Mô phỏng phổ năng lượng nơtron của chùm nơtron nhiệt truyền qua phin lọc

DALAT UNIVERSITY JOURNAL OF SCIENCE Volume 10, Issue 3 , 2020 90-97 
90 
SIMULATION OF NEUTRON ENERGY SPECTRA OF FILTERED 
THERMAL NEUTRON BEAM 
Phu Chi Hoaa*, Pham Ngoc Sonb, Huynh Thanh Sonc 
aDalat University, Lamdong, Vietnam 
bDalat Nuclear Research Institute, Lamdong, Vietnam 
cHoang Van Thu High School, Khanh Hoa, Vietnam 
*Corresponding author: Email: pnson.nri@gmail.com 
Article history 
Received: May 22nd, 2020 
Received in revised form: June 18th, 2020 | Accepted: September 24th, 2020 
Abstract 
In this paper, simulation calculations of the energy spectra distribution of thermal neutrons 
transmitted through a filter section of sapphire and bismuth crystals were carried out. 
Techniques used sapphire and bismuth as neutron filters. The PHITS (Particle and Heavy 
Ion Transport System) simulation code was used to characterize the neutron energy spectra 
based on the material design parameters, geometrical structure, and shielding thickness. 
Keywords: Bismuth; Neutron filter; PHITS; Sapphire. 
DOI:  
Article type: (peer-reviewed) Full-length research article 
Copyright © 2020 The author(s). 
Licensing: This article is licensed under a CC BY-NC 4.0 
DALAT UNIVERSITY JOURNAL OF SCIENCE [NATURAL SCIENCES AND TECHNOLOGY] 
91 
MÔ PHỎNG PHỔ NĂNG LƯỢNG NƠTRON CỦA CHÙM 
NƠTRON NHIỆT TRUYỀN QUA PHIN LỌC 
Phù Chí Hòaa*, Phạm Ngọc Sơnb, Huỳnh Thanh Sơnc 
aTrường Đại học Đà Lạt, Lâm Đồng, Việt Nam 
bViện nghiên cứu hạt nhân, Lâm Đồng, Việt Nam 
cTrường Trung học phổ thông Hoàng Văn Thụ, Khánh Hòa, Việt Nam 
*Tác giả liên hệ: Email: pnson.nri@gmail.com 
Lịch sử bài báo 
Nhận ngày 22 tháng 5 năm 2020 
Chỉnh sửa ngày 18 tháng 6 năm 2020 | Chấp nhận đăng ngày 24 tháng 9 năm 2020 
Tóm tắt 
Trong bài báo, các tính toán mô phỏng về phân bố phổ năng lượng của các neutron nhiệt truyền 
qua phin lọc của tinh thể sapphire và bistmut đã được thực hiện. Kỹ thuật nơtron phin lọc sử dụng 
bismuth, sapphire đã được áp dụng. Mô phỏng PHITS (Particle and Heavy Ion Transport System) 
đã được áp dụng để mô tả đặc điểm của phổ năng lượng neutron dựa trên các tham số thiết kế vật 
liệu, cấu trúc hình học, và độ dày lớp che chắn. 
Từ khóa: Bismuth; Kỹ thuật nơtron phin lọc; PHITS; Sapphire. 
DOI:  
Loại bài báo: Bài báo nghiên cứu gốc có bình duyệt 
Bản quyền © 2020 (Các) Tác giả. 
Cấp phép: Bài báo này được cấp phép theo CC BY-NC 4.0 
Phu Chi Hoa, Pham Ngoc Son, and Huynh Thanh Son 
92 
1. INTRODUCTION 
Neutron filter techniques have been used with nuclear reactors in many countries, 
such as Ukraine, the USA, Russia, Japan, Korea, and Vietnam. These techniques have 
been applied to research on experimental prompt gamma neutron activation analysis and 
boron neutron capture therapy. Neutron filter techniques have been used at the Dalat 
Nuclear Research Institute, and some filtered neutron beams have been investigated and 
developed (Phạm, Vương, Phù, & Trần, 2014; Vương, Phạm, Nguyễn, Trần, Nguyễn, 2014). 
Bismuth and sapphire crystal filters have been previously investigated by Turkolgu (2012). 
The PHITS calculation program (Sato et al., 2018) is a particle transport 
simulation program developed on the basis of the Monte Carlo simulation method by 
Hiroshi Takemiya’s group at the Center for Computational Science and Electronic 
Systems of the Japanese Atomic Energy Agency (JAEA). PHITS simulates the transport 
and collision of nearly all particles, including neutrons, protons, photons, ions, and 
electrons with energy spectra from 10-4 eV to 1 TeV. 
