Measurement of the half-life of79Se with accelerator mass spectrometry

Author(s): Dou, L; Jiang, S; Wang, XB; Dong, KJ; Wu, SY; Yang, XR; Wang, XM; Lan, XX; Xia, QL; He, M | Abstract: ©2014 Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd. The accelerator mass spectrometry (AMS) is an effective method for the determination of the half-life of long-lived radionuclides. In this paper, we report a method for measurement of the half-life of 79Se. The number of 79Se atoms was determined from measured 79Se/Se absolute ratios with the AMS system at the China Institute of Atomic Energy and the decay rate of 79Se was determined by counting the emitted β-rays with a liquid scintillation spectrometer. The major improvements of our measurements include using the high abundance of an 79Se sample which was cooled for many years to exclude the interference of short-lived nuclides, the extraction of SeO2- molecular ions, that results in a suppression of the 79Br background by as much as about five orders of magnitude. Also, an AMS measurement of the absolute ratio of 79Se/Se was developed to avoid systematic errors. The results show that 79Se/Se is (2.35±0.12)×10-7 in the reference sample and the radioactivity of 79Se is (1.24±0.05) Bq/g, so the half-life of 79Se is (2.78±0.18)×105 a.