低本底反康普顿γ谱仪分析谷物中放射性核素

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～1.46MeV)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~(137)Cs系统本底且反康抑制达4～5倍,测到4个样品中~(137)Cs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,~(234)Th探测限(0.2～0.4Bq/kg,对63keV)和~(228)Ac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,~(226)Ra(测~(214)Pb352keV峰)探测限有点高(0.7～1Bq/kg),反康未起作用.样品中的~(40)K高达22～144Bq/kg.

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

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 Comp-ton-suppression is discussed. It shows that the Compton background continuum is reduced remarkably a-bout 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 it-self. Thanks to no background and with Compton suppression factor of 4～5, ~(137)Cs are detected to be-tween 0. 03～0.06Bq/kg in four samples, while they are all below the LLDs if without Anti-Compton.The LLDs of ~(234)Th (0. 2～0.4Bq/kg, by 63keV) and ~(228)Ac (～0.1Bq/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 efect to improve the LLDs for measuring ~(226)Ra (by 352keV of ~(214)Pb) which are somewhat high (0. 7～1Bq/kg). ~(40)K in four samples is high to 22～144Bq/kg.