Low-Lying Structure of Ar50 and the N=32 Subshell Closure

D. Steppenbeck, S. Takeuchi, N. Aoi, P. Doornenbal, M. Matsushita, H. Wang, Y. Utsuno, H. Baba, S. Go, J. Lee, K. Matsui, S. Michimasa, T. Motobayashi, D. Nishimura, T. Otsuka, H. Sakurai, Y. Shiga, N. Shimizu, P.-A. Söderström, T. Sumikama, R. Taniuchi, J. J. Valiente-Dobón, and K. Yoneda
Phys. Rev. Lett. 114, 252501 – Published 25 June 2015

Abstract

The low-lying structure of the neutron-rich nucleus Ar50 has been investigated at the Radioactive Isotope Beam Factory using in-beam γ-ray spectroscopy with Be9(Ca54,Ar50+γ)X, Be9(Sc55,Ar50+γ)X, and Be9(Ti56,Ar50+γ)X multinucleon removal reactions at 220  MeV/u. A γ-ray peak at 1178(18) keV is reported and assigned as the transition from the first 2+ state to the 0+ ground state. A weaker, tentative line at 1582(38) keV is suggested as the 41+21+ transition. The experimental results are compared to large-scale shell-model calculations performed in the sdpf model space using the SDPF-MU effective interaction with modifications based on recent experimental data for exotic calcium and potassium isotopes. The modified Hamiltonian provides a satisfactory description of the new experimental results for Ar50 and, more generally, reproduces the energy systematics of low-lying states in neutron-rich Ar isotopes rather well. The shell-model calculations indicate that the N=32 subshell gap in Ar50 is similar in magnitude to those in Ca52 and Ti54 and, notably, predict an N=34 subshell closure in Ar52 that is larger than the one recently reported in Ca54.

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  • Received 20 April 2015

DOI:https://doi.org/10.1103/PhysRevLett.114.252501

© 2015 American Physical Society

Authors & Affiliations

D. Steppenbeck1,*, S. Takeuchi2,†, N. Aoi3, P. Doornenbal2, M. Matsushita1, H. Wang2, Y. Utsuno4, H. Baba2, S. Go1,‡, J. Lee2,§, K. Matsui5, S. Michimasa1, T. Motobayashi2, D. Nishimura6, T. Otsuka1,5, H. Sakurai2,5, Y. Shiga7, N. Shimizu1, P.-A. Söderström2, T. Sumikama8,∥, R. Taniuchi5, J. J. Valiente-Dobón9, and K. Yoneda2

  • 1Center for Nuclear Study, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan
  • 2RIKEN Nishina Center, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan
  • 3Research Center for Nuclear Physics, University of Osaka, Ibaraki, Osaka 567-0047, Japan
  • 4Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
  • 5Department of Physics, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan
  • 6Department of Physics, Tokyo University of Science, Noda, Chiba 278-8510, Japan
  • 7Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501, Japan
  • 8Department of Physics, Tohoku University, Sendai, Miyagi 980-8578, Japan
  • 9Istituto 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, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
  • Present address: Department of Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996-1200, USA.
  • §Present address: Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong.
  • Present address: RIKEN Nishina Center, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan.

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Vol. 114, Iss. 25 — 26 June 2015

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