Lifetime measurements with fast-timing scintillators

Lifetime of a nuclear excited state is one of the main observables in the nuclear structure studies. The lifetime determines the reduced electromagnetic transition probability which is used to be compared with predictions derived by using theoretical nuclear structure models and thus provides an essential nuclear observable to test the model dependent structure of the nuclear excited states. There are different ways to measure lifetime of an excited state and their use depends on the magnitude of the value we are interested in. In this research we focused on the - coincidence technique and its implementation with the scintillation detectors, especially the inorganic LaBr3(Ce) scintillators. In the first part of this work, the main characteristics and components of a scintillator detector, together with the main pick-off methods in timing measurements, are discussed. In the second part, timing performance and some important linked properties of seven LaBr3(Ce) scintillators of two different kind, equipped with a 3"x3" cylindrical crystal and a 1.5"x1.5"x1" truncated cone crystal respectively, are analysed. Energy resolution, efficiency and time resolution have been evaluated by using different radioactive type of sources and the detector time response has been optimized by the tuning of the electronics parameters, especially the constant fraction discriminator parameters. Finally, the lifetime of the 121keV-energy state of 152Sm has been measured thanks to the slope method. The experiment was performed at the Legnaro National Laboratory as part of the GALILEO project.