Re: Sandy's EPD Comments

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

In response to John's questions,,, please see my comments below:

> Sandy- You wrote earlier:
> 
> "I will just state that the "electronic 
> dosimeter" can only be considered viable for "dose of record" if the 
> working environment is stable, the spectra in which the worker is 
> exposed does not change, and that the calibration factors don't 
> change, based on all of the above. Experience has demonstrated 
> that this is not often the case. The fact that the primary spectra 
> happens to be high energy photons, with whatever beta spectra 
> you have within your facility, does not mean that when there is a 
> "radiological incidence" that the spectra doesn't change. It does 
> and it will. The calibration of the device drives the final dose 
> determination, as well as the dose rate. When there is a change, 
> the values obtained are no longer valid, and can result in  severe 
> under-response, often leading to a dose that could exceed 
> regulatory limits, exceed administrative guidelines, etc. In essence, 
> while the manufacturers swear that the "electronic dosimeter" is 
> not a processing dosimeter, such as found with dose determination 
> from a film or TLD, it is just that. There are built in algorithms and 
> parameters set and those that are hidden, within the device, and if 
> those factors changes, so does the final dose reported."
> 
> Sandy- Your last sentence had me wondering- What's the difference between an
> electronic dosimeter running its own internal algorithms to determine
> radiation type, energy and dose, and a dosimetry vendor applying ITS
> algorithms to a film or tld badge to determine radiation type, energy
> and dose?  Are you saying that in some way the vendor's combination of
> dosimeter and algorithm is inherently superior?  If so, how?

The above comment is in response to the manufacturers, and 
users of EPDs, who state that 10CFR20 , Section 1501 does not 
require NVLAP or any proficiency testing .... (c) All personnel 
dosimeters (except for direct and indirect reading pocket ionization 
chambers and those dosimeters used to measure the dose to the 
extremities) that require processing to determine the radiation dose 
and that are used by licensees to comply with § 20.1201, with 
other applicable provisions of this chapter, or with conditions 
specified in a license must be processed and evaluated by a 
dosimetry processor--  

I am also saying that a dosimeter that does have an algorithm is 
more apt to be superior, be it film, TLD or whatever, when it is 
capable of defining the spectrum, and accounting for the 
appropriate dose calculation. If a doismeter is only calibrated to Cs-
137, and that is the only "dose algorithm" available, the resultant 
dose will be either an over-resposne or an under-response, 
dependent on the actual spectrum in which it was exposed.

> Also, your statement about changes in radiation environment leading
> to possible overexposures because the epd underresponded seems a bit too
> alarmist to me.  Before you purchase any kind of epd OR dosimetry service,
> you need to ensure the dosimeter can handle the various radiations
> that could be encountered.  Assuming you have done that homework, would
> you still stick by your statement? 

I stick by my statement. Not only have I used EPDs within the 
power reactor world, I have also assessed them as a NVLAP 
assessor. All you need to do is speak to anyone who is currently 
using them in the field to determine how it responds in an 
environment that it was not calibrated to respond to.

> 
> We have used Landauer for our dosimetry of record for years, and I trust
> their results.  We have also used Siemens EPD-2's for several years as an
> additional tool to assist with exposure monitoring and control, and I
> have been very impressed with their capabilities as well, so perhaps I'm
> biased.

I have no quarrels with the above statement. However, please 
provide data on what type of radiation and energy are your workers 
exposed to. What internal fudge factor do you apply, if any, to the 
EPD result, before the EPD provides a result. Does your 
environment change, i.e., beta, gamma and x-ray spectrum? Did 
you accredit your EPD through the NVLAP program, and if so, 
what NIST Categories did you test? Do you routinely test your EPD 
to Cs-137 and OTHER photon energies? If not, how do you know 
the response of your EPD to other energies IF the calibration is 
performed using Cs-137?

Perhaps you missed my post's purpose. The EPD is a good dose 
control tool in that it makes the indivdual aware of their radiation 
exposure environment. The EPD response is only as good as to 
what it was calibrated, and, how the internal parameters are set. 

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

"The object of opening the mind, as of opening 
the mouth, is to close it again on something solid"
              - G. K. Chesterton -
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