Detection of small radiation sources: the effect of mode of count-rate presentation

We used an observer-performance study to compare four different modes of presenting count-rate data from a radiation detector. Observers searched for small, concealed radioactive sources using a hand-held radiation-detector probe. The modes of count-rate presentation were a ratemeter, howler, multichannel scaler, and HRM III. The HRM III calculates the statistical significance of the difference between current and previous count rates and presents the result as an audio signal. We tested six observers with each mode of count-rate presentation, calculated receiver operating characteristic (ROC) curves, and used the areas under the ROC curves to compare the different modes. Observer performance was better with the multichannel scaler and HRM III than with either the ratemeter or the howler. The results suggest that observer performance with devices that use ratemeters or howlers can be enhanced by improving the mode of count-rate presentation.