J. Byun a b, J. Seo a b, Y. Kim b c, J. Park a d, K. Shin a d, W. Lee d e, K. Lee e, K. Kim e, B. Park a b f
a Dept. of Health and Safety Convergence Science, Korea University, Seoul, 02841, South Korea
b Interdisciplinary Program in Precision Public Health, Korea University, Seoul, 02841, South Korea
c Marine Radioactivity Monitoring Group, Korea Marine Environment Management Corporation, Busan, 48931, South Korea
d Transdisciplinary Major in Learning Health Systems, Graduate School, Korea University, Seoul, 02841, South Korea
e Dept. of Health and Environmental Science, Korea University, Seoul, 02841, South Korea
f Liquid Crystals Research Center, Konkuk University, Seoul, 05029, South Korea
## Abstract
Neutron is an indirectly ionizing particle without charge, which is normally measured by detecting reaction products. Neutron detection system based on measuring gadolinium-converted gamma-rays is a good way to monitor the neutron because the representative prompt gamma-rays of gadolinium have low energies (79, 89, 182, and 199 keV). Low energy gamma-rays and their high attenuation coefficient on materials allow the simple design of a detector easier to manufacture. Thus, we designed a cadmium zinc telluride detector to investigate feasibility of simultaneous detection of gamma-rays and neutrons by using the Monte-Carlo simulation, which was divided into two parts; first was gamma-detection part and second was gamma- and neutron-simultaneous detection part. Consequently, we confirmed that simultaneous detection of gamma-rays and neutrons could be feasible and valid, although further research is needed for adoption on real detection.
## 1. Introduction
A neutron is an indirectly ionizing particle without a charge, which is normally measured by detecting reaction products. Detection systems of neutrons are determined depending on the neutron energy, where the thermal neutron is normally measured with reactions such as 10B(n,α)7Li, 6Li(n,α)3H, and 3He(n,p)3H. However, in these cases, it is challenging to eliminate the gamma-ray signal acting as noise in (n, α) and (n, p) type detector, and to resolve the problem from wall effect that secondary charged ions (α and p) get lost by wall of detector [1]. Another way to detect the neutron is the measuring prompt gamma-rays [2], which are emitted after neutron capture of nuclei. For resolving the prompt gamma-rays, detectors with good energy resolution are needed.
CdTe-based semiconductor detectors [[4], [5], [6], [7]] (i.e. CdTe, CdZnTeSe, CdMnTeSe etc) became commercialized and actively researched because of sufficient properties as gamma detectors such as high atomic number, prominent stopping power, wide band gap, transport property, and room-temperature operation. Mobility-lifetime product of electrons in CdZnTe(CZT) reached at 10−2 cm2/V, and energy resolution on 662 keV gamma-ray energy were approximately from 1% to 3% when virtual Frisch grid (VFG) was introduced [[8], [9], [10]]. Thus, CZT with VFG could serve as a good energy resolution, which is needed for measuring the prompt gamma-rays.
There are three mechanisms to detect the neutron with CZT detector as shown in Fig 1. Fig. 1 (middle) shows a diagram of VFG CZT detector with converter, which converts neutrons to charged particles such as alpha and proton. However, a vacuum condition needs to be set to detect these charged particles, because converted particles can be shielded by ambient air while the prompt gamma-rays penetrate the air in ease. Given the geometry in Fig. 1 (right), the large volume of the detector is required because prompt gamma-rays taking place in a CZT detector should be attenuated in that detector [2]. Fig. 1 (left) shows the Gd-converted CZT detector, which can be an ideal neutron detector. Moreover, gadolinium has a high cross-section on neutron [11], and energy of prompt gamma-ray emitted from Gd(n, γ) reactions is relatively lower than other prompt gamma-rays [3]. Low energy gamma-rays allow simple designs and thinness of the detectors, because low energy gamma-rays are easily absorbed with relatively thin materials. Thus, we choose the geometry in Fig. 1 (left) to design the neutron detector using the Monte-Carlo simulation. We divided a single CZT to two parts to investigate the feasibility of simultaneous detection of neutrons and gamma-rays with a single CZT detector; first was gamma-detection part and second was gamma- and neutron-simultaneous detection part.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/thesis/monte-carlo-simulation-for-detecting-neutron-and-gamma-ray-simultaneously-with-cdznte-half-covered-by-gadolinium-film.html