Real-time, in situ detection of 90Sr and 238U in soils via scintillating-fiber-sensor technology

A revolutionary sensor has been developed for observing the highly energetic beta particles that originate from the decay daughters of 238U and 90Sr. This is accomplished through 1) constructing flat ribbons that are each composed of numerous square scintillating fibers, 2) stacking these ribbons and coupling each bundled end to a photomultiplier tube, and 3) using custom-designed electronic circuitry to measure both interlayer and intralayer coincident events. By observing the relative penetration depths of incident particles, this sensor is able to discriminate between the highly energetic betas of interest and those of lower energy. After placing the sensor on the target surface and initiating data acquisition, one obtains in a few seconds to a few minutes an accurate indication of the contaminant activity per unit weight of material (in the uppermost millimeters) directly below the sensor. This combination of speed and efficiency allows rapid surface coverage in a relatively short period of time, thereby facilitating the timely removal of these contaminants. Laboratory evaluations of a prototype version of this sensor have indicated that contamination levels less than 5 pCi/g (1.8x102 Bq/kg) can be determined within a few minutes. ((orig.))