Anne MEYER, "Experimental study of the 13N(a,p)16O and 30P(p,g)31S reactions, and impact on extremely high 13C, 15N and 30Si isotopic abundances in presolar grains" (Pôle Physique Nucléaire)

100/-1-A900 - Auditorium Joliot Curie (IJCLab)

100/-1-A900 - Auditorium Joliot Curie


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Title of Defense

Experimental study of the 13N(a,p)16O and 30P(p,g)31S reactions, and impact on extremely high 13C, 15N and 30Si isotopic abundances in presolar grains.


Primitive meteorites contain several types of dust grains that condensed in different stellar environments and survived destruction in the early Solar System. The stellar sources where these presolar grains come from are identified through comparisons between measurements of isotopic abundances and predictions by stellar models. In this manuscript is presented a detailed analysis of two experiments performed at the ALTO facility, using the split-pole magnetic spectrometer, aiming at reducing the nuclear uncertainties associated to two reactions which rate uncertainty affects the synthesis of isotopes used to identify putative novae grains. These grains are characterised by extremely high 13C, 15N and 30Si isotopic abundances, but isotopic signatures found in a few grains indicate also a possible core-collapse supernovae (CCSN) origin. We first study the impact of the 13N(a,p)16O reaction rate uncertainty on 13C abundances predicted by recent CCSN models. We perform a re-evaluation of this reaction rate using a Monte Carlo approach to obtain meaningful statistical uncertainties. Alpha partial widths of states in the 17F compound nucleus are determined using the spectroscopic informations of the analog states in the 17O mirror nucleus that were measured using the 13C(7Li,t)17O alpha-transfer reaction. We then study the 30P(p,g)31S reaction, which is one of the few remaining reactions which rate uncertainty has a strong impact on classical novae model predictions, in particular for 30Si abundances. To reduce the nuclear uncertainties associated to this reaction, we studied the 31P(3He,t)31S reaction. Triton and proton decays from the populated states in 31S were detected simultaneously using the spectrometer and silicon strip detectors. The study of the angular correlations of proton decays is presented and branching ratios are extracted.

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Membres du jury :
Fairouz HAMMACHE, IJCLab, CNRS, Directeur de thèse
François DE OLIVEIRA, GANIL, Rapporteur
Georges MEYNET, Université de Genève, Rapporteur
Elias KHAN, IJCLab, Université Paris-Saclay, Président
Sandrine COURTIN, IPHC, CNRS, Examinateur
Nicolas DE SEREVILLE, IJCLab, Université Paris-Saclay, Examinateur