The astrophysically important 3+ state in 18Ne and the 17F(p,γ)18Ne stellar rate

Knowledge of the 17F(p,γ)18Ne reaction rate is important for understanding stellar explosions, but it was uncertain because the properties of an expected but previously unobserved 3+ state in 18Ne were not known. This state would provide a strong s-wave resonance for the 17F+p system and, depending on its excitation energy, could dominate the stellar reaction rate at temperatures above 0.2 GK. We have observed this missing 3+ state by measuring the 1H(17F,p)17F excitation function with a radioactive 17F beam at the ORNL Holifield Radioactive Ion Beam Facility (HRIBF). We find that the state lies at a center-of-mass energy of Er=599.8±1.5stat±2.0sys keV (Ex=4523.7±2.9 keV) and has a width of Γ=18±2stat±1sys keV. The measured properties of the resonance are only consistent with a Jπ=3+ assignment.