Precision half-life measurement of the 4-fold forbidden β decay of 50V

A sensitive search of the 4-fold forbidden nonunique decay of 50V has been performed. A total mass measuring time product of 186 kg d has been accumulated. A reliable half-life value with the highest precision so far of (2.29±0.25)x1017 years of the electron capture decay of 50V into the first excited state of 50Ti could be obtained. A photon emission line following the β decay into the first excited state of 50Cr could not be observed, resulting in a lower limit on the half-life of the β-decay branch of 1.7x1018 years. This is not in good agreement with a claimed observation of this decay branch published in 1989.