Thanks June for re-posting, One must also recognize that the EADs of the 1999 vintage (and earlier) have some different characteristics than compared to some of the EADs today. Their design and technical advancements have "minimized" some of Mike's points. As you may be ware, Mike has been working with me at Mirion Technologies for about 2 years now and routinely consults to many of the reactor sites (be they our client, in-house or other provider).
Regards, Sandy ----------------------------------- Sander C. Perle President Mirion Technologies Dosimetry Services Division 2652 McGaw Avenue Irvine, CA 92614 +1 (949) 296-2306 (Office) +1 (949) 296-1130 (Fax) Mirion Technologies: http://www.mirion.com/ From: June Scott <[email protected]<mailto:[email protected]>> Reply-To: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Date: Wed, 30 Nov 2011 15:00:55 -0600 To: powernet <[email protected]<mailto:[email protected]>> Subject: Re: Powernet: RE: period TLD-ED dose discrepancy criteria This list of EAD response is an excerpt from a radsafe discussion from Mike Lantz (1/29/1999) in response to Sandy Perle. It defines some of the EAD response characteristics and the effect on CRE and EAD individual response. It provides testing data for EAD response and the resulting bias that is being used. Also, if you look at the TLD-EAD bias by binning the data in 30 mrem increments you distinctly see the changes in EAD to TLD response from low doses to high doses. In a plant setting it is quite often the perceived need to “match” the doses less than 30 mrem that require the EAD over response to be set high. This is confirmed also by the data on John’s graph in the lower left of the page. Tracking of dose >100 mrem in a month and in photon fields close to the calibration energy correlate closely. 1) Exposure to high energy photons from underneath, such as standing on = a high integrity container of rad waste, TLD =3D 600 mrem, SRD =3D 575 = mrem and ED =3D 250 mrem because of significant angular dependence. = This factor of more than 2 increases to a factor of 4 underresponse if = the transmitter is added to the ED.=20 2) ED's have underresponded by a factor of 3 to noble gas submersion = (dominated by Xe-133) even though testing shows the ED responds = accurately to 80 kev photons at perpendicular incidence. Again, a = serious angular dependence. 3) Low energy photons from the side, top or underneath have been = measured to respond a factor of 14 low (!) in laboratory testing by the = vendor. In my article a few years ago, I worried if these ED's were = being used by flouroscopists because of the likelihood of significant = underresponse.=20 4) The vast majority of ED's in use in the US will significantly = underrespond to any photons below approximately 60 keV at perpendicular = incidence, and worsens dramatically as the angle moves from 0 degrees. 5) ED's will saturate and underrespond in VHRA's; and the underresponse = will be relatively unknown. We recently tested a brand new dosimeter = type that responded well at 90 R/hr, but at 120 R/hr indicated NO = response, nothing! Its secondary dead time correction in its = complicated dose rate to dose conversion algorithm, which is known to NO = users, failed and the dosimeter stopped working until the dose rate was = reduced to below 100 R/hr! We also tested ED's to NVLAP Proficiency = Testing and 2 dosimeters read 54% and 65% lower than expected because = they were irradiated to a high dose rate. 6) Drills, motors, and magnetic fields have placed ED's into a latent = state where they are completely UNRESPONSIVE to radiation, regardless of = the dose rate. 7) The energy response characteristics of individual pin diode detectors = have been documented to be much more variable than I have ever seen in = TLD or film testing. Variable responses, certainly more notable as the = energy of photons is decreased, have been found, possibly related to = dopants in the pin diode materials; errors up to 60%. 8) ED's have been found to change calibration factors by a factor of 2 = in the field; and then correct themselves. 9) The current crop of ED's are fairly new. I find this the hardest = part to swallow that people think they just work; and will continue to = work or be supported by the vendor for years, even as the vendors move = to newer designs. As they have aged, loss and repair rates have been = significant. Speakers for the alarms fail. And so little has been = published.=20 10) Computer software and hardware that is not in a mature state yet = controls the tracking of all doses to be recorded by ED's. Examples of = data loss (ie, dose) include a recent situation where a terminal to = verify that the ED was turned on actually turned off random ED's. Other = software problems continue to lose dose by ED's. This is part of the list of problems with EDs that I wrote about in = 1996. One of our many duties must be to continue to set standards for = personnel dosimetry that guarantee our facility personnel high quality = dosimetry that works in all spectra, angles and environments that they = will encounter. The vendors have continued to improve their products = and we should be proud that we were part of the push for that = improvement. Mike Lantz, CHP [email protected]<mailto:[email protected]>
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