Abstract
beta decays from heavy, neutron-rich nuclei with A ~ 190 have been investigated following their production via the relativistic projectile fragmentation of an E/A = 1 GeV 208Pb primary beam on a ~2. 5 g/cm29 Be target. The reaction products were separated and identified using the GSI FRagment Separator (FRS) and stopped in the RISING active stopper. The active stopper consisted of an array of 5 cm x 5 cm Double Sided Silicon Strip Detectors (DSSSDs), each pixellated into 16 strips in both horizontal and. vertical directions to measure the position of the implanted ions and correlate these with subsequent (3 decays detected in the same pixels. l decays were observed and correlated with these secondary ions on an event-by-event basis such that 7 ray transitions following from both internal (isomeric) and beta radioactivity decays were recorded. The particle identification procedure was confirmed by the observation of the previously reported isomers in 188Ta, 190W, 192Re and 193Re. The current data also show evidence for previously unreported isomeric states in 187Hf, 189, 190Ta and 191 W. A number of discrete, beta-delayed gamma-ray transitions associated with B decays from 194Re to excited states in 194Os have been observed, including previously reported decays from the yrast I pi = (6+) state. Three previously unreported 7-ray transitions with energies 194, 349 and 554 keV are also identified; these transitions are associated with decays from higher spin states in 194Os in the present work. A B-decay half-life for 194Re has been determined for the first time in this work by measuring the time differences between the implanted secondary ions in the active stopper and their subsequent correlated beta particles in the same pixel. The results of these investigations are compared with theoretical predictions from Nilsson Multi Quasi Particle (MQP) calculations and potential energy surface calculations. The structure of the neutron-rich N = 128 isotones 208Hg and 209TI has also been investigated following their production via relativistic projectile fragmentation of a E/A=l GeV 238U beam. Decays from metastable states in these nuclei have been identified and the yrast structures up to spin-parity 8+ and 17/2+ respectively have been observed. The results are compared with restricted basis shell model calculations, which allow the first detailed verification of the shell-model approach in the region determined by magic numbers Z 126.