Low-energy spectra of nobelium isotopes: Skyrme random-phase-approximation analysis

Abstract

Low-energy spectra in the isotopic chain ${}^{250-262}$No are systematically investigated within the fully self-consistent Quasiparticle Random-Phase-Approximation (QRPA) using Skyrme forces SLy4, SLy6, SkM* and SVbas. QRPA states of multipolarity $\lambda \mu$=20, 22, 30, 31, 32, 33, 43, 44 and 98 are considered. The main attention is paid to isotopes ${}^{252}$No and ${}^{254}$No where the most extensive experimental spectroscopic information is available. In these two nuclei, a reasonable description of $K^{\pi }=8^{-},2^{-}$and $3^{+}$ isomers is obtained with forces SLy4 and SLy6. The disputed $8^{-}$ isomer in ${}^{254}$No is assigned as neutron two-quasiparticle configuration $nn[734\uparrow ,613\uparrow ]$. The isomers are additionally analyzed using Skyrme functionals UNEDF1, UNEDF2 and UNEDF1${}^{\mathrm{SO}}$. At the energies 1.2 - 1.4 MeV, the 2qp $K$-isomers $4^{-},7^{-}$ in ${}^{252}$No and $4^{-},6^{-},7^{-}$ in ${}^{254}$No are also predicted. In ${}^{254}$No, the $K^{\pi }=3^{+}$ isomer should be accompanied by the nearby $K^{\pi }=4^{+}$ counterpart. It is shown that, in the chain ${}^{250-262}$No, some features of ${}^{252}$No and ${}^{254}$No should exhibit essential irregularities caused by a noticeable shell gap in the neutron single-particle spectrum and corresponding reduction of the neutron pairing. In particular, low-energy pairing-vibrational $K^{\pi }=0^{+}$ states in ${}^{252,254}$No are predicted.

The version published in Phys. Rev. C 111, 064322 (2025). 19 pages, 14 tables, 7 figures. As compared with the previous arXiv version, the missprints in the text and some figures were corrected

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