低本底反康普顿γ谱仪分析谷物中放射性核素  

Low Background Anti-Compton Gamma-ray Spectrometer for Measurement of Radioactivity in Cereal Crops

作　　者：张佳媚[1] 许启初[1] 门蒙 

机构地区：[1]西北核技术研究所,西安710024 [2]陕西省辐射环境监督管理站,西安710048

出　　处：《核电子学与探测技术》2009年第6期1461-1465,1474,共6页Nuclear Electronics & Detection Technology

摘　　要：通过比较低本底反康普顿HPGeγ谱仪两种操作模式(有反康和无反康)测量4种谷物样品中放射性活度的异同,讨论反康普顿抑制的优越性。结果显示,有反康时能谱中的康普顿基线本底有显著抑制,从低能区的2倍至高能区的5倍(60keV^1.46M eV)不等。但对特定核素的分析探测限不仅与康普顿本底有关,还与系统自身可能存在的特定能峰的本底净计数率有关。由于无137Cs系统本底且反康抑制达4~5倍,测到4个样品中137Cs比活度在0.03~0.06Bq/kg,而如没有反康则都低于探测限。由于系统中本底几乎可以忽略,234Th探测限(0.2~0.4Bq/kg,对63keV)和228Ac探测限(~0.1Bq/kg,对911keV)有反康时下降了20%~30%。由于测量期间的高氡环境本底,226Ra(测214Pb352keV峰)探测限有点高(0.7~1Bq/kg),反康未起作用。样品中的40K高达22~144Bq/kg。By contrasting two operation modes （with and without Anti-Compton） of a low Background gamma-ray spectrometer for radioactivity measurement of four cereal crop samples, the effect of Compton-suppression is diseussed It shows that the Compton background continuum is reduced remarkably about 2 to 5 times from low energy region to high energy region （60keV-1. 46MeV） with Anti-Compton. However, the lower limits of detection （LLD） for different nuclides are depend on not only Compton baselines but also net counting rates for specific （ peaks which maybe come from the detector system itself. Thanks to no background and with Compton suppression factor of 4 - 5, 137Cs are detected to between 0. 03-0. 06Bq/kg in four samples, while they are all below the LLDs if without Anti-Compton. The LLDs of Z34Th （0. 2-0. 4Bq/kg, by 63keV） and 228Ac （n0. 1Bq/kg, by 911keV） with backgrounds are almost negligible are decreased 20%-30% by Compton suppression. Due to the high level of Radon in environment during the time of measurment, anti-Compton has no effect to improve the LLDs for measuring 236Ra （by 352keV of 214Pb） which are somewhat high （0. 7-1Bq/kg）. 40K in four samples is high to 22-144Bq/kg.

关 键 词：反康普顿γ谱仪 谷物 探测限 

分 类 号：TL817.2[核科学技术—核技术及应用]