Re: Low Positive Doses in Personnel Monitoring

["Scott O. Schwahn" <schwahn@CEBAF.GOV>]

...>Assuming that 
>you've dealt with the vendor to eliminate factors such as control badge
>problems,  then how do you proceed?

First thing, especially if your are seeing badges read 20-30 mrem when the
user has not even used the badge, talk to the vendor again.  Make the vendor
provide you proof positive that in these cases the correct background badge
was subtracted.  It wouldn't be the first time that has happened.

...>1)  Do you do some sort of followup action on ALL positives...

...>2)  Do you set a limit below which you ignore low positives and only 
>do investigations of higher doses (this would mean that you accept 
>the low positives as reported)?  ...

...>How would you assign dose in the following scenario? 

No, we don't follow up on all positives, except to note if a large group
gets a low dose, as alluded to in my first comment.  I recommend trending
collective dose, as well as other routine statistical analyses.  We have
what are typically referred to as "Administrative Alert Levels," annual
levels that are about 1/4 of the Administrative Limit, which is again a
fraction of federal limits.  We do an investigation (actually, more of a
fact-finding mission) when a person's quarterly dose exceeds 1/4 of the
annual Administrative Alert Level (effectively, 60 mrem/quarter W.B., 250
mrem/quarter lens, or 620 mrem/quarter extramity/skin.  If a person actually
goes above the Administrative Alert Level, then we do a full-blown dose
investigation, and recommend ways to maintain dose ALARA.

There is not enough information on your scenario for me to attempt to assign
dose.  Have you looked for contamination of the badges/racks?  Checked with
the vendor to see if there are chemicals you are using that could affect
dose readings?  I guess if you are really suspicious of these low-level
doses, I would first recheck the vendor's  control badge subtraction, then
look for contamination or other source of radiation.  Make sure your badge
racks are in a low-backgound area like your controls.  

That's about all the advice I'd give without knowing more about your
facility.  Would be happy to discuss further in a private e-mail or phone call.

Scott O. Schwahn, CHP
Thomas Jefferson National Accelerator Facility
Newport News, VA
schwahn@jlab.org