the atmosphere sampled on the several flights which campled through
appreciable vertical thickness.
the Texas figure in italics.
A few flights made in Arizona are shown on
The arrows at the top of Fig. 2 (Minneapolis)
indicate the dates of the large Russian nuclear detonations which presumably
injected debris into the temperate or polar stratosphere.
Similarly, the
arrows at the top of Fig. 4 (Panama) indicate the megaton range devices
detonated by the United States and the United Kingdom in tropical latitudes.
An inspection of the data shows that there is 4 large variability.
This variability may be real, and a measure of the true state of affairs in
the ‘stratosphere, or it may be a function of the collection or analysis
techniques.
Some of the variability must be a reflection of recent injections
into the stratosphere.
For example, the high values over Minneapolis in late
April and May of 1957 may be a result of the April Russian thermonuclear tests,
similarly the high value over South America in July, 1957, may reflect injections from the U. K. tests of the preceding month.
A major difficulty in making a quantitative estimate of the Sr-90 content
of the stratosphere results from the lack of precise knowledge of the efficiency
of the filter material at the low pressures and flow rates encountered, together
with a lack of knowledge of the particle sizes involved.
Although theoretical
and laboratory studies on the characteristics of the filter system have
yielded information for particles as small as 0.083 u, a comparison of
collections made by aircraft at 40,000 feet simultaneously with balloon
collections indicate that the collection efficiency curves must be extrapolated
to 0.0@u or smaller particles to explain the Sr-90 values.
Using this semi-
empirical approach, a series of filter efficiency factors for Sr-90 particles
of 0.02 were obtained (Table 2).
Table 2
NAS
Filter effictency for 0.02u particles
Altitude,
feet, MSL
Filter
Efficiency
50,000
0.30
65,000
0.38
80 ,000
0.60
90,000
0.82
7
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