KinexiaLEARN PHYSICS

DIY Cloud Chamber

See the invisible: with dry ice and alcohol vapor, you can watch subatomic particles streak through your room.

Safety:

Dry ice causes frostbite — always handle with insulated gloves or tongs, never bare hands. Isopropyl alcohol is flammable: no open flames nearby, and ventilate the room. Adult supervision required.

Materials

  • A clear plastic or glass container with a lid
  • Black felt, dark paper, or a black metal plate
  • Isopropyl alcohol, 90% or higher
  • A chunk of dry ice (about 500 g)
  • Insulated gloves or tongs
  • A bright flashlight
  • A dark room

Procedure

1

Prepare the vapor source

Soak the felt or line the container base with alcohol-soaked dark paper. The dark base makes the white tracks visible.

2

Chill the chamber

With gloves, place the dry ice flat and set the container on top of it, base down. Seal the lid. The bottom gets extremely cold while the top stays warm.

3

Wait for the gradient

Wait 5 to 10 minutes for a steep temperature gradient to form — this creates the supersaturated layer just above the cold base.

4

Watch for tracks

Darken the room and shine the flashlight horizontally just above the base. Watch for fine white lines blooming and fading.

5

Classify what you see

Count tracks for 2 minutes. Note long thin ones (cosmic-ray muons) versus short thick ones (alpha particles from background radiation).

What to observe

  • After a few minutes, thin white vapor lines appear and fade every few seconds.

  • Some tracks are long and straight; others are short and thick.

  • Shining the flashlight sideways makes the tracks pop against the dark base.

Why it happens

The chamber holds isopropyl alcohol vapor in a supersaturated state — desperate to condense but with nowhere to start. When a charged particle (a cosmic-ray muon or an alpha particle from natural background radiation) streaks through, it rips electrons off air molecules along its path, and droplets condense on those ions, drawing a visible white line. You are watching individual subatomic particles: thin straight tracks are cosmic muons, short fat ones are alpha particles. This is the detector that revealed the positron in 1932.

Try variations

  • Hold an old lantern mantle or granite sample near the chamber (do not open it) — does the track rate change?

  • Try different wait times. Is there a sweet spot where tracks are clearest?