Internal γ decay and the superallowed branching ratio for the β+ emitter Km38

Abstract

The branching ratio for the superallowed β+ decay of Km38 was measured at TRIUMF's ISAC radioactive ion beam facility. The M3 internal transition between the isomer and the ground state of Km38 was observed with a branching ratio of 330(43)ppm. A search for the nonanalogue β-decay branch to the first excited 0+ state in Ar38 was also performed and yielded an upper limit of ≤12ppm at 90%C.L. These measurements lead to a revised superallowed branching ratio for Km38 of 99.967(4)%, and increase the Km38 ft value by its entire quoted uncertainty to ft=3052.1(10)s. Implications for tests of the nuclear-structure dependent corrections in superallowed β decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element Vud are discussed. © 2008 The American Physical Society.