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Identification of Prompt Proton Emission in $N = Z - 1$ ${}^{61}{Ga}$ : Isospin Symmetry at the Limit of Nuclear Binding

Y. Hrabar ^1,*, P. Golubev ¹, D. Rudolph ¹, L. G. Sarmiento ¹, C. Müller-Gatermann ², W. Reviol ², D. Seweryniak², J. Wu^2,†, H. M. Albers ³ et al.

J. T. Anderson², M. A. Bentley ⁴, B. G. Carlsson¹, M. P. Carpenter ², C. J. Chiara ⁵, P. A. Copp^2,‡, D. M. Cox ¹, J. Ekman ⁶, C. Fahlander¹, U. Forsberg^1,§, T. Huang^2,∥, A. Idini ¹, H. Jayatissa ^2,‡, T. Lauritsen ², X. Pereira-Lopez ^4,¶, S. Stolze², S. Uthayakumaar ^4,**, and G. L. Wilson^2,7,††

¹Department of Physics, Lund University, SE-22100 Lund, Sweden
²Physics Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
³GSI Helmholtzzentrum für Schwerionenforschung, DE-64291 Darmstadt, Germany
⁴School of Physics, Engineering and Technology, University of York, Heslington, York, YO10 5DD, United Kingdom
⁵U.S. Army Combat Capabilities Development Command Army Research Laboratory, Adelphi, Maryland 20783, USA
⁶Department of Materials Science and Applied Mathematics, Malmö University, SE-20506 Malmö, Sweden
⁷Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA

^*Contact author: yuliia.hrabar@fysik.lu.se
^†Present address: Brookhaven National Laboratory, Brookhaven, USA.
^‡Present address: Physics Division, Los Alamos National Laboratory, Los Alamos, USA.
^§Present address: Cyclife Sweden AB, Nyköping, Sweden.
^∥Present address: Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China.
^¶Present address: Center for Exotic Nuclear Studies, Institute for Basic Science, Daejeon, Republic of Korea.
^**Present address: Facility for Rare Isotope Beams, Michigan State University, East Lansing, USA.
^††Present address: United Kingdom Atomic Energy Authority, Abingdon, United Kingdom.

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Phys. Rev. Lett. 135, 222503 – Published 25 November, 2025

DOI: https://doi.org/10.1103/kwm2-9bmd

Abstract

Excited states in the proton drip line nucleus ${}^{61}{Ga}$ were populated via the fusion-evaporation reaction ${}^{24}{Mg} ({}^{40}{Ca}, p 2 n) {}^{61}{Ga}$ . The experimental setup at Argonne National Laboratory comprised a novel combination of the Gammasphere array with two CD-shaped double-sided Si-strip detectors inside the Microball CsI(Tl) charged-particle detection array, as well as the Neutron-Shell liquid scintillators and the Fragment Mass Analyzer. Owing to the setup’s unprecedented in-beam proton spectroscopy and tracking capabilities, a coincidence between a 957.6(5)-keV $γ$ ray and a 1.876(24)-MeV proton line was observed, which identifies the quasibound proton $π g_{9 / 2}$ single-particle state in ${}^{61}{Ga}$ at $E_{x} = 2150 (34) keV$ . This probes isospin symmetry at the limit of nuclear binding by providing a unique challenge for the shell-model interpretation of mirror nuclei beyond doubly magic ${}^{56}{Ni}$ .

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Phys. Rev. Lett. 135, 222503– Published 25 November, 2025

Vol. 135, Iss. 22 — 26 November 2025

Received 2 September 2024
Revised 23 September 2025
Accepted 7 November 2025

DOI: https://doi.org/10.1103/kwm2-9bmd

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by Bibsam.

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Identification of Prompt Proton Emission in $N = Z - 1$ ${}^{61}{Ga}$ : Isospin Symmetry at the Limit of Nuclear Binding

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Identification of Prompt Proton Emission in N=Z−1 Ga61: Isospin Symmetry at the Limit of Nuclear Binding

Abstract

Physics Subject Headings (PhySH)

Article Text

Supplemental Material

References (52)

Identification of Prompt Proton Emission in $N = Z - 1$ ${}^{61}{Ga}$ : Isospin Symmetry at the Limit of Nuclear Binding