The electron capture of nuclides ⁵⁵Co and ⁵⁶Ni in the process of stellar core collapse

Abstract

Using Shell-Model Monte Carlo (SMMC) method and Random Phase Approximation (RPA) theory, the electron capture (EC) and the electron capture cross section (ECCS) of nuclei ⁵⁵Co and ⁵⁶Ni are investigated. We also discuss the rates of the change of electron fraction (RCEF) and the error factor C, which is compared our results with those of AFUD, which calculated by the method of Aufderheide. The results show that the ECCS and the EC rates for ⁵⁵Co and ⁵⁶Ni increased about four orders of magnitude at relative high temperature (such as T ₉=5,7,9). On the other hand, the RCEF for two nuclides decreased greatly, and even exceed four orders of magnitude. The error factor shows ours is agreed reasonably well with AUFD under the higher density surroundings (e.g. ρ7=106, Y _e =0.43; ρ7=506, Y _e =0.42; ρ7=4010, Y _e =0.41). But under the lower density surroundings (e.g. ρ7=3.36, Y _e =0.48) the maximum error is ∼14.5 % for ⁵⁵Co but is ∼14.0 % for ⁵⁶Ni. The error is ∼9.5 % and ∼9.0 % for ⁵⁵Co, ⁵⁶Ni at ρ7=5.86, Y _e =0.47 respectively.