A RETROSPECTIVE OF FALLOUT MONITORING IN CANADA

From 1945 to 1980, 520 nuclear weapons were exploded in the atmosphere resulting in fallout mostly in the northern hemisphere. From 1959 to the present, Canada has operated a national radioactivity network invo lving stations from coast to coast and in the high Arctic to determine the distribution of fallout across the country. The information from almost 40 y of operation of this network and data for the Ottawa Valle y including H-3 and C-14 measurements are summarized. Some spatial and temporal trends are discussed. The results of these years of observat ion demonstrate the relatively rapid removal of radioactivity from the environment following cessation of the contaminating events.