79Se的AMS测量方法研究

测定⁷⁹Se时由于⁷⁹Se尚无标准样品，需要建立⁷⁹Se/Se（⁷⁹Se、Se原子个数比，余同）的AMS测量方法。在⁷⁹Se/Se的绝对测定中，为尽可能避免测量Se的同位素之间的差异，通常利用探测器测量⁷⁹Se离子，本文用法拉第筒对⁷⁸Se和⁸⁰Se进行测量，但这造成两个测量系统之间的系统误差。为避免这种系统误差，利用同一探测器测定⁷⁹Se、⁷⁸Se和⁸⁰Se。考虑到⁷⁸Se和⁸⁰Se的计数率非常高，在CIAE-AMS系统中的静电分析器前和靶室内安装衰减片以降低⁷⁸Se和⁸⁰Se的计数率。实验结果表明：通过两个衰减片的衰减作用，能将⁷⁸Se和⁸⁰Se的束流降低到半导体探测器的检测范围内，实现了样品中⁷⁹Se/Se的绝对测定，得到⁷⁹Se/Se为(2.08±0.10)×10^-7，为准确测定⁷⁹Se半衰期奠定了基础。

Study on AMS Measurement of 79Se

As there is no ⁷⁹Se standard sample for measurement of ⁷⁹Se, the characterizations of ⁷⁹Se are conducted by isotope ratio of ⁷⁸Se/Se or ⁸⁰Se/Se since the abundances of ⁷⁸Se and ⁸⁰Se are well known. However, beams of ⁷⁸Se and ⁸⁰Se both exceed the upper limit of semiconductor detector resulting in measurement failure. As a result, attenuators were introduced into the CIAE AMS system with the aim to measure the ⁷⁹Se. The results indicate that the beam of ⁷⁸Se and ⁸⁰Se is decreased into the detecting range of semiconductor detector by two attenuators, which would improve measurement sensitivity and efficiency significantly. In addition, the uncertainty of measurement is reduced greatly and it lays the foundation for the accuracy measurement of the half life of ⁷⁹Se.