IAEA 2008年国际比对水体样品中总α/β放射性分析

Gross α/β Analysis of IAEA 2008 World-Wide Open Proficiency Test on Determination of Natural Radionuclides in Spiked Water

为了评估本实验室对环境样品中天然放射性核素的分析和测量技术,本实验室参加了IAEA2008年世界开放实验室国际比对磷石膏和水体样品天然放射性核素的分析测定活动。本工作主要针对水体样品中总α/β放射性活度的测量进行讨论。按照比对要求,应用比较测量法,以UO2(NO3)2和KCl分别作为总α和总β分析的亚基准物和基准物,采用MPC 9604超低本底α/β计数器分别测定了IAEA提供的Sample03、Sample04和Sample05三个水体样品中总α/β放射性活度。反馈结果表明,三个样品总α和总β的测量结果全部在IAEA给出的参考值范围之内,接受率为100%。此外,本工作还对测量中可能引起误差的几个主要因素诸如α/β计数器灵敏度的确定、基准物质的选择、测控曲线的绘制等方面进行了分析与讨论。测量结果表明,当选用UO2(NO3)2取代U3O8基准物作为总α分析的亚基准物时,由于本实验室所使用的UO2(NO3)2中238U与234U尚未达到久期平衡,故其总α放射性远小于国标GB 5750—85的推荐值,但通过α谱仪对238U和234U准确定量后,不影响总α的分析结果。

In order to evaluate the analysis and determination technique of naturally occurring radioisotopes in our lab for environmental samples,we participated in the IAEA 2008 world-wide open proficiency test on the determination of natural radionuclides in phosphogypsum and spiked water.This paper mainly focuses on the gross α/β analysis in spiked water.According to the requirement of IAEA,Sample03,Sample04 and Sample05 were tested for the gross α/β radioactivity.Comparative determination method was chosen,and UO2（NO3）2 and KCl were selected as sub-standard and standard reference substances for gross α analysis and gross β analysis,respectively,by determining radioactivity with MPC 9604 ultra low level α/β counter.The feedback statistics from IAEA final report show that the values of gross α/β of all of the three samples fell in the acceptable range of IAEA.The influence factors of gross α/β analysis such as the sensitivity of the α/β counter,the selection of standard reference substances and how to monitor the background and efficiency for daily determination and so on were also discussed.The results indicate that when one selected UO2（NO3）2 as sub-standard reference substance for gross α analysis,the total α activity of UO2（NO3）2 is much lower than that of standard U3O8 which is recommended by GB 5750—85,just because the 238U and 234U do not reach the secular equilibrium for our lab sub-standard UO2（NO3）2 reagent.But no effect of such UO2（NO3）2 on the analysis of gross α activity is observed after activity of 234U and 238U are qualitative measured by α spectrometry.