基于三晶体耦合γ射线方向探测器的放射源定位

Locating radioactive source based on three coupled-crystals directional detector of γ rays

为了快速定位并寻回丢失的放射源,设计了一种由NaI、CsI、锗酸铋(Bi4Ge3O12,BGO)三种晶体与铅耦合组成的γ射线方向探测器,并采用基于蒙特卡罗方法的通用软件包MCNP(Monte Carlo N Particle Transport Code)研究了铅晶比例、射线能量、剂量率等因素对探测器角度分辨率的影响。结果表明,对于137Cs源,在空气吸收剂量率≥0.331μGy·h^(-1)处,定位角度偏差≤0.99°;对于60Co源,在空气吸收剂量率0.586μGy·h^(-1)处,测量的平均角度偏差为0.46°;对于水平距离7 m、高度4 m的3.7×107Bq 137Cs源,相对定位偏差约为5%。

Background： With the increase application of radioactive sources, the possibility of radiation accidents is raised as well in recent years. Purpose： This study aims to fastly locate lost radioactive sources using a directional detector of 3＇ rays. Methods： Three different coupled scintillators, i.e., NaI, CsI, Bi4Ge3012 （BGO）, together with center lead cylinder were employed to build the 3＇ ray directional detection system. Localizing spatial radioactive source and the influences of angular resolution caused by lead-crystal ratio, rays energy and source dose rate were simulated by using MCNP （Monte Carlo N particle transport code）. Results： The angle deviation is less than 0.99, provided that the air absorbed dose rate of 137Cs source is not lower than 0.331 μ^tGy.h-k The average angle measurement deviation is 0.46° when the air absorbed dose rate of 60Co source is 0.586 ktGy＇h-1. The positioning deviation of 3.7x107 Bq 137Cs source at a distance of 7 m and height of 4 m is about 5%. Conclusion： The three-coupled-crystals directional detector of 3/rays can be used to identify the direction of incident γ rays and locate the spatial position of unknown radioactive source with reasonable radiant intensity.