Abstract： Accelerator mass spectrometry （AMS） measurement of 59Ni has been HI-13 tandem accelerator and the recently developed AE-Q3D detection system established at CIAE with the 59Ni standard and commercial NiO samples were measured to check the performance of the △E-Q3D detection system on 59Ni isobar separation and suppression. An overall suppression factor of about 107 for the interfering isobar 59Co resulting in detection sensitivity as low as 3.8×10-13 atomic ratio （59Ni/Ni） has been obtained. Based on these techniques, the AMS measurement method of 59Ni with high sensitivity is developed.
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 SeO-2molecular 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^-7in 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）×10^5a.
