Speaker
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Nuclear weak rates relevant to the study of astrophysical processes in stars are evaluated with the use of shell-model Hamiltonians that prove to be successful in describing Gamow-Teller (GT) and spin-dipole (SD) strengths in nuclei. Electron-capture and β-decay rates in stellar environments induced by GT transitions in sd-shell and pf-shell are applied to study nuclear URCA processes in degenerate ONeMg cores in stars with 8-10 solar masses [1] and synthesis of iron-group nuclei in type Ia supernovae [2].
Structure of $^{31}$Mg in the island of inversion are studied with an effective interaction in sd-pf shell obtained by the extended Kuo-Krenciglowa method [3]. The weak rates for the nuclear pair with A=31, which are important for the Urca process in neutron star crusts [4], are evaluated with the effective interaction [5].
The multipole expansion method of Walecka as well as the Behrens-Buhring (BB) method are used to evaluate the weak rates induced by first- and second-forbidden transitions. The SD strengths and e-capture rates for $^{78}$Ni are evaluated by shell-model with full pf-sdg shells including up to 5p-5h excitations outside the $^{78}$Ni-core [5,6]. Results obtained are compared with RPA calculations and the effective rate formula [7].
Electron-capture rates for the second-forbidden transition in $^{20}$Ne are evaluated by taking account of the conserved-vector-current (CVC) relation for the transverse E2 matrix element. Importance of the CVC relation is pointed out, while the difference in the rates between the Walecka and BB methods is found to be small as far as the CVC relation is satisfied [5]. Possible important contributions of the forbidden transition to heating of the ONeMg core by double e-captures on $^{20}$Ne in a late stage of the evolution of the core and implications on the final fate of the core, whether core-collapse or thermonuclear explosion, are discussed [5,8,9].
[1] H. Toki, T. Suzuki, K. Nomoto, S. Jones, and R. Hirschi, Phys. Rev. C 88, 015806 (2013);
T. Suzuki, H. Toki, and K. Nomoto, ApJ. 817, 163 (2016).
[2] K. Mori, M. Famiano, T. Kajino, T. Suzuki et al., ApJ. 833, 179 (2016).
K. Mori, T. Suzuki, M. Honma, et al, Astrophys. J. 904, 29 (2020).
[3] N. Tsunoda, T. Otsuka, N. Shimizu, M. Hjorth-Jensen, K. Takayanagi and T. Suzuki, Phys. Rev. C 95, 021304 (2017).
[4] H. Schatz et al., Nature 505, 62 (2014).
[5] T. Suzuki, Prog. Part. Nucl. Phys. 126, 103974 (2022).
[6] Y. Tsunoda, T. Otsuka, N. Shimizu, H. Monma, and Y. Utsuno, Phys. Rev. C 89, 031301 (R) (2014).
[7] C. Sullivan, E. O’Connor, R. G. T. Zegers, T. Grubb, and S. M. Austin, ApJ. 816, 40 (2016).
[8] S. Zha, S-C. Leung, T. Suzuki, and K. Nomoto, ApJ. 886, 22 (2019).
[9] O. S. Kirsebom et al., Phys. Rev. Lett. 123, 262701 (201); Phys. Rev. C 100, 065805 (2019).
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