Re: Plutonium detection levels in Urinalysis

[Holloway3@aol.com]

Just a couple of comments on your questions.  Any useful definition of MDA or
LLD includes the possibility that a certain percentage of false positives
will be
reported and that a certain percentage of true positives will not be detected
as true
positives.  There is no certainty when dealing with results near the
detection limits
and there is no way to remove that uncertainty.  It is inherent in the
counting statistics.  Secondly, you mention results that have an error term
of plus or minus 50%.  When dealing with results at or below the detection
limits, error terms of this magnitude are a reality and there is not much
that can be done about it.  The counting time can be extended and that will
produce some improvement, but in many cases the counting time is already as
long as is feasible.  Of course if you wish to set your dividing line high
 enough between detectable and non-detectable, 
you can reach a point where you can have high confidence that a detected
result is real, but the price you pay for that is an increased probability of
falsely classifying some results as below detection limits when they actually
represent real 
counts of plutonium.   In conclusion, there is no certainty, only
probability.

                                                                  Robert
Holloway
 
                                                                  Nevada
Technical Associates, Inc. 










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