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. Estrad\'e, M. Famiano, A. Gade, C., Langer, M. Mato\v{s}, W. Mittig, F. Montes, D. J. Morrissey, J. Pereira, H., Schatz, J. Schatz, M. Scott, D. Shapira, K. Smith
TL;DR
This study reports new mass measurements of argon isotopes, providing strong evidence for a closed neutron shell at N=28 in argon, and compares the results with shell model calculations.
Contribution
First mass measurements of 48Ar and 49Ar confirming the N=28 shell closure in argon, the lowest even-Z element with this feature.
Findings
Mass excess of 48Ar: -22.28(31) MeV
Mass excess of 49Ar: -17.8(1.1) MeV
Strong evidence for N=28 shell closure in argon
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 48Ar and 49Ar 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 shellmodel calculations in the sd-pf shell using SDPF-U and SDPF-MU Hamiltonians.
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