The branching ratio in the decay of 7Be

Abstract

A measurement of the branching ratio for electron capture (EC) decay of 7Be to the 478-keV level in 7Li is reported. The reaction 10B(p, α)7Be was used and the 7Be recoils were detected and stopped in a particle detector thin enough to transmit the protons. The absolute γ-ray emission rate of 478-keV γ rays from the implanted detector was determined with a well-shielded intrinsic Ge detector. The absolute efficiency of the Ge detector was established with 22Na, 137Cs, and 88Y standard sources. A value of 11.4 ± 0.7% was obtained for the EC branch to the 478-keV state. Calculations suggest that the axial vector coupling constant GA must be reduced by a factor of 0.94 ± 0.02 to obtain agreement with the experimental result.