高纯锗探测器制作和运输中产生的宇生放射性核素  

Cosmogenic radionuclides produced in high-purity germanium detectors during fabrication and transport

作　　者：张秋丽 张鹏[1] 景明坤 曾志[1] 马豪[1] ZHANG Qiuli;ZHANG Peng;JING Mingkun;ZENG Zhi;MA Hao(Department of Engineering Physics,Tsinghua University,Beijing 100084,China)

机构地区：[1]清华大学工程物理系,北京100084

出　　处：《清华大学学报（自然科学版）》2024年第1期146-154,共9页Journal of Tsinghua University(Science and Technology)

摘　　要：暗物质探测和寻找无中微子双β衰变(0υββ)等稀有事例实验是当前重要的基础前沿课题。高纯锗(HPGe)探测器具有极低本底,成为开展此类研究的重要设备。然而,探测器在制作和运输过程中会被宇宙射线活化,产生的长寿命宇生放射性核素对本底有长期贡献,会严重影响稀有事例实验的探测灵敏度。该文研究了一个新定制的高纯锗探测器在生产和运输中产生的宇生核素。该探测器在制作完成后立即运送到中国锦屏地下实验室(CJPL),而后在不同时间测量该探测器在屏蔽条件下的本底能谱。利用GEANT4 Monte Carlo程序模拟锗晶体内、外宇生核素的衰变能谱并计算了宇生核素的探测效率,最终通过能谱分析得到宇生核素的比活度,即锗晶体中^(57)Co:0.016 mBq/kg,^(58)Co:0.046 mBq/kg,^(54)Mn:0.012 mBq/kg;结构铜中^(57)Co:0.452 mBq/kg,^(58)Co:1.245 mBq/kg,^(54)Mn:0.382 mBq/kg,^(60)Co:0.389 mBq/kg。该结果有助于深入理解本底能谱的构成,同时该文计算宇生核素比活度的思路可以为使用高纯锗探测器开展稀有事例探测的宇生本底评估提供参考。[Objective]Currently,experiments searching for rare event,such as the interaction of weakly interacting massive particles or the nuclear double beta decay,are important frontier topics in fundamental physics.Due to the considerably low probability of nuclear processes,experiments require ultralow background conditions,particularly for all materials in detection systems.Low-level high-purity germanium(HPGe)gamma-ray spectrometer with an extremely low threshold,high energy resolution,and ultralow radioactive background is critical in material selection for rare event experiments.However,cosmogenic radionuclides contaminate the germanium crystals and other materials of detectors during fabrication,storage,and transport.Effective removal of long-lived radionuclides inside germanium crystals,such as 60Co and 54Mn,within a short period is difficult,which can be considerably problematic for achieving the required sensitivity and seriously affect rare event searches.The direct,experimental information regarding the quantification of cosmogenic activation yields is scarce since analyzing cosmogenic radionuclides requires tracing the entire process from detector material preparation to the implementation of experiments.Most simulation methods were considered to quantify the activation yields of the long-lived radioisotopes that were cosmogenically induced on the ground in germanium crystals and cupreous detector components,such as YIELDX,ACTIVIA,TALYA,and GEANT4.[Methods]Herein,the cosmogenic activation of a newly customized low-level HPGe gamma-ray spectrometer was experimentally investigated.The detector was stored in underground plants except during assembly and manufacture.Immediately after the fabrication,the detector was transported by rail to the China Jinping underground laboratory(CJPL)for background measurement.The cosmogenic activation of materials in the underground can be considered negligible because the flux of cosmic nucleons in the CJPL was suppressed at depths of a few kilometers of water equivalent.Backg

关 键 词：高纯锗(HPGe)探测器 宇生放射性核素 比活度 

分 类 号：O572.212[理学—粒子物理与原子核物理]