Magicity versus Superfluidity around ^{28}O viewed from the Study of ^{30}F

Area of Science:

• Nuclear Physics
• Atomic Physics
• Quantum Mechanics

Background:

• The N=20 shell gap is a key feature in nuclear structure theory.
• Understanding the properties of neutron-rich isotopes near the drip line is crucial for testing nuclear models.

Purpose of the Study:

• To observe the neutron-rich unbound fluorine isotope ^{30}F for the first time.
• To determine the mass and one-neutron-separation energy of ^{30}F.
• To investigate the N=20 shell gap and nuclear shell evolution in this region.

Main Methods:

• Measurement of neutron decay of ^{30}F using the SAMURAI spectrometer at RIKEN.
• Utilizing a quasifree proton knockout reaction on ^{31}Ne nuclei at 235 MeV/nucleon.
• Analysis of the invariant-mass spectrum to determine the separation energy.

Main Results:

• The isotope ^{30}F was observed for the first time.
• The one-neutron-separation energy of ^{30}F was determined to be S_{n}=-472±58(stat)±33(sys) keV.
• The N=20 shell gap is not restored near ^{28}O, contrary to some expectations.

Conclusions:

• The observed properties of ^{30}F indicate a near degeneracy and reordering of neutron orbitals (d and fp).
• ^{28}O may exhibit strong superfluidity due to neutron pairs scattering across shells.
• ^{29,31}F are identified as potential candidates for two-neutron halo nuclei.