AW: [ RadSafe ] TLD Readings in Checked Luggage

[Flood, John]

At the Nevada Test Site, we have been seeing about a half dozen "suitcase doses" (our local term) every quarter until very recently.  In the most recent 2 quarters (2007 Q1 and Q2 data), the quarterly totals more than doubled.  I know that the TSA's initial use of the CT scans was done on a sample of the checked luggage.  I don't know if the recent jump in cases is a result of switching to 100% testing or perhaps an increase in the number of operational systems nationally.

I have our TLD software set up to look for element ratios that are typical of irradiation at extreme angles, and most suitcase doses trigger this flag.  The suitcase dosimeter element patterns consistently indicate about 70 keV average energy, even at the largest angles.  I don't know if there are variations in the hardware used around the country or in the settings used, so that average energy may be dominated by the hardware in our local airport, or it could be characteristic of the national system - I don't know.

We get about 110-170 mrem per CT scan, so we see doses of that magnitude or multiples of that kind of number.  (We see the same general response pattern, but at lower doses - typically less than 80 mrem - from medical exposures - e.g., wearing the TLD too soon after a stress test.)  We have a couple of organizations that travel routinely, and we've worked to educate them about taking the TLD as carry-on, but they hire new people at times and folks will sometimes forget, so we've had suitcase doses as high as 850 mrem in our end-of-quarter processing.  The response pattern of the dosimeter elements makes these cases very identifiable.

The gate security x-ray machines for carry-on items are pulsed x-ray machines, designed that way to reduce the x-ray dose to the point where they don't require heavy shielding to meet exposure regulations for the operators.  Without this design, airport security systems would crush the structures they are housed in.

The pulsed machines use a flash of x-rays to produce an image that can be held on a screen for the operator to view.  On at least some machines, the image can be zoomed, and can be moved left and right.  If the image is moved, the belt on the machine is moved in unison, so the operator can center an object on the screen and take another shot of it because the item is also centered.  The operator has very little adjustment of the beam intensity - that would defeat the design's light weight feature.

A dosimeter run through a gate security x-ray machine five times showed no measurable dose.  We tell our traveling employees to take the dosimeter as carry-on, and when they do, we have no problems at all.  It's only when they forget and put the TLD in a checked bag that we see a significant exposure.

By the way, the gate security machines won't harm your film - if you still use film (how quaint), but the CT scans for checked luggage will most certainly fog your film, even the slowest speed stuff.

Bob Flood
Nevada Test Site




-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf Of Doug Aitken
Sent: Thursday, September 06, 2007 9:21 AM
To: Rainer.Facius at dlr.de; LMS1 at pge.com; radsafe at radlab.nl
Subject: Re: AW: [ RadSafe ] TLD Readings in Checked Luggage

I'm not sure that this is totally correct, given the vast range of 
inspection equipment being used around the world, including heavy dose 
X-ray machines in some less up-to date places. In the US (I guess this is 
the focus of Linda's query), we have seen some higher than normal doses on 
TLD (L!7) and OSL (Al2O3) badges that have been attributed to airport 
security scans. However, as these are quarterly badges of workers 
performing source manipulations, it is a little difficult to attribute 
actual doses to airport exposures. Perhaps Sandy can give some more 
coherent information?

Regards
Doug

At 07:02 AM 9/6/2007, Rainer.Facius at dlr.de wrote:
>Linda:
>
>Unless you remove your TLD chips after passing the (hand-) luggage check 
>and read them out before take-off of your plane, the dose received during 
>the flight (several micro-Sv) may well dwarf the dose from the check 
>(approx. 1 - 2 micro-Sv).
>
>Best regards, Rainer
>
>Dr. Rainer Facius
>German Aerospace Center
>Institute of Aerospace Medicine
>-----Ursprüngliche Nachricht-----
>
>Has anyone had any experience with the TLD doses to expect if a TLD is 
>placed in checked luggage? If so, please give me a call or send me an 
>e-mail with the dose received and the estimated energies.
> > Linda Sewell, CHP
>Senior Health Physicist
> > Diablo Canyon Power Plant

Doug Aitken                     Cell Phone    713 562-8585
QHSE Advisor
D&M Operations Support
Schlumberger Technology Corporation 

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