[ RadSafe ] TLD Sensitivity

[Flood, John]

The difference in response to x-rays between a whole body dosimeter and
the same dosimeter configured as a wrist dosimeter will be determined by
the filtration over the phosphors.  Typically a wrist configuration will
employ less filtration than a whole body assembly, leading to a higher
response per mrem in the wrist assembly.

If the dosimeter is exposed during transit through a gate security x-ray
machine, you are unlikely to see an effect - the delivered dose is too
small.  These machines are pulsed x-ray systems designed to meet
occupational exposure regulations without requiring a lot of heavy
shielding (floor loading issues in airports).  Thus, the x-ray tube is
pulsed enough to cause a usable image on a CRT, but no more.

Luggage that is checked at the ticket counter is a different story.
Most such bags today are subjected to CT scans.  Our experience is to
expect 100-300 mrem and strong angularity to the irradiation.

If the whole body and wrist dosimeters are not the same phosphors, then
the response will be more dependent on phosphor characteristics than
filtration.  Lithium-based phosphors (LiF, LiBO) are approximately
tissue equivalent and yield a relatively flat response per mrem versus
photon energy until the energy drops below about 30 keV, where
under-response is expected.  Calcium phosphors (CaF, CaSO) are denser
than tissue and show a strong energy dependence for photons.

I hope this helps.  If you have more specific questions, please let me
know.

Bob Flood
Nevada Test Site


-----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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