Study of Second Excited2+States of Some Even-Even Nuclei by Beta-Gamma Angular Correlations

Abstract

Beta-gamma directional correlations of several first-forbidden $\ensuremath{\beta}$ transitions leading to second excited states of even-even nuclei (${\ensuremath{\beta}}_{2}$ transitions) have been studied. The energy-dependence of the $\ensuremath{\beta}$ directional correlation factor ${A}_{2}(\ensuremath{\beta})$ in the $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ correlation function $W(\ensuremath{\theta})=1+{A}_{2}(\ensuremath{\beta}){A}_{2}(\ensuremath{\gamma}){P}_{2}(cos\ensuremath{\theta})$ has been measured for the ${\ensuremath{\beta}}_{2}$ transitions of ${\mathrm{As}}^{76}$, ${\mathrm{Sb}}^{122}$, ${\mathrm{I}}^{126}$, ${\mathrm{Sb}}^{124}$, and ${\mathrm{La}}^{140}$, and the reduced $\ensuremath{\beta}$ coefficient ${R}_{2}(W)=\frac{{A}_{2}(\ensuremath{\beta})}{(\frac{{\ensuremath{\lambda}}_{2}{p}^{2}}{W})}$ was determined. In all cases ${R}_{2}(W)$ was found to be very different from ${R}_{1}(W)$, the reduced $\ensuremath{\beta}$ factor describing the ${\ensuremath{\beta}}_{1}$ transition to the first excited state of the daughter nucleus. The results indicate that the relative magnitudes of the nuclear $\ensuremath{\beta}$-matrix elements in the ${\ensuremath{\beta}}_{1}$ transition and in the ${\ensuremath{\beta}}_{2}$ transition are significantly different, although the $\mathrm{ft}$ values are very similar. The implication of these experimental results for the structure of first and second excited states of even-even spherical nuclei is discussed.