Speaker
Description
Experimental data of isomerism in the neutron-rich N ≥ 126 region are important to test the predictability of shell evolution beyond the N = 126 shell closure by shell-model calculations. Moreover, the predicted properties of more exotic isotopes could affect the abundance of actinides in r-process calculations [1]. However, these information are scarcely available as it is challenging to access this region by current facilities.
We will present new isomeric transitions in the BRIKEN experiment [2] at RIBF, RIKEN Nishina Center. Particle identification of isotopes with mass ranging 200 ≲ A ≲ 220 was confirmed by the BigRIPS separator and the novel silicon dE telescope. For the first time at RIBF, decays of nuclei southeast of 208Pb were measured by the BRIKEN array [3]. New isomers in 213Tl and 215Tl [4] were observed by correlation among implantation, Meitner-Ellis electron [5] and γ events using WAS3ABi active stopper [6] and high-purity germanium (HPGe) clover detector. Our proposed isomeric level schemes [4] are compared to the shell-model calculations [7] to explain shell evolution. Plans to further investigate isomeric transitions and β decays in the same region will be introduced.
References
[1] E. Holmbeck et al., Astrophys. J. 870(1), 23 (2019).
[2] J. Wu et al., RIBF NP-PAC Proposal NP1712-RIBF158 (2017).
[3] A. Tolosa-Delgado et al., Nucl. Instrum. Methods. Phys. Res. A 925-133 (2019).
[4] T. T. Yeung, A. I. Morales, J. Wu, M. Liu, C. Yuan et al., First Exploration of Monopole-Driven Shell Evolution above the N = 126 shell closure: new Millisecond Isomers in 213Tl and 215Tl, arXiv:2401.06428 (2024). https://arxiv.org/abs/2401.06428
[5] H. E. Mahnke, Notes Rec. 76(1), 107-116 (2022).
[6] S. Nishimura, Prog. Theor. Exp. Phys. 2012(1), 03C006 (2012).
[7] C. Yuan et al., Phys. Rev. C 106(4), 044314 (2022).
