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Discussion
There are at least five possible explanations for the anomalously
high Pu-239/Sr-90 ratios observed in surface air since mid-1968.
These
are as follows:
1.
Systematic analytical bias.
The possibility of a systematic
error in the radiochemical analyses seems very remote because
through the period of anomalous ratios, both the stratospheric and
surface air samples were analyzed by a single contractor laboratory
(Trapelo/Wwest).
The performance of the contractor during this period
was monitoried by analysis of coded quality control samples and found
to be excellent.
Furthermore,
the data are seen to be internally
consistent, allowing for relatively smooth contouring.
2.
Non-representative sampling.
The representativeness of the
Samples in both the Airstream and Surface Air programs have always
been considered adequate.
the debris,
The filter media,
the particle size of
the face velocities and the general conditions of
sampling were all considered in design of the equipment in these
programs.
In this light,
erratic bias in the samplers seems highly
unlikely.
In addition the continuing balance in the Sr-90 budget in
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