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21.10.Dr, 21.60.Cs, 27.50.+e, 32.10.Bi
Abstract:
High-precision mass measurements of more than 30 neutron-rich nuclides around the Z = 28 closed proton
shell were performed with the triple-trap mass spectrometer ISOLTRAPat ISOLDE/CERN to address the question
of a possible neutron shell closure at N = 40. The results for 57,60,64−69Ni (Z = 28), 65−74,76Cu (Z = 29), and
63−65,68−78Ga (Z = 31) have a relative uncertainty of the order of 10−8. In particular, the mass of 76Cu was
measured for the first time. We analyze the resulting mass surface for signs of magicity, comparing the behavior
of N = 40 with that of known magic numbers and with midshell behavior. While the classic indications from
the mass surface show no evidence for a shell closure at N = 40, there is evidence for a weak—and very
localized—effect for Z = 28, consistent with findings from nuclear spectroscopy studies.
