Beta-Gamma Directional Correlation in the Decay ofEu154

Abstract

The directional correlation for the (1855 kev-beta) (123 kev-gamma) cascade in the decay of ${\mathrm{Eu}}^{154}$ has been measured. The directional correlation coefficient $A_2$ varies from -0.15 at a beta energy of 1100 kev to -0.18 at a beta energy of 1600 kev. In terms of a single nuclear matrix element parameter, ${\zeta }_1$, the directional correlation suggests ${\zeta }_1=2.6\mathrm{} or -0.2\mathrm{}$ while the beta spectral shape correction suggests ${\zeta }_1=1.3\mathrm{}$. The results suggest that the attenuation of ordinary first-forbidden matrix elements relative to $B_{\mathrm{ij}}$ is less marked in ${\mathrm{Eu}}^{154}$ than in the comparable transition in ${\mathrm{Eu}}^{152}$. Interpretation of the data in terms of a less restrictive formulation of the theory is investigated. Relations between matrix element ratios may be found but no unique set of matrix element ratios is demanded by the experimental data.