-5 1E-4 1E-3 0,01 0,1 0,5 1 2 5

103

104

105

106

107

Neu

tron

Flu

x (n

cm-2s-1

)


At image plane At aperature plane

Fig. 12 The Neutron flux calculated at aperture and image plane for

the configuration 2 of neutron generator based thermal neutron

radiography facility

Table 1 The thermal neutron radiography parameters with variable

aperture next the image plan D0 for L/D = 50 cm (Abreviations: D0:

diameter of the aperture next the image plan; L: length of collimator;

D: diameter of the aperture next the neutron generator; fth: thermal

neutron flux; TNC: Thermal neutron content and n/c: the neutron to

gamma ratio)

D0 (cm) D (cm) L (cm) D/L (cm) fth (ncm-2 s-1) TNC (%) n=c (n/cm2 mR)

12 1 50 50 7.02E?03 19 1.07E?06

18 1 50 50 1.46E?04 27 1.86E?06

22 1 50 50 1.98E?04 31 2.13E?06

26 1 50 50 2.21E?04 33 2.83E?06

30 1 50 50 2.29E?04 32 2.37 E?06

40 1 50 50 2.62E?04 31 2.63E?06


sapphire filter length for L/D = 50 cm

Sapphire filter (cm) fth (ncm-2 s-1) TNC (%) n=c (n/cm2 mR)

0 2.21E?04 33 2.83E?06

2 2.21E?04 32 2.39E?06

6 2.10E?04 35 2.31E?06

10 1.87E?04 42 2.08E?06

14 1.42E?04 43 1.62E?06

18 1.02E?04 45 1.23E?06

22 7.69E?03 49 1.02E?06


Lead filter length for L/D = 50 cm

Lead filter (cm) fth (ncm-2 s-1) TNC (%) n=c (n/cm2 mR)

0 2.21E?04 33 2.83E?06

5 9.20E?03 27 4.19E?06

10 4.95E?03 23 3.71E?06

15 3.89E?03 29 3.15E?06

20 1.91E?03 21 1.52E?06

Table 4 The thermal neutron radiography parameters for different

L/D ratio

L D L/D fth (ncm-2 s-1) TNC (%) n=c (n/cm2 mR)

Experimental collimation

150 15 10 3.06E?03 25 5.91E?05

Optimized collimation

150 15 10 3.25E?04 27 1.65E?06

50 1 50 2.21E?04 33 2.83E?06

50 2 25 2.36E?04 28 2.48E?06

50 4 12.5 3.29E?04 24 3.16E?06

75 1 75 4.00E?03 22 1.60E?06

75 2 37.5 5.96E?03 23 2.41E?06

75 4 18.5 7.78E?03 17 2.80E?06

100 1 100 1.22E?03 16 1.10E?06

100 2 50 1.65E?03 13 1.85E?06

100 4 25 1.97E?03 9.25 1.89E?06

100 6 16.66 3.80E?03 11 2.72E?06

125 1 125 3.81E?02 9 1.34E?06

125 2 62.5 8.34E?02 13 4.14E?06

125 4 31.4 8.94E?02 8 1.79E?06

125 6 20.83 1.73E?03 10 3.26E?06

125 8 15.62 3.13E?03 11 4.38E?06

150 1 150 2.38E?02 13 1.12E?06

150 2 75 2.97E?02 9 1.49E?06

150 4 37.5 6.78E?02 11 2.51E?06

150 6 25 9.73E?02 8 2.55E?06

150 8 18.75 1.33E?03 8 3.38E?06

150 10 15 2.02E?03 8 4.13E?06


123

Conclusions

A fast and thermal neutron radiography facility has been

constructed using a laboratory neutron generator. To

improve image quality, a collimator structure has been

designed using the MCNPX to reduce background noise

and increase the thermal and fast neutron flux. The colli-

mator provides significant improvement in neutron flux and

a decrease in background radiation compared to the

experimental arrangement. The optimized design for ther-

mal neutron radiography provides a thermal neutron flux of

3.29 9 104 ncm-2 s-1 at the image plane using an L/D

ratio of 12.5. The resulting neutron to gamma ratio is

3.16 9 106 n/cm2 mR. For the fast neutron radiography

facility the maximum neutron flux corresponding to the

optimal configuration and L/D = 12.5 cm provided a fast

neutron flux equal to 1.83 9 105 ncm-2 s-1 and an un-

collided fast neutron flux 7.55 9 104 ncm-2 s1. The next

stage of this project will be to construct the proposed

collimators and measure the flux, gamma rejection and

resolution that can be achieved.

Acknowledgments This paper was developed under (IAEA

TUN2003 project) ‘‘Installation of neutron activation analysis labo-

ratory based on a neutron generator’’. The authors would like to thank

Dr. Fantidis G. and Dr. Nicolaou GE., from the University of Thrace,

Xanthi, Greece for their help and also would like to thank the Radi-

ation Safety Information Computational Center (RSICC) for provid-

ing the MCNP code.

References

1. Fischer CO, Stade J, Bock W (1997) In: Proceedings of fifth

world conference on neutron radiography. June 17–20, 1996.

