Study And Application Of Fast Timing Scintillation Detectors

Scintillation detector is a kind of widely-used particle detector. Because of its very fast timing property, scintillation detector is often used for timing measurement in experiments with delayed coincidence method or time-of-flight technique.The absolute electromagnetic transition probability provides a very sensitive probe for determining the properties of nuclear structure and collective motion, which is a crucial quantity for testing various nuclear structure models. The electromagnetic transition probability is usually deduced from the level lifetime. In Chapter2one of the most widely used methods for lifetime measurements—the fast timing method will be introduced, which is based on using fast timing scintillation detectors to determine the time difference between β-γ or γ-γ in coincidence.To the fast timing method, the time resolution of the timing detectors is the key factor which limits the shortest lifetime being measured. In Chapter3the study and fabrication of three fast timing scintillation detectors will be presented in detail—ncluding a BaF、 a LaBr3(Ce) and a Pilot U plastic scintillator. The testing results indicate that all the three scintillation detectors have sub-nanosecond time resolution.Slow neutron capture process (s-process) is an important way for the synthesis of stable nuclides beyond iron. S-process mainly takes place in the He-burning layers of low-mass (1.5-3M☉) asymptotic giant branch (AGB) stars and during the He-and C-burning phases of massive stars (>8M☉).The typical temperature range for s-process is T8-0.9-3.5, where Tg is the dimensionless temperature defined by T8=T/(108K). The velocities of neutrons produced in the stellar interior satisfy the Maxwell-Boltzmann distribution. To calculate the neutron capture reaction rate one must measure the Maxwellian-averaged cross sections (MACS). One of the most effective methods to determine neutron capture MACS is to measure neutron capture cross sections with Maxwellian neutron source of corresponding temperature. Production of a Maxwellian-spectrum neutron source is described in Chapter4.Experiment to obtain a Maxwellian-spectrum neutron source is presented in Chapter5. The experiment was carried out on the2x1.7MV tandem accelerator of China Institute of Atomic Energy via the7Li(p, n)7Be reaction. In the experiment time-of-flight (TOF) technique was used to measure the neutron energy spectrum, and the timing detector was a Li glass scintillation detector. The results indicate that the neutron energy spectrum obtained in the emission angle of60°matches the Maxwell distribution of kT≈20K.