10 II, Sr” in Chicago Rains A. Summary of Chicago Rain Data, 1953 through 1955 Table 1 shows the estinated monthly and yearly totals of Sr90 deposited per square foot in the Chicago arca, together with totals for rains actually reasurcds The 1953 rain samzles were roof run-off samples collected by the Chicago Tritium Research Group, Tor these, it is assumed that the result in disintecra tions per minute was constant for each rain, and the gr90 deposited per square foot was computed from the total precivitation in inches rcported by tue Veaths: Bureau for the University of Cnicrgo station. The 1954 samples were individualreins collected in a galvanized wash tub on the roof of tne Jones Chemistry Laboratory building. For tnese, the total sample activit: divided by the collection arza was taken as the Sr?0 deposited per square foot for individual rains, For voth 1953 and 195), rains, the total monthly decosit was estimated »y multiplying the denosit in disintegrations per minute per square foot ner inch of rain fer the rains measured br the total nonthly precipitation in inches. Table 2 shows the total monthly deposits for 1955 rains, At all three locations the 1955 collections were made in galvanized tubs, and the total monthly precipitation was taken, For these, tne deposit per square foot was computed from total sammle activity divided by collection area, The 1955 NYOO collections were made with the tubs exncsed ccntinuously and thus any dry material falling out betwecn rains vas included in the sample.