Re: LLD for TLD and ED

["Sandy Perle" <sandyfl@earthlink.net>]

> Each location on site where badges are stored has a least one rack
> monitor.  Many locations have multiple rack monitors.  The rack monitors
> are in different colored holders to distinguish them from personnel badges.
>  At the end of the wear period, we collect the personnel badges and the
> rack monitors and have them processed using the control badge as a
> subtraction for background radiation.  If the rack monitor indicates a
> reportable dose, we can take a look at those individuals who regularly
> store their badges on the rack to assess whether or not it is a false
> positive reading.  If a significant fraction have reportable readings, then
> that usually indicates an elevated background reading in that area and we
> can take appropriate actions (dose adjustments, relocation of the storage
> rack, additional measurements, etc.).

In essence, what Elaine has stated above, is the appropriate 
method to determine the effective background that should be 
subtracted. What I would like to add is, that the rack monitors are 
in effect, the Control Badges, and should be the dosimeters used 
to make the background subtraction from the personnel 
dosimeters, in that they are located where the personnel 
dosimeters are stored, when they are not being worn. The Control 
Badges that are maintained in the Dosimetry Program Office 
should only be processed, and compared to the various dose 
responses from the rack dosimeters. This is useful to determine if 
there is a higher than expected background in the dosimeter 
storage location. Even if there is a higher background, this is what 
should be subtracted since the rack dosimeters do represent the 
background. I would not use the Control Badges for any 
subtraction, for they only represent the background in an area 
where dosimeters are not stored (if I read Elaine's post correctly). If 
a majority of the rack dosimeters exhibit a higher than expected 
result, that does not automatically correlate to a false positive. An 
investigation needs to be conducted to determine if there is any 
causal agent that may have resulted in an elevated response, 
during the time frame of interest.

The background subtraction is best conducted when derived from 
multiple dosimeters. If the variance is high, there is generally a 
problem, and it needs to be identified. Relying on a small sample 
to perform the background subtraction often leads to an error in the 
background subtraction. A single dosimeter used in a large 
population of personnel dosimeters often leads to false positives, 
or, could easily result in subtracting too much background, leading 
to non-reportable dose.



Sandy Perle
E-Mail: sandyfl@earthlink.net 
Personal Website: http://www.geocities.com/capecanaveral/1205

"The object of opening the mind, as of opening 
the mouth, is to close it again on something solid"
              - G. K. Chesterton -
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