Keywords:Radioactive concentration in the atmosphere, Rapid detection, Monitoring, Gamma-ray, Spectrometer, Difficult-to-return zone, temporary access
We have propsed the rapid detection method of radioactive particles in the atmosphere1). It consists of a conventional gamma-spectrometer with the novel shaped shield with two-pi aperture to zenith direction. To apply this method to Cesium airborne monitoring in “Difficult –to-return zone” of Fukushima, measurements, evaluation and design improvements were carried out. As the result, we confirmed that the state of 30Bq/m3 can be detected with 11min. measurement, and concluded that this method is a promising way of rapid airborne monitoring system in “difficult-to-return zone” of Fukushima.