基于单/双层壁电离室的强钴源低能γ成分评估方法  

Evaluation for low energy γ proportion of cobalt source high dose rate field based on plane-parallel ionization chamber

作　　者：李磊[1] 石建敏[1] 杨娜[1] 庞元龙[1] 刘许强[1] 曾光[1] 杨桂霞[1] LI Lei;SHI Jianmin;YANG Na;PANG Yuanlong;LIU Xuqiang;ZENG Guang;YANG Guixia(Institute of Nuclear Physics and Chemistry,Chinese Academy of Engineering Physics, Mianyang 621900, China)

机构地区：[1]中国工程物理研究院核物理与化学研究所,绵阳621900

出　　处：《核技术》2018年第7期13-20,共8页Nuclear Techniques

摘　　要：利用重金属工艺可提高器件可靠性,低能γ将使器件高Z/低Z界面附近产生剂量增强效应,影响器件抗辐射性能评估。介绍了一种强钴源低能散射γ成分评价方法,利用铝单层室壁/金铝双层室壁平板型电离室辐射电流比值对γ能量敏感的特性,通过比较电流比值实测与参考值的差异,估计散射γ(≤300 ke V)成分是否过多,典型钴源能谱计算结果表明:参考值可取为2.8。研制了量程为0.01~2.3 Gy·s^(-1)(Si)的电离室探头,搭建了长距离辐射电流测量系统。单板钴源实验结果表明:空场条件和铅铝容器(散射抑制)内辐射电流比值实测结果与预期相符,方法可行;能够检验能谱硬化技术的有效性;可从剂量角度关联不同辐射场或相同辐射场不同辐照工位。[Background] Heavy metal process is widely used to improve the reliability of electronic devices, which introduces interface formed by high Z and low Z material. There will be dose enhancement effect within region near such interface when exposing to low energy γ-ray field. This phenomenon could affect the reliability of hardness assurance tests. [Purpose] A method was introduced to evaluate the proportion of low energy scattering γ-ray within high dose rate irradiation field formed by cobalt source. [Methods] Two types of ionization chambers were designed, which utilize single layer Al（aluminum） wall and double layers Au（gold）/Al wall respectively. The γ-ray induced current of the latter ionization chamber varied more rapidly with the change of γ-ray energy than the former one. Consequently, the ratio of those two currents was sensitive to γ-ray energy, and the variation between measured and reference value of ratio could indicate whether the proportion of low energy γ-ray was over expectation obviously. [Results] It was advised that the reference value could be set as 2.8 based on analysis of typical energy spectrums of cobalt source. In addition, an ionization chamber dosimeter system with the range of 0.012.3 Gy·s-1（Si） was designed with which the ratios were measured in free field and Pb（lead）/Al box reducing the amount of low energy γ-ray. There was an agreement between experimental and calculated results. [Conclusion] The method is effective for evaluating the proportion of scattering γ-ray and the effectiveness of spectral hardening technology. Furthermore, it could help correlate different irradiation fields or irradiation positions within specific irradiation field from the aspect of irradiation dose.

关 键 词：剂量增强效应 强钴源辐射场 低能散射γ 评估方法 平板电离室 

分 类 号：TL929[核科学技术—核燃料循环与材料] TB114.1[理学—运筹学与控制论]