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β decay of the proton-rich nucleus Si24 and its mirror asymmetry

Y. Ichikawa1,2,*, T. K. Onishi1, D. Suzuki1, H. Iwasaki1, T. Kubo2, V. Naik3, A. Chakrabarti3, N. Aoi2, B. A. Brown4 et al.

N. Fukuda2, S. Kubono5, T. Motobayashi2, T. Nakabayashi6, T. Nakamura6, T. Nakao1, T. Okumura6, H. J. Ong7, H. Suzuki1, M. K. Suzuki1, T. Teranishi8, K. N. Yamada2, H. Yamaguchi5, and H. Sakurai1,2

  • 1Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
  • 2RIKEN Nishina Center, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
  • 3Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata-700 064, India
  • 4Department of Physics and Astronomy, and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824-1321, USA
  • 5Center for Nuclear Study, University of Tokyo, RIKEN Campus, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
  • 6Department of Physics, Tokyo Institute of Technology, 2-12-1 Oh-okayama, Meguro, Tokyo 152-8551, Japan
  • 7Research Center for Nuclear Physics, Osaka University, 10-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
  • 8Department of Physics, Kyushu University, 6-10-1 Hakozaki, Higashi, Fukuoka 812-8581, Japan

  • *ichikawa@ribf.riken.jp; present address: RIKEN Nishina Center, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
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Phys. Rev. C 80, 044302 – Published 5 October, 2009

DOI: https://doi.org/10.1103/PhysRevC.80.044302

Abstract

β-decay spectroscopy of the proton-rich nucleus Si24 was performed. The decay scheme was reconstructed from results of delayed γ-ray and proton measurements. We observed two β branches to bound states in Al24 for the first time. The branching ratios were determined to be 31(4)% and 23.9(15)% for the 11+ state at 0.426 MeV and the state at 1.090 MeV, respectively. The observation of an allowed transition to the 1.090-MeV state enabled us to firmly determine its spin-parity as 1+. In the proton measurements performed with the ΔE−E method, we observed a new unbound level at 6.735 MeV. The branching ratios to three unbound states, including the new level, were also determined for the first time. Based on the decay scheme, the B(GT) values of Si24 were deduced. The B(GT) values were smaller than those of the mirror nucleus Ne24 by 22% and 10% for the 11+ and 12+ states, respectively. The mirror asymmetries of B(GT), observed in both the 11+ and the 12+ states, indicate changes in configuration in the wave function associated with the Thomas-Ehrman shift. To clarify the mechanism of this asymmetry, a comparison with shell-model calculations is also discussed. The calculations attribute the changes in configuration to the lowering of the 1s1/2 orbital.

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Phys. Rev. C 80, 044302– Published 5 October, 2009
  • Received 26 June 2009

© 2009 American Physical Society

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