Beta-Gamma Directional Correlation inRe186

Abstract

The directional correlation between the nonunique first forbidden 934-kev beta group and the 137-kev $E2$ gamma transition in the decay of ${\mathrm{Re}}^{186}$ has been measured as a function of beta energy above 150-kev. Analysis of the experimental data included a correction for the finite energy resolution of the anthracene crystal scintillation spectrometer, which takes into account the effect of the backscattering of electrons from the crystal. The differential anisotropy increases with increasing beta energy to 0.158\ifmmode\pm\else\textpm\fi{}0.006. The directional correlation $W(\ensuremath{\theta})=1+(0.105\ifmmode\pm\else\textpm\fi{}0.003){cos}^{2}\ensuremath{\theta}$ for beta energies of 257-934 kev, with no evidence for a ${cos}^{4}\ensuremath{\theta}$ term, in agreement with theoretical expectation for a first forbidden beta transition.Limited ranges for the ratios of the nuclear matrix elements governing the beta decay were obtained by comparison with theory, assuming the following: the spin and parity sequence (1-, 2+, 0+); the beta interaction mixture scalar plus tensor; point nuclear charge. Higher order terms in $\frac{2\ensuremath{\rho}}{\ensuremath{\alpha}Z}$ were included.