ia | Evaluation of Sr90_Data In estimating the validity of gummed film values for sr, we have available radiochemical Sr? measurements in monthly pot samples and in soil samples. The earliest useful pot data began in April 1954 at New York City but even as late as January 1957, only a few stations were available. For the soil collections, a few locations were sampled in October of 1955 and a larger number in 1956 and 1958, Pot samples, like gummed film, are a measure of fallout rate. The analyses are available on a monthly basis and no decay corrections are required, The comparison of calculated and measured values must be made with a degree of caution and the pot values should not be automatically assumed as correct. In all of the comparative tables we have indicated where certain pot values are suspect, Suspicion is raised where other radiochemical data, such. as Strontium-89/90 ratios indicate possible error in the sr70 analysis, It is also possible, of course, that other pot samples may have suffered losses in the sample transfer without disturbing the 89/90 ratio. There is a possible added factor in that many. pot~gummed fim comparisons are made for cases when the two collectors are separated by some distance even though in the same city. Three sets of data are presented for New York City. Table 3 shows the pot data’ and the computed sr? values based on the original single burst assumption for several months in 1956, The computed sr?0 is obviously very low and the apparent age of the fallout is much greater than was assumed, This disagreement was the reason for seeking a better model, Table 4 compares pot values with Sr computed by the present model, Inspection of this table brings out several points: -14- x st