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

M. A. Mardyban, V. O. Nesterenko

TL;DR

The paper investigates low-lying $K^\pi=0^+$ and $8^-$ excitations in even-even nobelium isotopes $^{250-260}$No using a fully self-consistent QRPA framework with the Skyrme SLy4 interaction. It analyzes deformations, single-particle spectra, and pairing to understand isomerism and non-rotational collectivity. A key finding is a neutron pairing minimum at $A=252$ and $A=254$ arising from a deformation-shell gap in the neutron $s$-$p$ spectrum, which correlates the $0^+$ and $8^-$ spectra. The $8^-$ states are predominantly neutron two-quasiparticle excitations, while the lowest $0^+$ states arise from mixing of pairing vibrations and β-vibrations, with predictions in reasonable agreement with data for $^{252,254}$No, shedding light on pairing and deformation effects in transfermium nuclei.

Abstract

Low-lying $K^π=0^+$ 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 $β$-vibrations. The results are in a reasonable agreement with available experimental data for $^{252,254}$No.

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

TL;DR

The paper investigates low-lying and excitations in even-even nobelium isotopes No using a fully self-consistent QRPA framework with the Skyrme SLy4 interaction. It analyzes deformations, single-particle spectra, and pairing to understand isomerism and non-rotational collectivity. A key finding is a neutron pairing minimum at and arising from a deformation-shell gap in the neutron - spectrum, which correlates the and spectra. The states are predominantly neutron two-quasiparticle excitations, while the lowest states arise from mixing of pairing vibrations and β-vibrations, with predictions in reasonable agreement with data for No, shedding light on pairing and deformation effects in transfermium nuclei.

Abstract

Low-lying and isomeric states in even-even isotopes 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 =252, 254, which significantly affects the properties of and states and leads to a correlation of their spectra. It is shown that isomers are basically low-energy two-quasiparticle (2qp) states. The appearance or absence of these isomers in No is explained as a combined effect of the s-p spectra and pairing. The collective 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 -vibrations. The results are in a reasonable agreement with available experimental data for No.

Paper Structure

This paper contains 7 sections, 3 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Results and Discussion
  3. Deformations, pairing, mean field
  4. $8^-$ isomers
  5. $0^+$ states
  6. Conclusions
  7. Acknowledgments

Figures (3)

  • Figure 1: Neutron s-p spectra near Fermi levels in $^{250-260}$No. Transitions resulting in $8^-$ states (see Table \ref{['tab:8-']}) are marked by black arrows. Fermi levels are labeled by (F).
  • Figure 2: The same as in Fig. \ref{['sps_n']} but for the proton s-p spectra in $^{250-260}$No.
  • Figure 3: The lowest QRPA 0$^+$ and 8$^-$ states in $^{250-260}$No.