Real-Time Neutron Radiography System Performance—Measurements and Methods

Abstract

The University of Virginia's real-time neutron radiography facility was characterized by measurement of the total neutron flux, gold/cadmium ratio, neutron/gamma ratio, and the effective collimar length-to-aperture diameter (L/D) ratio. The real-time neutron imaging system and collimator were further characterized by measuring the modulation transfer function (MTF) of the system. The collimator effectiveness was measured by using the MTF to determine the ''unparallelism'' of the neutron beam. The computer-based image processing system allowed rapid calculation of the MTF and the collimator effectiveness. The results of these measurements, using no collimator and a simple tube collimator, demonstrated the method's ability to determine the effective L/D ratio. The MTF measurement scheme provided a fast, reliable, and reproducible means of monitoring any changes in the real-time system, including both the neutron beam and the electronic components. This paper describes the methods and measurements implemented to characterize the changes in the radiographic system performance. These include standard measurements of the neutron, flux, neutron-to-gamma ratio, the effective collimator length-to-aperture diameter (L/D) ratio, and effective neutron temperature.