Isospin-symmetry-hindered branch of 42Sc β-decay

Abstract

The branching fraction for the isospin-symmetry-hindered positron decay of 42Sc to 42Ca (1.837 MeV) was measured to be (6.3 ± 2.6) × 10 −5 by observation of delayed γ-rays. This branch alone corresponds to a reduction of the superallowed ground-state Fermi strength by (0.043 ± 0.018)%. The 42Sc sources were produced by the 42Ca(p, n) 42Sc reaction at 7.7 MeV.The measured branching agrees with Coulomb-mixing calculations by Rappleyea and Kunz and by Towner, but is smaller than other calculations.This result is of interest in connection with the intercomparison of the super-allowed 0 + → 0 + pure Fermi decays, which determine the effective vector coupling constant of nuclear β-decay.