动态γ辐射场中的气溶胶监测系统优化设计北大核心CSCD

为满足核电站及应急监测环境中具有动态强γ本底的α、β放射性气溶胶在线监测的需求,本文结合该监测场景的源项特点,对表面钝化的离子注入型(PIPS)半导体探测器晶体结构进行了优化设计。并使用蒙特卡罗方法,对探测系统结构优化后的集成双PIPS探测器,进行了角度响应模拟。为满足大角度范围更为优异的角度响应相对标准偏差指标(根据现场工作及实验总结要求小于15%),对集成双PIPS探测器探测系统(包括:探筒、走纸部分及气溶胶输运管路)结构进行了优化,并将整个探测系统置于立体设备处。将改进后的设备分别置于^(60)Co和^(137)Cs参考辐射场中,进行了线性、能量和角度响应实验。实验结果表明:(1)经优化设计的集成双探测器结构在角度、能量及线性响应方面的性能更优异;(2)整机组件材料的结构及密度的各向异性可仅通过对探测系统局部的结构优化,实现角度响应不大于5%,从而避免对整机进行改造。最终将优化后的设备置于空气比释动能为10μGy/h的137 Cs参考辐射场中运行,测量结果表明:经γ补偿及天然氡、钍子体扣除后,α气溶胶的探测限小于0.03 Bq/cm^(3),β气溶胶的探测限小于0.4 Bq/cm^(3),且在长期稳定运行中未出现误报警。

The optimal design of an aerosol monitor in dynamic gamma radiation field

To meet the needs of online monitoring of α/β radioactive aerosols for dynamic variation of high γ radiation in nuclear power stations and emergency monitoring environments, ion implanted semiconductor detector with passivated surface is redesigned and improved, based on the characteristics of the source term of the monitoring scene. Monte Carlo method was used to simulate the angular response of the optimized dual PIPS detector, and then the structure of the probe was improved. In order to decrease relative standard deviation for angle response, the structure of detection system is improved. Optimized equipment is placed in the ⁶⁰Co and ¹³⁷Cs reference radiation field. Linearity, energy and angular response experiments were performed. It is shown that: 1) The newly designed integrated dual detector has better performance in angular response. 2) Due to anisotropy of the structure and density of assembly material, the construction of probe is optimized, the angular response is no more than 5%, thereby the weight of equipment is effectively reduced. In addition, the linearity and energy response data of the equipment are fitted and the formula is input into the data processing program. Finally, the operating equipment was placed in a ¹³⁷Cs reference radiation field with 10 μGy/h. The test data have shown that the minimum detection limit (MDL) is less than 0.03 Bq/cm³ (for α aerosol) and 0.4 Bq/cm³ (for β aerosol), respectively. As a result, false alarm is significantly avoided.