The $\beta -\gamma$ angular correlation for the decay of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ has been measured using a symmetric four detector system. The ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ activity was produced by the ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}\mathrm{}(p,n)\mathrm{}{}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$ reaction and transported by a He jet to the detector chamber. Care was exercised to ensure that the $\beta$ source was well defined. Correlation data were acquired for ${\theta }_{\beta -\gamma }=90\mathrm{}° \mathrm{and} 180°$ as a function of positron energy. The correlation data were analyzed for both linear and quadratic energy dependence. We report as the best estimate for the linear coefficient (- 5.0 ± 0.8) × ${10}^{-3\mathrm{}}$ ${\mathrm{MeV}}^{-1\mathrm{}}$ and for the quadratic coefficient (2.9 ± 0.8) × ${10}^{-4\mathrm{}}$ ${\mathrm{MeV}}^{-2\mathrm{}}$. Incorporating the results with other measurements in the $A=20\mathrm{}$ system, we find an upper limit for the second class current contribution to the correlation which is no more than 20% of the weak magnetism contribution and is consistent with zero.

NUCLEAR REACTIONS Radioactivity ${}_{}{}^{20}{}_{}{}^{}\mathrm{Na}$; measured $\beta -\gamma$ angular correlation. Determined induced weak currents.

• Received 19 November 1980

DOI:https://doi.org/10.1103/PhysRevC.23.2245