Cloud Chamber

Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★★ Requires a more experienced teacher
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff

Categories: Atoms, Nuclear Physics

Alternative titles: Alcohol Cloud Chamber Tracks

Summary

A cloud chamber makes it possible to see the invisible tracks of cosmic rays and other charged particles as they pass through alcohol vapor. Using dry ice and isopropanol, students can build a detector that reveals trails left by subatomic particles.

Procedure

Refer to links below for instructions and experiments.

Links

DIY cloud chamber: no dry ice required - how to make, how it works! - PhysicsHigh:

How to build a Cloud Chamber - US LHC:

📄 How to make your own cloud chamber - CERN: https://home.cern/news/news/experiments/how-make-your-own-cloud-chamber

Variations

Take photographs of tracks and compare them to particle identification charts to distinguish different particles.
Use a stronger light source or LED strip to improve visibility of tracks.
Try placing a weak radioactive source (if legally permitted and supervised) near the chamber to increase the number of visible tracks.
Build a larger chamber for group demonstrations.

Safety Precautions

Handle dry ice with insulated gloves to prevent burns.
Work in a well-ventilated area when using isopropanol, and keep away from open flames (it is highly flammable).
Ensure the chamber does not leak liquid alcohol onto surfaces.
Supervise all student handling of dry ice and alcohol.

Questions to Consider

Why do the streaks appear inside the chamber? (Charged particles ionize the vapor, and droplets form around ions.)
Why are the tracks different shapes and lengths? (Different particles have different charges, masses, and energies.)
What does this experiment demonstrate about the invisible world of subatomic particles? (It provides direct, visual evidence of cosmic rays and radiation passing through us constantly.)
Why do we use alcohol vapor instead of water vapor? (Alcohol vapor condenses more easily at low temperatures, making particle tracks clearer and more stable.)