Shielding Radiation

I recently did a physics experiment that involved placing an alpha source under a Geiger counter. The radiation count was measured over 60 seconds and then a piece of paper was placed over the alpha source and the radiation was measured again over a 60 second period. The amount of radiation decreased considerably however, when another piece of paper was placed over the source, the radiation count remained approximately equal. This continued as subsequent pieces of paper were added. How come the Geiger counter continued to detect radiation greater than the background radiation even when the source was completely covered by multiple pieces of paper?
- Maddy (age 18)
Australia

The basic logic of what you saw strongly suggests that there are two different types of radiation coming from your source. One is easily blocked by paper. The other isn't.

Looking up the properties of different types, it's likely that the paper blocked the alpha radiation. Maybe your source also has beta radiation, harder to block with paper.

Mike W.

(published on 08/31/2013)