ED TLD LLDs

[Mike Lantz <mlantz33@cybertrails.com>]

(Hopefully this email doesn't include all that junk)

Jim and Sergio make some excellent points about:  1) the many factors that we have to deal with to evaluate TLD readings at low doses above background; and  2) the good statistics of electronic dosimeters at low doses.  I always agree with them over good technical issues.  So I won't spend a lot of time reminding everyone that good TLD's are spectrometers, but that most ED's have only a single sensitive element that will only measure personnel dose appropriately if calibrated to the representative photon spectra.  Sandy Perle and Bob Flood clarified that.  Or that EDs must continue to get smaller to deal with the significant angular dependence issues.  Or that peer-reviewed information on EDs remains minimal.

However,  I would like add to a minor point to Jim's note that the ED LLD that he is discussing is still a PER ENTRY LLD.  And if a facility would choose to record 0.1 mrem increments, there could be other problems.  For one, they could be setting themselves up for extra plant dose; i.e., natural background recorded as occupational dose.  Our workers wear their EDs for eight to 12 hours and would incur 0.1 mrem each from natural background.  

IF the EDs do not spike, as these electronic devices have been doing today at low and high doses because of many factors (RFI, welding, motors, shock, etc), and the EDs operate correctly without incident, you would obtain a reading of 0.1 mrem for practically everyone in the RCA.  Maybe we could train our workers to believe that THEIR 0.1 mrem per shift is not related to the radiation fields at our facility, and maybe not.  If not, it would add up to a great deal of recorded dose for our many thousands of entries each year; about 30 Man-Rem last year. 

However, still more importantly, let's see YEARS of stable ED low dose measurements first before we think about recording tenths of a mrem for every entry  ---  years without 0.5 mrem spikes and 13 mrem spikes and 1857 mrem spikes.  Then we maybe we can deal with this natural background subtraction issue.  I know that my TLDs integrate those 0.1, 0.2, 0.3 mrem entries very well, whether it's dose above background or the dose that is natural background.

Very glad to see the manufacturers of these dosimeters watching, listening and making better products.  

Mike Lantz, CHP

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