摘要
放射性氙的4种同位素131 Xem、133 Xe、133 Xem和135 Xe是地下核试验最重要的示踪气体,是目前CTBTO全球监测系统监测的主要核素。本文设计并研制了一种针对低水平放射性氙测量的叠层闪烁探测器,可实现放射性氙4种同位素的β-γ符合测量,简化了探测器结构。利用MCNP5工具包模拟了两种结构的探测器,获得了β闪烁层的最佳厚度,1.5mm厚塑料闪烁体BC404几乎完全屏蔽4种氙同位素的β信号,135 Xe的910keV特征β射线仅0.8%沉积在γ闪烁层CsI(Tl)中,而对133 Xe的81keV特征γ射线吸收低于6.5%;观察到明显的氙气样品自吸收效应,氙气气压由0.1 MPa增加到0.25 MPa时,氙气对133 Xe的346keVβ射线吸收增加45.6%。基于模拟结构设计,研制了用于放射性氙测量的叠层闪烁探测器,初步实验结果表明叠层闪烁探测器能有效抑制本底计数,抑制因子约96.4±1.0。
Several isotopes of xenon are sufficiently produced in fission and a few of them have suitable half‐lives and radiation to be detected .These are ^131Xem ,^133Xe , ^133Xem and ^135Xe and they have been selected for continuous monitoring in CTBTO inter‐national monitoring system .Employing the phoswich technology with β‐γ coincidence counting capability accompanied by digital signal processing of PM T pulse ,the current coincidence detectors were simplified . The radiation transport simulations were performed using MCNP toolkit to determine the optimum design and estimate the detection efficiency of the β and γ rays in phoswich detector .The results show that almost all of the beta particles deposite in plastic scintillator BC 404 as its thickness is set to 1.5 mm . The self‐absorption of radioxenon sample was also observed . The absorption of 346 keV β ray increases by 45.6% as the pressure from 0.1 M Pa to 0.25 MPa .The data acquisition and analysis system was developed as the phoswich detector for radioxenon detection was constructed recently . The preliminary experi‐ments demonstrate that the phoswich detector is efficient in reducing the background and the inhibiting factor is about 96.4 ± 1.0 .
出处
《原子能科学技术》
EI
CAS
CSCD
北大核心
2015年第3期552-559,共8页
Atomic Energy Science and Technology
