Re: Electronic Dosimetry

[Bob Flood <bflood@SLAC.Stanford.EDU>]

At 01:38 PM 3/7/97 -0600, you wrote:
>     The EPD has passed 
>     "mock" NVLAP Proficiency testing in all categories with the exception 
>     of 3A shallow and Neutrons.

Neither of these is critical for using an ED in a nuclear power plant
environment. A supplemental neutron dosimeter can be used for those few
situations where neutron dose is expected. Dose from low energy photons at
nuclear plants arises mainly from noble gas submersion, and this dose can
be calculated from air sample data (and generally is throughout the industry).

Reliability of EDs has been generally good - the self-diagnostic features
that can be built into such devices make an undetected failure a low
frequency event. However...

Electronic dosimeters make sense only if they are used as shared
dosimeters, i.e., the user takes one to enter a controlled area and returns
upon exiting (otherwise, you've just replaced a $20 TLD with a $300 ED).
The user rarely gets the same dosimeter in succession, and a given ED will
be used by a large number of people, especially during an outage. My
greatest concern about EDs as the sole dosimeter for dose of record is the
QC failure where the device reads too low. An infrequent event, to be sure,
but such a failed dosimeter could have an impact on potenially thousands of
people's dose totals. Identifying every user, obtaining coworker data from
same or similar jobs, evaluating the data and deciding which to use and
which to exclude in the dose investigation on each case, plus management
reviews, data entry to correct dose totals, and documentation of it all
could be man-years of work per failed dosimeter! 

The other concern I have is about abandoning the use of secondary
dosimetry. It isn't needed for everyone, but there are a lot of jobs where
there's a real risk of data loss if an ED is damaged or destroyed. The last
time I discussed this with someone from ANI (a few years ago), they were
opposed to using an unaccredited dosimeter when an accredited one is
available, and they, too, didn't like the lack of secondary dosimetry.

Nevertheless, EDs can provide very good measurements. I just suggest that
you discuss it with your company lawyers and your insurer before making a
final decision.

Another note: Not all EDs are easy to calibrate or test in quantity. If you
have a system that is not automated, you may need more manpower to operate
a stand-alone ED system than it would take to operate an automated TLD with
pocket chamber system. Something to consider.


Bob Flood
Stanford Linear Accelerator Center
(415) 926-3793     bflood@slac.stanford.edu
Unless otherwise noted, all opinions are mine alone.