=-2those studies under the direction of the Division of Biology and Medicine, and to those of more than local interest. The program dealing with the large-scale distribution of radioactivity has developed to its present state during a period dominated by the need to assess the world-wide hazard due to strontium-90 released in weapons tests. So much so, that the AEC program dealing with atmospheric radioactivity has been almost completely. identified with the so-called "Sunshine" or strontium program. The scope of these studies hasbeen gradually broadened, however, to include an increasing number of radionuclides and to include basic studies of mechanisms and models of global transport and deposition. Small scale atmospheric distribution and transport of radioactive wastes due to the industrial applications of atomic energy have, of course, also been receiving steady attention. However, this part of the AEC program has become familiar to students of atmospheric turbulence and diffusion, and will be left out of the present discussion. 2. Fallout monitoring networks The fallout sampling networks summarized in Table I provide the bulk of the AEC-sponsored measurements of radioactivity in the atmosphere and in precipitation (Table I). Where AEC is listed, this indicates that the analysis of samples is under the supervision of the Health and Safety Laboratory. The gummed film collector (Fig. 1) consists of a square foot of cellulose acetate film coated with rubber-base cement (Ref. 1). each station per day. Two are exposed at At the end of the collection period the films are folded and mailed in a pre-addressed envelope to the AEC Health and Safety DOE ARCHIVES Laboratory, New York, where they are simply ashed and counted. Sampling stations are operated by the U.S. Weather Bureau and by many cooperating 4