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

Z Meisel¹, S George², S Ahn³

¹National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA and Department of Physics and Astronomy, Michigan State University, East Lansing, 48824 Michigan, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, 48824 Michigan, USA.

Physical Review Letters

|January 31, 2015

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 ^{48}Ar and ^{49}Ar 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.

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