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It should be noted that irrespective of which of the three suggested
explanations account for the higher Cs-137/Sr-90 ratio, the Sr-90 in the
stratosphere is most likely depleted compared to the expected production.
This means that a true sample of the radioactive debris (nad the depletion
not taken place) would contain a smaller ratio of short lived isotopeto
Sr-90 giving an older apparent age and a smaller fraction of October 18th
debris.
We have no knowledge concerning fractionation or other depletion effects
If there were fractionation or other
for any of the shorter-lived isotopes.
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depletion effects, the apparent age would be shortened and the fraction of
Cctober 18th debris increased.
It should be noted that fractionation or
depletion of an isotope within the first few days or weeks is irrelevant be~
cause it will affect both fallout and the stratospheric samples.
The most
likely source of error, if indeed there is an error, in the comparison of
apparent age of fallout and stratospheric samples is due to the sampling
devices themselves.
At the moment, it appears unlikely that the difference in apparent age
or fraction of October 18th Sr-90 can be attributed to these kinds of arti-
facts.
The results of the Ce-144/Sr-90 ratios show an appreciably larger percentage of October 1958 Sr-90 than was found from the Sr-89 and Zr-95 radioisotopes.
The determination of the percentage of debris assigned to a given
date of origin implies that all of the short-lived radioisotopes originate
at this time.
When test series are widely spaced relative to the half life
of the short-lived isotope, this assumption is reasonably correct.
In each
of the cases (using either Sr-89, Zr-95 or Ce-144) the fraction of October
1958 debris must be a maximum for this reason but in the case of Ce-144,
with its 275-day hal? life, the maximum may greatly exceed the true value.
The Panama percentage values indicate this feature since it is very unlikely
that any U.S.S.R. Sr-90 (from October 1958) was actually present at Panama
in November and December 1958.
:
NAS
The Ce-lkh/Sr-90 ratio results, in a few cases, in impossible apparent
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ages (formation later than sampling) and percentage contributions (100%).
If the radiochemical analysis is accepted as valid, the implication is again
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