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Phys. Rev. Lett. 100, 152502 (2008) [5 pages]

Determination of the N=16 Shell Closure at the Oxygen Drip Line

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C. R. Hoffman1,*, T. Baumann2, D. Bazin2, J. Brown3, G. Christian2,4, P. A. DeYoung5, J. E. Finck6, N. Frank2,4,†, J. Hinnefeld7, R. Howes8, P. Mears5, E. Mosby9, S. Mosby9, J. Reith5, B. Rizzo8, W. F. Rogers9, G. Peaslee5, W. A. Peters2,4,‡, A. Schiller2,§, M. J. Scott6, S. L. Tabor1, M. Thoennessen2,4, P. J. Voss6, and T. Williams3
1Department of Physics, Florida State University, Tallahassee, Florida 32303, USA
2National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA
3Department of Physics, Wabash College, Crawfordsville, Indiana 47933, USA
4Department of Physics & Astronomy, Michigan State University, East Lansing, Michigan 48824, USA
5Department of Physics, Hope College, Holland, Michigan 49423, USA
6Department of Physics, Central Michigan University, Mt. Pleasant, Michigan, 48859, USA
7Department of Physics & Astronomy, Indiana University at South Bend, South Bend, Indiana 46634, USA
8Department of Physics, Marquette University, Milwaukee, Wisconsin 53201, USA
9Department of Physics, Westmont College, Santa Barbara, California 93108, USA

Received 22 December 2007; published 17 April 2008

The neutron unbound ground state of 25O (Z=8, N=17) was observed for the first time in a proton knockout reaction from a 26F beam. A single resonance was found in the invariant mass spectrum corresponding to a neutron decay energy of 770-10+20  keV with a total width of 172(30) keV. The N=16 shell gap was established to be 4.86(13) MeV by the energy difference between the ν1s1/2 and ν0d3/2 orbitals. The neutron separation energies for 25O agree with the calculations of the universal sd shell model interaction. This interaction incorrectly predicts an 26O ground state that is bound to two-neutron decay by 1 MeV, leading to a discrepancy between the theoretical calculations and experiment as to the particle stability of 26O. The observed decay width was found to be on the order of a factor of 2 larger than the calculated single-particle width using a Woods-Saxon potential.

© 2008 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.100.152502
DOI:
10.1103/PhysRevLett.100.152502
PACS:
21.10.Pc, 25.60.−t, 27.30.+t, 29.30.Hs

*calem.hoffman@gmail.com

†Present address: Physics Department, Illinois Wesleyan University, Bloomington, IL 61701, USA.

‡Present address: Department of Physics & Astronomy, Rutgers University, Piscataway, NJ 08854, USA.

§Present address: Department of Physics & Astronomy, Ohio University, Athens, OH 45701, USA.

 
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