water are obtained by considering the 10 rainfall sampling stations nearest New Haven,
Pittsburgh, and New York,
The best comparison between rain water data and total fallout should be obtained using
gummed film data, since the gummed film network covers the same area as the rain water
stations and was operated over the same sampling period. The positioning of the two sampling
networks is shown in Fig. 4. Because only 14 of the stations are duplicated, geographic exTATOOSH ISLE
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Force site, ©, gummed film site.
trapolation is employed to obtain values for the rain water sites that are not covered by gummed
film stations. Distances of 100, 150, 200, and 300 miles were used as extrapolation radii, but it
was found that the distance used madelittle difference in the final correlation. The optimum
distance was chosen as 150 miles because, when circles of this radius were drawn around the
rain water sites, a maximum number of gummed film stations fell within the given areas with
a minimum number of circles overlapping.
With this scheme there are 11 results that may be compared in March, 30 in April; 20 in
May; 25 in June; and 23 in July. The highest correlation coefficient obtained, using the gummed
film data’ as predicted Sr®’ and rain water data as measured Sr*’, is 0.49. This relation is
shown in Fig. 5, using May 1956 as an illustration. The ratios of average Sr” in rain to average Sr” in gummed film range from 1.9 to 45. Table 6 is a summary of this comparison.
4
CONCLUSIONS
The relation between fallout in rainfall with total fallout measurements using the pot type
of collector is good, but there is poor agreement between the rain water data and gummed
film measurements. It is believed that the Sr*’ values calculated from gummedfilm activity
are low owing to incorrect arbitrary burst assignments uSed in the calculations.®
Considering only the rainfall data, no over-all correlation exists between rainfall and the
level of Sr*” activity. It is interesting that, although the testing of atomic weapons takes place
in southern latitudes, the Sr’? deposition is higher at northern latitudes. If the fallout were of
recent tropospheric origin, this northward movement could be due to surface winds. However,
the high percentage of Sr®° indicates that the debris is old and entered the troposphere from
the stratosphere.