S. M. R. Puglia

A Novel Approach to Measure the Cross Section of the 18O(p, α)15N Resonant Reaction in the 0-200 keV Energy Range

The 18O(p, ?)15N reaction is of primary importance to pin down the uncertainties, due to nuclear physics input, affecting present-day models of asymptotic giant branch stars. Its reaction rate can modify both fluorine nucleosynthesis inside such stars and oxygen and nitrogen isotopic ratios, which allow one to constrain the proposed astrophysical scenarios. Thus, an indirect measurement of the low-energy region of the 18O(p, ?)15N reaction has been performed to access, for the first time, the range of relevance for astrophysical application. In particular, a full, high-accuracy spectroscopic study of the 20 and 90 keV resonances has been performed and the strengths deduced to evaluate the reaction rate and the consequences for astrophysics.

New measurement of the 11B(p,α0)8Be bare-nucleus S(E) factor via the Trojan horse method

A new measurement of the 11B(p,?0)8Be has been performed applying the Trojan horse method (THM) to the 2H(11B,?80Be)n quasi-free reaction induced at a laboratory energy of 27 MeV. The astrophysical S(E) factor has been extracted from ?600 keV down to zero energy by means of an improved data analysis technique and it has been compared with direct data available in the literature. The range investigated here overlaps with the energy region of the light element LiBeB stellar burning and with that of future aneutronic fusion power plants using the 11B+p fuel cycle. The new investigation described here confirms the preliminary results obtained in the recent TH works. The origin of the discrepancy between the direct estimate of the 11B(p,?0)8Be S(E)-factor at zero energy and that from a previous THM investigation is quantitatively corroborated. The results obtained here support, within the experimental uncertainties, the low-energy S(E)-factor extrapolation and the value of the electron screening potential deduced from direct measurements.

Measurement of the 20 and 90 keV resonances in the 18O(p,alpha)15N reaction via the Trojan horse method.

The

On the Measurement of the 13C(α, n)16O S-factor at Negative Energies and its Influence on the s-process

^{18}{\rm O}(p,\alpha)^{15}{\rm N}

Measurement of the 20 and 90 keV resonances in the

reaction is of primary importance in several astrophysical scenarios, including fluorine nucleosynthesis inside AGB stars as well as oxygen and nitrogen isotopic ratios in meteorite grains. Thus the indirect measurement of the low energy region of the

{}^{18}{\rm O}(p,\alpha){}^{15}

^{18}{\rm O}(p,\alpha)^{15}{\rm N}

N reaction via THM

reaction has been performed to reduce the nuclear uncertainty on theoretical predictions. In particular the strength of the 20 and 90 keV resonances have been deduced and the change in the reaction rate evaluated.

Measurement of the 10 keV resonance in the B 10 ( p , α 0 ) Be 7 reaction via the Trojan Horse method

The 13C(?, n)16O reaction is the neutron source for the main component of the s-process, responsible for the production of most of the nuclei in the mass range 90 A 208. This reaction takes place inside the helium-burning shell of asymptotic giant branch stars, at temperatures 108?K, corresponding to an energy interval where the 13C(?, n)16O reaction is effective in the range of 140-230?keV. In this regime, the astrophysical S(E)-factor is dominated by the ?3?keV sub-threshold resonance due to the 6.356?MeV level in 17O, giving rise to a steep increase in the S-factor. Its contribution is still controversial as extrapolations, e.g., through the R-matrix and indirect techniques such as the asymptotic normalization coefficient (ANC), yield inconsistent results. The discrepancy amounts to a factor of three or more precisely at astrophysical energies. To provide a more accurate S-factor at these energies, we have applied the Trojan horse method (THM) to the 13C(6Li, n 16O)d quasi-free reaction. The ANC for the 6.356?MeV level has been deduced through the THM as well as the n-partial width, allowing us to attain unprecedented accuracy for the 13C(?, n)16O astrophysical factor. A larger ANC for the 6.356?MeV level is measured with respect to the ones in the literature, ?fm?1, yet in agreement with the preliminary result given in our preceding letter, indicating an increase of the 13C(?, n)16O reaction rate below about 8 ? 107?K if compared with the recommended values. At ~108?K, our reaction rate agrees with most of the results in the literature and the accuracy is greatly enhanced thanks to this innovative approach.

Indirect measurement of the 18O(p, α)15N reaction rate through the THM

The

A new study of

^{18}{\rm O}(p,\alpha)^{15}{\rm N}