Gamow-Teller strength distributions at finite temperatures and electron capture in stellar environments

Abstract

We propose a new method to calculate stellar weak-interaction rates. It is based on the thermofield dynamics formalism and allows calculation of the weak-interaction response of nuclei at finite temperatures. The thermal evolution of the ${\mathrm{GT}}_{+}$ distributions is presented for the sample nuclei $^{54,56}\mathrm{Fe}$ and $^{76,78,80}\mathrm{Ge}$. For Ge we also calculate the strength distribution of first-forbidden transitions. We show that thermal effects shift the ${\mathrm{GT}}_{+}$ centroid to lower excitation energies and make possible negative- and low-energy transitions. In our model we demonstrate that the unblocking effect for ${\mathrm{GT}}_{+}$ transitions in neutron-rich nuclei is sensitive to increasing temperature. The results are used to calculate electron capture rates and are compared to those obtained from the shell model.