In this study, we used the PHITS code (Sato et al., 2018) to study and calculate 
the energy spectral characteristics and thermal neutron flux corresponding to the new 
bismuth and sapphire filters in the neutron channel of the Dalat Nuclear Research 
Reactor. 
2. PHITS CALCULATION 
The basic steps to create a new filter in the horizontal channel of the research 
reactor include 
• Calculating to choose the size and combination of the most suitable materials 
to make the filter so that the neutron spectrum has as high a relative intensity 
as possible (from 85 to 97%). 
• Processing, installing filters, and collimating neutron flow. 
The cornerstone of the thermal neutron filter technique (Gritzay et al., 2007) is 
the use of a sufficiently large amount of monocrystalline material with a minimum 
distribution in the neutron total cross-section in the energy region near En=0.0253 eV. 
The PHITS code (Sato et al., 2018) was developed in collaboration between 
JAEA, RIST, KEK, and several other institutes. We used the PHITS code to calculate and 
pick the parameters of size, density, material combination, and energy spectrum 
distribution for the horizontal neutron channel of the Dalat Nuclear Research Reactor. 
3. CALCULATION MODEL 
Bismuth and sapphire were selected to form a filter combination for obtaining 
neutrons with an average energy of 0.0253eV. Bismuth is an additional material used to 
DALAT UNIVERSITY JOURNAL OF SCIENCE [NATURAL SCIENCES AND TECHNOLOGY] 
93 
decrease the intensity of gamma rays through the filter. The cone collimator has been 
designed for the horizontal channel of the Dalat Nuclear Research Reactor. 
The simulation model with the collimation shape designed for the horizontal 
neutron channel of the Dalat Nuclear Research Reactor is shown in Figure 1. 
Figure 1. Model of the filtered neutron guidance system in horizontal channel No.1 
for calculations with the PHITS program 
4. RESULTS OF SIMULATIONS 
Simulation results for the thermal neutron flux, the ratio of the thermal/epithermal 
neutrons, and the relative intensities of thermal neutrons are given in Tables 1, 2, and 3. 
The energy spectra of thermal neutrons are shown in Figures 2-4. 
From the calculations, it was found that the thermal neutron flux of the cone 
collimation was 1.6 times higher than that of the cylindrical collimation. The flux of 
thermal neutrons, the ratio of thermal/epithermal neutrons, and the relative intensities of 
thermal neutrons depend very strongly on the filter components such as crystal or normal 
filters. For crystal bismuth and sapphire filters, the thermal neutron relative intensity 
parameter is much higher than that of normal bismuth and sapphire filters. 
Table 1. Characteristic parameters of neutron spectra for crystal and normal 
cones using bismuth-6cm and sapphire-15cm filters 
Cone 
Thermal 
neutron flux 
(n/cm2/s) 
Fast 
neutron flux 
(n/cm2/s) 
Full 
spectrum flux 
(n/cm2/s) 
Thermal/epithermal 
 ratio 
Thermal neutron relative 
intensity 
Crystal 9.36E+07 1.16E+06 9.47E+07 80.97 98.78% 
Normal 7.68E+05 1.11E+06 1.88E+06 0.69 40.95% 
Phu Chi Hoa, Pham Ngoc Son, and Huynh Thanh Son 
94 
Table 2. The characteristic parameters of neutron spectra for crystal cones 
and cylinders using bismuth-6cm and sapphire-15cm filters 
Collimation 
Thermal 
neutron flux 
(n/cm2/s) 
Fast neutron 
flux 
(n/cm2/s) 
Full spectrum 
flux 
(n/cm2/s) 
Thermal/epithermal 
Ratio 
Thermal 
Neutron relative 
intensity 
Cone 9.36E+07 1.16E+06 9.47E+07 80.97 98.78% 
Cylinder 5.80E+07 7.11E+05 5.87E+07 81.60 98.79% 
Table 3. The characteristic parameters of neutron spectra for a crystal cone 
