Neutron unbound states in ${}^{28}$Ne and ${}^{25}$F

Unbound states in ${}^{28}$Ne and ${}^{25}$F were populated in the reaction of a 102 MeV/nucleon ${}^{29}$Na beam on a beryllium target. The measured decay energy of 32(22) keV in the ${}^{27}$Ne+$n$ system corresponds to an unbound excited state in ${}^{28}$Ne at 3.86(11) MeV. This is the first measured unbound state of ${}^{28}$Ne. The decay energy of the ${}^{24}$F+$n$ system was measured as 300(170) keV. This places the second measured unbound state of ${}^{25}$F at 4.66(17) MeV.

Figure 1

${}^{28}$Ne decay energy spectrum and best fit to data. The simulated lineshape includes a 32 keV resonance (dashed blue line), a high-lying $s$-wave lineshape with $-2$ fm scattering length (dotted purple line), and a high-lying resonance at 1.15 MeV with a fixed width of 200 keV (dot-dashed green line). Inset is a level scheme showing the measured bound states for ${}^{27}$Ne and theoretical calculated unbound states in ${}^{28}$Ne.

Figure 2

${}^{28}$Ne experimental and theoretical calculated levels. Only the positive parity states from the SDPF-M calculation are shown. The horizontal dashed line indicates the one-neutron separation energy from Ref. [17]. The lowest two experimental levels are from Ref. [20]. The highest state, assigned to the $4_2^{+}$ state, is from Ref. [24]. The level marked “c.w.”, which is the level presented in the current work, is just above the neutron separation energy.

Figure 3

${}^{25}$F decay energy spectrum and best fits to data. Top panel simulation includes a 300 keV Breit-Wigner resonance (dashed blue line) and a nonresonant background (dotted purple line). Bottom panel shows a fit that includes the measured resonance from Ref. [2] (filled grey curve) populated at 15$\%$ the strength of the population of the resonance.

Figure 4

${}^{25}$F experimental and calculated levels. The measured bound states are from Refs. [30, 31] and the lowest measured unbound state is from Ref. [2] (adjusted relative to the neutron separation energy). The measured state from the current work is denoted with “c.w.” The horizontal dashed line indicates the one-neutron separation energy from Ref. [29].