title: Mass measurements demonstrate a strong N=28 shell gap 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 ^{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.
authors: 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.
authors: Z
authors: Z
authors: Meisel
authors: 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.
authors: S
authors: S
authors: George
authors: 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.
authors: S
authors: S
authors: Ahn
authors: 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.
authors: J
authors: J
authors: Browne
authors: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA.
authors: D
authors: D
authors: Bazin
authors: 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.
authors: B A
authors: BA
authors: Brown
authors: Department of Physics, Western Michigan University, Kalamazoo, 49008 Michigan, USA.
authors: J F
authors: JF
authors: Carpino
authors: Department of Physics, Western Michigan University, Kalamazoo, 49008 Michigan, USA.
authors: H
authors: H
authors: Chung
authors: 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.
authors: R H
authors: RH
authors: Cyburt
authors: School of Physics and Astronomy, The University of Edinburgh, EH8 9YL Edinburgh, United Kingdom.
authors: A
authors: A
authors: Estradé
authors: Department of Physics, Western Michigan University, Kalamazoo, 49008 Michigan, USA.
authors: M
authors: M
authors: Famiano
authors: 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.
authors: A
authors: A
authors: Gade
authors: 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.
authors: C
authors: C
authors: Langer
authors: Department of Physics and Astronomy, Louisiana State University, Baton Rouge, 70803 Louisiana, USA.
authors: M
authors: M
authors: Matoš
authors: 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.
authors: W
authors: W
authors: Mittig
authors: 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.
authors: F
authors: F
authors: Montes
authors: 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.
authors: D J
authors: DJ
authors: Morrissey
authors: 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.
authors: J
authors: J
authors: Pereira
authors: 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.
authors: H
authors: H
authors: Schatz
authors: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA.
authors: J
authors: J
authors: Schatz
authors: 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.
authors: M
authors: M
authors: Scott
authors: Oak Ridge National Laboratory, Oak Ridge, 37831 Tennessee, USA.
authors: D
authors: D
authors: Shapira
authors: 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.
authors: K
authors: K
authors: Smith
authors: 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.
authors: J
authors: J
authors: Stevens
authors: Department of Physics, University of Notre Dame, South Bend, 46556 Indiana, USA.
authors: W
authors: W
authors: Tan
authors: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA.
authors: O
authors: O
authors: Tarasov
authors: Department of Physics, Western Michigan University, Kalamazoo, 49008 Michigan, USA.
authors: S
authors: S
authors: Towers
authors: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA.
authors: K
authors: K
authors: Wimmer
authors: 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.
authors: J R
authors: JR
authors: Winkelbauer
authors: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824 Michigan, USA.
authors: J
authors: J
authors: Yurkon
authors: 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.
authors: R G T
authors: RG
authors: Zegers