Decay of Rhenium-187

Abstract

The end-point energy for $^{187}\mathrm{Re}$ has been determined to be 2.62\ifmmode\pm\else\textpm\fi{}0.09 keV by use of ${({\mathrm{C}}_{5}{\mathrm{H}}_{5})}_{2}$ReH vapor in a proportional-counter spectrometer. The $^{187}\mathrm{Re}$ half-life determined from the proportional-counting experiments is (6.6\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}${10}^{10}$ year. This is identified as the ${\ensuremath{\beta}}^{\ensuremath{-}}$ half-life for decay to continuum states only. When this is combined with the total half-life of (4.3\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{10}$ year obtained from $^{187}\mathrm{Re}$/$^{187}\mathrm{Os}$ ratios in geologically dated minerals, the ratio of bound-state to continuum-state decays is found to be 0.5\ifmmode\pm\else\textpm\fi{}0.3.