Beta-Gamma Directional Correlation Measurement inAs76

Abstract

The $\beta -\gamma$ directional correlation of the first forbidden nonunique $2^{-}$ → $2^{+}$ $\beta$ transition of ${\mathrm{As}}^{76}$ was measured at ten $\beta$ energies ranging from 1.33 to 2.18 MeV. The angular correlation coefficient $A_2\mathrm{}\left(W\right)\mathrm{}$ varies from 0.076±0.005 to 0.106±0.005 in this energy range. The modified $B_{\mathrm{ij}}$ approximation was used to investigate the structure of the first excited state in ${\mathrm{Se}}^{76}$. A configuration of either ${\left(f_{\frac{5}{2}}\right)}^{\pi }{\left(g_{\frac{9}{2}}\right)}^2$ or ${\left(f_{\frac{5}{2}}\right)}^4{\left(g_{\frac{9}{2}}\right)}^{\nu }$ is in agreement with the experimental data. In the first case the $g_{\frac{9}{2}}$ shell would have 2 neutrons with seniority 2, while an even number of $\pi$ protons with seniority 0 are in the $f_{\frac{5}{2}}$ shell. The other possibility would mean 4 protons in the $f_{\frac{5}{2}}$ shell with seniority 2 and an even number of $\nu$ neutrons with seniority 0 in the $g_{\frac{9}{2}}$ shell. The values $-4.2\mathrm{}<~V<~-3.2\mathrm{}$ and $-2.8\mathrm{}<~Y<~-2.2\mathrm{}$ for the nuclear matrix-element parameters are consistent with experimental data.