Double β decay of50Cr

Abstract

The intensity of positron annihilation radiation emitted by a sample of natural chromium trioxide, ${\mathrm{CrO}}_{3},$ containing 4.7 g of ${}^{50}\mathrm{Cr},$ was measured for 30 days. The background was measured with samples of iron, copper, and no sample at all (air), during a similar period of time. From the net intensity of the 511-keV line in the HpGe coincidence spectrum the partial half-life for the positron-electron capture double beta decay of ${}^{50}\mathrm{Cr},$ ${T}_{1/2}({\ensuremath{\beta}}^{+}EC,2\ensuremath{\nu}+0\ensuremath{\nu})=1.3(12)\ifmmode\times\else\texttimes\fi{}{10}^{18}\mathrm{yr}$ at the 95% CL was deduced. Alternatively, at 95% CL the effect may be considered absent, the resulting lower limit for this half-life of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{18}\mathrm{yr}$ now representing an order of magnitude improvement over the existing result.