- Physical Review Journals
All JournalsPhysics Magazine

Physical Review C

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access

Spectroscopy of excited neutron configurations of Ca54

F. Browne1,2,*, S. Chen3,1,4,5, P. Doornenbal1, A. Obertelli6,7,1, K. Ogata8, Y. Utsuno9,10, K. Yoshida10,11, N. L. Achouri12, H. Baba1 et al.

D. Calvet7,†, F. Château7, N. Chiga1, A. Corsi7, M. L. Cortés1, A. Delbart7, J-M. Gheller7, A. Giganon7, A. Gillibert7, C. Hilaire7, T. Isobe1, T. Kobayashi13,†, Y. Kubota1,9, V. Lapoux7, H. N. Liu7,14, T. Motobayashi1, I. Murray15,1, H. Otsu1, V. Panin1, N. Paul7,16, W. Rodriguez17,1,18, H. Sakurai1,19, M. Sasano1, D. Steppenbeck1, L. Stuhl9, Y. L. Sun7, Y. Togano20,1, T. Uesaka1, K. Wimmer19,1,‡, K. Yoneda1, O. Aktas14, T. Aumann6,21, K. Boretzky21,1, C. Caesar6,21,1, L. X. Chung22, F. Flavigny15, S. Franchoo15, I. Gasparic23,6,1, R.-B. Gerst24, J. Gibelin12, K. I. Hahn25, M. Holl6, J. Kahlbow6, D. Kim25, D. Körper21, T. Koiwai19, Y. Kondo26, P. Koseoglou6,21, J. Lee3, C. Lehr6, B. D. Linh22, T. Lokotko3, M. MacCormick15, K. Moschner24, T. Nakamura26, S. Y. Park25, D. Rossi6,21, E. Sahin27, H. Simon21, P-A. Söderström6, D. Sohler28, S. Takeuchi26, H. Törnqvist6,21, J. Tscheuschner6, V. Vaquero29, V. Wagner6, S. Wang30, V. Werner6, X. Xu3, H. Yamada26, D. Yan30, Z. Yang1,4, M. Yasuda26, and L. Zanetti6

  • *Contact author: frank.browne@manchester.ac.uk
  • †Deceased.
  • ‡Present address: Institut für Kernphysik, Universität zu Köln, D-50937 Cologne, Germany.
PDF

Phys. Rev. C 114, 014316 – Published 15 July, 2026

DOI: https://doi.org/10.1103/s6dz-2tbn

Abstract

Despite its nucleon numbers not coinciding with the traditional nuclear magic numbers, the structure of Ca54 shows signatures of a doubly closed shell nucleus. This article details the structures of neutron-excited states up to beyond the two-neutron emission threshold populated by the Ca55(p,pn) reaction at ∼200 MeV/nucleon. Level energies and population cross sections were determined through γ-ray spectroscopy and invariant-mass spectroscopy of Ca54. Large-scale shell model calculations with protons and neutrons allowed to occupy the sd−pf−sdg orbitals were performed to predict energy levels and spectroscopic factors. Distorted wave impulse approximation calculations provided single-particle knockout cross sections and momentum distributions of the reaction products. The theoretical calculations reproduce the data well. Both theory and experiment are suggestive of a well-preserved shell structure at high excitation energy. Also, inelastic scattering of Ca54, carried out within the same experiment, validates previously proposed level schemes.

View figure in article

Physics Subject Headings (PhySH)

Article Text

Supplemental Material

References (49)

