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 J^π = 3⁺ assignment.