This project came from InventGeek.com. I figured I already had all the stuff, so I'd give it a try. The basic idea is to remove the radiation source from an old smoke alarm and place it as close as you can to the ccd in a webcam. The folks over at InventGeek built a box lined with copper sheeting to block out all the light and stray radiowaves.
I didn't go to any of that trouble. I just took the lens out and put the source right on the ccd. Then I turned out the lights and put put the camera under a table to shield it from the computer screen. It worked well enough. I was mainly doing this as a proof of concept. At some point when I find another free/cheap webcam I'll make a permanent one. It might also be interesting to see how the number of alpha particle hits is related to distance. I assume it would be an inverse square relationship.
You can see the results below. As I understand it, each flash is caused by the ccd being impacted by an alpha particle. If you have trouble seeing the flashes below you can download the original video (just right click on the link and select "save link as"). It is in Quicktime format. Quicktime will allow you to go through the video frame by frame, just use your arrow keys. The flashes are most obvious when you view the video full screen.