Nuclear Structure Properties and Stellar Weak Rates for 76Se: Unblocking of the Gamow Teller Strength

Abstract

At finite temperatures ($\geq 10^7$K), $^{76}$Se is abundant in the core of massive stars and electron capture on $^{76}$Se has a consequential role to play in the dynamics of core collapse. The present work may be classified into two main categories. In the first phase, we study the nuclear structure properties of $^{76}$Se using the interacting boson model-1 (IBM-1). The IBM-1 investigations include the energy levels, $B(E2)$ values, and the prediction of the geometry. We performed the extended consistent-Q formalism (ECQF) calculation and later the triaxial formalism calculation (constructed by adding the cubic term to the ECQF). The geometry of $^{76}$Se can be envisioned within the formalism of the potential energy surface based on the classical limit of the IBM-1 model. In the second phase, we reconfirm the unblocking of the Gamow-Teller (GT) strength in $^{76}$Se (a test case for nuclei having $N > 40$ and $Z < 40$). Using the deformed pn-QRPA model, we calculate GT transitions, stellar electron capture cross section (within the limit of low momentum transfer), and stellar weak rates for $^{76}$Se. The distinguishing feature of our calculation is a state-by-state evaluation of stellar weak rates in a fully microscopic fashion. Results are compared with experimental data and previous calculations. The calculated GT distribution fulfills the Ikeda sum rule. Rates for $\beta$-delayed neutrons and emission probabilities are also calculated. Our study suggests that at high stellar temperatures and low densities, the $\beta^+$-decay on $^{76}$Se should not be neglected and needs to be taken into consideration along with electron capture rates for simulation of presupernova evolution of massive stars.