There has been a great deal of interest in the use of LaBr3 (Ce) detectors for fast timing measurements. Due to their excellent energy resolution, ≈ 3% at 1MeV, they offer an improved signal to background over BaF2 which has ≈ 9% energy resolution. Many groups are planning arrays of LaBr3 detectors. The 8π collaboration has recently acquired a small array of 6 2”x 2” cylindrical LaBr3 detectors to replace its BaF2 detectors. We have been investigating the effects of detector-to-detector scattering on timing resolution. We have further investigated the use of Compton-suppression shields with LaBr3 detectors. This will also be the first testing of the DANTE acquisition system in the 8π. A summary of the results of our optimization, scattering studies, and Compton-suppression tests will be presented.

Ces travaux de thèse ont permis de développer une voie d’accès à des systèmes polycycliques complexes contenant un cyclooctatétraène par réactions en cascade palladocatalysées à partir de substrats de départ originaux. Le mécanisme de formation de ces composés est tout à fait particulier. Une étude mécanistique approfondie, corroborée notamment par des calculs DFT, a mis en avant une étape de réaction inédite : une électrocyclisation conrotatoire 8pi d’un système triènyne formant ainsi un cyclooctadiènallène palladé. Cette méthodologie a permis de synthétiser de nombreux cyclooctatétraènes présentant une large diversité moléculaire. Les différents substituants du cyclooctatétraène ont pu être variés ainsi que la taille des cycles fusionnés à ce cyclooctatétraène. / This thesis work focused on the development of a new synthetic pathway leading to complex polycyclic molecules containing a cyclooctatetraene moiety via palladium-catalyzed cascade reactions from original starting substrates. The mechanism of formation of these compounds is very special. A thorough mechanistic study, supported in particular by DFT calculations, highlighted an unprecedented reaction step: an conrotatory 8pi electrocyclization of a trienyne system forming a palladiated cyclooctadienallene. This methodology allowed the synthesis of many cyclooctatetraenes showing a broad molecular diversity. The different substituents bearing by the cyclooctatetraene core were varied as well as the size of the fused rings to the cyclooctatetraene.