======Inverse-Square Law of Radiation======


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**Alternative titles:** Geiger Counter Inverse-Square Demonstration
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====Summary====                   
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====Procedure====  
  - Place a radioactive source near a Geiger counter detector at the smallest safe distance (e.g., 20 mm).
  - Record the count rate for a set period of time (e.g., 15 seconds).
  - Repeat the measurement several times to find an average count rate.
  - Move the source further away (e.g., in steps up to 90 mm) and record counts again at each distance.
  - Plot a graph of count rate versus distance.
  - Compare how the measured values decrease as the source is moved further from the detector.
  - Discuss how the count rate relates to the inverse-square law: doubling the distance reduces the counts to about one quarter.



====Links==== 
INVERSE-SQUARE LAW - A-level Physics Required Practical - Science Shorts: 
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📄 Exploring the Intensity of Radiation - farLabs: [[https://www.farlabs.edu.au/nuclear/explore-inverse-square-law/]]\\


====Variations====
  * Test different radioactive sources (alpha, beta, gamma) to see if distance affects them differently.
  * Measure at smaller or larger distances to refine the curve.
  * Add shielding materials (paper, aluminum, lead) to compare how absorption interacts with the distance effect.
  * Use the same method with a non-radioactive source of waves (e.g., light or sound) to show that inverse-square applies generally.



====Safety Precautions====
  * Handle radioactive sources carefully and keep exposure time short.
  * Use only approved, low-activity classroom sources.
  * Wash hands after handling radioactive materials.
  * Keep food and drink away from the work area.
  * Always return sources to their shielded storage when not in use.




====Questions to Consider====
  * What does the shape of your graph suggest about how radiation spreads? (It shows that intensity decreases according to the inverse-square law.)
  * If you double the distance, what happens to the count rate? (It falls to about one quarter.)
  * Would the graph shape be different for alpha, beta, or gamma sources? (The overall inverse-square relationship remains, but alpha radiation may drop off faster because it is easily absorbed by air.)
  * Why does radiation decrease with distance in this way? (As particles or photons spread out in all directions, their intensity is diluted over the surface area of a growing sphere.)