Speakers
Description
Nuclear shape coexistence, defined as the presence of competing intrinsic configurations such as spherical, prolate and oblate shapes at comparable excitation energies within a single nucleus, is now established as a widespread phenomenon across the nuclear chart, arising from the interplay of shell effects, pairing correlations and collective deformation mechanisms [1, 2]. While its spectroscopic manifestations are well documented, the quantitative influence of shape coexistence on nuclear decay properties, particularly half-lives and branching ratios, has not been systematically explored, despite its relevance for nuclear-structure studies and astrophysical nucleosynthesis calculations [3].
We present a comprehensive investigation of the impact of shape coexistence on decay properties for approximately 1500 even-even nuclei spanning the range $8 \leq Z \leq 118$ and $8 \leq N \leq 184$. Potential energy surfaces are mapped using the macroscopic-microscopic Nilsson-Strutinsky method (NSM) together with NL3$^{*}$, DD-ME2 and DD-PC1. Nuclei exhibiting near-degenerate minima within a small energy interval are identified as candidates for shape coexistence. For nuclei with experimentally known decay data from the NUBASE2020 evaluation [4], deformation-dependent established semi-empirical formulas for $\alpha$, $\beta^{-}$ and $\beta^{+}$/EC decay are applied, explicitly incorporating quadrupole deformations of both parent and daughter nuclei, motivated by earlier study [5, 6]. Deformation inputs from multiple nuclear-structure models are combined using Bayesian model averaging to reduce systematic bias.
The results show that nuclear shape coexistence has a systematic impact on decay properties by modifying the decay $Q$-values and the structural overlap between parent and daughter nuclei. When more than one shape lies close in energy, decay pathways involving different shape configurations lead to noticeable variations in calculated half-lives and branching ratios. Calculations that consider only the lowest-energy shape generally reproduce the overall decay trends, but including shape-changing transitions often improves the agreement with experimental data, particularly in regions where competing shapes are separated by small energy differences. In such cases, the decay outcome depends on whether the transition connects similar or different shapes, leading to a redistribution among competing decay modes.
This study demonstrates that nuclear shape coexistence introduces quantitatively meaningful changes in decay $Q$-values, half-lives, and branching ratios. Explicit inclusion of deformation effects is therefore necessary for a reliable description of nuclear decay and for providing more robust nuclear-physics inputs for astrophysical nucleosynthesis calculations.
References:
[1] K. Heyde and J. L. Wood, Rev. Mod. Phys. 83, 1467 (2011).
[2] P. E. Garrett, M. Zielińska, and E. Clément, Prog. Part. Nucl. Phys. 124, 103931 (2022).
[3] J. J. Cowan et al., Rev. Mod. Phys. 93, 015002 (2021).
[4] M. Wang et al., Chin. Phys. C 45, 030003 (2021).
[5] A. Jain, P. Parab, G. Saxena, and M. Aggarwal, Sci. Rep. 14, 28368 (2024).
[6] M. Aggarwal, P. Parab, A. Jain, and G. Saxena, Nuclear Physics A 1067, 123321 (2026).