Introduction: How to Make a Cloud Chamber (Cosmic Ray Detector)

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6 year old Samatha shows how to build a Cloud Chamber (simple, elegant, & inexpensive Cosmic Ray Detector) at home and detect cosmic ray muons/electrons, and alpha particles.

Step 1: Tools to Build a Cloud Chamber

1. 99% Isopropyl alcohol
2. Dry-ice

3. Black Felt

4. Clear plastic cup

5. Play-Doh or Plasticine

6. Black metal plate/pan

7. Flash Light

8. 2 neodymium magnets

9. Styrofoam cooler lid

All these items are available in grocery stores ( Meijer or Walmart), otherwise you can buy them online (Amazon or ebay).

Step 2: Place Metal Plate on the Dryice

  • Take the Styrofoam cooler lid and put some dryice (solid CO2) on it.
  • Caution: Make sure that you wear insulated gloves when handling dryice (-109.3°F or -78.5°C)
  • Now place metal plate on the dryice and wait for few minutes until the surface becomes very cold

Step 3: Put a Piece of Felt Inside the Plastic Cup

Step 4: Put the Magnets Inside and Outside the Cup So the Felt Won't Fall Off

Step 5: Soak the Felt With Isopropyl Alcohol

Pour isopropyl alcohol in the cup, soak the felt well and if extra isopropyl is left in the cup just pour it on the dry-ice.

Caution: Wear safety goggles when you are using isotropy alcohol.

Step 6: Use Play-doh Around the Top Edge of the Cup

To avoid any leakage of the alcohol vapor between the cup and metal plate, use paly-doh.

Step 7: Invert the Plastic Cup on to the Metal Plate

  • Invert the plastic cup on the metal plate and press firmly so that plastic cup sticks to the plate.
  • If your play-doh becomes too dry after coming in contact with isopropyl alcohol then switch to plasticine.

Step 8: Focus Flashlight at the Base of the Cup

  • Wait for 2 or 3 minutes and you will see alcohol mist inside the cup due to temperature gradient between the top and the bottom of the plastic cup.
  • This implies more alcohol vapor at the top of the cup becomes super cooled by the time it gets to the bottom of the cup where the temperature is too low for the vapor to exist, this is known as super-saturated state.
  • When an electrically charged particle zips through the supersaturated alcohol vapor, it will ionize the vapor atoms by ripping off the electrons along its path. This will trigger the condensation process and we can see trail (thread of droplets = cloud) of the charged particle.
  • Focus flashlight at the bottom of the cup to see tracks of charged particles which pass through the super saturated alcohol vapor.

Image: University of Birmingham, http://www.ep.ph.bham.ac.uk/DiscoveringParticles/detection/cloud-chamber/

Step 9: Identifying Subatomic Particles in the Cloud Chamber

Different types of charged particles will leave different trails:

  • Thick small tracks are alpha particles (due to radon atoms in the atmosphere, not related to cosmic rays)
  • Thin and long tracks are muons (originating from cosmic rays)
  • Wiggly tracks are low energy electrons, wiggly because of multiple scattering

Safety & Precautions:
THIS EXPERIMENT SHOULD ONLY BE PERFORMED UNDER THE SUPERVISION OF AN ADULT.

1) Handling dry-ice with out proper gloves is very dangerous. Always use insulated gloves when handling dry ice. It is highly recommended that all dry ice handling should be done by an adult.

2) Wear safety goggles when you are using isotropy alcohol.

3) Wearing an insulated apron is highly recommended all through the experiment.