Re: Low Positive Doses in Personnel Monitoring

["Sue M. Dupre" <dupre@arundel.Princeton.EDU>]

Franz,

You said the following:
> Sorry, I do not understand your concern. When a dosemeter shows that
> a person has received 10, 20 or 30 mrem (I suppose, it is per month
> - you did not mention it), then it is with an almost 100% certainty
> from background radiation, which everybody - occupational radiation
> workers as well - are exposed to. If this person has not been
> working with radioactive material, but his or her neighbour in the
> lab, then the person has been exposed to radiation, whether him- or
> herself is working with it or not. If you receive a reading of zero
> mrem, then you can be absolute sure that there is something wrong
> with the dosemeter or its evaluation.

Just to clarify what I believe to be standard practice for institutions 
in the U.S. who use a commercial dosimetry vendor: our badges are 
shipped to us and later returned to the vendor with a control 
badge included with every shipment.  The intent of this is to control 
for dose received during shipment as well as background dose received 
during the monitoring period.  If the vendor then correctly subtracts 
the control badge dose from each worker's badge, the dose report for 
any worker's badge should indicate only the dose received from 
non-background sources.  Consequently, at my institution, most 
workers' badges are reported as having received less than the minimum 
detectable dose (for our vendor minimum detectable dose is 10 mrem) - 
no numerical dose is reported for these badges - and few badges are 
reported as having received 10 mrem or more.  It is these badges with 
reported doses of 10 mrem or more which I refer to as positives.  It 
sometimes happens that low positive doses are reported when there is 
good reason to think that the badge should not have any dose reported 
for it at all (for instance, when the worker was out of town for the 
entire monitoring period, or when a worker only used S-35, etc.). 

You also said: 
> If I were responsible for your monitoring program I would take hard action
> against persons, who do not wear their badges!!!!!
 
Please understand that I was not referring to workers who refuse to 
wear their badges.  I was referring to researchers who may have been 
out of town during the monitoring period or not in the lab at all for 
some other reason.  Of course, those workers would not have used 
their badges.

with regards,

Sue M. Dupre, Health Physicist

Office of Occupational Health and Safety       
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Princeton University                           
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