Properties of resonant states in 18Ne relevant to key 14O(alpha,p)17F
breakout reaction in type I x-ray bursts
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abstract
The $^{14}$O($\alpha$,$p$)$^{17}$F reaction is one of the key reactions
involved in the breakout from the hot-CNO cycle to the rp-process in type I
x-ray bursts. The resonant properties in the compound nucleus $^{18}$Ne have
been investigated through resonant elastic scattering of $^{17}$F+$p$. The
radioactive $^{17}$F beam was separated by the CNS Radioactive Ion Beam
separator (CRIB) and bombarded a thick H$_2$ gas target at 3.6 MeV/nucleon. The
recoiling light particles were measured by using three ${\Delta}$E-E silicon
telescopes at laboratory angles of $\theta$$_{lab}$$\approx$3$^\circ$,
10$^\circ$ and 18$^\circ$, respectively. Five resonances at $E_{x}$=6.15, 6.28,
6.35, 6.85, and 7.05 MeV were observed in the excitation functions. Based on an
$R$-matrix analysis, $J^{\pi}$=1$^-$ was firmly assigned to the 6.15-MeV state.
This state dominates the thermonuclear $^{14}$O($\alpha$,$p$)$^{17}$F rate
below 1 GK. We have also confirmed the existence and spin-parities of three
states between 6.1 and 6.4 MeV. As well, a possible new excited state in
$^{18}$Ne was observed at $E_{x}$=6.85$\pm$0.11 MeV and tentatively assigned as
$J$=0. This state could be the analog state of the 6.880 MeV (0$^{-}$) level in
the mirror nucleus $^{18}$O, or a bandhead state (0$^+$) of the six-particle
four-hole (6$p$-4$h$) band. A new thermonuclear rate of the
$^{14}$O($\alpha$,$p$)$^{17}$F reaction has been determined, and its
astrophysical impact has been examined within the framework of one-zone x-ray
burst postprocessing calculations.
