Etude des corrélations dans les noyaux légers riches en neutrons

Abstract : Correlations play a crucial rôle in understanding the structure of light nuclei at and beyond the neutron dripline. In this context, the two-neutron halo nucleus 6He and the unbound systems 5H, 7,9He and 10Li have been studied via measurements of the breakup of beams of 6He and 11,12Be. The CHARISSA and DEMON detector arrays were employed. The interpretation were facilitated by a simulation code (SILLAGE) which provided for the setup. In the case of 7He, the existence of an excited state with Er ~ 1 MeV and gamma ~ 0.75 MeV was confirmed. The virtual character of the s-wave ground state of 10Li was also confirmed and a scattering length of as ~ -16 fm deduced. The results obtained for 9He suggest that a virtual s-wave state may exist just above threshold. The study of the three-body breakup of 6He found that the decay of the first 2+ state is essentially direct, while the decay of the remaining continuum strength is sequential – passage via 5He. Using the technique of intensity interferometry an rms separation between the halo neutrons of 7.7 +- 0.8 fm was derived. This result was confirmed by a complementary method utilizing Dalitz plots. In the case of 5H, the invariant mass spectrum was found to exhibit a broad (gamma ~ 2MeV) structure some 1.8 MeV above threshold. Comparison with recent three-body model calculations suggest that this corresponds to the predicted 1/2+ ground state. An rms valence neutron separation of some 5.5 fm was estimated. A search was also carried out for the 4n system using the 12Be* (2 alpha +Xn decay channel). No signal was observed beyond that expected on the basis of the known background processes.
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Nuclear Theory [nucl-th]. Université de Caen, 2004. French


https://tel.archives-ouvertes.fr/tel-00008393
Contributor : Guillaume Normand <>
Submitted on : Tuesday, February 8, 2005 - 10:41:48 AM
Last modification on : Wednesday, July 1, 2015 - 1:09:14 AM

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G. Normand. Etude des corrélations dans les noyaux légers riches en neutrons. Nuclear Theory [nucl-th]. Université de Caen, 2004. French. <tel-00008393>

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