Vanishing Fermi—Gamow-Teller mixing in the positron decay ofCo58

Abstract

The asymmetry parameter, ${A}_{\ensuremath{\beta}}$, in the positron decay of polarized $^{58}\mathrm{Co}$ has been measured to be +0.341\ifmmode\pm\else\textpm\fi{}0.013. Assuming the standard $T$-invariant $V\ensuremath{-}A$ weak interaction theory, the Fermi to Gamow-Teller mixing ratio, $y=\frac{{C}_{V}{M}_{\mathrm{F}}}{{C}_{A}{M}_{\mathrm{GT}}}$, was determined to be -0.005\ifmmode\pm\else\textpm\fi{}0.008. The vanishing value of $y$ is consistent with the isospin selection rule for the Fermi matrix element.RADIOACTIVITY $^{58}\mathrm{Co}$; measured $\ensuremath{\beta}(\ensuremath{\theta})$, $\ensuremath{\gamma}(\ensuremath{\theta})$; deduced source $P$, $\ensuremath{\beta}$ asymmetry coefficient, Fermi to Gamow-Teller mixing ratio.