Preparation of radiochemically pure 79Se and highly precise determination of its half-life

Reliable knowledge of the 79Se half-life is crucial, e.g. for the safety assessments of final repositories for nuclear waste. However, a literature survey reveals an inconsistent picture, indicating remarkably difficult experimental conditions. This work reports a new value of 3.27(8)×105 a for the half-life of 79Se. The uncertainty is less than half of the latest published result. The sample was prepared radiochemically pure from a reprocessing solution by exploitation of reductive deposition on Cu, anion exchange chromatography and sublimation. The specific activity was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and liquid scintillation counting (LSC). Hydride generation multicollector inductively coupled plasma mass spectrometry (HG-MC-ICP-MS) was applied for the establishment of the isotopic composition.