Speaker
Description
Studies of superheavy nuclei provide important insights into nuclear structure at the limit of stability and allow for stringent tests of state-of-the-art nuclear models [1]. These nuclei may exhibit $K$-isomers, providing a unique probe of single-particle structure [2].
One prominent example is the $K^{\pi}=8^{-}$ isomer in $^{254}$No. Despite numerous $\gamma$-spectroscopic studies, the quasiparticle configuration remained for many years unresolved [3-5], largely because earlier experiments weakly populated the isomer’s rotational bands. This has prevented reliable $M1/E2$ branching ratio and $g$-factor measurements, leaving configuration assignments to rely mainly on indirect spectroscopic evidence and theoretical calculations [5].
We have performed complementary experiments using in-gas-jet laser ionization spectroscopy of the $K^{\pi}=8^{-}$ isomer in $^{254}$No ($T_{1/2}=259(7)\,\text{ms}$ [5]) with the JetRIS apparatus at the focal plane of the SHIP velocity filter at GSI, Darmstadt. The hyperfine spectroscopy of this short-lived isomeric state enabled the determination of the magnetic dipole moment, electric quadrupole moment, and isomer shift in a nuclear-model-independent way. The subsequent determination of the isomer's $g$-factor allows us to determine the quasiparticle configuration unambiguously.
[1] M. Block et al., Prog. Part. Nucl. Phys. 116 (2021) 103834.
[2] P. Walker and Z. Podolyák, Phys. World 34 (2021) 29.
[3] R.-D. Herzberg et al., Nature 442 (2006) 896.
[4] F. P. Heßberger, arXiv:2309.10468 (2023).
[5] S. G. Wahid et al., Phys. Rev. C 111 (2025) 034320.