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Phys. Rev. Lett. 85, 266 - 269 (2000)

Direct Evidence for the Breakdown of the N  =  8 Shell Closure in 12Be

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A. Navin1,2, D. W. Anthony1,3, T. Aumann1 *, T. Baumann1, D. Bazin1, Y. Blumenfeld1 †, B. A. Brown1,4, T. Glasmacher1,4, P. G. Hansen1,4, R. W. Ibbotson5, P. A. Lofy1,3, V. Maddalena1,4, K. Miller1,4, T. Nakamura1,6, B. V. Pritychenko1,4, B. M. Sherrill1,4, E. Spears1,4, M. Steiner1, J. A. Tostevin7, J. Yurkon1, and A. Wagner1 ‡
1National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824
2Nuclear Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India
3Department of Chemistry, Michigan State University, East Lansing, Michigan 48824
4Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824
5Brookhaven National Laboratory, Upton, New York 11973-5000
6Department of Physics, University of Tokyo, 7-3-1 Hongo Bunkyo, Tokyo 113-0033, Japan
7Department of Physics, University of Surrey, Guildford, Surrey, GU2 5XH, United Kingdom

Received 18 November 1999

Partial cross sections and corresponding momentum distributions have been studied in the one-neutron knockout reaction ( 12Be,11Be+γ) on a 9Be target at 78 MeV/nucleon. The resulting spectroscopic factors for the only two bound states of 11Be are 0.42±0.06 ( 1/2+) and 0.37±0.06 ( 1/2-), where the errors are experimental only. This result shows that N  =  8 is not a good closed shell in the neutron-rich 12Be and that the last neutron pair is two-thirds in the ( 1s2+0d2) intruder configuration.


©2000 The American Physical Society

URL: http://link.aps.org/doi/10.1103/PhysRevLett.85.266
DOI: 10.1103/PhysRevLett.85.266
PACS: 25.60.-t, 21.60.Cs, 24.10.-i, 27.20.+n

* Present address: Gesellschaft für Schwerionenforschung, Planckstrasse 1, 64291 Darmstadt, Germany.
† Permanent address: Institut de Physique Nucleaire, IN2P3-CNRS, 91406 Orsay, Cedex, France.
‡ Present address: Institute of Nuclear and Hadron Physics, PB 510119, D-01314 Dresden, Germany.

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