The 24th International Spin Symposium

Roles of spin-dependent transitions in nuclei on astrophysical processes in stars

20 Oct 2021, 12:25

20m

Room 303-304 (Kunibiki Messe)

Parallel Session Presentation Spin in Nuclear Reactions and Nuclei Spin in Nuclear Reactions and Nuclei

Speaker

Prof. Toshio Suzuki (Nihon University)

Description

Due to recent advances in shell-model studies on spin modes in nuclei, precise evaluations of Gamow-Teller (GT) strengths become feasible and electron-capture and $\beta$-decay rates in stellar environments have been updated.
The weak rates in $sd$-shell obtained with the USDB Hamiltonian are applied to nuclear Urca processes in O-Ne-Mg cores in stars with 8-10 solar masses [1,2]. The Urca processes for the nuclear pairs with A=23 and 25 are found to be important for the cooling of the core [1].
Here, the weak rates important for the Urca processes in accreted neutron star crusts [3] are investigated. The e-capture and $\beta$-decay rates are evaluated for the nuclear pair with A=31, ${}^{31}$Al $\leftrightarrow$ ${}^{31}$Mg, in $sd$-$pf$ shell and the pair with A=61, ${}^{61}$V $\leftrightarrow$ ${}^{61}$Cr, in $fp$-$gd$ shell. ${}^{31}$Mg belongs to the island of inversion, where admixtures of $sd$- and $fp$-shells become important. Energy levels in ${}^{31}$Mg are found to be well reproduced with the use of EEdf1 interaction obtained by the extended Kuo-Krensiglowa (EKK) method [4], which can properly treat Q-box calculations in two-major shells without divergence problems. The weak rates evaluated with the EKK method prove to lead to Urca processes.
The GT strengths in ${}^{61}$V is evaluated with the GXPF1J Hamiltonian [5]. The calculated strength between the ground states of ${}^{61}$V and ${}^{61}$Cr is found to be consistent with the recent experimental data [6]. This suggests that the Urca process for the A=61 pair would be more moderate than considered before. Results with an extension to the $fp$-$gd$ shell-model space will be also reported.
The weak rates in fp-shell obtained with the GXPF1J are applied to nucleosynthesis in Type Ia supernova explosions [7]. The electron screening effects are taken into account [8]. Overproduction problem of neutron-rich iron-group elements for the previous weak rates is found to be considerably suppressed.

[1] H. Toki, T. Suzuki, K. Nomoto, S. Jones, and R. Hirschi, Phys. Rev. C $\mathbf{88}$, 015806 (2013).
[2] T. Suzuki, H. Toki, and K. Nomoto, ApJ. $\mathbf{817}$, 163 (2016).
[3] H. Schatz, S. Gupta, P. Moller et al., Nature $\mathbf{50}$, 62 (2014).
[4] N. Tsunoda, T. Otsuka, N. Shimizu, M. Hjorth-Jensen, K. Takayanagi, and T. Suzuki, Phys. Rev. C $\mathbf{95}$, 021304 (R) (2017).
[5] M. Honma et al., J. Phys. Conf. Ser. $\mathbf{20}$, 7 (2005).
[6] W. J. Ong et al., Phys. Rev. Lett. $\mathbf{125}$, 262701 (2020).
[7] K. Mori et al,, M. A. Famiano, T. Kajino et al., ApJ. $\mathbf{863}$, 176 (2018);
[8] K. Mori, T. Suzuki, M. Honma et al., ApJ $\mathbf{904}$, 29 (2020).

Presentation materials

spin2021_Suzuki.pdf