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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

We have measured the cross section of the 7Be(p,gamma)8B reaction for E(c.m.) = 185.8, 134.7, and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta+ and alpha particles from 8B and 8Be* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5+/-2.4 eV b and a weighted mean value of 18.8+/-1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies.

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γ-ray production cross sections have been measured in proton irradiations of N, Ne and Si and α-particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong γ-ray lines of 16 O produced in proton and α-particle irradiations of O. For the measurements gas targets were used for N, O and Ne and a thick foil was used for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for α-particles have been delivered by the IPN-Orsay tandem accelerator. The γ rays have been detected with four HP-Ge detectors in the angular range 30 • to 135 • . We extracted 36 cross section excitation functions for proton reactions and 14 for α-particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular the agreement of cross section calculations in the nuclear reaction code TALYS with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei 14 N, 20,22 Ne and 28 Si. The importance of these results for the modeling of nuclear γ-ray line emission in astrophysical sites is discussed.