Measuring Background Radiation

Students use Geiger counters to measure background radiation, analyze variation in results, and explore why scientists must account for natural background levels before measuring radioactive sources.

1. Begin with an analogy: compare radiation detection to counting drops from a water sprinkler, emphasizing that results vary but follow an average.
2. Introduce the concept of radiation, radioactive decay, and how a Geiger counter detects particles.
3. Distribute Geiger counters to student groups.
4. Have students measure background radiation by counting Geiger counter clicks for one minute. Record results in a class data table.
5. Repeat the measurement two more times per group to analyze variation.
6. Discuss whether results vary between trials and why (instrument error, natural variation, or counting error).
7. Compare group averages, ranges, and patterns of clustering or pauses in clicks.
8. Extend the activity by testing background radiation in different locations (indoors vs outdoors, higher floors vs basement).
9. Optionally test shielding effects using paper, metal, or other materials.

Using a Geiger counter - UNSW Physics:

📄 BACKGROUND RADIATION - STEM in the lab: https://inl.gov/content/uploads/2023/07/Background-Radiation-Grades-9-12-1.pdf

• Compare measurements on sunny vs cloudy days to test environmental effects.
• Have all groups measure in the same location to check instrument variation.
• Rotate groups through multiple room locations to test whether building materials affect readings.
• Introduce a known radioactive source and measure how shielding changes detection.

• Handle Geiger counters with care—do not attempt to disassemble them.
• Use only approved low-level demonstration sources, never unregulated radioactive materials.
• Wash hands after handling any materials used with the Geiger counter.
• Ensure students understand that natural background radiation is not harmful at these levels.

• What is background radiation, and where does it come from? (Natural sources include cosmic rays, radon gas, terrestrial rocks, and isotopes in our bodies.)
• Why might Geiger counter results vary even in the same location? (Radiation occurs in random bursts, and instruments may differ slightly.)
• Why do scientists measure background radiation before testing radioactive samples? (To subtract natural levels and obtain accurate readings of the source.)
• Were the Geiger counter clicks evenly spaced or clustered? What does this tell us about radioactive decay? (It is random, not steady.)
• How might measurement accuracy improve? (Take longer measurements, repeat trials, and average results.)
• Why do people at higher elevations experience more background radiation than those at lower elevations? (Less atmospheric shielding from cosmic radiation.)