Remeasurement of the Half-Life of 79 Se with the Projectile X-Ray Detection Method

Remeasurement of the half-life of 79 Se has been carried out with projectile x-ray detection (PXD) in accelerator mass spectrometry. We made two major improvements over our earlier 79 Se half-life determination [ Nucl. Instrum. Methods B 123 (1997) 403]. Firstly, the PXD technique has been used for separation of 79 Se and 75 Se from 79 Br and 75 As isobars respectively. Secondly, the half-life of 79 Se has been measured relative to the known precise half-life of 75 Se(119.79±0.04 d). A more reliable half-life of 79 Se measured with the PXD technique is (2.95±0.38)×10 5 y, about a factor of one third lower than the previous value, 1.1 × 10 6 y. The problems in the previous measurement are discussed.