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Aspects dynamiques de la désexcitation nucléaire : de la fission à la multifragmentation.

Abstract : In this work we study the evolution and nature of reaction and decay mechanisms of hot nuclei produced in heavy ion collisions from E = 8 to 25MeV/A measured with INDRA. In central Xe+Sn collisions from E = 8 to 25 MeV/A, three-fragment events present a signi_cant cross section without the underlying production mechanism being clearly established. We have shown that fragments arise from two successive binary splittings. The time interval between these two splittings decreases with increasing incident energy, becoming compatible with a simultaneous three-body break-up above E = 20 MeV/A, which was interpreted as the signature of the onset of multifragmentation. Then we have investigated the nature of the multifragmentation process. A statistical analysis of the largest fragment charge (Zmax) distribution produced in central Xe+Sn collisions at E = 25-50MeV/A allowed us to establish that multifragmentation is a dynamical aggregation process. It also demonstrates the e_ects of collective radial expansion on multifragmentation partitions through the link between the timescale of the process and the shape of the Zmax distribution. The comparison of fragmentation paterns of comparable size systems produced in symmetric (Xe+Sn) and asymmetric (Ta+Zn) central collisions, which are supposed to follow di_erent trajectories in the nuclear phase diagram, con_rm the link between collective radial expansion and fragment partitions in multifragmentation.
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Diego Gruyer. Aspects dynamiques de la désexcitation nucléaire : de la fission à la multifragmentation.. Physique Nucléaire Expérimentale [nucl-ex]. Université de Caen-Basse Normandie, 2014. Français. ⟨tel-01079916v2⟩

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