  1. T. Otsuka, A. Gade, O. Sorlin, T. Suzuki, and Y. Utsuno, Evolution of shell structure in exotic nuclei, Rev. Mod. Phys. 92, 015002 (2020).
  2. T. Otsuka, R. Fujimoto, Y. Utsuno, B. A. Brown, M. Honma, and T. Mizusaki, Magic numbers in exotic nuclei and spin-isospin properties of the NN interaction, Phys. Rev. Lett. 87, 082502 (2001).
  3. A. Huck, G. Klotz, A. Knipper, C. Miehé, C. Richard-Serre, G. Walter, A. Poves, H. L. Ravn, and G. Marguier, Beta decay of the new isotopes K52, Ca52, and 52Sc; a test of the shell model far from stability, Phys. Rev. C 31, 2226 (1985).
  4. D. Steppenbeck et al., Evidence for a new nuclear ‘magic number’ from the level structure of Ca54, Nature (London) 502, 207 (2013).
  5. H. N. Liu et al., How Robust is the N=34 Subshell Closure? First Spectroscopy of Ar52, Phys. Rev. Lett. 122, 072502 (2019).
  6. F. Wienholtz et al., Masses of exotic calcium isotopes pin down nuclear forces, Nature (London) 498, 346 (2013).
  7. S. Michimasa et al., Magic nature of neutrons in Ca54: First mass measurements of Ca55–57, Phys. Rev. Lett. 121, 022506 (2018).
  8. A. Gade et al., Cross-shell excitation in two-proton knockout: Structure of Ca52, Phys. Rev. C 74, 021302(R) (2006).
  9. S. Chen et al., Quasifree neutron knockout from Ca54 corroborates arising N=34 neutron magic number, Phys. Rev. Lett. 123, 142501 (2019).
  10. M. Enciu et al., Extended p3/2 neutron orbital and the N=32 shell closure in Ca52, Phys. Rev. Lett. 129, 262501 (2022).
  11. Q. B. Zeng et al., β-decay half-lives of neutron-rich sulfur to potassium evolution of the N=32 and 34 subshell closures below calcium, Phys. Rev. Lett. 135, 232501 (2025).
  12. W.-J. Ong et al., Beta-decay half-lives beyond Ca54 a systematic survey of decay properties approaching the neutron dripline, Phys. Rev. Lett. 136, 092502 (2026).
  13. R. F. Garcia Ruiz et al., Unexpectedly large charge radii of neutron-rich calcium isotopes, Nature Phys. 12, 594 (2016).
  14. T. Koiwai et al., A first glimpse at the shell structure beyond Ca54: Spectroscopy of K55, Ca55, and Ca57, Phys. Lett. B 827, 136953 (2022).
  15. P. Li et al., Spectroscopy of deeply bound orbitals in neutron-rich Ca isotopes, Phys. Lett. B 855, 138828 (2024).
  16. S. Chen et al., Level structures of Ca56,58 cast doubt on a doubly magic Ca60, Phys. Lett. B 843, 138025 (2023).
  17. O. B. Tarasov et al., Discovery of Ca60 and Implications For the Stability of Ca70, Phys. Rev. Lett. 121, 022501 (2018).
  18. Y. Tsunoda, T. Otsuka, N. Shimizu, M. Honma, and Y. Utsuno, Novel shape evolution in exotic Ni isotopes and configuration-dependent shell structure, Phys. Rev. C 89, 031301(R) (2014).
  19. S. M. Lenzi, F. Nowacki, A. Poves, and K. Sieja, Island of inversion around Cr64, Phys. Rev. C 82, 054301 (2010).
  20. A. Magilligan, B. A. Brown, and S. R. Stroberg, Data-driven configuration-interaction Hamiltonian extrapolation to Ca60, Phys. Rev. C 104, L051302 (2021).
  21. M. Cortés et al., Shell evolution of N = 40 isotones towards Ca60: First spectroscopy of Ti62, Phys. Lett. B 800, 135071 (2020).
  22. F. Browne et al., Pairing Forces Govern Population of Doubly Magic Ca54 from Direct Reactions, Phys. Rev. Lett. 126, 252501 (2021).
  23. T. Wakasa, K. Ogata, and T. Noro, Proton-induced knockout reactions with polarized and unpolarized beams, Prog. Part. Nucl. Phys. 96, 32 (2017).
  24. Y. Yano, The RIKEN RI Beam Factory Project A status report, Nucl. Instrum. Meth. Phys. Res. B 261, 1009 (2007).
  25. T. Kubo et al., BigRIPS separator and ZeroDegree spectrometer at RIKEN RI Beam Factory, Prog. Theor. Exp. Phys. 2012, 03C003 (2012).
  26. N. Fukuda, T. Kubo, T. Ohnishi, N. Inabe, H. Takeda, D. Kameda, and H. Suzuki, Identification and separation of radioactive isotope beams by the BigRIPS separator at the RIKEN RI Beam Factory, Nucl. Instrum. Meth. Phys. Res. B 317, 323 (2013).
  27. T. Kobayashi et al., SAMURAI spectrometer for RI beam experiments, Nucl. Instrum. Meth. Phys. Res. B 317, 294 (2013).
