Comparing a recursive digital filter with the moving-average and sequential probability-ratio detection methods for SNM portal monitors

A recursive digital filter proposed as a detection method for French special nuclear material monitors is compared with detection methods that employ a moving-average scaler or a sequential probability-ratio test. Each of the nine test subjects repeatedly carried a test source through a walk-through portal monitor that had the same nuisance-alarm rate with each method. It is shown that the average detection probability for the test source is also the same for each method. 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. The influence of each test subject on the monitor's operation was examined by measuring individual attenuation factors for background and source radiation. The subjects' attenuation factors are ranked against their individual probabilities for detecting the test source. The one inconsistent ranking is attributed to the subject's unusually long stride.< >