Direct Evidence for the Breakdown of the <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="italic">N</mi><mspace></mspace><mo>=</mo><mspace></mspace><mn>8</mn><mn></mn></math></span> Shell Closure in <span class="aps-inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>B</mi></mrow><mprescripts></mprescripts><mrow></mrow><mrow><mn>12</mn></mrow><mrow></mrow><mrow></mrow></mmultiscripts></mrow><mi>e</mi></math></span>

A. Navin; D. W. Anthony; T. Aumann; T. Baumann; D. Bazin; Y. Blumenfeld; B. A. Brown; T. Glasmacher; P. G. Hansen; R. W. Ibbotson; P. A. Lofy; V. Maddalena; K. Miller; T. Nakamura; B. V. Pritychenko; B. M. Sherrill; E. Spears; M. Steiner; J. A. Tostevin; J. Yurkon; A. Wagner

doi:10.1103/PhysRevLett.85.266

Direct Evidence for the Breakdown of the $N = 8$ Shell Closure in ${}^{12}B e$

A. Navin, D. W. Anthony, T. Aumann, T. Baumann, D. Bazin, Y. Blumenfeld, B. A. Brown, T. Glasmacher, P. G. Hansen, R. W. Ibbotson, P. A. Lofy, V. Maddalena, K. Miller, T. Nakamura, B. V. Pritychenko, B. M. Sherrill, E. Spears, M. Steiner, J. A. Tostevin, J. Yurkon, and A. Wagner

Phys. Rev. Lett. 85, 266 – Published 10 July 2000

Abstract

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

Received 18 November 1999

DOI:https://doi.org/10.1103/PhysRevLett.85.266

Authors & Affiliations

A. Navin^1,2, D. W. Anthony^1,3, T. Aumann^1,*, T. Baumann¹, D. Bazin¹, Y. Blumenfeld^1,†, B. A. Brown^1,4, T. Glasmacher^1,4, P. G. Hansen^1,4, R. W. Ibbotson⁵, P. A. Lofy^1,3, V. Maddalena^1,4, K. Miller^1,4, T. Nakamura^1,6, B. V. Pritychenko^1,4, B. M. Sherrill^1,4, E. Spears^1,4, M. Steiner¹, J. A. Tostevin⁷, J. Yurkon¹, and A. Wagner^1,‡

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

^*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.