Speaker
Description
The study of nuclear structure under conditions of extreme excitation has emerged as one of the thrust areas of contemporary nuclear physics research, motivated by both experimental advances in accessing exotic nuclei near drip lines [1] and their relevance to astrophysical environments [2]. Structural transitions involving changes in deformation and shell effects provide critical insight into the stability and decay properties of nuclei far from stability [3]. Our earlier investigations have demonstrated that such transitions can lead to the emergence of rare shape phases and significantly alter nuclear stability [4]. In this context, we perform global finite-temperature analysis to explore the interplay between structural transitions on particle stability and $\beta$-decay lifetimes, relevant at low and moderate densities during pre-collapse and the early high-temperature evolutionary stellar stage [5].
This work presents a comprehensive study on the impact of thermal excitations on shell effects, such as shell quenching with increasing excitation, deformation and separation energy fluctuations and $\beta$-decay characteristics along with their lifetimes. We investigate the nuclear isotopic chains in the mass region $Z = 28$-$50$ that have been known to have relevance in the r-process nucleosynthesis and weak interactions in the hot stellar environments [6]. We employ a simple yet effective microscopic theoretical framework based on the statistical theory of hot nuclei, combined with the triaxially deformed Nilsson Hamiltonian and Strutinsky’s prescription [7]. Our calculations [8] show that around the critical temperature ($T_c \sim 1$-$2$ MeV), where shell quenching effects become predominant, nuclear deformation reduces significantly, accompanied by an enhancement in the one- and two-neutron separation energies. This unexpected enhancement shifts the last unbound nucleon to a bound configuration, leading to a modest expansion of the one- and two-neutron drip lines in a few nuclei. Furthermore, temperature-induced changes in deformation exhibit a strong correlation with variations in the calculated $Q_{\beta}$ values and $\beta$-decay lifetimes. The reduced $Q_{\beta}$ values near the critical temperature result in increased $\beta$-decay lifetimes, indicating a slowing down of weak decay rates in thermally excited systems. These findings highlight the crucial role of finite-temperature structural effects in governing nuclear stability and decay dynamics, with important implications for modeling the evolution of hot stellar matter and nucleosynthesis pathways.
References
[1] M. Thoennessen, Rep. Prog. Phys. 76 (2013) 056301.
[2] A. Ravlić, E. Yüksel, T. Nikšić, and N. Paar, Nat. Commun. 14 (2023) 4834.
[3] M. Rajasekaran and Mamta Aggarwal, Phys. Rev. C 58 (1998) 5.
[4] Mamta Aggarwal, Phys. Lett. B 693 (2010) 489.
[5] K. Langanke and G. Martı́nez-Pinedo, Rev. Mod. Phys. 75 (2003) 819.
[6] M. Arnould, S. Goriely, and K. Takahashi, Phys. Rep. 417 (2005) 97.
[7] Mamta Aggarwal, Phys. Rev. C 69 (2004) 034602.
[8] Mamta Aggarwal, Pranali Parab, Gaurav Saxena, Phys. Lett. B 875 (2026) 140298.