MDA and LLD

["Michael P. Grissom" <MIKEG%SLACVM.bitnet@vmd.cso.uiuc.edu>]

Forwarded-from: MIKEG

1.  This sounds like the US DOE radioactive material release issue
driven the last few years by the Environmental Management Office
(in response to a shipment of mixed waste containing uranium from
a border state national lab not identified as containing rad).

2.  The definitions of MDA and L(sub c) are apparently more
controversial than the textbooks (and NCRP reports) would seem to
indicate.  The bottom line was if your release criteria utilized
equipment of sufficient sensitivity (not portable survey
instruments!), i.e., high sensitivity and low background operation,
then your release criteria might be approved.

3.  As an example, if our confirmation laboratory (located in a
southwestern state) did not detect any tritium above their
backgrounds, the result was listed as less than 500 pCi/l (their LLD,
not the days' MDA).

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The opions expressed above are    |  The opinions above also do not
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From: Steven Hand <SHAND@umdacc.bitnet>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Subject: MDA and LLD
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From: shand

At the University of Maryland we are required to sample the water
from a C0-60 Irradiator, approximately 30 kCi for conductivity, pH
and activity.  We are also required to take air samples in the
Training Reactor, as well as water samples in the pool, and discharge
sump for the same reasons as the Irradiator above.

Last year the NRC inpsected the Reactor's License and informed us
that the MDA and the LLD must be recorded with error analysis.

Of course, any measurement must have an error analysis associated
with it.  However there are conflicting views on the recording of
the MDA and LLD with errors.  One view says this is already a
calculation of the error, the other view as well as the NCRP No. 58
seems to say that it is both a number and an error.  So which is it ?

For those who calculate the MDA and/or LLD's for any sampling how do
you record the results ?

MDA as we define it is  4.65*squ(background/time).

This MDA in turn is then used for the LLD.

Is the error, by use of the equation LLD = 2.71 + MDA, .05 or
or 5% of this number ?  This is what NCRP No. 58 seems to imply
as well as the recent (1992) reg guide outlining air sampling and
the LLD.


Thanks


steve at UMCP