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The 17 O(p, α) 14 N and 17 O(p, γ ) 18 F reactions are of major importance to hydrogen-burning nucleosynthesis in a number of different stellar sites. In particular, 17 O and 18 F nucleosynthesis in classical novae is strongly dependent on the thermonuclear rates of these two reactions. The previously estimated rate for 17 O(p, α) 14 N carries very large uncertainties in the temperature range of classical novae (T = 0.01-0.4 GK), whereas a recent measurement has reduced the uncertainty of the 17 O(p, γ ) 18 F rate. We report on the observation of a previously undiscovered resonance at E c.m. = 183.3 keV in the 17 O(p, α) 14 N reaction, with a measured resonance strength ωγ pα = (1.6 ± 0.2) × 10 −3 eV. We studied in the same experiment the 17 O(p, γ ) 18 F reaction by an activation method, and the resonance strength was found to amount to ωγ pγ = (2.2 ± 0.4) × 10 −6 eV. The excitation energy of the corresponding level in 18 F was determined to be 5789.8 ± 0.3 keV in a Doppler shift attenuation method measurement, which yielded a value of τ < 2.6 fs for the level lifetime. The 17 O(p, α) 14 N and 17 O(p, γ ) 18 F reaction rates were calculated using the measured resonance properties and reconsidering some previous analyses of the contributions of other levels or processes. The 17 O(p, α) 14 N rate is now well established below T = 1.5 GK, with uncertainties reduced by orders of magnitude in the temperature range T = 0.1-0.4 GK. The uncertainty in the 17 O(p, γ ) 18 F rate is somewhat larger because of remaining obscurities in the knowledge of the direct capture process. These new resonance properties have important consequences for 17 O nucleosynthesis and γ -ray emission of classical novae.A. CHAFA et al. PHYSICAL REVIEW C 75, 035810 (2007) 035810-2 E R (keV) a

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Intense and purified radioactive beam of post-accelerated 14 O was used to study the low-lying states in the unbound 15 F nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E R =4.757(6)(10) MeV with a width of Γ=36(5)(14) keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a 12 C core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the 2s 1/2 shell.

γ -ray production cross sections for proton and α-particle interactions with 12 C, 16 O, 24 Mg, and Fe have been measured in the energy range 5-25 MeV with proton beams and 5-40 MeV with α-particle beams. Isotopically pure foils of 24 Mg and foils of natural isotopical composition of C, MgO, and Fe have been used. γ -ray angular distributions were obtained with five high-purity Ge detectors with bismuth germanate Compton shields placed at angles of 45 • to 157.5 • . Cross sections for more than 50 different γ -ray transitions were extracted, and for many of them no data have been published before. Comparison of present data with data available in the literature shows mostly good to excellent agreement. In addition to the production cross sections, high-statistics, low-background line shapes of the 4.438 MeV 12 C γ ray from inelastic scattering off 12 C and spallation of 16 O were obtained. Comparison with nuclear reaction calculations shows that these data place interesting constraints on nuclear reaction models.