Development of determination system for radon concentration using air luminescence

空气发光法测定了~（40）<222>Rn及其子体核素。为了改善光收集，两个光电倍增管（PMT）被封闭在一个不透光的腔室，并覆盖有反射器。光电倍增管输出的脉冲被送入放大器、符合电路和1024道脉冲高度分析器。对噪声脉冲和来自真实的发光事件的脉冲的鉴别是令人满意的，使用标准α发射核素（~（14）<241>Am）和已知量~（14）<222>Rn的系统的计数效率分别为2.4%和7.38%。这种计数效率的差异可能归因于^<222>Rn伴随着两个短寿命的α发射子核素（^<218>Po，^<214>Po）。本研究中观察到的发光归因于α粒子在空气中通过引起的氮和氧的电离和激发。基于氮发光的较高计数效率，提出了一种有效的空气中环境氡的采样方法：去除空气中的CO_2和O_2后，将空气中的氡和氮气冷却至约100 ℃，再将空气中的氡和氧气冷却至约100 ℃，然后将空气中的氡和氧气冷却至约100 ℃，再将空气中的氡和氧气冷却至约100 ℃，然后将空气中的氡和氧气冷却至约100 ℃，再将空气中<222><222>的氡和氧气冷却至约100 ℃，最后将空气中的氡和氧气冷却至约100 ℃，再将空气中的氡和氧气冷却至约100 ℃，最后将空气中的氡和氧气冷却至约100 ℃。195.82℃，使用氮气液化装置。因此，浓缩的环境^<222>Rn与氮一起收集，并且通过该方法容易地测量。

Air luminescence method has been applied for the determination of ^<222>Rn and the daughter nuclides. In order to improve light collection, the two photo-multiplier tubes (PMTs) were enclosed in a light-tight chamber and covered with reflectors. The pulses from the PMTs were fed into an amplifier, a coincidence circuit, a 1024-channel pulse height analyzer. Discrimination between noise pulses and pulses from real luminescence events was satisfactory.The counting efficiency of this system using a standard alpha-emitting nuclide (^<241>Am) and known amounts of ^<222>Rn was found to be 2.4 and 7.38%, respectively. This difference in counting efficiencies may be attributed to the fact that ^<222>Rn is accompanied by two short-lived alpha-emitting daughter nuclides (^<218>Po, ^<214>Po).Luminescence observed in this study is attributed to the ionization and excitation of nitrogen and oxygen caused by the passage of alpha-particles in air. Therefore, the counting efficiency for nitrogen luminescence and oxygen luminescence was also measured using a liquid scintillation system and found to be 60.2 and 28.2%, respectively.Based on the relatively high counting efficiency of nitrogen luminescence, an effective method for sampling environmental ^<222>Rn in air was developed : After removal of CO_2 and O_2 from air, ^<222>Rn and nitrogen gas in air was cooled to ca.-195.82℃ using an apparatus for liquefaction of nitrogen gas. Thus, concentrated environmental ^<222>Rn was collected together with nitrogen and easily measured by this method.