Berlin, Germany

2. Fantidis JG, Nicolaou GE, Tsagas NF (2010) A transport neutron

radiography system. J Radioanal Nucl Chem 284:479–484

3. Mishra KK (2005) Development of a thermal neutron imaging

facility at the N.C. State University PULSTAR reactor. Ph.D.

thesis. Faculty of North Carolina State University. USA, pp 108

4. Elbio C, Burkhard S, Florian G (2005) Construction and assembly

of the neutron radiography and tomography facility ANTARES at

FRM II. Nucl Instrum Method Phys Res A 542:38–44

5. Husin W, Thiagu S, Azali M, Abdul AM, Faridah MI (2009)

Determination optimal aperture parameters for neutron collimator

design using MCNP code. J Nucl Related Technol 6(2):49–62.

http://www.nuklearmalaysia.org

6. Pelowitz DB (ed) (2011) MCNPX user’s manual, version 2.7.0. Los

Alamos National Laboratory Report LA-CP-11-00438, April 2011

7. http://www.adelphitech.com. Accessed January 2009

8. Reijonen J (2005) Compact neutron generators for medical home

land security and planetary exploration. In Proceedings of the

2005 IEEE particle accelerator conference (PAC 05). 16–20 May

2005, Knoxville, Tennessee. 21st IEEE Particle accelerator con-

ference, p. 49

9. Popov V, Degtiarenko P, Musatov I (2010) New detector for use

in fast neutron radiography, 12th International workshop on

radiation imaging defectors, July 11–15 2010, Robinson College,

Cambridge, UK, Published by IOP Published for SISSA

10. Patil BJ, Chavan ST, Pethe SN, Krishnan R (2011) Collimator

design for 15 MeV linear accelerator based thermal neutron

radiography facility. Proceedings of particle accelerator confer-

ence, New York, NY, USA, from March 28 to April 1, 2011

11. Domanus JC (1987) Collimators for thermal neutron radiography:

an overview. D. Reidel Publishing Company. http://www.worldcat.

org

12. Hawkesworth MR (1977) Neutron radiography: equipment and

methods. At Energy Rev 15(2):169–220

13. Barton JP (1967) Material Evaluation 25:45A–46A

Table 5 Fast neutron flux at

the image plan with different

collimators configurations

Number of

configurations

Fast neutron

flux Ffast

(ncm-2 s-1)

Configuration 1 4.29E?04









Table 6 The fast neutron radiography parameters for different L/D

ratio

L D L/D Ffast

(ncm-2 s-1)

Uncollided Ffast

(ncm-2 s-1)

lG

(cm)

Experimental collimation

150 15 10 3.69E?04 1.88E?04 0.05

Optimized collimation

150 15 10 6.26E?04 2.19E?04 0.05

50 1 50 1.08E?05 3.06E?04 0.010

50 2 25 1.34E?05 4.85E?04 0.020

50 4 12.5 1.83E?05 7.55E?04 0.040

100 1 100 9.67E?03 3.46E?03 0.005

100 2 50 1.35E?04 7.51E?03 0.010

100 4 25 2.75E?04 1.68E?04 0.020

100 6 16.66 3.71E?04 1.98E?04 0.030

150 1 150 2.66E?03 1.18E?03 0.003

150 2 75 5.16E?03 2.87E?03 0.006

150 4 37.5 1.06E?04 6.27E?03 0.013

150 6 25 1.3E?04 8.75E?03 0.020

150 8 18.75 2.06E?04 9.01E?03 0.026

150 10 15 2.07E?04 9.02E?03 0.033

200 1 200 5.63E?02 4.76E?02 0.002

200 2 100 2.19E?03 1.39E?03 0.005

200 4 50 5.68E?03 3.89E?03 0.010

200 8 25 9.78E?03 5.05E?03 0.020

200 10 20 1.08E?04 5.15E?03 0.025


123

http://www.nuklearmalaysia.org

http://www.adelphitech.com

http://www.worldcat.org

http://www.worldcat.org

14. Mildner DFR, Arif M, Stone CA (1993) Neutron transmission of

single crystal sapphire filters. J Appl Cryst 26:438–447

15. Adib M, Kilany M (2003) On the use of Bismuth as a neutron

filter. Radiat Phys Chem 66:81–88

16. Fantidis JG, Nicolaou GE, Tsagas NF (2010) Optimization study

of a transportable neutron radiography unit based on a compact

neutron generator. Nucl Instrum Method Phys Res A 618:331–335

17. Cremer JT, Williams DL, Gary CK, Piestrup MA, Faber DR,

Fuller MJ, Vainionpaa JH, Apodaca M, Pantell RH, Feinstein J

(2012) Large area imaging of hydrogenous materials using fast

neutrons from a DD fusion. Nucl Instrum Method Phys Res A

675:51–55

18. Fantidis JG (2012) A study of a transportable thermal neutron

radiography unit based on a compact RFI linac. J Radioanal Nucl

Chem 293:95–101

19. Zawisky M, Hameed F, Dyrnjaja E, Springer J (2008) Digitized

neutron imaging with high spatial resolution at a low power

research reactor: I. Analysis of detector performance. Nucl In-

strum Method Phys Res A 587:342–349

20. Chankow N, Punnachaiya S, Wonglee S (2010) Neutron radi-

ography using neutron imagingplate. Appl Radiat Isot 68:662

21. Fantidis JG, Nicolaou GE, Tsagas NF (2009) A transportable

neutron radiography system based on a SbBe neutron source.

Nucl Instrum Method Phy Res A 606:806–810

22. Jafari H, Feghhi SAH (2012) Design and simulation of neutron

radiography system based on 241Am–Be source. Radiat Phys

Chem 81:506–511

23. Bucherl T, Kutlar E, Von Gostomski C L, Calzada E, Pfister G,

Koch D (2004) Radiography and tomography using fission neu-

trons at FRM-II. Appl Radiat Isot 61:537


123

Design, testing and optimization of a neutron radiography system based on a Deuterium–Deuterium...

Documents

Transcript of Design, testing and optimization of a neutron radiography system based on a Deuterium–Deuterium...