Isospin-symmetry-hindered branch of ^(42)Sc β-decay

Abstract

The branching fraction for the isospin-symmetry-hindered positron decay of ^(42)Sc to ^(42)Ca (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 ^(42)Sc sources were produced by the ^(42)Ca(p, n)^(42)Sc 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.

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