基于极低本底γ谱分析的海水直接测量研究

为实现便捷、灵敏的海水放射性测量,建立了基于中国锦屏地下实验室低本底高纯锗γ谱仪GeTHU的海水直接测量方法。使用GeTHU直接测量了分别来自西太平洋及上海、青岛、厦门近岸海域的4个体积均接近8.8 L的海水样品,约18小时的直接测量能够探测到⁴⁰K及来自²³⁸U、²³²Th天然放射系的一些关键放射性核素。基于GeTHU的直接测量方法对人工放射性核素同样具有较好的灵敏度,⁵⁷Co、¹³¹I、¹³⁴Cs、¹³⁷Cs的最小可探测活度浓度经过12小时的测量可以降低到25 mBq/L以下,其中¹³⁷Cs的最小可探测活度浓度在48小时的测量后可以达到约8.6 mBq/L。GeTHU将会被持续用于海水放射性的直接测量,尤其是用于需要测量大量样品的紧急监测任务。

Study on direct seawater measurement by ultra-low background gamma spectrometry

In order to realize the convenient and sensitive measurement of radioactivity in seawater, the direct measurement method is established based on the low background HPGe gamma spectrometer GeTHU in China Jinping underground Laboratory (CJPL). 4 nearly 8.8 L seawater samples from the western Pacific Ocean and the coastal waters of Shanghai City, Qingdao City, Xiamen City respectively are directly measured by GeTHU, and the 18-hour measurement can detect ⁴⁰K as well as some key radionuclides from the ²³⁸U and ²³²Th decay chains. The method with GeTHU also shows an excellent sensitivity to artificial radionuclides. The MDACs for ⁵⁷Co, ¹³¹I, ¹³⁴Cs and ¹³⁷Cs can drop below 25 mBq/L after 12 hours and the MDAC for ¹³⁷Cs is ~8.6 mBq/L after 48 hours. GeTHU will be continuously dedicated in direct measurements of radioactivity in seawater, especially for the urgent monitoring task with massive samples.