Sequential probability ratio test for long-term radiation monitoring

Among the possible decision-making algorithms for sequentially-acquired radiation sensor data is the Sequential Probability Ratio Test (SPRT). The suitability of the SPRT for long-term monitoring applications is discussed and the decisionmaking performance of the SPRT is compared to that of the commonly used single-interval test (SIT). The analysis spans a wide range of signal and background count rates so that results are applicable to sensors of all sizes operating in different ambient conditions, with a spectrum of alarm thresholds. It is demonstrated that, for these simulated long-term monitoring scenarios, decisions to issue an alarm when the measured count rate equals the threshold count rate are made 3 to 5 times faster using the SPRT than with the SIT. The ability of the SPRT to provide an "all-clear" indication and the need for SPRT truncation strategies to limit decision times when the measured count rate falls between background and the specified threshold are also discussed.