Indirect techniques for astrophysical reaction rates determinations

Direct measurements of nuclear reactions of astrophysical interest can be challenging. Alternative experimental techniques such as transfer reactions and inelastic scattering reactions offer the possibility to study these reactions by using stable beams. In this context, I will present recent results that were obtained in Orsay using indirect techniques. The examples will concern various astrophysical sites, from the Big-Bang nucleo synthesis to the production of radioisotopes in massive stars

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

International audienceThe 12C(a,g )16O reaction plays an important role in helium burning in massive stars and their evolution. However, despite many experimental studies, the low-energy cross section of 12C(a,g )16O remains highly uncertain. The extrapolation of the measured cross sections to stellar energies (E=300 keV) is made difficult by the presence of the two sub-threshold states at 6.92 (2+) and 7.12 (1−) MeV of 16O. In order to further investigate the contribution of these twosubthreshold resonances to the 12C(a,g )16O cross section, we performed a new determination of the a-reduced widths of the 6.92 and 7.12 MeV of 16O via a measurement of the transfer reaction 12C(7Li,t)16O at two incident energies, 34 and 28 MeV. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the a-reduced widths for the 2+ and 1− sub-threshold states and their effect on the R-matrix calculations of 12C(a,g )16O

Study of key resonances in the 30P(p,γ)31S reaction in classical novae

Among reactions with strong impact on classical novae model predictions, 30P(p,γ)31S is one of the few remained that are worthy to be measured accurately, because of their rate uncertainty, as like as 18F(p,α)15O and 25Al(pγ)26Si. To reduce the nuclear uncertainties associated to this reaction, we performed an experiment at ALTO facility of Orsay using the 31P(3He,t)31S reaction to populate 31S excited states of astrophysical interest and detect in coincidence the protons coming from the decay of the populated states in order to extract the proton branching ratios. After a presentation of the astrophysical context of this work, the current situation of the 30P(p,γ)31S reaction rate will be discussed. Then the experiment set-up of this work and the analysis of the single events will be presented

Study of the 26Al(n,p)26Mg and 26Al(n,α)23Na reactions using the 27Al(p,p')27Al inelastic scattering reaction

26Al was the first cosmic radioactivity ever detected in the galaxy as well as one of the first extinct radioactivity observed in refractory phases of meteorites. Its nucleosynthesis in massive stars is still uncertain mainly due to the lack of nuclear information concerning the 26Al(n,p)26Mg and 26 Al(n,α)23Na reactions. We report on a single and coincidence measurement of the 27Al(p,p')27Al(p)26Mg and 27Al(p,p')27Al(α)23Na reactions performed at the Orsay TANDEM facility aiming at the spectroscopy study of 27Al above the neutron threshold. Fourteen states are observed for the first time within 350 keV above the 26Al+n threshold

Patrimoine : voyage des mots. Heritage, Erbe, Beni culturali, Turâth, Tigemmi

International audienc

Patrimoine: voyages des mots. Heritage, Erbe, Beni culturali, Turâth, Tigemmi

Cette réflexion consacrée aux mots du patrimoine couvre plusieurs langues européennes et extra- européennes (français, anglais, allemand, italien, arabe, kabyle), tout en focalisant sur les années 1970 à nos jours, période de la montée en puissance en France de la notion de patrimoine et l’alignement de son sens à l’échelle mondiale. On favorisera une approche comparative par contraste afin de saisir les convergences et décalages d’un contexte à l’autre. L’entrée en la matière est toutefois vaste: elle peut être étymologique et linguistique, culturelle et sociologique, économique ou juridique. Ce dernier volet n’est pas à négliger car la mise en place de conventions internationales du patrimoine mondial, a posé comme langue principale de communication le français, mais a nécessité par la suite d’établir un lexique en plusieurs langues, faisant découvrir l’absence dans les cultures extra-européennes, africaine ou extrême-orientale par exemple, d’une terminologie équivalente. Cela ne veut pas dire que la notion de patrimoine y était inexistante mais qu’elle se présentait différemment. Il n’est pas aisé en effet de normaliser et de fixer un terme unique pour signifier une notion aussi étendue que celle de «patrimoine», autour de laquelle gravitent souvent d’autres notions liées à l’histoire et la mémoire, à l’identité culturelle, aux langues, à la dimension politique. Comment signifier une notion à travers des mots qui peuvent être réducteurs si l’on considère les multiples pratiques sociales et culturelles

New Study of the Astrophysical Reaction 12C(α\alpha,γ\gamma)16O via the 12C(7Li,t)16O Transfer Reaction

International audienceThe 12C(alpha,gamma)16O reaction plays an important role in helium burning in massive stars and their evolution. However, despite many experimental studies, the low-energy cross section of 12C(alpha,gamma)16O still highly uncertain. The extrapolation of the measured cross sections to stellar energies (E~300 keV) is made difficult by the presence of the two sub-threshold states at 6.92 and 7.12 MeV of 16O. In order to further investigate the contribution of these two-subthreshold resonances to the 12C(alpha,gamma)16O cross section, we performed a new determination of the alpha -reduced widths via a measurement of the transfer reaction 12C(7Li,t)16O at two incident energies, 34 and 28 MeV. The measured and calculated differential cross sections will be presented as well as the obtained spectroscopic factors and the alpha -reduced width

Indirect study of 12^{12}C(α\alpha, γ\gamma)16^{16}O reaction

International audienceThe radiative capture reaction 12 C(α, γ) 16 O 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 16 O. Hence, to further investigate the contribution of these two-subthreshold resonances to the 12 C(α, γ) 16 O cross section, a new determination of their α-reduced widths and so their α-spectroscopic-factors was performed using 12 C(7 Li,t) 16 O 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 α-reduced widths as well as the assymptotic normalization constants (ANC) for the 2 + and 1 − sub-threshold states. Finally, the results obtained from the R-matrix calculations of the 12 C(α, γ) 16 O cross section using our obtained α-reduced widths for the two sub-threshold resonances are presented and discussed

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

The 12C(α,γ )16O reaction plays a crucial role in stellar evolution. The rate of this reaction determines directly the 12C-to-16O abundance ratio at the end of the helium burning phase of stars and consequently has a big effect on the subsequent nucleosynthesis and even on the evolution of massive stars. However, despite many experimental studies, the low-energy cross section of 12C(α,γ )16O remains uncertain. The extrapolation of the measured cross sections to stellar energies (E ∼ 300 keV) is made particularly difficult by the presence of the 2+ (Ex = 6.92 MeV) and 1− (Ex = 7.12 MeV) subthreshold states of 16O. To further investigate the contribution of these two subthreshold resonances to the 12C(α,γ )16O cross section, we determine their α-reduced widths via a measurement of the transfer reaction 12C(7Li, t )16O at two incident energies, 28 and 34 MeV. The uncertainties on the determined α-spectroscopic factors and the α-reduced widths were reduced thanks to a detailed distorted-wave Born approximation analysis of the transfer angular distributions measured at the two incident energies. The R-matrix calculations of 12C(α,γ )16O cross section using our obtained α-reduced widths for the 2+ and 1− subthreshold resonances lead to an E1 S factor at 300 keV of 100 ± 28 keV b, which is consistent with values obtained in most of the direct and indirect measurements as well as the NACRE collaboration compilation while the result for the E2 component SE2 (300 keV) = 50 ± 19 keV b disagrees with the NACRE adopted value

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.SCOPUS: cp.jinfo:eu-repo/semantics/publishe