T. Al-Abdullah

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

A preliminary indirect investigation of the 18O(p, α)15N reaction via the THM is discussed, focusing on the extraction of the resonance parameters of the 656 keV resonance (corresponding to the state at Ex = 8.65 MeV in 19F), which gives strong contribution both at low and high temperatures, being quite broad. Even though a non-negligible discrepancy is found, both as regards the strength and the energy of the resonance, no change in the reaction rate is apparent in the astrophysically relevant temperature range.

Peripheral elastic and inelastic scattering of 17,18O on light targets at 12 MeV/nucleon

The elastic and inelastic scattering of 17,18O with light targets has been undertaken at 12 MeV/nucleon in order to determine the optical potentials needed for the transfer reaction 13C(17O,18O)12C. Optical potentials in both incoming and outgoing channels have been determined in a single experiment. This transfer reaction was used to infer the direct capture rate to the 17F(p,γ)18Ne which is essential to estimate the production of 18F at stellar energies in ONe novae. We demonstrate the stability of the ANC method and OMP results using good quality elastic and inelastic scattering data with stable beams. The peripherality of our reaction is inferred from a semiclassical decomposition of the total scattering amplitude into barrier and internal barrier components. Comparison between elastic scattering of 17O, 18O and 16O projectiles is made.The elastic and inelastic scattering of 17,18O with light targets has been undertaken at 12 MeV/nucleon in order to determine the optical potentials needed for the transfer reaction 13C(17O,18O)12C. Optical potentials in both incoming and outgoing channels have been determined in a single experiment. This transfer reaction was used to infer the direct capture rate to the 17F(p,γ)18Ne which is essential to estimate the production of 18F at stellar energies in ONe novae. We demonstrate the stability of the ANC method and OMP results using good quality elastic and inelastic scattering data with stable beams. The peripherality of our reaction is inferred from a semiclassical decomposition of the total scattering amplitude into barrier and internal barrier components. Comparison between elastic scattering of 17O, 18O and 16O projectiles is made.

Astrophysical Reaction Rates Obtained By Indirect Techniques

Indirect techniques have been used to obtain information about reaction rates for several proton capture reactions that occur on short‐lived nuclei. The techniques used to carry out the measurements are reviewed and the results obtained are presented. Also future prospects for further measurements with a new facility, T‐REX are discussed.

First measurement of the 18O(p,α)15N cross section at astrophysical energies

The 18O(p,α)15N reaction rate has been deduced by means of the Trojan horse method. For the first time the contribution of the 20 keV resonance has been directly evaluated, giving a value about 35% larger than the one in the literature. Moreover, the present approach has allowed to improve the accuracy by a factor 8.5, as it is based on the measured strength instead of spectroscopic measurements. The contribution of the 90 keV resonance has been also determined, which turned out to be of negligible importance to astrophysics.

Astrophysical S factor for the radiative capture (12)N(p,gamma)(13)O determined from the (14)N((12)N,(13)O)(13)C proton transfer reaction

The cross section of the radiative proton capture reaction on the drip line nucleus 12 N was investigated using the asymptotic normalization coefficient (ANC) method. We have used the 14 N( 12 N, 13 O) 13 C proton transfer reaction at 12 MeV/nucleon to extract the ANC for 13 O → 12 N + p and calculate from it the direct component of the astrophysical S factor of the 12 N(p, γ) 13 O reaction. The optical potentials used and the distorted-wave Bom approximation analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time as the transfer measurement. From the transfer, we determined the square of the ANC, C 2 P1/2 ( 13 O g.s. ) = 2.53 ± 0.30 fm -1 , and hence a value of 0.33(4) keV b was obtained for the direct astrophysical S factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of S total (0) = 0.42(6) keV b. The 12 N(p, γ) 13 O reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot pp-chain nuclear burning processes, possibly occurring in such objects.

