[ RadSafe ] TLD Sensitivity

[Neill Stanford]

Marvin,
You have received responses from some very knowledgeable dosimetrists with a
pile of information that is probably more confusing than helpful. You have
heard about angularity, phosphor types and filtration. You even got a
response from a TLD material vendor, in case you want to buy some of your
own. In my opinion, Kim McMahon's response was the most appropriate: we need
more information to provide a thorough response. 

The short answer to your question is: 
"No. There is no inherent basis for a difference in sensitivity of wb and
wrist badges to screening x-rays."

Both whole body and wrist (extremity) dosimetry stystems (TLD, film, or OSL)
are generally calibrated to respond accurately to photon energies from 20
keV up (some are not appropriate for low eneries, you can find out by
checking the NVLAP scope of accreditation for the particular badge at
http://ts.nist.gov/ts/htdocs/210/214/scopes/dosim.htm )

You do not need to know what phosphor type, what filtration, how many
elements are used etc. This is all taken into account within the dose
calculation methodology. Both systems (whole body and extremity) normally
report a shallow dose and it should be the same. In fact, many wrist
dosimeters are simply a whole body dosimeter strapped to the wrist. Same
measurement system. There is a small difference in dose conversion factors
for extremity (wrist) vs whole body shallow dose but it is small enough that
I doubt it is causing the difference you are questioning. 

So, if you have seen a significant difference between a wrist and whole body
dosimeter the reason is either that they were not irradiated under the same
conditions or there was a problem with one of the systems. There are a pile
of possible causes, some but not all were mentioned in previous posts. 

Neill Stanford, CHP
-----------------------------------------------------
Stanford Dosimetry, LLC 
2315 Electric Ave.
Bellingham, WA 98229
 
www.stanforddosimetry.com
360 527-2627 (voice)
360 715 1982 (fax)
360 770-7778 (cell)
------------------------------------------------------

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
Of Marvin M. Turkanis
Sent: Tuesday, April 25, 2006 2:04 PM
To: RadSafe at radlab.nl
Subject: [ RadSafe ] TLD Sensitivity

Is there a basis for a difference in sensitivity of whole body and wrist
TLDs to X-rays from the security systems for checked airline luggage?

Marvin M. Turkanis

marvintur at erols.com
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