The quenching effects of nuclear and $\Delta$ excitations on the $\beta$ decay of ${}_{}{}^{40}{}_{}{}^{}\mathrm{K}$ are examined. It is found that although configuration mixing still provides the largest retardation, the inclusion of isobar-hole excitation is necessary to bring the calculation within calling distance of the experimental decay rate.

RADIOACTIVITY ${}_{}{}^{40}{}_{}{}^{}\mathrm{K}$(${\beta }^{-}$)${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. Shell model calculation including isobar-hole excitations.

• Received 2 November 1981

DOI:https://doi.org/10.1103/PhysRevC.25.2148