Measurement and Modeling of Light Yield Nonproportionality in Neutron Detectors

A methodology for simulating a neutron detector's pulse-height spectra (PHS) utilizing semiempirical equations for the light yield nonproportionality of organic scintillators is described. Using these simulations, suitable material synthesis techniques are established for optimizing the performance of neutron scintillators. A MATLAB program suite was developed to automate the process of generating the PHS by pairing these semiempirical equations with results generated using Monte Carlo radiation transport code (MCNPX) particle track (PTRAC) output files. This is accomplished by first calculating the energy deposited in a detector from each charged-particle reaction product generated from a neutron absorption event by postprocessing the MCNPX PTRAC output files. The energy deposited from each charged particle is then used in semiempirical light yield equations to determine the fluorescent light energy output by each charged particle. Finally, the individual contributions from each charged particle are recombined to accurately simulate the pulse generated from the neutron absorption event.