Aerial measurements with helicopters to determine accidental releases from nuclear facilities

Aerial gamma ray spectrometry is a useful tool for providing a rapid and comprehensive assessment of the dispersion and deposition of radionuclides over wide areas in post accident situations in nuclear facilities. This paper describes an aerial measuring system for nuclide specific measurements of soil contaminations and for detecting sources of gamma radioactivity. The measuring device consists of several components that can be separately installed in an Alouette II type helicopter. The central unit is a computerized gamma ray spectrometer with a high purity Ge-semiconductor detector and a 121 volume NaI(TI) scintillation detector array. At a flight altitude of 100 m, soil contaminations of some kBq/m(2) of Cs-137 can be measured (measuring time: 60 s, flight speed: 100 km/h). This aerial measuring system was for the first time operatively applied for measuring the deposition of artificial radionuclides in the southern part of Germany after the Chernobyl accident. Nuclide specific soil contamination measurements were also performed in the former USSR in a region north of Chernobyl, with values of up to 2 MBq/m(2) for nuclide deposition, and in selected areas in Finland. The results from these measuring campaigns are presented here.