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