Contribution of excited states to stellar weak-interaction rates in odd-Anuclei

Abstract

Weak-interaction rates, including β decay and electron capture, are studied in several odd-A nuclei in the pf -shell region at various densities and temperatures of astrophysical interest. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus. The nuclear structure involved in the weak processes is studied within a quasiparticle random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree-Fock mean field with pairing correlations. In the range of densities and temperatures considered, it is found that the total rates do not differ much from the rates of the ground state fully populated. In any case, the changes are not larger than the uncertainties due to the nuclear-model dependence of the rates.

Ab initio calculations of Gamow-Teller strengths in the sd shell

“…Final β−decay (n,p) (d, 2 He) (t, 3 He) ( 3 He,t) (p,n) CCEI IM-SRG USDB Ref. In order to describe the measured GT strength distribution in sd shell nuclei, we have performed shell model calculations with two modern ab initio approaches: The in-medium similarity renormalization group (IM-SRG) [19] and the coupled cluster effective interaction (CCEI) [22][23][24].…”

“…Comparison between the experimental and theoretical centroid energy of GT distributions for sd shell nuclei.S.No. InitialFinal β−decay (n,p) (d, 2 He) (t,3 He) ( 3 He,t) (p,n) CCEI IM-SRG USDB 1. 20 Ne(0 + )…”

Gamow-Teller strengths of some sd-shell nuclei in the shell model framework

“…The strongest peak in the 26 Mg (t, 3 He) reaction located at excitation energy E x ( 26 Na)= 0.08 MeV and for 26 Mg(d, 2 He) reaction the strongest peak is located at also at E x ( 26 Na)= 0.08 MeV. There are only four experimental values for both 26 Mg(t, 3 He) and 26 Mg(d, 2 He) reactions and they are distributed over excitation energy E x ( 26 Na)= 0.08-5.02 MeV. Theoretical calculations of USDA and USDB interactions reach to exciation energy ∼ 12 MeV.…”

“…They are not only involved in nuclear physics, they also play an important part in supernova explosions and nuclear synthesis. The GT reaction of core elements in the medium-mass region (MMR) is important to assess the precollapse production of supernova [1][2][3][4]. Electron capture reaction and β-decay were significant nuclear processes at the beginning of the supernova core collapse [5][6][7].…”

Microscopic calculations of weak decays in superheavy nuclei

“…The GT strength distributions and β-decay half-lives have been studied in the past within this model in various mass regions that include neutron-deficient isotopes in the A ≈ 70 mass region [44,45] and in the lead region [39,46,47]; neutron-rich isotopes in medium-mass [48][49][50][51], and rare-earth nuclei [52]; and f p-shell nuclei [53][54][55]. The sensitivity of the GT strength distributions to different ingredients of the theoretical formalism were studied in those works with especial emphasis on the deformation dependence of the decay properties.…”