not be discharged, and the photographic paper (Experi ment 4) will show nothing.

    Test as many different materials as you can find; keep a log that records whether or not each specific material blocks alpha rays. Try to include a thin sheet of mica in your tests. Perhaps your chemistry or science teacher may be able to lend you a piece. You will find that this material allows alpha rays to pass through.

    Testing materials for their ability to stop gamma rays is not as simple as the alpha ray experiment. For this you need a gamma source and a Geiger counter, which detects radioactivity.  If,  as  suggested  in  Experiment  8,  your class has built a Geiger counter and has a gamma source, you can investigate a much wider range of materials. Some possibilities include concrete, steel, water, and lead.