Study of $0^+$ and $8^-$ states in even-even $^{250-260}$No isotopes

TL;DR

This study uses QRPA with Skyrme SLy4 to analyze low-lying $K^{ ext{pi}}=0^+$ and $8^-$ states in even-even $^{250-260}$No isotopes, revealing pairing effects, isomeric states, and collective excitations with reasonable experimental agreement.

Contribution

It provides a detailed theoretical analysis of specific nuclear states in No isotopes, highlighting the role of pairing and single-particle spectra in their properties.

Findings

Neutron pairing minima at A=252, 254 significantly influence state properties.

$8^-$ isomers are mainly low-energy two-quasiparticle states.

Predicted collective $0^+$ states as superpositions of pairing and $eta$-vibrations.

Abstract

Low-lying $K^{\pi}=0^+$ and isomeric $8^-$ states in even-even isotopes $^{250-260}$No are explored within the Quasiparticle Random-Phase Approximation (QRPA) method with Skyrme parametrization SLy4. The deformations, single-particle (s-p) spectra and pairing in the isotopes are inspected. The calculations predict a pronounced minimum in the neutron pairing at $A$=252, 254, which significantly affects the properties of $0^+$ and $8^-$ states and leads to a correlation of their spectra. It is shown that $8^-$ isomers are basically low-energy two-quasiparticle (2qp) states. The appearance or absence of these isomers in $^{250-260}$No is explained as a combined effect of the s-p spectra and pairing. The collective $0^+$ states are predicted in all the isotopes as the lowest multipole non-rotational excitations. These states are interpreted as a superposition of pairing vibrations and $\beta$-vibrations. The results are in a reasonable agreement with available experimental data for $^{252,254}$No.