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

TL;DR

This study uses self-consistent QRPA with Skyrme forces to analyze low-energy spectra and isomers in nobelium isotopes, providing detailed predictions and assignments of nuclear states.

Contribution

It offers a comprehensive QRPA analysis of nobelium isotopes with multiple Skyrme functionals, including new state assignments and insights into nuclear structure irregularities.

Findings

Reasonable description of isomers in $^{252}$No and $^{254}$No

Assignment of the $8^-$ isomer in $^{254}$No as neutron two-quasiparticle

Prediction of low-energy pairing-vibrational $K^{}^+$ states in $^{252,254}$No

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$^{\rm SO}$. 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.