加速器质谱法测定超低钾污染物
Measurement of Ultra-Low Potassium Contaminations with Accelerator Mass Spectrometry
摘要：
在低本底实验中，有源探测器材料的痕量放射性纯度是一个主要关注的问题。在放射性同位素中，$\k40$是最丰富的同位素之一，但其特征很难被拒绝。设计了用加速器质谱法（AMS）测量无机盐CsI以及有机液体闪烁体（LS）中痕量钾浓度的程序，分别给出$\sim 10^{-10}$和$\sim 10^{-13}$ g/g的$\k40$ -污染水平。测量的灵活性和灵敏度比传统方法得到了提高。如果未观察到钾信号超过背景，CsI和LS的预计极限灵敏度分别为$8 \times 10^{-13}$ g/g和$3 \times 10^{-17}$ g/g。LS样品的研究表明，放射性污染主要来自染料溶质，而基础溶剂是几个数量级的清洁。这项工作证明了用AMS技术测量天然同位素的可能性。
英文摘要：
Levels of trace radiopurity in active detector materials is a subject of major concern in low-background experiments. Among the radio-isotopes, $\k40$ is one of the most abundant and yet whose signatures are difficult to reject. Procedures were devised to measure trace potassium concentrations in the inorganic salt CsI as well as in organic liquid scintillator (LS) with Accelerator Mass Spectrometry (AMS), giving, respectively, the $\k40$-contamination levels of $\sim 10^{-10}$ and $\sim 10^{-13}$ g/g. Measurement flexibilities and sensitivities are improved over conventional methods. The projected limiting sensitivities if no excess of potassium signals had been observed over background are $8 \times 10^{-13}$ g/g and $3 \times 10^{-17}$ g/g for the CsI and LS, respectively. Studies of the LS samples indicate that the radioactive contaminations come mainly in the dye solutes, while the base solvents are orders of magnitude cleaner. The work demonstrate the possibilities of measuring naturally-occurring isotopes with the AMS techniques.
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