AbstractA Monte Carlo simulation model has been developed to predict the unscattered gamma-ray intensities of an in situ neutron capture prompt gamma-ray analysis system for assaying the elemental concentrations of material that move on a conveyor belt. The model incorporates all pertinent neutron and photon interactions for the assay of coal and all variance reduction techniques necessary to make every history a success. Prompt gamma-ray intensities from all elements of interest over a range of elemental compositions of the sample matrix are calculated in one execution of the program. The calculated results are verified with experimental results on a coal sample in a test configuration that is spiked with variable amounts of sulfur and titanium as two sample elements of interest. The model is expected to be very useful for the optimum design and calibration of on-line neutron capture prompt gamma-ray analysis systems operating in the conveyor belt geometry.