大面积超低本底α电离室的研制

Development of Large-area Ultra-low Background Alpha Ionization Chamber

摘要: 研制了一台大面积超低本底α电离室用于超低α表面发射率测量。电离室充入高纯气体并采用流气工作模式，由于对宇宙射线中的μ子和环境中的γ射线不灵敏，去除氡气后电离室的本底主要来自于内表面发射的α粒子。利用脉冲形状分析技术，可分辨出α粒子是来自电离室内表面还是样品，甄别掉内表面发射的α本底，电离室即可达到超低本底，可进行超低α表面发射率样品测量。该电离室的有效探测面积为1521 cm²，α本底可达3×10^-4 cm^-2•h^-1。

Abstract: An ionization chamber was developed for measuring alpha particle emissivity at ultra-low background levels. The ionization chamber is filled with high purity gas and operated in flow mode. Consequently the ionization chamber is insensitive to muon showers in cosmic ray and gamma ray from environment. After removing the radon by flowing gas, the alpha background mostly emanates from different surfaces inside the chamber. The pulse shape analysis method was employed to distinguish the location of emanation of each alpha particle. While alpha particles from chamber surfaces are rejected, only alpha particles emanating from the sample are finally counted at ultra-low levels. The chamber has a 1 521 cm² sample area and a background of 3×10^-4 cm^-2•h^-1.