1.2 Precipitation Collections for Radiostrontium and Radiobariu In precipitation collections, two collectors are simultaneously exposed during dry and rainy weather. The collection period terminates immediately after a precipitation or after a week of no rainfall. 1.21 Pittsburgh, Pennsylvania Since February 1955, precipitation collections have been made by Nuclear Science and Engineering Corporation in galvanized tubs (exposed surface 2.58 rte per tub). Table , up-dates the Pittsburgh precipitation data in HASL-~l2, "Environmental Contamination from Weapon Tests". illustrates the cumulative Sr90 fallout. Figure 2 graphically The error terms represent the standard error of counting. | Until February 1957, the contents of the two tubs were combined resulting in one analysis for the collection period. Since February 1957, the contents of each tub have been analyzed separately. Precipitation values were obtained from the United States Weather Bureau until Jume 19, 1957. Since then, precipitation has been measured by Nuclear Science and Engineering personnel using a Fisher # 1-22-5 United States Weather Bureau type rain gauge. - 36 -