COMPARING A RECURSIVE DIGITAL-FILTER WITH THE MOVING-AVERAGE AND SEQUENTIAL PROBABILITY-RATIO DETECTION METHODS FOR SNM PORTAL MONITORS

We compared a recursive digital filter proposed as a detection method for French special nuclear material monitors with our detection methods, which employ a moving-average scaler or a sequential probability-ratio test. Each or our nine test subjects repeatedly carried a test source through a walk-through portal monitor that had the same nuisance-alarm rate with each method. We found that the average detection probability for the test source is also the same for each method. However, the recursive digital filter may have one drawback: its exponentially decreasing response to past radiation intensity prolongs the impact of any interference from radiation sources or radiation-producing machinery. We also examined the influence of each test subject on the monitor's operation by measuring individual attenuation factors for background and source radiation, then ranked the subjects' attenuation factors against their individual probabilities for detecting the test source. The one inconsistent ranking was probably caused by that subject's unusually long stride when passing through the portal.