[ RadSafe ] FW: OSL/TLD Comparison Experience

[Debra McCroskey]

Dan,

I was confronted with this same conundrum when I started as ALARA
Engineer at my facility about 10 years ago. My company placed Panasonic
814 environmental TLDs on our boundary fence line. Our regulators
co-located OSL dosimeters at several positions around the boundary. What
I was originally seeing was a wide variability between the OSL & TLD
readings, with the majority of the OSL readings being higher, and only a
few lower. So I did some research on TLD comparison studies and found
very little material other than promotional brochures for both types.
However, in the January 2002 issue of the Health Physics Journal I found
an article titled "First International Intercomparison of Luminescense
Techniques using Samples from the Techa River Valley" which concluded
that they "observed that the average of doses of background samples
measured using TL are systematically approximately 10% lower than doses
obtained using OSL." Unfortunately, the authors didn't offer any
suggestions as to why this discrepancy occurred. So I proceeded to
comparatively track the readings using the proffered data from the
regulators and our own results. I also performed a close visual
examination of the OSL badge positions. What I found was that the OSL
badges were placed in a basket "facing" in random directions, while our
TLDs were carefully mounted to "face" directly inward toward the site.
With the cooperation of our regulators, they started "facing" the OSLs
inward identical to the TLDs. Subsequent comparisons from this point
forward were all the same, the OSLs read 10% to 20% higher than the TLDs
at every location. So I espouse that the OSLs do have directional issues
in addition to whatever the reason is that they read higher than TLDs.
We continue to use TLDs at our site, as approved under our license,
their precision and accuracy supported by the certified vendor who
supplies them and performs the reads. In addition, we perform weekly
dose rate surveys, at the same locations, that support the TLD readings.

I have comparative data now that spans nearly 10 years, and I have seen
no change, the OSLs continue to be higher. If the dose levels you are
tracking are much, much less than regulatory limits, then you could
consider the OSLs a conservative device for your reporting requirements.
However, if you are operating closer to 75% or 80% of the respective
limit values, the higher OSL readings could be an opportunity for
discussion with your regulatory authorities.

This is not a new topic to Radsafe. You can research the other
discussions from the string that was started July 21, 2004, subject
"Badge Reading Differences."

Debra McCroskey, CHP



-----Original Message-----
From: Hoffman, Daniel E <Daniel.Hoffman at covidien.com>
Sent: Friday, April 23, 2010 8:21 AM
To: radsafe at health.phys.iit.edu <radsafe at health.phys.iit.edu>
Subject: [ RadSafe ] FW:  OSL/TLD Comparison Experience


Hi All.  I just realized that I misstated the facts in my original post.
What I meant to say was that the OSL results have been higher (not
lower) than the TLD results in some departments.  Sorry about the
miscommunication.

Dan

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Hoffman,
Daniel E
Sent: Thursday, April 22, 2010 12:39 PM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] OSL/TLD Comparison Experience

Hello RadSafers.  Our plant (nuclear medicine production involving both
reactor- and accelerator-produced isotopes) is seeing significantly
lower results using OSL badges vs. TLD badges, but only in some
departments.  For other departments the results are virtually the same.
Has anyone else had similar experiences at their facilities?

I know the 'dosimetry bunch' will enjoy kicking this one around.

Please feel free to contact me offline if you prefer.

Thanks.

Dan Hoffman

Daniel E. Hoffman, CHP, CSP
Radiation Safety Officer
Covidien
2703 Wagner Place
Maryland Heights, MO 63043
314-654-7906 (office)
314-625-1881 (cell)

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