Electron and positron capture rates on 55Co in stellar matter

Abstract

55 Co is not only present in abundance in presupernova phase but is also advocated to play a decisive role in the core collapse of massive stars. The spectroscopy of electron capture and emitted neutrinos yields useful information on the physical conditions and stellar core composition. B(GT) values to low-lying states are calculated microscopically using the pn-QRPA theory. Our rates are enhanced compared to the reported shell model rates. The enhancement is attributed partly to the liberty of selecting a huge model space, allowing consideration of many more excited states in our rate calculations. Unlike previous calculations the so-called Brinks hypothesis is not assumed leading to a more realistic estimate of the rates. The electron and positron capture rates are calculated over a wide temperature (0.01 × 10 9 − 30 × 10 9 K) and density (10 − 10 11 gcm −3 ) grid.

Expanded calculations of proton–neutron quasi-particle random phase approximation (pn-QRPA) electron capture rates on 55Co for presupernova and supernova physics

“…10. The main reason for this enhancement was that FFN placed the GT centroid at too low excitation energies [10,23]. Our rates were also enhanced as compared to the FFN calculations.…”

“…Aufderheide and collaborators [5] placed 55 Co among the list of top ten most important electron capture nuclei during the presupernova evolution. Realizing the importance of 55 Co in astrophysical environments, Nabi et al [10] reported the calculation of electron and positron capture rates on 55 Co using the pn-QRPA theory. Realizing the importance of 55 Co in astrophysical environments, Nabi et al [10] reported the calculation of electron and positron capture rates on 55 Co using the pn-QRPA theory.…”

Detailed microscopic calculation of stellar electron and positron capture rates on24Mg for O+Ne+Mg core simulations

“…The f ′ ij s are the phase space integrals. Details of the calculations of phase space integrals, reduced transition probabilities and choice of Gamow-Teller strength parameters can be found in [12,13,25].…”

“…Later the decay and capture rates of nuclei of astrophysical importance were studied separately in detail and were compared with earlier calculations wherever possible both in sd-shell [14] and fp-shell (e.g. [15][16][17]) regions. Compared to shell model calculations, the pn-QRPA gives similar accuracy in reproducing beta-decay and capture rates in sd-shell nuclei [14].…”

Electron Capture Cross Sections for Stellar Nucleosynthesis

“…The first calculations of stellar electron capture rates for iron group nuclei have been performed by employing the Independent Particle Model (IPM) [2]. Recently, similar studies have been addressed by using Continuum RPA (CRPA) [21], large scale shell model [22,23], RPA [9], etc [24]. In the present work e − -capture cross sections are obtained within a refined version of the Quasi-Particle Random Phase Approximation (QRPA) which is reliable for constructing all the accessible final (excited) states of the daughter nuclei in the iron group region of the periodic table [25][26][27][28][29][30][31][32][33][34].…”