with a filter using bismuth-6cm and sapphire crystal lengths ranging from 0 to 20cm 
Sapphire 
filter 
Thermal neutron 
flux 
(n/cm2/s) 
Fast neutron flux 
(n/cm2/s) 
Full spectrum 
flux 
(n/cm2/s) 
Thermal/epithermal 
Ratio 
Thermal 
neutron 
relative 
intensity 
0 cm 8.58E+08 4.09E+08 1.27E+09 2.10 67.71% 
1cm 1.59E+08 6.63E+07 2.26E+08 2.40 70.63% 
3cm 1.47E+08 3.42E+07 1.81E+08 4.31 81.15% 
5cm 1.36E+08 1.82E+07 1.54E+08 7.47 88.20% 
7cm 1.26E+08 9.92E+06 1.36E+08 12.69 92.70% 
9cm 1.17E+08 5.54E+06 1.22E+08 21.04 95.46% 
10cm 1.12E+08 4.20E+06 1.17E+08 26.77 96.40% 
11cm 1.08E+08 3.19E+06 1.11E+08 33.92 97.14% 
12cm 1.04E+08 2.47E+06 1.07E+08 42.23 97.69% 
13cm 1.01E+08 1.91E+06 1.03E+08 52.71 98.14% 
14cm 9.70E+07 1.48E+06 9.85E+07 65.57 98.50% 
15cm 9.36E+07 1.16E+06 9.47E+07 80.97 98.78% 
16cm 9.03E+07 8.99E+05 9.12E+07 100.41 99.01% 
17cm 8.71E+07 7.17E+05 8.79E+07 121.55 99.18% 
18cm 8.41E+07 5.73E+05 8.46E+07 146.76 99.32% 
19cm 8.11E+07 4.68E+05 8.16E+07 173.41 99.43% 
20cm 7.83E+07 3.71E+0 7.87E+07 211.11 99.53% 
DALAT UNIVERSITY JOURNAL OF SCIENCE [NATURAL SCIENCES AND TECHNOLOGY] 
95 
Figure 2. The monoenergetic neutron spectrum of a crystal cone 
and a normal cone 
Figure 3. The monoenergetic neutron spectrum of a crystal cone 
and a crystal cylinder 
Phu Chi Hoa, Pham Ngoc Son, and Huynh Thanh Son 
96 
Figure 4. The monoenergetic neutron spectra of a crystal cone 
with a sapphire filter of various lengths 
5. CONCLUSION 
The calculations show that the cone collimation is more effective than the 
cylindrical collimation. In this paper, we choose to design with a cone-shaped collimator, 
6 cm single-crystal bismuth filter, and a single-crystal sapphire filter with alternative 
lengths from 15 cm to 20 cm for estimation of the expected thermal neutron flux for 
various applications. 
The results provide significant supporting information, such as neutron flux, 
thermal/epithermal ratio, and energy distribution, for the development of the thermal 
neutron channel in the horizontal channel of the Dalat Nuclear Reactor. 
ACKNOWLEDGMENTS 
This study was supported by the national project under grant number 
KC.05.08/16-20. 
REFERENCES 
Gritzay, O., Kolotyi, V., Pshenichnyi, V., Gnidak, M., Kalchenko, O., Klimova, N.,  
Korol, O. (2007). Neutron filter technique and its use for fundamental and applied 
DALAT UNIVERSITY JOURNAL OF SCIENCE [NATURAL SCIENCES AND TECHNOLOGY] 
97 
investigations. Paper presented at The 6th Conference on Nuclear and Particle 
Physics, Egypt. 
Phạm, N. S., Vương, H. T., Phù, C. H., & Trần, T. A. (2014). Development of 24 and 59 
keV filtered neutron beams for neutron capture experiments at Dalat Research 
Reactor. World Journal of Nuclear Science and Technology, 4, 59-64. 
https://doi.org/10.4236/wjnst.2014.42010. 
Sato, T., Iwamoto, Y., Hashimoto, S., Ogawa, T., Furuta, T., Abe, S.,  Niita, K. (2018). 
Features of particle and heavy ion transport code system (PHITS) version 3.02. 
Journal of Nuclear Science and Technology, 55(6), 684-690. 
https://doi.org/10.1080/00223131.2017.1419890. 
Turkoglu, D. (2012). Design, construction and characterization of an external neutron 
beam facility at the Ohio State University Nuclear Reactor Laboratory. Ohio, 
USA: The Ohio State University-Graduate Program in Nuclear Engineering 
Publishing. 
Vương, H. T., Phạm, N. S., Nguyễn, N. Đ, Trần, T. A, & Nguyễn, X. H. (2014). Progress 
of filtered neutron beams development and applications at the horizontal channels 
No.2 and No.4 of Dalat Nuclear Research Reactor. Nuclear Science and 
Technology, 4(1), 62-69.