Lawrence Berkeley National Laboratory Recent Work Title Measurement of the half-life of 79 Se with accelerator mass spectrometry Permalink

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 Se. The number of Se atoms was determined from measured Se/Se absolute ratios with the AMS system at the China Institute of Atomic Energy and the decay rate of Se 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 Se 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 Br background by as much as about five orders of magnitude. Also, an AMS measurement of the absolute ratio of Se/Se was developed to avoid systematic errors. The results show that Se/Se is (2.35±0.12)×10−7 in the reference sample and the radioactivity of Se is (1.24±0.05) Bq/g, so the half-life of Se is (2.78±0.18)×105 a.