Arhhg! This is only kind of true. YES, x-rays DO expose film. They're
just not particularly good at exposing film well enough to produce a
nice image with the low radiation levels which people prefer to be
exposed to for diagnostic imaging. This is what happens. . .there is
the "Potter-Bucky diaphragm" which acts almost like little louvers
to filter out scattered xray photons to offer a clearer image, which
I think is the closest thing you'll find to what was described. Why
do you have scatter? When an x-ray photon hits something which it
doesn't penetrate, it scatters like you will have if you direct a
stream of water at a solid object. I'd explain more, but that
actually requires effort :) I'm lazy. Check out this site which I
found with a quick web search for an in-depth explaination:
http://www.noetics.com/lect46.html and search for "Bucky."
Now what your BiL was referring were phosphor screens which are
called intensifying screens. So xrays hit the phosphors, which
then emit light, which are detected by the photographic film! So
you have a sheet of film sandwiched between two phosphor screens
inside a light-tight cassette. The two phosphor screens I believe
are also inside reflective sheets to maximize the phosphor effect.
Check out http://www.noetics.com/lect48.html!
This is not to even start describing the new filmless digital
acquisition systems. . .
X-rays striking the zipper will be scattered and blocked. They
don't cause photons or anything else. That's why you have the
zipper shadow! But you knew that!
Disclaimer: I'm not a physicist but I do know how medical x-ray
systems work.
> My brother-in-law is the head of X-ray in a hospital in Florida. He
> explained to me that x-rays do not directly expose film. To get the image
> they need, a fine wire grid is sandwitched with the film in the film
> holder. When the x-rays strike the wire, they cause it to give off
> (photons?) thus exposing the film.
>
> I don't know if that also applies to 35mm film, but it would make sense
> that the x-rays striking the zipper could do the same thing. Anyone on the
> list a Physicist who can help us out?
>
> Gregg
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