ゲルマニウム半導体スペクトロメータのγ線バックグラウンドスペクトルに対する空気中ラドンの影響とその低減方法

抄録

It has been shown that the fluctuation of background spectrum of γ rays measured by pure germanium detector is caused by the variation of atmospheric radioactivity (²²²Rn, ²²⁰Rn and their daughters) . In order to diminish the fluctuation, nitrogen gas from the cryogen tank of the detector is flown into the lead vessel for shielding natural radiations. With the aid of the gas flow, peak counts of γ rays from daughters of ²²²Rn and ²²⁰Rn in the background spectrum can be so decreased that their fluctuations become within statistical uncertainties. The fluctuation of the total count (0-2800 keV) also becomes within the statistical uncertainty although the decrease of the count by the gas flow is at most 4%.