Radiation surveillance using an unmanned aerial vehicle

Radiation surveillance equipment was mounted in a small unmanned aerial vehicle. The equipment consists of a commercial CsI detector for count rate measurement and a specially designed sampling unit for airborne radioactive particles. Field and flight tests were performed for the CsI detector in the area where 137Cs fallout from the Chernobyl accident is 23–45 kBq m−2. A 3-GBq 137Cs point source could be detected at the altitude of 50 m using a flight speed of 70 km h−1 and data acquisition interval of 1 s. Respective response for 192Ir point source is 1 GBq. During the flight, the detector reacts fast to ambient external dose rate rise of 0.1 μSv h−1, which gives for the activity concentration of 131I less than 1 kBq m−3. Operation of the sampler equipped with different type of filters was investigated using wind-tunnel experiments and field tests with the aid of radon progeny. Air flow rate through the sampler is 0.2–0.7 m3 h−1 at a flight speed of 70 km h−1 depending on the filter type in question. The tests showed that the sampler is able to collect airborne radioactive particles. Minimum detectable concentration for transuranium nuclides, such as 239Pu, is of the order of 0.2 Bq m−3 or less when alpha spectrometry with no radiochemical sample processing is used for activity determination immediately after the flight. When a gamma-ray spectrometer is used, minimum detectable concentrations for several fission products such as 137Cs and 131I are of the order of 1 Bq m−3.