Production and Beta Half Lives of Nuclei Close TI the Nucleosynthesis R-Process Path at N=126
Résumé
Cold-fragmentation reactions of $^{208}$Pb projectiles impinging a beryllium target at 1 A GeV have been used to produce more than 190 nuclei “south” of lead, 25 of them for the first time. The beta half lives or upper limits of 13 of these new nuclei have been determined using position and time correlations between the nuclei and the betas in an active stopper. The measured half lives can only be described when first forbidden transitions are considered.