Objective:
– To demonstrate an application of radioactive decay, and the low penetrating power of alpha particles.
Apparatus:
- Smoke detector “board”
- Geiger counter
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Method:
- The smoke detector “board” contains two identical mounted smoke detectors.The first smoke detector is still sealed and mounted on a bracket. If you unscrew the smoke detector from the bracket, the label on the back contains information about the type of source and activity as of the manufacture date (Am-241, 1.0 μCi on November 2013).
- The other smoke detector has been pre-opened. Remove the outer case to reveal the circuit board. The source is inside the metal housing, which can also be removed. Am-241 is an α emitter with a half-life of 432 years.
- To demonstrate that α particles have low penetrating power, use the Geiger counter to measure the activity around the closed smoke detector. Now remove the outer plastic cover, and again measure the activity just outside of the metal housing. Finally, remove the metal housing and measure the activity near the source. When the source is exposed, you will have large readings on the Geiger counter, which you do not have even when the metal housing is in place.