Re: electronic dosimeters

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

Doug Turner stated the following:

> I think you are implying greater TLD accuracy than the NAVLAP standard 
> requires, especially in mixed fields.  As I remember from when I was involved 
> with NAVLAP the beta standard was +/- 50%.  We are routinely getting 
> agreement  better than +/- 10% EPD to TLD, and we don't calibrate either 
> dosimeter in house.  Different brands of TLD's or for that matter different 
> processors of the same brand TLD have trouble achieving +/- 5% agreement on a 
> gamma source (compare your environmental tld results to state colocated 
> tld's).

Doug, I am not comparing actual dosimeter response to any 
Standard. The Standard, ANSI N13.11-1993 does use a |B+s| of 
<0.3 for Cat I and II and 0.5 for Cat III through IX. The TLD 
processors can get excellent accuracy, within a few %, all 
depending on the program and algorithms used. This can be done 
for all fields, mono and mixtures. The electronic dosimeter on the 
other hand can get excellent correlation specifically at the radiation 
type and energy that to which it was calibrated. From that spectra 
out, the accuracy will drop off on both ends. The precision will 
remain OK, but without accuracy, the usefulness of the dosimeter 
is degraded.

Comparing environmental dosimeters to personnel dose 
assessments is mixing apples and oranges. While I say that, 
many environmental dosimeter inter-comparison tests have 
resulted in dose determinations within +/- 5%.

There are all kinds of TL materials. However, any dosimeter with 
the proper filtration and materials can result in very accurate 
algorithms. I have assessed dozens of NVLAP facilities, and most 
obtain excellent results, especially in laboratory blind testing. Field 
results also show good correlation. As you said, it depends on the 
facility and the length they are willing to go to enhance their 
technical programs.

In the end, there is still no better dosimeter for multi-purpose 
monitoring, especially in unknown fields, than the current TLD and 
film dosimeters that have been worn for decades.

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

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