Measuring Radioactivity with a Geiger Counter

Using a Geiger counter, radiation is measured from everyday objects such as a lantern mantle (thorium), a smoke detector (americium), and Fiesta ware (uranium). Additional natural sources like bananas (potassium-40) show that radiation is present in common materials. Shielding with lead illustrates how radiation can be blocked.

1. Turn on the Geiger counter with the audio enabled so that each detection event produces audible clicks.
2. Place the detector near a known radioactive sample such as:
   1. Coleman lantern mantle (thorium source)
   2. Smoke detector (americium source)
   3. Fiesta ware dinner plate (uranium oxide glaze)
3. Record the count rate for each source.
4. Place a piece of lead between the detector and the source to show how shielding reduces the count rate.
5. Extend the demo to everyday items:
   1. Place the detector near a banana (contains potassium-40).
   2. Place it near common household items (e.g., granite, salt substitute with potassium chloride).
6. Compare the background count rate to the different items to highlight relative levels of natural radioactivity.

Radioactivity Demo: Assorted sources - Physics Demos:

• Measure the count rate at different distances from the source to illustrate the inverse-square law of radiation intensity.
• Compare shielding effectiveness of paper, aluminum foil, and lead to show how different radiations penetrate materials.
• Use multiple everyday food items (bananas, Brazil nuts, potatoes) to compare natural potassium-40 levels.
• Measure background radiation in different locations around the room or building.

• Handle all radioactive materials carefully, especially unsealed items like lantern mantles.
• Wash hands thoroughly after handling sources.
• Do not attempt to open or modify smoke detectors or radioactive samples.
• Store radioactive objects in a secure location when not in use.
• Use lead shielding cautiously—avoid unnecessary handling.

• Why do some everyday items like bananas emit detectable radiation? (They contain potassium-40, a naturally occurring isotope.)
• Why does a smoke detector contain americium? (Americium-241 emits alpha particles that ionize air, allowing the detector to sense smoke.)
• Why does lead shielding reduce the radiation count? (Its high density absorbs or blocks radiation, especially gamma rays.)
• Why is it important to measure background radiation before testing samples? (It establishes a baseline for comparison.)