The Advanced Photon Source is basically a giant x-ray generator found at Argonne National Laboratory. Ok, that may be a bit of an understatement, since it is really a particle accelerator; but it gives an idea of what it is used for.
When I say x-ray generator I'm not talking wimpy little thing that your local dentist uses to find out which places he can justify jamming his drill into, I'm talking full-on instantaneous blinding, rip a hole through your head x-ray generator.
I had the pleasure to go to a lecture on the APS (I'm currently an intern at Argonne National Laboratory). I remember the little animation we were shown, showing how a particle accelerator works. All the synchrotrons and such, and how the point is to keep a bunch of particles moving fast so that when they bump into stuff it'll launch out x-ray's scientist can use to experiment with. But the main thing I remember about this lecture was the lead brick the lecturer showed us.
Now I'm not just talking any lead brick, this thing was about 2.5"x2.5"x5" or for the english measure challenged, about 6x6x13cm(which I'm sure is interesting enough by itself). The reason the man was showing us this brick was that they had let it sit in front of one of the x-ray emission points on the APS. This thing had about a 1" (2.5cm) diameter hole all the way through it(the 2.5x2.5 part). I'm not sure if they did this on purpose or not, but either way it was quite the prop.
For all the APS info you would want (or at least a start) visit the APS's site at http://www.aps.anl.gov