health and safety laboratory - Digital Collections

^valuation of Sr90 Data
In estimating the validity of gummed film values for Sr90 , we have
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available radiochemical Sr7W measurements in monthly pot samples and in soil
m 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 0 The
m analyses are available on a monthly basis and no decay corrections are required.
v» 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 Sr90 analysis.
g 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 film 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^O values based on the original single burst
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assumption for several months in 1956* The computed Sr is obviously very
low and the apparent age of the fallout is much greater than was assumed.
I This disagreement was ^the reason for seeking a better model 0
^ Table 4 couapares pot values with Sr^0 computed by the present model.
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Inspection of this table brings out several points: