New precise half-life measurement for the superallowed β+ emitter Ar34

Abstract

We have measured the half-life of $^{34}\mathrm{Ar}$, the parent of a superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ $\ensuremath{\beta}$ transition, to be 0.84646(35) s. With a precision of 0.04%, this result is an essential ingredient needed to complete a third pair of mirror superallowed transitions, $^{34}\mathrm{Ar}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{34}\mathrm{Cl}$ and $^{34}\mathrm{Cl}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{34}\mathrm{S}$, the ratio of whose $ft$ values would provide the most sensitive test yet of the isospin-symmetry-breaking corrections used to obtain ${V}_{ud}$. In a sequence repeated thousands of times, we implanted a very pure $^{34}\mathrm{Ar}$ beam into tape for 0.7 s, and then rapidly transported the collected source to a shielded $4\ensuremath{\pi}$ proportional gas counter, which detected the decay positrons from the combined decays of $^{34}\mathrm{Ar}$ and its daughter $^{34}\mathrm{Cl}$. The data were analyzed as a linked parent-daughter pair. Our new result replaces one we published 13 years ago.