In-beam measurements of sub-nanosecond nuclear lifetimes with a mixed array of HPGe and LaBr(3):Ce detectors

A fast-timing method to determine lifetimes of nuclear states in the sub-nanosecond domain is presented. It is based on in-beam measurements of triple-gamma coincidences in heavy-ion fusion-evaporation reactions, performed with an array of HPGe and LaBr(3):Ce detectors. The high-energy resolution HPGe detectors are used to define de-exciting cascades, while the fast LaBr(3):Ce detectors are used to determine the decay time spectra of selected levels fed by these cascades. A special method to treat the time information of an array of fast detectors is employed in order to fully use the efficiency of the array. Two measurements are presented to illustrate the method: a re-determination of the known half-life T(1/2) = 0.7 ns of 7/2(+) level in (107)Cd (test experiment), and the determination of a half-life T(1/2) = 0.7 ns of the E(x) = 205 keV, J(pi) = 7/2(+) level in (107)Cd (test experiment), and the determination of a half-life T(1/2) = 47 ps for the E(x) = 367 keV, J(pi) = 3/2(+) state of (199)Tl.