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 Schatz; M Scott; D Shapira; K Smith; J Stevens; W Tan; O Tarasov; S Towers; K Wimmer; J R Winkelbauer; J Yurkon; R G T Zegers

doi:10.1103/PhysRevLett.114.022501

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

Phys Rev Lett. 2015 Jan 16;114(2):022501. doi: 10.1103/PhysRevLett.114.022501. Epub 2015 Jan 15.

Authors

Z Meisel¹, S George², S Ahn³, J Browne¹, D Bazin⁴, B A Brown⁵, J F Carpino⁶, H Chung⁶, R H Cyburt³, A Estradé⁷, M Famiano⁶, A Gade⁵, C Langer³, M Matoš⁸, W Mittig⁵, F Montes³, D J Morrissey⁹, J Pereira³, H Schatz¹, J Schatz⁴, M Scott⁵, D Shapira¹⁰, K Smith¹¹, J Stevens¹, W Tan¹², O Tarasov⁴, S Towers⁶, K Wimmer⁴, J R Winkelbauer⁵, J Yurkon⁴, R G T Zegers¹

Affiliations

¹ National 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.
² National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, 48824 Michigan, USA and Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany.
³ National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, 48824 Michigan, USA.
⁴ National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA.
⁵ National 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.
⁶ Department of Physics, Western Michigan University, Kalamazoo, 49008 Michigan, USA.
⁷ School of Physics and Astronomy, The University of Edinburgh, EH8 9YL Edinburgh, United Kingdom.
⁸ Department of Physics and Astronomy, Louisiana State University, Baton Rouge, 70803 Louisiana, USA.
⁹ National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA and Department of Chemistry, Michigan State University, East Lansing, 48824 Michigan, USA.
¹⁰ Oak Ridge National Laboratory, Oak Ridge, 37831 Tennessee, USA.
¹¹ Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, 48824 Michigan, USA and Department of Physics, University of Notre Dame, South Bend, 46556 Indiana, USA.
¹² Department of Physics, University of Notre Dame, South Bend, 46556 Indiana, USA.

PMID: 25635542
DOI: 10.1103/PhysRevLett.114.022501

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.