低放射性本底金属钛冶炼工艺研究  

Investigation of vacuum melting technique for low background titanium

作　　者：张涛 韩柯 刘江来 孟月 姚玉坤 王思广[3] 李渤渤 刘茵琪 裴腾 ZHANG Tao;HAN Ke;LIU Jianglai;MENG Yue;YAO Yukun;WANG Siguang;LI Bobo;LIU Yinqi;PEI Teng(Sichuan Research Institute,Shanghai Jiao Tong University,Chengdu 610213,China;School of Physics and Astronomy,Shanghai Jiao Tong University,Shanghai 200240,China;School of Physics,State Key Laboratory of Nuclear Physics and Technology and Center for High Energy Physics,Peking University,Beijing 100871,China;Luoyang Shuangrui Titanium Precision Casting Co.,Ltd.,Luoyang 471000,China)

机构地区：[1]上海交通大学四川研究院,成都610213 [2]上海交通大学物理与天文学院,上海200240 [3]北京大学物理学院核物理与核技术国家重点实验室,北京100871 [4]洛阳双瑞精铸钛业有限公司,洛阳471000

出　　处：《核技术》2022年第11期22-30,共9页Nuclear Techniques

基　　金：四川省科学技术厅杰出青年基金(No.2020JDJQ0077)资助。

摘　　要：以暗物质、无中微子双β衰变探测为代表的稀有事例实验所期望的信号极其稀少与微弱,从而对探测器所用材料的放射性本底要求十分苛刻。低本底控制是此类实验的核心工作之一。^(238)U、^(232)Th衰变链前端的^(226)Ra和^(228)Ra具有低沸点高蒸气压的特点,去除^(226)Ra与^(228)Ra就可以截断^(238)U衰变链,或者在一定时间内控制^(232)Th衰变链后端活度,从而降低对稀有事例实验有明显负面影响的核素含量,为探测器运行创造低本底环境。比较不同的冶炼设备,发现高温、高真空环境有助于K、Cs、Ra、Pb、Po、Rn等低沸点高蒸气压放射性杂质的挥发,冶炼试验结果说明,高温高真空冶炼有去除放射性核素的迹象。在真空电子束炉中冶炼的纯钛,^(232)Th-^(228)Ac可小于1.26 mBq∙kg^(−1),^(238)U-^(222)Rn可小于0.55 mBq∙kg^(−1),性能较为稳定,可用于下一代PandaX探测器。[Background]The expected signal rate of rare decay experiments,such as instance dark matter and neutrino less double beta decay experiments,is extremely low,which requires that the detector building materials have extremely low radioactivity.Low radioactive background control is one of the essential works in the rare decay experiments.^(226)Ra and^(228)Ra produced in the early decay chain of^(238)U and^(232)Th have low boiling point and high vapor pressure,removing the element Ra can break the^(238)U decay chain and keep a low radioactivity of^(232)Th-late for a long time.[Purpose]This study aims to investigate vacuum melting technique for low background titanium to reduce the impurity of isotopes that have negative impact on rare decay experiments and creating a low background environment for the detector running.[Methods]Firstly,the low background material samples were acquired by manual separation of radionuclides using physical and chemical methods.Then,radioactive impurity elements,such as K,Cs,Ra,Pb,Po and Rn with low boiling point and high vapor pressure,were volatilized in environment with high temperature and high vacuum level.Finally,radioactivity of these testing samples were measured by two sets of high-purity germaniumγspectrometer with measurement time extended to 7 days.[Results]Measurement results show signs of removal of radioactive isotopes by smelting-vacuum method,and the impurity in pure titanium smelted in vacuum electron beam furnace can reach the levels of(0.13±0.69)mBq∙kg^(−1)for^(232)Th-^(228)Ac,and(0.07±0.29)mBq∙kg^(−1)for^(238)U-^(222)Rn,respectively.[Conclusions]The smelting-vacuum method could provide reliable low background material for the container of the next generation PandaX detector.

关 键 词：低本底 稀有事例实验 暗物质 无中微子双β衰变 真空冶炼 

分 类 号：TL99[核科学技术—核技术及应用]