Preliminary Study on Rapid Measurement of Gross Alpha/Beta and 90Sr Activities in Surface Soil by Mobile ZnS(Ag)/PTV Array and Handheld PVT Rod with Gated Energy Channels

Surface soil radiation monitoring around nuclear facilities is important to classify and characterize the contaminated areas. A scanning and direct measurement technique can survey the sites rapidly before starting sampling analysis. Regarding this, we test and suggest a measurement technique for gross alpha/beta and 90Sr activities in surface soil based on a mobile ZnS(Ag)/PVT (polyvinyltoluene) array and a handheld PVT rod, respectively. To detect 90Sr selectively in soil mixed with naturally occurring radioactive materials, chosen energy channel counts from the multichannel analyzers were used instead of whole channel counts. Soil samples contaminated with exempt liquid 90Sr with 1 Bq·g−1, 3 Bq·g−1, and 10 Bq·g−1 were prepared and hardened by flocculation. The mobile ZnS(Ag)/PVT array could discriminate gross alpha, gross beta, and gamma radiation by the different pulse-shaped signal features of each sensor material. If the array is deployed on a vehicle, the scan minimum detectable concentration (MDC) range will be about 0.11–0.17 Bq·g−1 at 18 km·h−1 speed, highly sensitive to actual sites. The handheld PVT rod with 12 mm (Φ)×20 mm (H) size can directly measure 90Sr selectively if channels on which energies are from 1,470 and 2,279 keV are gated, minimizing cross-detection of other radionuclides. These methods were verified by measuring soil samples fabricated with homogeneous 90Sr concentrations, showing static MDC of 2.16 Bq·g−1 at a measurement time of 300 seconds. Based on the results, comprehensive procedures using these detectors are suggested to optimize soil sites survey