Precision half-life measurement of the 4-fold forbiddenβdecay ofV50

Abstract

A sensitive search of the 4-fold forbidden nonunique decay of 50 V 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) × 10 17 years of the electron capture decay of 50 V into the first excited state of 50 Ti could be obtained. A photon emission line following the β decay into the first excited state of 50 Cr could not be observed, resulting in a lower limit on the half-life of the β-decay branch of 1.7 × 10 18 years. This is not in good agreement with a claimed observation of this decay branch published in 1989.

New investigation of half-lives for the decay modes of V50

“…This result is about one order of magnitude better than the one in [27] and approaches the theoretical prediction of 2 × 10 19 yr in [28]. The obtained improvement is due to a factor of 7.9 more exposure and a factor of 3.2 lower background level.…”

“…I. A first clear observation of the EC-branch decay to 50 Ti has been reported by [27]. In the meantime a first theoretical nuclear shell model calculation has been performed for the β − -decay mode which predicts a half-life value of about 2 × 10 19 yr [28].…”

Experimental searches for rare alpha and beta decays

“…While low temperature scintillating bolometers look like a good technique to investigate α and β decays to the ground states of daughter nuclei, HPGe γ spectrometry is a favorable technique to study the α and β decays to excited levels owing to their excellent energy resolution, the low background achieved with the HPGe technique, and the possibility of long time operation (see the review [289] and the original works [256,81,231]).…”

New Half-life Results On Very Long-living Nuclei

“…while the beta-decay into the Cr-50 branch resulted in a lower limit of T 1/2 > 1.5 × 10 18 years [8]. This triggered some shell model calculations to predict the missing half-live.…”