Etude de noyaux chauds : Existe-t-il vraiment une limite pour l'énergie d'excitation que peut supporter un noyau ? Application au système $^{40}$Ca + $^{27}$AI à 25 et 35 MeV/A

Abstract : Hot nuclei produced in the 40Ca+ 27Al reaction have been studied at 25 and 35 MeV/u. In a first part, we remind the experimental context which brings us to perform this experiment and to use the AMPHORA multidetector. AMPHORA's efficiency for the most violent collisions has then been verified. The hot nuclei study requires the definition of a criterion to select central collisions. We established that a light particles multiplicity greater or equal to 9 selected a special class of these collisions. We exhibit the experimental results deduced from these hot nuclei study: source velocity, excitation energy, temperature. After comparison with an evaporation code, we deduce excitation energies per nucleon of 6 MeV/u at 25 MeV/u and 7.5 MeV/u at 35 MeV/u. Despite the significant increase of hot nuclei excitation energies, we do not observe a strong evolution for the associated charge distributions and heavy fragments multiplicities. Rare events where 75% of total charge are carried away by light particles have then been studied. They are associated with very hot nuclei and we call them vaporization events. The comparison between experimental results and those of a statistical evaporation code confirms that we selected nuclei with high excitation energy. The agreement is generally good except for charge distributions evolution depending on the source's excitation energy. However, these problems should not challenge the statistical nature of evaporation mechanisms
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Sylvie Groult. Etude de noyaux chauds : Existe-t-il vraiment une limite pour l'énergie d'excitation que peut supporter un noyau ? Application au système $^{40}$Ca + $^{27}$AI à 25 et 35 MeV/A. Physique Nucléaire Expérimentale [nucl-ex]. Université de Caen (France), 1991. Français. ⟨tel-02068057⟩

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