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  • 1 Niigata Prefectural Institute of Environmental Radiation Monitoring, Kashiwazaki, Niigata, 945-0034 Japan
  • 2 ZCOSMOS Co., Ltd., Tokyo, Japan
  • 3 Department of Chemistry, Faculty of Science, Niigata University, 950-2181 Niigata, Japan
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A portable system for high-speed time interval analysis (TIA) method was constructed. The system installed with an original time counting board could record pulse incident time of 1 MHz precisely. During the measurement, calculation of time intervals for all the pulses and on-line display of the results were performed simultaneously. Using this system, the correlated decay events of 214Bi to 210Po in the airborne dust collected on filter paper were counted, together with a dual-phosphor type alpha/beta detector. A rapidly detective technique of artificial radioactivity under the variations of naturally occurring radioactivities is discussed.