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Mass spectrometry of $^{75}$Zn ground and isomeric states from in-trap decay of $^{75}$Cu

M. Müller, N. A. Althubiti, D. Atanasov, K. Blaum, R. B. Cakirli, T. E. Cocolios, F. Herfurth, S. Kreim, D. Lunney, V. Manea, N. Minkov, D. Neidherr, M. Rosenbusch, L. Schweikhard, A. Welker, F. Wienholtz, R. N. Wolf

Abstract

We report on high-precision mass measurements of the ground and first isomeric state of $^{75}$Zn, performed using the time-of-flight ion-cyclotron-resonance technique at the ISOLTRAP Penning-trap mass spectrometer at ISOLDE/CERN. The isomeric state was produced using in-trap decay of $^{75}$Cu. This marks the first direct investigation of the isomeric state of $^{75}$Zn via mass spectrometry. The isomer was observed at an excitation energy of 123.7(20) keV, in 2$\,σ$ agreement with the value previously determined through decay spectroscopy. In addition, our measurements correct a misassignment of the ground-state mass excess based on a previous measurement by Baruah et al., revising the value to -62681.0(21) keV. To further investigate the earlier discrepancy, we explored the spin-parity assignments of the ground and isomeric states in $^{75}$Zn using Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer theoretical calculations, given the absence of definitive experimental data. In light of the laser spectroscopy results from Wraith et al., our results add strong evidence for a spin-1/2 ground state, which would agree with large-scale shell-model predictions as well as explaining disagreements with the Monte Carlo Shell Model.

Mass spectrometry of $^{75}$Zn ground and isomeric states from in-trap decay of $^{75}$Cu

Abstract

We report on high-precision mass measurements of the ground and first isomeric state of Zn, performed using the time-of-flight ion-cyclotron-resonance technique at the ISOLTRAP Penning-trap mass spectrometer at ISOLDE/CERN. The isomeric state was produced using in-trap decay of Cu. This marks the first direct investigation of the isomeric state of Zn via mass spectrometry. The isomer was observed at an excitation energy of 123.7(20) keV, in 2 agreement with the value previously determined through decay spectroscopy. In addition, our measurements correct a misassignment of the ground-state mass excess based on a previous measurement by Baruah et al., revising the value to -62681.0(21) keV. To further investigate the earlier discrepancy, we explored the spin-parity assignments of the ground and isomeric states in Zn using Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer theoretical calculations, given the absence of definitive experimental data. In light of the laser spectroscopy results from Wraith et al., our results add strong evidence for a spin-1/2 ground state, which would agree with large-scale shell-model predictions as well as explaining disagreements with the Monte Carlo Shell Model.
Paper Structure (7 sections, 5 equations, 3 figures, 2 tables)

This paper contains 7 sections, 5 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Experiment and Data Analysis
  3. Ion production and in-trap decay
  4. ToF-ICR mass measurement
  5. Data Analysis
  6. Results and Discussions
  7. Conclusions

Figures (3)

  • Figure 1: Schematic of the ISOLTRAP setup. The black arrows illustrate the ion path for the ions of interest, originating from the ISOLDE RIB source, and for the reference ions, produced by an offline alkali ion source, as they pass through the four ion traps of the ISOLTRAP system. The inset displays the decay scheme of $^{75}$Cu to the ground and isomeric states of $^{75}$Zn with the associated half-lifes NUBASE2020.
  • Figure 2: One of the nine recorded ToF double-resonances with binned ion counts (blue), averaged ToF values (black), and a fit to the data using the model described in the text (red).
  • Figure 3: (Left): Comparison of the mass excess values obtained in this work with those adopted in AME2020. The measured isomeric mass agrees within one combined standard deviation with the AME2020 value, determined 100% by Baruah2008, indicating a previous misassignment. (Right): Two-neutron separation energies for nuclei in the vicinity of $^{75}$Zn. Incorporating the present experimental results yields a smoother $S_{2n}$ trend. The inset highlights the adjusted values at $N=45$ and $N=47$.