P. Roussel

Search for new resonant states in C-10 and C-11 and their impact on the cosmological lithium problem

The observed primordial 7Li abundance in metal-poor halo stars is found to be lower than its Big-Bang nucleosynthesis (BBN) calculated value by a factor of approximately three. Some recent works suggested the possibility that this discrepancy originates from missing resonant reactions which would destroy the 7Be, parent of 7Li. The most promising candidate resonances which were found include a possibly missed 1- or 2- narrow state around 15 MeV in the compound nucleus 10C formed by 7Be+3He and a state close to 7.8 MeV in the compound nucleus 11C formed by 7Be+4He. In this work, we studied the high excitation energy region of 10C and the low excitation energy region in 11C via the reactions 10B(3He,t)10C and 11B(3He,t)11C, respectively, at the incident energy of 35 MeV. Our results for 10C do not support 7Be+3He as a possible solution for the 7Li problem. Concerning 11C results, the data show no new resonances in the excitation energy region of interest and this excludes 7Be+4He reaction channel as an explanation for the 7Li deficit.

Indirect study of 12C(α,γ)16O reaction

The radiative capture reaction 12C(α,γ)16O plays an important role in helium burning in massive stars and their subsequent evolution [1]. However, despite various experimental studies, the cross section of this reaction at stellar energies remains highly uncertain. The extrapolation down to stellar energy (Ecm~300 keV) of the measured cross sections at higher energies is made difficult by the overlap of various contributions of which some are badly known such as that of the 2+ (Ex=6.92 MeV) and 1− (Ex=7.12 MeV) sub-threshold states of 16O. Hence, to further investigate the contribution of these two-subthreshold resonances to the 12C(α,γ)16O cross section, a new determination of their a-reduced widths and so their a- spectroscopic-factors was performed using 12C(7Li,t)16O transfer reaction measurements at two incident energies and a detailed DWBA analysis of the data [2]. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the a- reduced widths as well as the assymptotic normalization constants (ANC) for the 2+ and 1− subthreshold states. Finally, the results obtained from the R-matrix calculations of the 12C(α,γ)16O cross section using our obtained a-reduced widths for the two sub-threshold resonances are presented and discussed.

Indirect study of the 13C(alpha,n)16O reaction via the 13C(7Li,t)17O transfer reaction

The

Indirect Study of 13C(α,n)16O

^{13}\mathrm{C}

Is the one-photon state of an optical field a physical state?

(

Indirect study of the 12C(α,γ)16O reaction via the 12C(7Li,t)16O transfer reaction

\ensuremath{\alpha},n

Nucleosynthesis of Al 26 in massive stars: New Al 27 states above α and neutron emission thresholds

)

Spectroscopy of

^{16}\mathrm{O}

^{61}

reaction is considered the main neutron source for the s process in low mass asymptotic giant branch (AGB) stars. In the Gamow peak, the cross section sensitively depends on the

Fe via the neutron transfer reaction

1/{2}^{+}