  28. A. Obertelli et al., MINOS: A vertex tracker coupled to a thick liquid-hydrogen target for in-beam spectroscopy of exotic nuclei, Eur. Phys. J. A 50, 8 (2014).
  29. S. Takeuchi, T. Motobayashi, Y. Togano, M. Matsushita, N. Aoi, K. Demichi, H. Hasegawa, and H. Murakami, DALI2: A NaI(Tl) detector array for measurements of γ rays from fast nuclei, Nucl. Instrum. Meth. Phys. Res. A 763, 596 (2014).
  30. I. Murray et al., RIKEN Accel. Prog. Rep. 51, 158 (2018).
  31. S. Agostinelli et al., Geant4—a simulation toolkit, Nucl. Instrum. Meth. Phys. Res. A 506, 250 (2003).
  32. K. Boretzky et al., NeuLAND: The high-resolution neutron time-of-flight spectrometer for R3B at FAIR, Nucl. Instrum. Meth. Phys. Res. A 1014, 165701 (2021).
  33. T. Nakamura and Y. Kondo, Large acceptance spectrometers for invariant mass spectroscopy of exotic nuclei and future developments, Nucl. Instrum. Meth. Phys. Res. B 376, 156 (2016).
  34. M. Honma, T. Otsuka, B. A. Brown, and T. Mizusaki, Effective interaction for pf -shell nuclei, Phys. Rev. C 65, 061301(R) (2002).
  35. M. Honma, T. Otsuka, B. A. Brown, and T. Mizusaki, New effective interaction for pf -shell nuclei and its implications for the stability of the N=Z=28 closed core, Phys. Rev. C 69, 034335 (2004).
  36. Y. Utsuno, T. Otsuka, B. A. Brown, M. Honma, T. Mizusaki, and N. Shimizu, Shell evolution around and beyond N=28 studied with large-scale shell-model calculations, Prog. Theor. Phys. Suppl. 196, 304 (2012).
  37. N. Shimizu, T. Mizusaki, Y. Utsuno, and Y. Tsunoda, Thick-restart block Lanczos method for large-scale shell-model calculations, Comput. Phys. Commun. 244, 372 (2019).
  38. K. Ogata, K. Yoshida, and Y. Chazono, PIKOE A computer program for distorted-wave impulse approximation calculation for proton induced nucleon knockout reactions, Comput. Phys. Commun. 297, 109058 (2024).
  39. P. F. Mantica et al., β decay of neutron-rich Ca53–56, Phys. Rev. C 77, 014313 (2008).
  40. See Supplemental Material at http://link.aps.org/supplemental/10.1103/s6dz-2tbn for details of relative-energy spectra fitting, γ-ray coincidences from the p,p′ channel, and a more complete list of results from the shell model calculation, which also includes Refs. [48, 49].
  41. T. Aumann et al., Quenching of single-particle strength from direct reactions with stable and rare-isotope beams, Prog. Part. Nucl. Phys. 118, 103847 (2021).
  42. Y. Sun et al., Restoration of the natural E(1/21+)−E(3/21+) energy splitting in odd-K isotopes towards N=40, Phys. Lett. B 802, 135215 (2020).
  43. M. L. Cortés et al., N=32 shell closure below calcium: Low-lying structure of Ar50, Phys. Rev. C 102, 064320 (2020).
  44. H. L. Crawford et al., β decay and isomeric properties of neutron-rich Ca and Sc isotopes, Phys. Rev. C 82, 014311 (2010).
  45. G. Hagen, M. Hjorth-Jensen, G. R. Jansen, R. Machleidt, and T. Papenbrock, Evolution of shell structure in neutron-rich calcium isotopes, Phys. Rev. Lett. 109, 032502 (2012).
  46. J. D. Holt, T. Otsuka, A. Schwenk, and T. Suzuki, Three-body forces and shell structure in calcium isotopes, J. Phys. G 39, 085111 (2012).
  47. J. D. Holt, J. Menéndez, J. Simonis, and A. Schwenk, Three-nucleon forces and spectroscopy of neutron-rich calcium isotopes, Phys. Rev. C 90, 024312 (2014).
  48. M. Vandebrouck et al. (R3B Collaboration), Effective proton-neutron interaction near the drip line from unbound states in F25,26, Phys. Rev. C 96, 054305 (2017).
  49. A. Revel et al. (SAMURAI21 Collaboration), Extending the Southern Shore of the Island of Inversion to F28, Phys. Rev. Lett. 124, 152502 (2020).

Outline

Information

Phys. Rev. C 114, 014316– Published 15 July, 2026
  • Received 15 April 2026
  • Accepted 2 June 2026
Crossmark - Check for updates button
Creative Commons Logo

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.

Published by the American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation