Gamma-ray fast-timing coincidence measurements from the O-18+O-18 fusion-evaporation reaction using a mixed LaBr3-HPGe array

Abstract

We report on a gamma-ray coincidence analysis using a mixed array of hyperpure germanium and cerium-doped lanthanum tri-bromide (LaBr3:Ce) scintillation detectors to study nuclear electromagnetic transition rates in the pico-to-nanosecond time regime in P-33,P-34 and S-33 following fusion-evaporation reactions between an O-18 beam and an isotopically enriched O-18 implanted tantalum target. Energies from decay gamma-rays associated with the reaction residues were measured in event-by-event coincidence mode, with the measured time difference information between the pairs of gamma-rays in each event also recorded using the ultra-fast coincidence timing technique. The experiment used the good full-energy peak resolution of the LaBr3:Ce detectors coupled with their excellent timing responses in order to determine the excited state lifetime associated with the lowest lying, cross-shell, I-pi = 4(-) "intruder" state previously reported in the N=19 isotone P-34. The extracted lifetime is consistent with a mainly single-particle M2 multipolarity associated with a f(7/2) -> d(5/2) single particle transition. (C) 2011 Elsevier Ltd. All rights reserved.