Energy-Dependent Beta-Gamma Circular Polarization and Nuclear Matrix Elements ofRb86

The energy-dependent $\beta -\gamma$ circular polarization was measured in order to set better limits on the matrix-element ratio $\Lambda =\int \frac{\overrightarrow{\alpha }}{\left(\int \frac{i\overrightarrow{\mathrm{r}}}{\rho }\right)}$ for the 696-keV first-forbidden $\beta$ transition of ${\mathrm{Rb}}^{86}$. The results show that $\Lambda$ is consistent with the Fujita-Eichler relation, so the contributions of the off-diagonal matrix elements of the Coulomb Hamiltonian to $\Lambda$ are small for this transition. The nuclear matrix elements are in agreement with previous results, but the limits of error have been reduced.