2 ~~» -850,000, 65,000, 80,000 and 90,000 ft at each of four stations once a month. These stations were originally Minneapolis, Minn.; San Angelo, Texas; France Air Force Base, Canal Zone; and Sao Paulo, Brazil. has recently been replaced by Sioux City, Iowa. The Minneapolis station The Brazil and Panama stations are being closed down after two years of operation. The filters are analyzed for 5r90, five other fission products and two tracers (Table I). Development of reliable analytical procedures has been very difficult due to the extremely minute concentrations of the radioisotopes in the air, and to the relatively low collection efficiency of the filter system. Although reporting of results by commercial analytical laboratories initially lagged more than a year behind the first routine sampling flights, this lag has been reduced to a few months. Nearly two years’ data are now available in an unclassified AEC document (Ref. 11). Cross sections of the average $r20 concentrations for two 6-month periods are shown in Fig. 14, prepared by R. J. List. There are still considerable uncertainties in the collection efficiency and radiochemical analysis, but these are being narrowed. The very small number of sampling points introduces even greater uncertainties in the estimate of global inventory. However, the total amount of sr90 in the stratosphere estimated on the basis of these measurements up to last spring would appear to be closer to 1 than to 3 megacuries. Studies are underway to attempt to recon- cile all the available data. 3. Smaller-scale researchprojects The projects discussed so far are all of an operational monitoring nature, aimed at obtaining large-scale distributions of the radioactivity in the atmosphere or in fallout by direct measurement. approach, DOE ARCHIVES This is the "brute force” | O