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.
ASJC Scopus subject areas
- Physics and Astronomy (all)