暗物质寻找实验中CsI(Tl)晶体反符合探测器实验研究

一个正在建设的位于韩国Y2L地下实验室的低能暗物质探测实验中, 采用了CsI(Tl)晶体反符合探测器作为主动屏蔽体. 本工作对CsI(Tl)晶体反符合探测器的实验性能进行了研究. 通过FADC系统记录的脉冲波形数据, 研究了探测器的能量分辨率和波形甄别的能力; 研究相同能量γ射线入射到反符合探测器不同位置的相对光输出将有助于选择探测器的工作参数; 为了解晶体自身放射性对暗物质测量的影响, 利用低本底HPGe探测器对CsI(Tl)晶体内部的放射性进行了测量, 得到晶体内部Cs同位素的放射性活度. 探测器系统进行了约18d的试运行取数. 实验数据表明, CsI(Tl)晶体探测器的反符合效率约为31% HPGe探测器的本底计数率水平约为133cpd. 为了进行暗物质探测研究, 需要采取有效的方法进一步降低探测器的本底水平.

Experimental Study on the CsI(Tl) Crystal Anti-Compton Detector for Dark Matter Search

A dark matter search experiment is being carried out with ultra-low energy HPGe detector at Y2L underground laboratory in Korea. Before the system was set up, the active shielding, CsI(Tl) anti-Compton detector, was studied for its performance. By using some radioactive source and recorded data with an FADC, the pulse shape was studied to get a better energy resolution and further PSD method application. The relative light output of crystal at different particle incident positions were compared for setting the threshold for CsI(Tl) detector. The internal background of the crystal was measured with an HPGe detector and the content of 137Cs and 134Cs isotopes were obtained. An about 18-day test run has been finished and the veto efficiency of CsI crystal anti-Compton detector is about 31% and the event rate of background spectrum of HPGe detector is about 133cpd. Further methods have to be explored to suppress the background level.