Re: Airport explosive detection system

[Schoenhofer <schoenho@via.at>]

At 12:48 1996-06-21 -0500, you wrote:
>This thread reminded me of an interesting (and somewhat embarrassing)
>event that happened on my way to the HPS meeting a few years ago in
>Atlanta.  As my carry-on bag passed through the x-ray machine, the
>person had a perplexed look and mumbled something about some darkening
>on the screen.  A security guard came over and proceeded to inspect my
>bag.  When they reached down and pulled out my old Westclox clock, and
>noted that area of the bag as the location of the darkening, I explained
>that the clock did have a radium dial.  It was on the edge of my bag
>with the dial facing outward, but I was a bit surprised that it would
>cause such darkening.  
>
>P.S. In case anyone was wondering, those Westclox bells beat any buzzer
>or telephone to wake up to.
>
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I am surprised too - how should the radium dial produce a darkening on an
x-ray screen? Gamma rays - even if they were enough intensive - would be
directed to a 4 pi geometry. Absorption of x-rays can cause a darkening, but
not emission of what so ever! So I rather believe that your clock has a
massive metal case which well absorbs the x-rays and causes the darkening. 

Franz Schoenhofer 
Schoenhofer
Habichergasse 31/7
A-1160 Wien
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