Speaker
Description
K-isomers are metastable nuclear excitations of predominant single-particle character, arising in well-deformed nuclei where the projection of the total angular momentum onto the symmetry axis, K, is an approximately good quantum number. When quasiparticles align their angular momentum projections along the symmetry axis, the resulting multi-quasiparticle configuration acquires a large K value, and decay to lower-lying states is strongly suppressed by the K-selection rule, leading to half-lives orders of magnitude longer than those of non-isomeric states at comparable excitation energies [1,2]. This makes K-isomers sensitive fingerprints of the single-particle structure near the Fermi surface [3], with additional interest in applied contexts ranging from nuclear medicine to proposals for high-density nuclear energy storage [4,5].
Within the Relativistic Hartree-Bogoliubov (RHB) framework, K-isomers are described as blocked multi-quasiparticle excitations within the Equal Filling Approximation, with full self-consistent readjustment of the mean field and pairing under blocking [6,7,8,9]. We present RHB calculations of high-K states in two regimes poorly explored at the covariant mean-field level: the N ≈ 116 shape-transition region (W–Os isotopic chains), where rapid structural evolution from prolate toward γ-soft shapes produces a rich and theoretically demanding landscape of competing configurations [10,11]; and oblate nuclei, where the reversed Nilsson level ordering leads to qualitatively different high-K structures compared to the well-studied prolate case. Excitation energies and configurations are compared with available data, and candidates for unobserved isomers are proposed.
References
[1] P. Walker and G. Dracoulis, Nature 399, 35 (1999)
[2] G. Dracoulis, P. Walker and F. Kondev, Rep. Prog. Phys. 79, 076301 (2016)
[3] A.K. Jain, B. Maheshwari and A. Goel, Nuclear Isomers: A Primer (Springer, 2021)
[4] C.J. Chiara and J.P. Carroll, Nature 556, 323 (2018)
[5] D. Belic et al., Phys. Rev. Lett. 83, 5242 (1999)
[6] S. Perez-Martin and L.M. Robledo, Phys. Rev. C 78, 014304 (2008)
[7] J. Xiang et al., Phys. Rev. C 102, 034311 (2020)
[8] K.E. Karakatsanis, G.A. Lalazissis, V. Prassa and P. Ring, Phys. Rev. C 102, 034311 (2020)
[9] V. Prassa, T. Nikšić, G.A. Lalazissis and D. Vretenar, Phys. Rev. C 86, 024317 (2012)
[10] Z.P. Li, T. Nikšić et al., Phys. Rev. C 84, 054304 (2011)
[11] H.L. Liu, F.R. Xu, P.M. Walker and C.A. Bertulani, Phys. Rev. C 83, 011303(R) (2011)