Single-nucleon transfer reactions on ${}^{18}\mathrm{F}$

Simultaneous measurement of the proton-transfer ${}^{18}\mathrm{F}{(d,n)}^{19}\mathrm{Ne}$ and neutron-transfer ${}^{18}\mathrm{F}{(d,p)}^{19}\mathrm{F}$ reactions were performed with a ${}^{18}\mathrm{F}$ radioactive beam at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The experiments clarify the nuclear structure of ${}^{19}\mathrm{Ne}$ near the proton threshold, which is relevant for understanding the rates of proton-induced reactions on ${}^{18}\mathrm{F}$ in novae. Analogs for several states in the mirror nucleus ${}^{19}\mathrm{F}$ have not yet been identified in ${}^{19}\mathrm{Ne}$, indicating that the level structure of ${}^{19}\mathrm{Ne}$ in this region is incomplete. We observed 15 levels in ${}^{19}\mathrm{Ne}$ from the ${}^{18}\mathrm{F}{(d,n)}^{19}\mathrm{Ne}$ measurement and 18 levels in ${}^{19}\mathrm{F}$ from the ${}^{18}\mathrm{F}{(d,p)}^{19}\mathrm{F}$ measurement. Angular distributions were extracted for all strongly populated states and compared to distorted-wave Born approximation calculations. The angular distributions for all the known states in the two nuclei determined in this work are consistent with their previously assigned spins and parities. The spectroscopic factors determined for these levels in the two nuclei are reported.

Figure 1

Schematic diagram of the six 5 $\times$ 5-cm $E$-$\Delta E$ detector telescopes employed for the measurement. The beam axis passes through the midpoint between the two inner telescopes.

Figure 2

The $E_{\mathrm{tot}}$-$\Delta E$ spectrum from the experiment for the inner detector (a) and the outer detector (b). The loci of nuclei detected by the detectors are indicated. There was complete isotopic separation for H and He and complete $Z$ separation but partial isotopic separation for heavier nuclei.

Figure 3

(a) The two-dimensional $Q$-value spectrum for $\alpha +{}^{15}\mathrm{O}$. $Q_0$ assumes ${}^2\mathrm{H}({}^{18}\mathrm{F},\alpha +{}^{15}\mathrm{O})n$ while $Q_1$ assumes ${}^1\mathrm{H}({}^{18}\mathrm{F},\alpha ){}^{15}\mathrm{O}$. (b) The projection of the two-dimensional plot to the $Q_0$ axis.

Figure 4

The two-dimensional plots of neutron ${\theta }_{\mathrm{c}.\mathrm{m}.}$ vs $\alpha +{}^{15}\mathrm{O}$ (a) and proton ${\theta }_{\mathrm{c}.\mathrm{m}.}$ vs $\alpha +{}^{15}\mathrm{N}$ (b) relative energy revealing observed states in ${}^{19}\mathrm{Ne}$ and ${}^{19}\mathrm{F}$, respectively. As an example, the closed line in (a) is the gate used to extract the angular distribution for that state.

Figure 5

The relative energy spectra for $\alpha +{}^{15}\mathrm{N}$ (a) and $\alpha +{}^{15}\mathrm{O}$ (b) coincidences leading to excited states in ${}^{19}\mathrm{F}$ and ${}^{19}\mathrm{Ne}$, respectively. The dots are experimental data and the red curves are the minuit fit. The corresponding excitation energies (in units of MeV) are written against the peaks.

Figure 6

The calculated coincidence efficiency for our geometry.

Figure 7

The calculated FWHM resolution for the reconstructed relative energy (solid curve) using our Monte Carlo simulations assuming $\alpha +{}^{15}\mathrm{O}$. Some observed experimental resolutions are indicated for $\alpha +{}^{15}\mathrm{O}$ (squares) and $\alpha +{}^{15}\mathrm{N}$ (circles).

Figure 8

The differential cross section for the ${}^{18}\mathrm{F}{(d,p)}^{19}\mathrm{F}$ reaction to various final states. The curves were obtained from DWBA calculations with the set of optical potentials in Table . The calculations have been scaled to the data with the spectroscopic factors determined in this work. All excitation energies are shown in keV.

Figure 9

The differential cross section for the ${}^{18}\mathrm{F}{(d,n)}^{19}\mathrm{Ne}$ reaction to various final states. The curves were obtained from DWBA calculations with the set of optical potentials in Table . The calculations have been scaled to the data with the spectroscopic factors determined in this work. All excitation energies are shown in keV.

Figure 10

Relative energy spectrum for $\alpha +{}^{15}\mathrm{O}$ around $E_x=6289$ keV, showing the fit for the 6419- and 6449-keV states in ${}^{19}\mathrm{Ne}$ used to constrain the width of the 6449-keV state.