Hand-held personnel and vehicle monitors

A light, rugged monitor has been developed for special nuclear materials (SNM) searches at material-access and protection-area exits. This monitor accepts gamma-ray pulses from a NaI(Tl) detector, integrates for a preset counting interval (typically 0.3 s), and produces an audible alarm whenever the counts in the interval exceed the trip level that is a preset multiple of the stored background count. Because the monitor is silent except when the alarm is operating, personnel with little special training can conduct more effective searches in a noisy and distracting environment than they can with conventional audible monitoring of individual radiation counts. The monitor is also more sensitive than conventional monitors that provide audible indication of the count rate