Nickel isotopes in stellar matter

Abstract

Isotopes of nickel play a key role during the silicon burning phase up to the presupernova phase of massive stars. Electron capture rates on these nickel isotopes are also important during the phase of core contraction. I present here the microscopic calculation of ground and excited states Gamow-Teller (GT) strength distributions for key nickel isotopes. The calculation is performed within the frame-work of pn-QRPA model. A judicious choice of model parameters, specially of the Gamow-Teller strength parameters and the deformation parameter, resulted in a much improved calculation of GT strength functions. The excited state GT distributions are much different from the corresponding ground-state distributions resulting in a failure of the Brink's hypothesis. The electron capture and positron decay rates on nickel isotopes are also calculated within the framework of pn-QRPA model relevant to the presupernova evolution of massive stars. The electron capture rates on odd-A isotopes of nickel are shown to have dominant contributions from parent excited states during as early as silicon burning phases. Comparison is being made with the large scale shell model calculation. During the silicon burning phases of massive stars the electron capture rates on ${}^{57,59}$Ni are around an order of magnitude bigger than shell model rates and can bear consequences for core-collapse simulators.

11 pages, 6 figures and 8 tables

References in corpus (4)

• Measurement of the Gamow-Teller Strength Distribution in 58Co via the 58Ni(t,3He) reaction at 115 MeV/nucleon
• Gamow-Teller transitions and deformation in the proton-neutron random phase approximation
• Electron Capture Strength for {60,62}Ni and {58,60,62,64}Ni(p,n){58,60,62,64}Cu reactions at 134.3 MeV
• Weak-interaction mediated rates on iron isotopes for presupernova evolution of massive stars

Cited by in corpus (4)

• Stellar electron-capture rates in pf-shell nuclei from quasiparticle random-phase approximation calculations
• Modification of the Brink-Axel Hypothesis for High Temperature Nuclear Weak Interactions
• Study of Gamow-Teller transitions in isotopes of titanium within the quasi particle random phase approximation
• Electron capture strength on odd-A nucleus ${}^{59}$Co in explosive astrophysical environment