Measurement of the 109Cd half-life

The half-life of 109Cd was measured by following the decay of sources from a radiochemically pure solution with two different measuring systems: an ionisation chamber and a high-purity germanium (HPGe) detector. The measurements were performed over a period of 3.6 years, i.e. about 2.8 half-lives of 109Cd. The resulting half-life values and detailed uncertainty budgets (k=1) are presented for both systems. The result obtained with the ionisation chamber, 462.36 (33) days, and the one obtained with the HPGe detector, 461.92 (76) days, are mutually consistent. The weighted mean of our measured values, T1/2(109Cd)=462.29 (30) days, is consistent with the currently recommended values of 461.4 (12) days ( Schönfeld and Dersch, 2004 and IAEA, 2007) and 462.0 (3) days (Xiaolong et al., 2010). From a set of selected experimental values published after 1970, a “partially weighted mean” (Pommé and Spasova, 2008) of T1/2(109Cd)=462.36 (39) days was calculated. More measurements are needed to resolve the discrepancies among literature data and to reduce the final uncertainty on the 109Cd half-life.