[ RadSafe ] FW: OSL/TLD Comparison Experience

Mon Apr 26 09:56:21 CDT 2010

Greetings All,

I recall another seasonal variation from a talk given by folks at PNNL (or
was it INEL) a while back.  This involved lower doses in the winter....

Which was attributed to snow drifting under and around their dosimeters....

Just keep in mind the simplest reason is usually the one.

Regarding OSL reading higher, since it is less tissue equivalent, it would
tend to over-respond more than LiF to any low energy component of the signal
if uncorrected.

The best way is to put them side by side and see the difference if any.  It
costs more, but the baseline data would be useful in times like these.  This
would be especially relevant for environmental monitoring.  The dosimeters
we use today are merely approximations to what is going on.  Each tool we
use brings its own bias to the equation.  It is hard to determine which is
the closest approximation.

Yours,

Rob

Robert J. Gunter, CHP
CHP Consultants
rjgunter at chpconsultants.com
www.chpconsultants.com
www.chpdosimetry.com
Tel:  +(865) 387-0028
Fax:  +(866) 491-9913 

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Neill Stanford
Sent: Friday, April 23, 2010 4:31 PM
To: 'Brennan, Mike (DOH)'; radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] FW: OSL/TLD Comparison Experience

Mike,
What you note in your point #3 is not good. There are seasonal variations,
but if you are seeing variations that you can be sure are due to fading of
the dosimeters in the heat, you should contact your vendor, or your system
if it is in-house. The effect of TL fade is minimized with a properly
controlled heat/collection process and further corrected in the analysis.
With a properly maintained system, any bias introduced by fade should not be
more than 5% (unless the badge had an acute exposure and the fade correction
assumptions were inappropriate.) While old and a bit out of date, ANSI N545
discusses this for environmental monitoring.
LiF is slightly more complicated due to pre-and post-irradiation fade, but
there are well established corrections for this developed by the
manufacturer. OSL, by the way, shows insignificant (thermal induced) fade
and requires no fade correction, even up to 12 months.

Sincerely,

Neill Stanford, CHP
Stanford Dosimetry, LLC
stanford at stanforddosimetry.com 
www.stanforddosimetry.com 
(360) 733-7367 (V)
(360) 933 1794 (F)

-----Original Message-----
From: Brennan, Mike (DOH) [mailto:Mike.Brennan at DOH.WA.GOV] 
Sent: Friday, April 23, 2010 8:56 AM
To: radsafe at health.phys.iit.edu
Subject: Re: [ RadSafe ] FW: OSL/TLD Comparison Experience

Hi, Dan.

This isn't my area of expertise, but I love a tech puzzle.  First, a
couple of the obvious questions:

1)  Is something new?  Have you just started using OSL badges, or have
you changed vender and/or crystal for your TLDs?

2)  Have you compared the energy spectra of the isotopes in the
different departments with the energy sensitivity of the OSL and TLD
systems?  

3)  With the environmental TLD programs I am familiar with, you can see
a seasonal variation due to more electrons escaping the traps in the
heat of the summer than in the cold of the winter.  Is the work and/or
badge storage environment noticeably hotter (thermally, not
radiologically) in the departments where the TLDs read low? 

-----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: Friday, April 23, 2010 6:21 AM
To: 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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