Airborne surveys of Swiss nuclear facility sites

Annually since 1989, biannually since 1994, the environs (similar to 50 km( 2)) of the Swiss nuclear facilities are surveyed (by helicopters) flying th e same survey lines. The equipment and the data processing software used fo r these surveys were built and developed at the Institute of Geophysics, ET H Zurich. For mapping of man-made radiation at or around nuclear facility s ites a pixel representation and the MMGC (man-made gross count) ratio is us ed. So far no artificial radioactivity that could not be explained by the C hernobyl event (1986) or by earlier nuclear weapon tests was detected outsi de the fenced sites of the nuclear facilities. (C) 2001 Elsevier Science Lt d. All rights reserved.