面向辐射环境监测的反康普顿γ能谱仪蒙特卡罗模拟研究

Monte Carlo optimization of a Compton suppression system for gamma-ray diagnosis of radioactive environment

摘要:

使用蒙特卡罗软件Geant4设计模拟了一套用于核事故等辐射环境监测的反康普顿γ能谱仪。主探测器采用HPGe探测器，选择新型闪烁体晶体LaBr3(Ce)作为次级探测器。利用Geant4对探测器系统进行模拟优化，确定最佳的探测器尺寸和结构。模拟的γ射线能量范围从500 keV到1500 keV。结果表明，增加主体LaBr3(Ce)晶体厚度能显著提升康普顿抑制系数，当主体LaBr3(Ce)晶体厚度达到60 mm时，提升效果明显减弱；在HPGe探测器的后方添加LaBr3(Ce)晶体也能一定程度提升抑制效果，而在HPGe探测器的前方增加LaBr3(Ce)晶体厚度对康普顿抑制系数的提升非常有限。在最优化条件下模拟测量了放射性核素I-131，Cs-134，Cs-137和K-40，对发射单能γ射线的Cs-137和K-40康普顿抑制效果很好，对存在级联衰变的I-131和Cs-134抑制效果相对较弱。

Abstract:

In this study, the Geant4 toolkit is used to simulate a Compton suppression system based upon a HPGe primary detector for radioactive environment such as nuclear plant accident. LaBr3(Ce) crystal is selected for the anti-coincidence secondary detector. Simulations for the detector system are performed to gain the optimal sizes for 500 keV – 1500 keV γ rays. Simulation results show that the Peak Compton Suppression Factors (Peak CSFs) increase significantly with the thickness increase of the body LaBr3(Ce) crystal from 10 to 60 mm, the Peak CSFs do not increase obviously after the thickness of the body LaBr3(Ce) crystal reaches 60-70 mm; Moreover, adding a LaBr3(Ce) crystal to the back of the HPGe detector can also improve the Peak CSFs, but adding a LaBr3(Ce) crystal to the front of the HPGe detector has little effect on improving the Peak CSFs. Finally, we simulate a variety of sources in our Compton suppression system under the optimal conditions: for Cs-137 and K-40 that decay via a single γ emission Compton suppression effects are good; for I-131 and Cs-134 that decay in cascade some improvements are still obtained.