Abstract:
The experimental states of nuclei, close to semi-magic nuclei, having one extra proton on top of closed
proton core, in general, connote the arrangement of proton orbitals within a shell. Herein, we have studied
the arrangement of proton orbitals (π0d5/2, π1s1/2 and π0d3/2) in sd-shell for Fluorine isotopes within
the nuclear shell model framework. The contribution of different components of effective nucleon-nucleon
interaction in the evolution of the energies of proton orbitals, and the orbital energy gaps π0d5/2 −π1s1/2
and π0d5/2 − π0d3/2 at 23,25F has been examined. Results show the evolution of quasi-shell gap at 23F
due to key contribution of central force, in particular, of its even-channel, and destructive interference in the
contribution of spin–orbit and tensor force. The excitation energies of 1
2
+
1 and 3
2
+
1 states of 23F, and 1
2
+
1
state of 25F are in good agreement with their respective orbital energy gaps. The origin of 3
2
+
1 state of 25F
and its excitation energy has been delineated as an effect of the breakdown of semi-magic core 24O.
