eo
standards are included in each batch of samples sent through our own facility
and other laboratories.
other
laboratories.
Our
We also cross count several of the samples sent to
quality-control
program
requires
that
blind
duplicates be within 10% of each other and that the standards be within 10% of
the Known value.
If such is not the case, the problem must be ascertained and
reanalysis completed if necessary; reanalysis has only rarely been necessary.
Most of the wet chemistry analyses for 905r, 239+240py, and 24am are
done by outside contractor laboratories.
To assure analytical reliability of
the data produced by the outside laboratories, we have established three
criteria governing the accountability of the results.
1.
errors.
The
.
first criterion places limits of acceptability on counting
Because radioactive decay is a statistical process, sufficient counts
must be collected to provide a level of confidence that the number reported is
a true measure of the radioactivity of the sample.
Until this criterion is
met it is difficult, if not impossible, to evaluate the data for the remaining
two criteria.
Consequently, we have established a set of acceptable counting
errors (Table 1}.
The requirements are scaled to the total radioactivity of
the sample, which is the product of the amount of sample available and its
Specific activity (activity per unit weight of sample).
Compliance can be
checked easily by the individual analyst because it is based on information
available
to him:
received.
the measured specific activity and weight of the sample
This criterion was developed to estimate the amount of sample
required by any competent laboratory to measure worldwide fallout.
sufficient size with higher activity are thus well
detection of the contracting laboratories.
Samples of
above the limits of
As a result, the data that are
reported are not machine limits, which would provide only upper limits to the
radionuclide
concentrations
in the
overestimate
of
of
the
amount
samples.
radioactivity
Such data would cause an
actually
present
in
the
environment when used as real values.
2. ‘The second criterion requires that the laboratories reproduce their
resuits on replicate analyses.
A set of blind duplicate samples is included
With each group of roughly 100 samples
(called DCD for the accompanying
Delivery Control Document) and results of the pair of analyses are considered
acceptable if they vary by less than twice the measurement accuracy required
in Table 1.
JOC03 14
Satisfactory performance on duplicates requires acceptability on