PURPOSE: Demonstrate radioactivity, the Geiger counter, and show some differences between alpha, beta, and gamma rays.

DESCRIPTION: Three sources are provided: an Am 241 source, mainly 5.47 MeV alphas; a Bi 207 source, pairs of electrons around 0.5 Mev, 1.0 Mev, and 1.7 Mev; and a chunk of U 238 natural ore with a large number of low-energy gamma rays.

The alpha particles have a range in air of about 2 or 3 cm; you must place the source close to the Geiger tube to observe the alphas. Inserting a piece of paper in the alpha beam stops them! The betas have a longer range in air, and are mostly unaffe cted by passing through a piece of paper. A thin lead sheet stops the betas, but some counting remains due to the presence of a some gammas in the beta source. The gammas are unaffected by the paper or the thin lead sheet, but can be stopped by a lead b rick!


REFERENCES: (PIRA 7D10.10) See Demonstration Reference File for information about this experiment and data on the full spectra of these sources.

EQUIPMENT: Geiger tube with audio amplifier and loudspeaker, alpha, beta, and gamma sources.


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