^(79)Se的AMS测量方法研究

Study on AMS Measurement of ^(79)Se

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80 Se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。

As there is no 79 Se standard sample for measurement of 79 Se, the characteriza- tions of r9Se are conducted by isotope ratio of 78Se/Se or 8＋Se/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, attenua tors were introduced into the CIAE-AMS system with the aim to measure the 79 Se. The results indicate that the beam of 78Se and 89Se 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.