LLD for TLD and ED

[Elaine Marshall <emarshall@fnal.gov>]

It is always difficult to determine the most appropriate location to keep
control badges when you have a very mobile workforce and/or a site that is
large enough where background levels will vary considerably.  We employ a
second set of badges, called rack monitors, in addition to the control
badges.  The control badges are maintained in the Dosimetry Program Office.
 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.).

There are problems with this method in that (1) additional badges are
required which could cause problems for those programs on a limited budget;
(2) it still can not account for differences in background for those
individuals who do not store their badges in the designated locations or
take them home; and (3) it can not determine an "average" control badge
reading.  However, it does eliminate problems with matching controls to a
given set of badges, which for me would be a nightmare (50-100 different
storage locations across 10 square miles for approximately 2000 badges a
quarter).  In the past, the rack monitors have identified areas in which
individuals with medical exposure have worked, areas with low level
radiation fields below 5 microrem/hour, and areas with elevated background
readings due to construction materials.  They have also helped in
investigating what we believe are false positive readings by providing
another data point.  It can not eliminate all false positive readings, but
may give you a better idea of what is there.  

Elaine

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Elaine Marshall
Fermilab
Kirk and Wilson Roads / WH-7E
PO Box 500, Mail Stop 119
Batavia, IL 60510

PH......: 630-840-8756
FAX.....: 630-840-3390

E-MAIL..: emarshall@fnal.gov

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