Re: MDL and Dose Effects

["PAUL E RUHTER" <RUH@inel.gov>]

Supervisor, Radiation Dosimetry & Records
User ID-RUH; Mail Stop-4147;  Ext. 6-1973
It is not fair to report all positive doses unless all negative doses
are also reported. We conducted a study here at the INEL of the raw data
over two years of TLD results (over 180,000 TLD readings) to refine our
minimum reporting level of 15 mrem. We discovered (?) that the most
accurate results were obtained if the net value is used, positive or
negative, with no minimum/threshold considered. In keeping with the
"theory of large numbers", this gives the best result, particularly for
exposures near background.

However, we were reluctant to tackle the explanation of why exposure
would occassionally be subtracted from an employee's record when the net
was negative, so we adopted a more traditional threshold approach. We
selected 10 mrem because it appeared to balance the false positives and
negatives, giving us the most accurate "station-total". Some employees
will receive undeserved small doses, but these will balance small doses
NOT recorded due to the threshold (minimum reporting level).As Steve
Croslin suggested, we have debated the wisdom of reporting all positive
values and decided against that approach.

*** Reply to note of 11/04/96 12:36

From: Steve Croslin
To: RADSAFE --INELMAIL RADSAFE

Subject: Re: MDL and Dose Effects


It might be worthwhile to add that ORNL, and I would assume most other
accredited dosimetry programs, not only have a much lower minimum reportable
dose threshold than in the past, but also now keep the raw data that goes
into dose determination.  This raw data, along with the criteria used to
calculate the minimum reportable dose, will allow epidemiologists and others
to "rehash" the numbers in retrospective studies. (In fact, that is one of
the primary reasons the raw data is maintained.) But it seems open to debate
whether all positive doses, even those with a large uncertainty, should be
reported to the worker.

Steve Croslin
ES&H Support
P.O. Box 2008
Oak Ridge National Laboratory
Oak Ridge, TN 37831-6017
Phone: (423) 576-5065




>In the study's conclusion, Tankersley wrote:
>
>''It is not possible to determine accurately the fraction of total dose
>unrecorded due to procedures where all readings less than the applicable MDL
>are set to zero. However, our investigations indicate that, in some cases,
>the amount is considerable.''
>
>The administrative practice of recording zeros for radiation doses at or
>below the MDL continues today at the government's Oak Ridge plants and other
>nuclear facilities around the country. However, the minimum detectable level
>for dosimeters is much lower than it used to be, and monitoring period is
>longer, too, which reduces the chance that a significant dose of radiation
>will be missed.
>
>Nonetheless, Tankersley urged authorities to change the policy and report
>all radiation doses as measured.
>
>
>Kim McMahan, CHP
>Office of Radiation Protection                             Sola fide ...
>Oak Ridge National Laboratory                            Sola gratia ...
>P.O. Box 2008   Oak Ridge, TN  37831-6290             Sola scriptura ...
>Ph:  (423) 576-1566                                  Soli Deo gloria .
>e-mail: mcmahankl@ornl.gov
>
>
>
>