Neutron-unbound states in ${}^{25,26}$F

Neutron-unbound states in ${}^{25}$F and ${}^{26}$F were populated via the reactions ${}^9$Be(${}^{26}$Ne,${}^{24}$F + n) and ${}^9$Be(${}^{26}$Ne,${}^{25}$F + n), respectively. A resonance close to the neutron separation energy in ${}^{25}$F was identified with a decay energy of $28\pm 4$ keV. This resonance corresponds to an excited state in ${}^{25}$F at $4249\pm 116$ keV assuming it decays to the ground state of ${}^{24}$F. Guided by shell-model calculations, a spin and parity of 1/2${}^{-}$ can be assigned to this state. In the spectrum of ${}^{26}$F, which was produced in a nucleon-exchange reaction, there are indications for an excited state with a decay energy of $\sim$270 keV.

Figure 1

The decay energy spectrum for ${}^{25}$F as produced in the reaction ${}^9$Be(${}^{26}$Ne,${}^{24}$F + n). The data (black points with error bars) are compared to the results of Monte Carlo simulations (thick solid line). The calculation is the sum of three resonances at 28 keV (thin solid line), 350 keV (dashed line), and 1200 keV (dotted line). The insets display the efficiency (a) and resolution in full width at half maximum (FWHM) (b) as a function of decay energy.

Figure 2

The decay energy spectrum for ${}^{26}$F as produced in the reaction ${}^9$Be(${}^{26}$Ne,${}^{25}$F + n). The data (black points with error bars) are compared to the results of Monte Carlo simulations (thick solid line). The calculation is the sum of a single 270-keV resonance (thin solid line) and a nonresonant background (dashed line).

Figure 3

Comparison of theoretical (left) and measured states (right) for ${}^{25}$F. The measured states are from this work (bold) and Refs. [9, 21]. The dashed line indicates the one-neutron separation energy [16].