Mass measurements demonstrate a strong N=28 shell gap in argon

Z. Meisel, S. George, S. Ahn, J. Browne, D. Bazin, B. A. Brown, J. F. Carpino, H. Chung, R. H. Cyburt, A. Estradé, M. Famiano, A. Gade, C. Langer, M. Matoš, W. Mittig, F. Montes, D. J. Morrissey, J. Pereira, H. Schatz, J. SchatzM. Scott, D. Shapira, K. Smith, J. Stevens, W. Tan, O. Tarasov, S. Towers, K. Wimmer, J. R. Winkelbauer, J. Yurkon, R. G.T. Zegers

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Abstract

We present results from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. We report the first mass measurements of Ar48 and Ar49 and find atomic mass excesses of -22.28(31)MeV and -17.8(1.1)MeV, respectively. These masses provide strong evidence for the closed shell nature of neutron number N=28 in argon, which is therefore the lowest even-Z element exhibiting the N=28 closed shell. The resulting trend in binding-energy differences, which probes the strength of the N=28 shell, compares favorably with shell-model calculations in the sd-pf shell using SDPF-U and SDPF-MU Hamiltonians.

Original languageEnglish
Article number022501
JournalPhysical Review Letters
Volume114
Issue number2
DOIs
StatePublished - Jan 15 2015

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