No abstract

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. E1-and E2-S of 12 alpha,gamma 0 16 O from gamma-ray angular distributions with a 4pi detector array

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