Re: Electronic Personal Dosimeters

[sandy_perle@email.fpl.com]

     MGP Electronic Dosimeter Evaluation:
     
     1. Accuracy is only as good as the source calibration and energy you 
     calibrate them to. 
     
     2. Precision is excellent.
     
     3. We passed ANSI N13.11-1993 Standard for Category IV (Cs-137 
     protection range), Category VI (Cs-137 and low-energy photon mix, B., 
     MFG, MFI, H150) (Note, this was only possible by adding a significant 
     correction factor to raise the low-energy photon under-response at the 
     detriment of the Cs-137 component, which ultimately over-responded)
     
     4. From item 4 you can see that the EPD highly under-responds to 
     low-energy photons, and under 51 keV there is essentially NO response 
     whatsoever.
     
     5. Angular dependence Category IX was passed without any difficulty.
     
     6. Category II, Accident case, Cs-137 failed due to 2 EPD results 
     failing the accuracy test by ~35 to 40%. We have replicated this .. 
     and there is an inherent problem where the EPD causes a spike at very 
     high dose rates, but not on all dosimeters. No lab normally calibrates 
     or checks these dosimeters at high dose, therefore, they will not know 
     if they have this defective dosimeter until the unit is exposed to 
     that level.
     
     7. Digital display is lost in high humidity environments .. ~ 1/3 of 
     the EPDs in service.
     
     8. Moisture has caused problems by getting inside the case ...
     
     9. Speaker issues where the wires are not well manufactured, 
     therefore, the alarms are not heard.. Need a program to ensure that 
     the speaker is functional, that the battery is ok .. etc.
     
     10. Intermittent problems where the dose starts to accumulate until it 
     is read .. this has been seen with a dose of ~ 3 rem (not real) to an 
     individual who had just exited the area. He was in a no or low dose 
     area the entire work evolution. 
     
     Key .. do a lot of testing .. create your own energy response curve .. 
     correlate and validate the dose rate you calibrate the EPD to with the 
     dose rate that you expect your workers environment to be. Do 
     comparison testing every quarter .. and then do some more evaluations.
     
     Hope this helps in your evaluation.
     
     
     Sandy Perle
     Supervisor Health Physics
     Florida Power and Light Company
     Nuclear Division
     
     (407) 694-4219 Office
     (407) 694-3706 Fax
     
     sandy_perle@email.fpl.com
     
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