Precision half-life measurement of the 4-fold forbidden electron capture of V-50

Abstract

A sensitive search of the 4-fold forbidden non-unique beta decay of V-50 has been performed. A total exposure of 185.8 kg x d has been accumulated. A reliable half-life value with the highest precision so far of $(2.29 \pm 0.25) \cdot 10^{17}$ years of the electron capture decay of V-50 into the first excited state of Ti-50 could be obtained. A photon emission line following the 4-fold forbidden beta decay into the first excited state of Cr-50 could not be observed, resulting in a lower limit on the half-life of the beta decay branch of $1.7 \cdot 10^{18}$ years. This is barely in agreement with a claimed observation of this decay branch.