Structure of Sc55 and development of the N=34 subshell closure

D. Steppenbeck, S. Takeuchi, N. Aoi, P. Doornenbal, M. Matsushita, H. Wang, H. Baba, S. Go, J. D. Holt, J. Lee, K. Matsui, S. Michimasa, T. Motobayashi, D. Nishimura, T. Otsuka, H. Sakurai, Y. Shiga, P.-A. Söderström, S. R. Stroberg, T. Sumikama, R. Taniuchi, J. A. Tostevin, Y. Utsuno, J. J. Valiente-Dobón, and K. Yoneda
Phys. Rev. C 96, 064310 – Published 11 December 2017

Abstract

The low-lying structure of Sc55 has been investigated using in-beam γ-ray spectroscopy with the Be9(Ti56,Sc55+γ)X one-proton removal and Be9(Sc55,Sc55+γ)X inelastic-scattering reactions at the RIKEN Radioactive Isotope Beam Factory. Transitions with energies of 572(4), 695(5), 1539(10), 1730(20), 1854(27), 2091(19), 2452(26), and 3241(39) keV are reported, and a level scheme has been constructed using γγ coincidence relationships and γ-ray relative intensities. The results are compared to large-scale shell-model calculations in the sdpf model space, which account for positive-parity states from proton-hole cross-shell excitations, and to ab initio shell-model calculations from the in-medium similarity renormalization group that includes three-nucleon forces explicitly. The results of proton-removal reaction theory with the eikonal model approach were adopted to aid identification of positive-parity states in the level scheme; experimental counterparts of theoretical 1/21+ and 3/21+ states are suggested from measured decay patterns. The energy of the first 3/2 state, which is sensitive to the neutron shell gap at the Fermi surface, was determined. The result indicates a rapid weakening of the N=34 subshell closure in pf-shell nuclei at Z>20, even when only a single proton occupies the πf7/2 orbital.

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  • Received 4 August 2017
  • Revised 22 September 2017

DOI:https://doi.org/10.1103/PhysRevC.96.064310

©2017 American Physical Society

Physics Subject Headings (PhySH)

Nuclear Physics

Authors & Affiliations

D. Steppenbeck1,*, S. Takeuchi2, N. Aoi3, P. Doornenbal1, M. Matsushita4, H. Wang1, H. Baba1, S. Go4,†, J. D. Holt5, J. Lee1,‡, K. Matsui6, S. Michimasa4, T. Motobayashi1, D. Nishimura7, T. Otsuka4,6,†, H. Sakurai1,6, Y. Shiga8, P.-A. Söderström1,§, S. R. Stroberg5, T. Sumikama9,†, R. Taniuchi1,6, J. A. Tostevin10, Y. Utsuno11, J. J. Valiente-Dobón12, and K. Yoneda1

  • 1RIKEN Nishina Center, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan
  • 2Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
  • 3Research Center for Nuclear Physics, University of Osaka, Ibaraki, Osaka 567-0047, Japan
  • 4Center for Nuclear Study, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan
  • 5TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia, Canada V6T 2A3
  • 6Department of Physics, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan
  • 7Department of Physics, Tokyo City University, Setagaya, Tokyo 158-8557, Japan
  • 8Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501, Japan
  • 9Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan
  • 10Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
  • 11Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
  • 12Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Legnaro 35020, Italy

  • *steppenbeck@riken.jp
  • Present address: RIKEN Nishina Center, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan.
  • Present address: Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong.
  • §Present address: Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany.

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Vol. 96, Iss. 6 — December 2017

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