New precise half-life measurement for the superallowed beta(+) emitter Ar-34

We have measured the half-life of Ar-34, the parent of a superallowed 0(+) -> 0(+) 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, Ar-34 -> Cl-34 and Cl-34 -> S-34, 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 Ar-34 beam into tape for 0.7 s, and then rapidly transported the collected source to a shielded 4 pi proportional gas counter, which detected the decay positrons from the combined decays of Ar-34 and its daughter Cl-34. The data were analyzed as a linked parent-daughter pair. Our new result replaces one we published 13 years ago.