Core of F25 in the rotational model

Abstract

In a recent experiment, carried out at RIBF/RIKEN, the 25 F(p, 2p) 24 O reaction was studied at 270 MeV/A in inverse kinematics. Derived spectroscopic factors suggest that the effective core of 25 F significantly differs from a free 24 O nucleus. We interpret these results within the Particle-Rotor Model and show that the experimental level scheme of 25 F can be understood in the rotation-aligned coupling scheme, with its 5/2 + 1 ground state as the band-head of a decoupled band. The excitation energies of the observed 1/2 + 1 and 9/2 + 1 states correlate strongly with the rotational energy of the effective core, seen by the odd proton, and allow us to estimate its 2 + energy at ≈ 3.2 MeV and a moderate quadrupole deformation, 2 ≈ 0.15. The measured fragmentation of the πd 5/2 singleparticle strength is discussed and some further experiments suggested.

To Shell Model, or Not to Shell Model, That Is the Question

“…Deformation in nuclei immediately adjacent to closed shells has become a recent focus in the odd-mass F (Z = 9) isotopes [177]. The data are consistent with deformed ground states.…”

Core of F25 studied by the F25(−p ) proton-removal

“…In our earlier works [20,21], we interpreted the structure of both 25,29 F in the framework of the Nilsson plus Particle Rotor model (PRM) [22][23][24] where the coupling of a proton d 5/2 Nilsson multiplet to an effective oxygen core of modest deformation, β 2 ∼ 0.16, can be understood in the rotation-aligned coupling limit. This gives rise to a decoupled band [25] in agreement with the observed levels where the d 5/2 strength is fragmented among the ground and excited states, consistent with the reduced d 5/2 strength in 25 F ground state, observed in the current work.…”

“…In the former, a 1 + −4 + multiplet arises from the renormalized single-particle states π |d 5/2 ⊗ ν |d 3/2 with the 1 + favored by the Gallagher-Moskowski rules [30]. In the later, the 1 + (4 + ) state can be interpreted as antiparallel (parallel) doubly-decoupled bandhead [21]. It seems clear, that high-resolution spectroscopy studies of excited states in 26 F (as well as 30 F where the oddneutron occupies the f 7/2 level) should be pursued.…”

“…Expanding upon the Particle Rotor model (PRM) interpretation of the 25 F structure of Ref. [21], here we have considered the coupling of a d 5/2 proton to a quadrupole vibrational core. Unsurprisingly, the Particle Vibration Coupling (PVC) approach also provides a good description of the experimental data by requiring an effective 24 O* core with a phonon energy, hω 2 = 3.2 MeV, and a B(E2) ≈ 2.7 W.u.…”