Beta-Gamma Directional Correlation inRb86andEu152

Measurements are reported on the energy dependence of the beta-gamma angular correlation coefficient in the special first forbidden cases of ${\mathrm{Rb}}^{86}$ and ${\mathrm{Eu}}^{152}$. Energy selection of the beta rays was accomplished with a magnetic beta-ray spectrometer having good transmission. It is shown that ${\mathrm{Rb}}^{86}$ cannot be analyzed in terms of the so-called modified $B_{\mathrm{ij}}$ approximation. The ${\mathrm{Eu}}^{152}$ decay, on the other hand, can be treated quite satisfactorily in this approximation. It is concluded in this case that a strong selection-rule effect is operative to suppress certain of the matrix elements relative to $B_{\mathrm{ij}}$. The nuclear parameter $Y$ (Kotani's notation) is found to be 0.69±0.06. This agrees well with the value which results from the measured spectrum shape factor.