SMARTER RADIATION MONITORS FOR SAFEGUARDS AND SECURITY

Radiation monitors for nuclear safeguards and security depend on internal control circuits to determine when diversion of special nuclear materials is taking place. Early monitors depended on analog circuits for this purpose; subsequently, digital logic controllers made better monitoring methods possible. Now, versatile microprocessor systems permit new, more efficient, and more useful monitoring methods. One such method is simple stepwise monitoring, which has variable alarm levels to expedite monitoring where extended monitoring periods are required. Another method, sequential probability ratio logic, tests data as it accumulates against two hypotheses—background, or background plus a transient diversion signal—and terminates monitoring as soon as a decision can be made that meets false-alarm and detection confidence requirements. A third method, quantitative monitoring for personnel, calculates count ratios of high- to low-energy gamma-ray regions to predict whether the material detected is a small quantity of bare material or a larger quantity of shielded material. In addition, microprocessor system subprograms can assist in detector calibration and trouble-shooting. Examples of subprograms are a variance analysis technique to set bias levels in plastic scintillators and a state-of-health routine for detecting malfunctions in digital circuit components.