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

Abstract

Beta-gamma directional correlations of several first-forbidden $\beta$ transitions leading to second excited states of even-even nuclei (${\beta }_2$ transitions) have been studied. The energy-dependence of the $\beta$ directional correlation factor $A_2\left(\beta \right)$ in the $\beta -\gamma$ correlation function $W\left(\theta \right)=1+A_2\left(\beta \right)A_2\left(\gamma \right)P_2\left(cos\theta \right)$ has been measured for the ${\beta }_2$ transitions of ${\mathrm{As}}^{76}$, ${\mathrm{Sb}}^{122}$, ${\mathrm{I}}^{126}$, ${\mathrm{Sb}}^{124}$, and ${\mathrm{La}}^{140}$, and the reduced $\beta$ coefficient $R_2\mathrm{}\left(W\right)=\frac{A_2\left(\beta \right)}{\left(\frac{{\lambda }_2{p}^2}{W}\right)}$ was determined. In all cases $R_2\mathrm{}\left(W\right)\mathrm{}$ was found to be very different from $R_1\mathrm{}\left(W\right)\mathrm{}$, the reduced $\beta$ factor describing the ${\beta }_1$ transition to the first excited state of the daughter nucleus. The results indicate that the relative magnitudes of the nuclear $\beta$-matrix elements in the ${\beta }_1$ transition and in the ${\beta }_2$ 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.