Astrophysical S factor for the radiative capture 12N(p, γ)13O determined from the 14N(12N, 13O)13C proton transfer reaction

The cross section of the radiative proton capture reaction on the drip line nucleus 12 N was investigated using the asymptotic normalization coefficient (ANC) method. We have used the 14 N( 12 N, 13 O) 13 C proton transfer reaction at 12 MeV/nucleon to extract the ANC for 13 O → 12 N + p and calculate from it the direct component of the astrophysical S factor of the 12 N(p, γ) 13 O reaction. The optical potentials used and the distorted-wave Bom approximation analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time as the transfer measurement. From the transfer, we determined the square of the ANC, C 2 P1/2 ( 13 O g.s. ) = 2.53 ± 0.30 fm -1 , and hence a value of 0.33(4) keV b was obtained for the direct astrophysical S factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of S total (0) = 0.42(6) keV b. The 12 N(p, γ) 13 O reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot pp-chain nuclear burning processes, possibly occurring in such objects.

AstrophysicalSfactor for the radiative captureN12(p,γ)O13determined from theN14(N12,O13)C13proton transfer reaction

The cross section of the radiative proton capture reaction on the drip line nucleus 12 N was investigated using the asymptotic normalization coefficient (ANC) method. We have used the 14 N( 12 N, 13 O) 13 C proton transfer reaction at 12 MeV/nucleon to extract the ANC for 13 O → 12 N + p and calculate from it the direct component of the astrophysical S factor of the 12 N(p, γ) 13 O reaction. The optical potentials used and the distorted-wave Bom approximation analysis of the proton transfer reaction are discussed. For the entrance channel, the optical potential was inferred from an elastic scattering measurement carried out at the same time as the transfer measurement. From the transfer, we determined the square of the ANC, C 2 P1/2 ( 13 O g.s. ) = 2.53 ± 0.30 fm -1 , and hence a value of 0.33(4) keV b was obtained for the direct astrophysical S factor at zero energy. Constructive interference at low energies between the direct and resonant captures leads to an enhancement of S total (0) = 0.42(6) keV b. The 12 N(p, γ) 13 O reaction was investigated in relation to the evolution of hydrogen-rich massive Population III stars, for the role that it may play in the hot pp-chain nuclear burning processes, possibly occurring in such objects.

α‐cluster structure in light N≠Z nuclei

The clustering phenomena in light N≠Z nuclei are discussed. Measurements of resonance elastic scattering of 14C on 4He, and the excitation functions for the 9Be(p,α)6Li(T = 1) reaction has been performed. All measurements were made in inverse kinematics. The excitation functions were analyzed in the framework of the R‐matrix approach. Many new states with large α reduced widths were identified in 18O. Strong cluster T = 1 states in 10B have been identified in 9Be. The results show that extra (in comparison with the self‐conjugate nuclei) nucleons make evident changes in the properties of the α‐cluster bands.

Recent astrophysical applications of the Trojan Horse Method to nuclear astrophysics

The Trojan Horse Method (THM) is an unique indirect technique allowing to measure astrophysical rearrangement reactions down to astrophysical relevant energies. The basic principle and a review of the recent applications of the Trojan Horse Method are presented. The applications aiming to the extraction of the bare astrophysical S{sub b}(E) for some two-body processes are discussed.

Indirect Measurement of 15N(p,α)12C and 18O(p,α)15N. Applications to the AGB Star Nucleosynthesis

The Trojan Horse Method has been recently applied to the study of reactions involved in fluorine nucleosynthesis inside AGB stars. Fluorine abundance is important since it allows to constrain mixing models from the comparison of the observed fluorine abundances with the ones predicted by models. Anyway direct measurements of the cross section do not extend down to the Gamow peak, which is the astrophysically relevant energy region. In particular the study focuses on the 15N(p,α)12C and the 18O(p,α)15N reactions which can influence fluorine yield as they are part of 19F production/destruction network.