HFETR放射性核素监测的反康普顿γ能谱仪蒙特卡罗模拟研究

燃料元件发生破损时大量放射性核素进入一回路系统,对放射性核素的含量进行监测,能及时有效地判断元件是否破损及破损程度。要准确分析燃料元件破损程度,目前在HFETR上利用一次水冷却剂样品进行核素分析,使用高纯锗(HPGe)探测器进行离线γ谱分析,这种方法性能不稳定,易受本底干扰,尤其在γ射线800keV以下具有很高的康普顿平台,不利于γ射线测量。使用蒙特卡罗软件Geant4设计模拟了一套用于监测放射性核素的反康普顿γ能谱仪,主探测器采用HPGe探测器,选择NaI(Tl)闪烁体作为次级探测器。模拟一次水取样样品中放射性核素Na-24,Kr-88,I-131,Xe-135,Cs-137进入探测器,结果表明,在γ谱非常复杂的情况下,通过反符合技术可以很好的抑制康普顿平台和探测系统本底,提高各核素特征峰(尤其是低能段的核素特征峰)的探测精度,便于更准确地计算一次水核素浓度变化及判断元件破损情况。

Detecting the nuclides in the primary system can estimate fuel elements failure, In HFETR, the primary system samples are analysed by HPGe detector, this analysis method is unstable which has the background noise and a high Compton plat eau under 800 KeV in γ-ray s pectra. In this study, the Geant4 toolkit was used to simulate a Compton suppression system based upon a HPGe primary detector in order to detecting the nuclides. Our γ-ray Compton suppression system consists of a HPGe detector and NaI(Tl) detectors. We simulate emitting Na-24, Kr-88, I-131, Xe-135, Cs-137 into the detector system. Simulation results show that the Compton continuum in complex γ-ray spectra of HPGe detector can be suppressed, and the peak-to-Compton ratio can be improved. The anticoincidence technique can improve the detecting precision, which contribute to estimate fuel element failure.