Fast-Neutron Spectroscopy in a Pool-Type Reactor with Activation Detectors

Measurement of the (54)Mn half-life

The half-life of (54)Mn was measured by following the decay of sources from a radiochemically pure solution using three different measuring systems: an ionisation chamber, a high-purity germanium (HPGe) detector and two 7.5 cm (diameter) × 7.5 cm (height) NaI(Tl) scintillation detectors in opposite position. The measurements were performed over a period of 3 years, i.e. about 3.5 half-lives of (54)Mn. The resulting half-life values and detailed uncertainty budgets are presented for the three measuring systems. The half-life obtained with the ionisation chamber, 312.32 (9) days, is consistent with but more precise than the ones obtained with the HPGe detector, 311.9 (5) days and the NaI(Tl) detectors, 311.9 (6) days, respectively. Our final half-life value of 312.32 (9) days is rather consistent with the currently recommended values of 312.29 (26) (IAEA, 2007) and 312.13 (3) days (Helmer and Schönfeld, 2004), even though the uncertainty of the latter may be underestimated. From a partially weighted mean (Pommé and Spasova, 2008) of selected experimental values published after 1970, a new best estimate of T(1/2)((54)Mn)=312.20 (8) days was calculated.