Simulation of nuclear detection capabilities in portal monitors

A technique for accurately predicting the response of a portal monitor to a given quantity of special nuclear material is described. The three dimensional Monte Carlo code MORSE is employed in the forward mode to calculate the response of large volume plastic scintillators. A technique is presented whereby the Monte Carlo calculation need to be done only once to obtain the detection rate for a given source located anywhere within the detection volume. In this work, the MORSE Monte Carlo code has been employed as a design tool to accurately predict the response of a given portal design to a specified photon source. 6 refs