The asymmetry parameter, $A_{\beta }$, in the positron decay of polarized ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$ has been measured to be +0.341±0.013. Assuming the standard $T$-invariant $V-A$ 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±0.008. The vanishing value of $y$ is consistent with the isospin selection rule for the Fermi matrix element.

RADIOACTIVITY ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$; measured $\beta \left(\theta \right)$, $\gamma \left(\theta \right)$; deduced source $P$, $\beta$ asymmetry coefficient, Fermi to Gamow-Teller mixing ratio.

• Received 16 February 1983

DOI:https://doi.org/10.1103/PhysRevC.28.345