of about 25.
ve over 40.
For very fresh debris, less than 2 months old, the ratio would
The proviso concerning fractionation and collection efficiency
is an important one, since unlike Sr-90, Ce-144 has no gaseous or volatile
precursor, which may indicate that larger particle sizes are involved having
greater fall rates.
These larger particles,
readily captured by the filter.
if present, may also be more
Absolute values of the ratio may be meaning-
less, but relative values may be useful in comparing ages of debris at the
same altitude.
Figures 8-11 show the Ce-144/Sr-90 ratio (large figures) superimposed
on the
Sr-90 data.
As with the other balloon filter results, there appear
to be random fluctuations in the data.
However, some patterns can be seen.
For example, increases in the Ce-144/Sr-90 ratio at 50,000 feet over
Minneapolis and at 50,000 and 65,000 feet over Texas in late
1957 and early
1958 could be the result of Russian injection during the autumn of 1957.
In
general, the values at 65,000 feet over the two northern stations indicate
much younger debris (higher Ce-144/Sr-90 ratio) than over Brazil at the same
altitude.
At Brazil, increases in the ratio can be seen as a result of the
British tests in the spring of 1957 and of the U. S. Pacific test series in 1958.
The foregoing discussion of the radiochemical data would seem to indicate
that some qualitative reliance may be placed on the results, but that the
variability seems to be larger than expected and may partially be a result of
analysis procedures.
The very minute quantities of debris captured by the
sampling equipment make the radiochemical procedures extremely difficult.
VI.
Conclusions
NAS
In evaluating the possible hazard from Sr~-90 and other long-lived fission
products,it has been established that stratospheric storage plays an important
role.
It then becomes necessary to know the content, distribution and rate of
removal of debris from the stratosphere.
Indirect determinations of the con-
tent, based on assumed initial injections, are too uncertain and meteorological
knowledge of stratospheric motions is too poor to satisfy questions on these
subjects.
We must rely on direct measurement of the stratosphere.
It is evident that there are many uncertainties in the data collected
in stratospheric sampling programs, but that a potential exists for a
}
A
12
keeRGOrUED [ROM THE COLLECTIONS
QF THE ANCHIVES OF THE
UATIONS, AOA LEM SP SCTENCES
ean
valuable contribution, by good sampling and analysis, both to the Sr-90 problem