Compound pulse characteristics of a heterogeneous composite scintillator in a gamma-ray field

An important aspect of radiation detection in scintillators is the time dependence of emitted fluorescence, which results in characteristic measured pulse shape. In some materials, a relatively strong dependence of the scintillation pulse shape on stopping power exists, which can provide reliable identification of the incident particle. An alternative method to realize particle identification is by combining materials with different fluorescence lifetimes into heterogeneous structures. Such composite scintillators derive their properties from both the constituent material characteristics and the geometry of the composite structure. In composite scintillators with a high degree of heterogeneous loading, a superposition of fluorescence contributions originating in multiple materials, which is observed as single waveform with an intermediate pulse shape, may affect its ability to reject gamma rays. We measure the time dependence of light output from a scintillator composed of Li-6-containing glass shards and scintillating polyvinyl toluene and identify events that exhibit such compound behavior when exposed to gamma rays and fast neutrons. We develop a modeling and simulation framework that reproduces the pulse shapes in heterogeneous scintillators and use it study the effect that the weight percentage of Li-6 glass has on gamma rejection. The modeling framework is applied to the experimentally studied scintillator, finding a good agreement. The developed modeling and simulation approach will help optimize the design of heterogeneous scintillators to meet the desired trade-off between neutron capture efficiency and gamma-ray rejection.