Modeling the Response of the Passive/Active Nuetron Counting System

The Monte Carlo code MCNP has been used to model the response of the passive/active neutron drum counter in use at the Rocky Flats Plant. The purpose of the modeling effort is to duplicate the detector response in both the passive and active mode of operation for the plutonium standards used in the calibration of the detector system. The modeling effort addresses the variability of the system response to movement of the calibration sources within the matrix, as well as, the derivation of a calibration response curve for the system over the range of plutonium loadings in the matrix. If the response of the detector system can be successfully modeled, then the need to build a suite of standards for each matrix type to be assayed on the system can, hopefully, be relaxed to the point of occasional bench mark measurements. Three matrices, cellulose, plastics, and leaded glove-box gloves, have been used to model the detector response in both the passive and active mode of operation. Comparison of the results of experimental data will be made with the computer results of the model.