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Low-lying level structures in $^{162}$Lu

N Susshma, S Deepa, K Vijay Sai, R Gowrishankar

TL;DR

This work applies the Two Quasiparticle Rotor Model (TQRM) to the odd-odd nucleus $^{162}$Lu to establish the low-lying level scheme, confirm the ground-state and two isomers with specific $J^{\pi}$ and orbital configurations, and assign their excitation energies $E_x$ at approximately 0 keV, 62 keV, and 157 keV, respectively. It builds a three-step procedure to identify relevant 1qp proton and neutron orbitals, construct physically admissible 2qp bandheads, and compute their energies, using neighboring nuclei data to calibrate each state. The analysis extends to neighboring Lu isotopes $^{164,166,168}$Lu, proposing isomer candidates and refining poorly known levels (e.g., $^{168}$Lu isomer at $\sim$100 keV). By linking spin-parity, configurations, and beta-decay branches to daughter $^{162}$Yb levels, the paper provides location-guides for future experiments and contributes to the systematic understanding of low-lying isomers in deformed odd-odd nuclei.

Abstract

The well-tested empirical two quasiparticle rotor model calculations are used to characterize low-lying isomers in the odd-odd nucleus $^{162}$Lu. Physically admissible 2qp bandheads are obtained to construct the low-energy level structure of the nucleus, assign spin-parity (J$^π$), orbital configuration, and level energies (E$_x$), for the gs and the two reported isomers. The spin-parity and orbital configuration of the 1.5 min isomer are confirmed to be J$^π$= 4$^-$\{$π$5/2$^+$[402$\uparrow$] $\otimes$ $ν$3/2$^-$[521$\uparrow$]\}. Its level energy has been estimated to be E$_x$ $\thickapprox$ 62 keV. The 1.9 min isomer is characterized for the first time with J$^π$= 6$^+$\{$π$9/2$^-$[514$\uparrow$] $\otimes$ $ν$3/2$^-$[521$\uparrow$]\} and energy E$_x$ $\thickapprox$ 157 keV. Based on these assignments, individual $β$-decay branches of gs and the two isomers to the daughter levels in $^{162}$Yb are proposed. The study is extended to neighboruing isotopes $^{164,166,168}$Lu. A short-lived isomer, tentatively proposed in a previous study of $^{164}$Lu, is identified as J$^π$= 6$^+$\{$π$7/2$^+$[404$\downarrow$] $\otimes$ $ν$5/2$^+$[402$\uparrow$]\} with energy E$_x$ $\thickapprox$ 52 keV. The energy of the J$^π$=3$^+$ isomer in $^{168}$Lu, currently listed with large uncertainty, is deduced as E$_x$ $\thickapprox$ 100 keV significantly improving its value.

Low-lying level structures in $^{162}$Lu

TL;DR

This work applies the Two Quasiparticle Rotor Model (TQRM) to the odd-odd nucleus Lu to establish the low-lying level scheme, confirm the ground-state and two isomers with specific and orbital configurations, and assign their excitation energies at approximately 0 keV, 62 keV, and 157 keV, respectively. It builds a three-step procedure to identify relevant 1qp proton and neutron orbitals, construct physically admissible 2qp bandheads, and compute their energies, using neighboring nuclei data to calibrate each state. The analysis extends to neighboring Lu isotopes Lu, proposing isomer candidates and refining poorly known levels (e.g., Lu isomer at 100 keV). By linking spin-parity, configurations, and beta-decay branches to daughter Yb levels, the paper provides location-guides for future experiments and contributes to the systematic understanding of low-lying isomers in deformed odd-odd nuclei.

Abstract

The well-tested empirical two quasiparticle rotor model calculations are used to characterize low-lying isomers in the odd-odd nucleus Lu. Physically admissible 2qp bandheads are obtained to construct the low-energy level structure of the nucleus, assign spin-parity (J), orbital configuration, and level energies (E), for the gs and the two reported isomers. The spin-parity and orbital configuration of the 1.5 min isomer are confirmed to be J= 4\{5/2[402] 3/2[521]\}. Its level energy has been estimated to be E 62 keV. The 1.9 min isomer is characterized for the first time with J= 6\{9/2[514] 3/2[521]\} and energy E 157 keV. Based on these assignments, individual -decay branches of gs and the two isomers to the daughter levels in Yb are proposed. The study is extended to neighboruing isotopes Lu. A short-lived isomer, tentatively proposed in a previous study of Lu, is identified as J= 6\{7/2[404] 5/2[402]\} with energy E 52 keV. The energy of the J=3 isomer in Lu, currently listed with large uncertainty, is deduced as E 100 keV significantly improving its value.

Paper Structure

This paper contains 17 sections, 1 equation, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Model Formulation
  3. Analysis and Results
  4. Low-lying level structure of $^{162}$Lu
  5. 1.4 min gs :
  6. 1.5 min isomer
  7. 1.9 min isomer:
  8. Other levels:
  9. Favored decay branches of gs and isomers
  10. Decay of 1.37 min $^{162}$Lu$^{gs}$
  11. Decay of the 1.5 min isomer:
  12. Decay of the 1.9 min isomer:
  13. Isomers in neighboring odd-odd isotopes
  14. $^{164}$Lu
  15. $^{166}$Lu
  16. ...and 2 more sections

Figures (4)

  • Figure 1: Energy systematics of 1qp p (left) and n (right) orbitals in the mass region neighboring $^{162}$Lu. The 1qp energies were taken from the updated ENSDF datasheets ENSDF of odd-mass Z=71 Lu isotopes and N=91 isotones in the mass region around A=162.
  • Figure 2: Plot of physically admissible 2qp bandheads in $^{162}$Lu up to 300 keV calculated using TQRM. The gs and isomeric states are highlighted in red. The 1qp p and n levels giving rise to the 2qp states are placed in the left and right side respectively.
  • Figure 3: Favored $\beta$-decay branches of the $^{162}$Lu gs and isomeric states to some of the daughter levels (not to scale) in $^{162}$Yb based on the $\beta$-decay selection rules for spin-parity and orbital configuration assignments made in the present work. The Q$_\beta$ and percentage $\beta$ decay data have been taken from ENSDF ENSDF.
  • Figure 4: Plot of model calculated energies of 2qp bandheads in $^{164}$Lu (center) upto E$_x$=300 keV along with the 1qp p and n orbital energies taken from isotopic neighbor $^{163}$Lu (left) and isotonic neighbor $^{163}$Yb (right). The gs and possible isomeric state as proposed in previous decay study Hunt are highlighted (in red).