Excited states in the neutron-rich nucleus ${}^{25}\mathrm{F}$

The structure of the nucleus ${}_9^{25}$F was investigated through in-beam $\gamma$-ray spectroscopy of the fragmentation of ${}^{26}\mathrm{Ne}$ and ${}^{27,28}\mathrm{Na}$ ion beams. Based on the particle-$\gamma$ and particle-$\gamma \gamma$ coincidence data, a level scheme was constructed and compared with shell model and coupled-cluster calculations. Some of the observed states were interpreted as quasi-single-particle states built on top of the closed-shell nucleus ${}^{24}\mathrm{O}$, while the others were described as states arising from coupling of a single proton to the $2^{+}$ core excitation of ${}^{24}\mathrm{O}$.

Figure 1

Decomposition of the $\gamma$-ray spectrum of ${}^{25}$F. The solid black (dark) line shows the final fit which includes the response functions from geant4 simulation [green (light) solid curves] and the additional exponential background plotted as dashed red line.

Figure 2

Spectra of ${}^{25}$F from $\gamma \gamma$ coincidence using the 750, 1720, and 3440 keV transitions as gates.

Figure 3

Proposed level scheme of ${}^{25}$F compared to the shell model calculations performed using the usd, usda, and usdb interactions. Energies are given along the transitions as well as their relative intensities in italics. The uncertainties of the relative intensities are below 20%. The 2140 keV line has been adopted from Ref. [18].

Figure 4

Relative energies of ${}^{25}$F calculated using coupled-cluster theory with two different interactions compared with experiment. The label N${}^2$LO refers to the optimized chiral interaction at third order [31], while the interaction labeled N${}^3$LO+3NF is the chiral interaction of Ref. [32] where the effect of three nucleon forces are treated as a density-dependent nucleon-nucleon force (see text for details).