in early 1957 and 26 to 3% MT in carly 1958.
In cither case, it is apparent
thet the uncertain estimate of the stratompheric content fron the balloon
data is appreciably smaller than that estimated from the budgeting of bomb
releases and the change from 1957 to 1958 is
in the opposite direction.
The discrepancy in the two calculations of the stratospheric Sr-90 con-
tent can result from a variety of causes.
The uncertainties of the estimate
based on the amount injected have been discussed.
An equal or possibly
larger uncertainty exists in the estimate derived from the balloon measureAmong the problems are:
pp
The representativeness of the limited number of measurements.
wD
Knowledge of the actual amount of air filtered on any given flight.
Qa
ments.
Efficiency of the filter for the particle sizes involved.
ogo
-
A.
Radiochemical analysis.
Representativeness of the data.
[If the high atmosphere is indeed as
variable as the stratospheric balloon flights indicate, then the few samples,
one flight a month at a total of 1€ places in the atmosphere (4 stations at 4
altitudes), cannot be considered adequate to define the world-wide stratospheric
content with the desired accuracy.
Although there is no conclusive evidence
to preclude the possibility that this variability is real, a consideration of
diffusion rates suggests that the fission products are not as patchy as the
balloon data indicate.
B.
Volume of air filtered.
The question of the reliability of the fan law
used in calculating the volume of air passing through the filter is under
investigation by General Mills.
In an atvempt to see if there is an obvious
bias in the results from this cause, the Sr-90 content of the samples was
plotted against the reported volume at the various stations and altitudes.
If a consistent error in the fan law were present, this would appear as a
relationship between the apparent volume of air filtered and the reported air
concentration.
No such relationship was found.
This,
of course,does not
rule out the possibility of other non-systematic errors in the determination
of the volume filtered.
C.
Filter efficiency.
NAS
Many studies have already been made on the problem
of the efficiency of air filters for small particles, but the basic problem -
the size of the particles with which we are dealing - has not been solved.
The extrapolation of laboratory determinations of collection efficiency based on
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