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Published on: July 27, 2018
Magicity versus Superfluidity around ^{28}O viewed from the Study of ^{30}F
J Kahlbow1,2, T Aumann1,3,4, O Sorlin5
1Institut für Kernphysik, <a href="https://ror.org/05n911h24">Technische Universität Darmstadt</a>, 64289 Darmstadt, Germany.
Abstract:
The neutron-rich unbound fluorine isotope ^{30}F_{21} has been observed for the first time by measuring its neutron decay at the SAMURAI spectrometer (RIBF, RIKEN) in the quasifree proton knockout reaction of ^{31}Ne nuclei at 235 MeV/nucleon. The mass and thus one-neutron-separation energy of ^{30}F has been determined to be S_{n}=-472±58(stat)±33(sys) keV from the measurement of its invariant-mass spectrum. The absence of a sharp drop in S_{n}(^{30}F) shows that the "magic" N=20 shell gap is not restored close to ^{28}O, which is in agreement with our shell-model calculations that predict a near degeneracy between the neutron d and fp orbitals, with the 1p_{3/2} and 1p_{1/2} orbitals becoming more bound than the 0f_{7/2} one. This degeneracy and reordering of orbitals has two potential consequences: ^{28}O behaves like a strongly superfluid nucleus with neutron pairs scattering across shells, and both ^{29,31}F appear to be good two-neutron halo-nucleus candidates.
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