Analysis of the pulse shape mechanism in a plastic scintillator with efficient neutron/gamma pulse shape discrimination

A sample of the new plastic scintillator recently formulated by Zaitseva et al., and shown by them to have efficient pulse shape discrimination properties, was exposed to pure gamma and mixed neutron/gamma radiation from different sources, and the pulse shapes recorded by a digitising oscilloscope. Separate average neutron and gamma pulse shapes were derived, using pulse shape discrimination where necessary. A theoretical pulse shape formula, based on the conventional two-lifetime description of pulse shape formation in organic scintillators, was then fitted to these measured shapes to obtain numerical values for the lifetimes and proportions of the scintillator excitations. It is found that, although the conventional model explains much of the observed pattern of values, there are hints of behaviour that is not consistent with its assumptions. -- Highlights: •A PSD-capable organic scintillator was exposed to neutron and gamma radiation. •Separate average neutron and gamma pulse shapes were derived. •A formula based on scintillator excitations was fitted to these shapes. •The behaviour of the deduced lifetimes and proportions largely matches expectation. •There is some evidence of an additional component with a very long lifetime