Re: electronic dosimeters

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

Doug Turner said:

> Evidently I don't understand the term in house.  I thought it signified 
> irradiating and reading your dosimeters onsite.  In house was Sandy's term 
> and I should have substituted on site for clarity.  Our dosimeter vendors 
> expose out dosimeters to known amounts of radiation to verify accuracy to a 
> variety of known rates and quantities.

As I stated in my second posting, there are many facilities who do 
calibrate both their TLDs and EPDs in-house. The term in-house 
does mean, internally performed by the facility to be used at the 
facility. The statement also went on to say that many facilities 
where I have performed a NVLAP on-site assessment showed that 
the EPDs were calibrated to correlate to the TLDs. In that case, 
one would expect excellent correlation, if the working environment 
was in fact, the same. If the energy spectra is not equivalent to 
high energy photon calibration spectra, as Cs-137, there will be a 
difference. The EPD (for many manufacturers - NOT ALL) will under-
respond when exposed to low energy x-ray (specifically below 
M100 NIST Beam Code, and higher energy photons, such as Co-
60). This is highly documented by many manufacturers, when you 
look at their energy response curves.

In summary, whatever dosimeter you use, be it TLD, film or EPD, 
they should be calibrated to a known source, and, the facility 
should understand their own radiation environment, whereby an 
algorithm can be used, or, special correction factors used to 
accurately assess a dose, if the device is irradiated to a spectra 
that is not equivalent to the calibration source used, and the dose 
is quite different, i.e. EPD irradiated to M60 for instance.

On another note, High Plains Drifter said the following:

> evidently Sandy's statement that he does not
> calibrated his EDs in-house may mean he has the vendor do it
> at their facilities.  It would be another bench mark for his
> QC program.

Whatever I had written was misunderstood. I don't use electronic 
dosimeters where I am now. Any comment made was in reference 
to Doug's posting. When I was at FPL, we used MGP electronic 
dosimeters, which were calibrated using a Cs-137 source from 
MGP, and were calibrated uniquely and independently, and NOT to 
the TLD. The MGP was calibrated and correction factors applied 
based on known spectra measurements made throughout the plant 
areas, and, we were also NVLAP accredited for the electronic 
dosimeter as well.

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

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