Electron capture cross sections and nuclear partition functions for fp-shell nuclei

We present calculation of electron capture cross sections (ECC), in the limit of zero momentum transfer, using the pn-QRPA model in stellar matter. Towards this aim we make use of our recently introduced recipe for estimation of nuclear partition functions. For low momentum transfer ($q\to 0$), the nuclear matrix elements of the $\sum \sigma {\tau }^{+}$ operator provide the leading contribution to the total cross section which we estimate using the pn-QRPA model in a multi-shell single-particle space with a schematic interaction. Key fp-shell nuclei (odd-A, even–even and odd–odd) bearing astrophysical importance were selected for the calculation of ECC in stellar environment. These fp-shell nuclei play a crucial role in presupernova evolution of massive stars and core collapse. We further present microscopic calculation of ground and excited states Gamow–Teller strength distributions and stellar electron capture rates on these suite of nuclei. We used two different sets of empirically determined pairing gaps to calculate the ECC and electron capture rates. Results are compared with experimental data and previous computations. Our calculated ECC are systematically smaller at low electron incident energies as compared to the shell-model results. (paper)