STUDY OF OPERATION CHARACTERISTICS OF LIQUID XENON PHOTOIONIZATION DETECTORS

稀有气体液体作为辐射探测器具有良好的电离和闪烁性能。已经证明，当电离和闪烁同时使用时，这些探测器可以是很好的探测器。光电离是其中的一种方法。在这种方法中，稀有气体液体分子中的光子被掺杂的有机分子吸收并电离。因此，闪烁被转化为电离。光电离探测器的一个重要特性就是时间稳定性，我们在本研究中测量了掺烯液态Ar的时间稳定性，并测量了超过60小时的稳定性。收费量随时间变化。虽然绝对电荷减少，但逐渐收集的电荷随着时间的变化而变化。绝对电荷量虽然减少，但逐渐接近纯液态Ar的电荷量，不会降低到低于这个水平。这意味着丙二烯的浓度随着时间的推移而降低。对漂移电子衰减长度的测量表明，电负性杂质的浓度也有所降低。研究发现，在三甲胺(TMA)掺杂的液体中，不需要的电负性杂质与TMA一起被引入到液体中。这可以通过在低温AS-110ﾟC下提纯甲基丙烯酸甲酯和在该温度下操作检测器来避免。实验结果表明，该稀有气液电离探测器能够稳定地工作。

Rare gas liquids have good properties both for ionization and scintillation as radiation detectors. It has been shown that these can be excellent detectors when ionization and scintillation are simultaneously utilized. Photoionization is one of the methods. In this method, photons from rare gas liquid molecules are absorbed by doped organic molecule and ionized the molecule. Thus scintillation is converted to ionization. One of important characteristics of the photoionization detectors is time stability, which we measured in this study.We measured the stability of allene doped liquid argon for more than 60 hours. Amount of collected charge varied with time. Although the absolute charge decreases, it gradually collected charge varied with time. Although the absolute charge decreases, it gradually approachs to the charge amount of pure liquid argon and does not reduce to less than the level. This means that the concentration of allene decreases with time. Measurement of attenuation length of drifting electrons showed concentration of electronegative impurity also decreases. As a results, effective abount of mixed molecules, whether it is desired or undesired, decreases with time.It was found that, in trimethylamine (TMA) doped liquid, xenon, undesired electronegative impurity was introduced together with TMA to the liquid. This can be avoided by purify TMA at low temperature as -110ﾟC and operating detectors also at the temperature. In this way, the collected charge of TMA doped liquid xenon does not change for more than 50 hours.In conclusion, it has been shown that rare gas liquid ionization detectors can be opetated stably.