Time-differential $\beta -\gamma$ angular correlations perturbed by the nuclear quadrupole interaction in a zinc single crystal were used to extract a value of $y=+0.030\mathrm{}\pm 0.015$ for the ratio $\frac{C_V{M}_F}{C_A{M}_{\mathrm{GT}}}$ of Fermi to Gamow-Teller matrix elements in the allowed ${\beta }^{-}$ decay from the $\frac{5}{2^{+}}$ ${}_{}{}^{19}{}_{}{}^{}\mathrm{O}$ ground state to the $\frac{5}{2^{+}}$, 197 keV state in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$. This leads to a figure of $M_F=(4.7\mathrm{}\pm 2.4)\times {10}^{-3\mathrm{}}$ for the isospin-forbidden Fermi matrix element. Other parameters which can be derived from this number are $\alpha =(2.7\mathrm{}\pm 1.4)\times {10}^{-3\mathrm{}}$ for the admixture of the analog of the ${}_{}{}^{19}{}_{}{}^{}\mathrm{O}$ ground state in the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ excited state and $\left|H_{\mathrm{CD}}\right|=20\mathrm{}\pm 10$ keV for the effective charge-dependent matrix element. A value of ${\omega }_0=+8.5\mathrm{}\pm 0.5$ μ${\sec }^{-1\mathrm{}}$ was determined for the nuclear quadrupole interaction of the ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ excited state in a zinc single crystal. The calibration provided by the pure Gamow-Teller decay to the $\frac{3}{2^{+}}$ 1.554 keV state in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ was used to remove effects of the implantation process, and data analysis was performed with a model which incorporated the effects of $\beta \text{'}\mathrm{s}$ backscattered by the thick crystal.

RADIOACTIVITY ${}_{}{}^{19}{}_{}{}^{}\mathrm{O}$; measured $\beta -\gamma$ ($\theta$) in Zn single crystal; deduced allowed $\beta$ decay matrix element, isospin mixing in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ level, and ${\omega }_0$ sign for ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ level in Zn.

• Received 27 February 1978

DOI:https://doi.org/10.1103/PhysRevC.18.2333