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

Picture of How to Make a Cloud Chamber (Cosmic Ray Detector)

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

Picture of 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

Picture of 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

Picture of 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

Picture of Put the Magnets Inside and Outside the Cup So the Felt Won't Fall Off

Step 5: Soak the Felt With Isopropyl Alcohol

Picture of 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

Picture of 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

Picture of 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

Picture of 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,

Step 9: Identifying Subatomic Particles in the Cloud Chamber

Picture of 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:

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.


KathyCeceri (author)2015-06-23

Do the magnets affect the experiment, or are they just to hold the felt on? I have made this with peel and stick black felt, no magnets.

Those two magnets are just to hold the felt on, initially we used peel and stick felt but when we soaked it with rubbing alcohol it used fall down from the cup, that is why we used magnets. And those magnets are not that powerful to change particles tracks direction.

Putting a powerful magnet on one side of the cup, we can identify particle and antiparticle by their track deflection, like electron and positron. But to deflect muon, we need very powerful magnet.

Really? To the best of my knowledge the magnets would ABSOLUTELY affect the experiment. This is because the particles you are detecting all have charges and ,as you may know, charged particles are affected by magnetic fields.

PaulA66 made it! (author)2015-10-01

Thanks so much for this instructable! As a kid, I tried to make a Wilson chamber many times, to no avail. The diffusion chamber version posted here worked great. A few suggestions.....

You recommend 99% isopropyl, that's the best, but 91% is more widely available and works fine. Use a regular aluminum pie pan or other piece of flat aluminum sheet stock that fits in the cooler lid, it doesn't have to be black. Instead, use a piece of black paper that's slightly bigger than the top of the cup. This will help prevent water moisture intrustion and frosting. Use a sponge instead of felt, if you cut it tightly for the cup, you don't need magnets to hold it in. Put the sponge in the cup first, soak it with isopropyl, then drain off any remaining liquid isopropyl. This will minimize the amount of alcohol that ends up on the Play-Doh, which can cause it to degrade. Roll out a long piece of Play-Doh that covers the whole edge of the cup instead of affixing small pieces, and attach it as a ring. When you buy dry ice, get it in the form of two rectangular pieces, many supermarkets have it like this in bags. The key to good observations is to provide maximum contrast (black paper) and keep water and water vapor out of the chamber (eliminate frosting). To minimize frosting, put everything together first (i.e. the cup, black paper, and aluminum pan or sheet) first before placing it on the dry ice. Put the two rectangular chunks of dry ice in the cooler lid, then put the assembled chamber on top of the dry ice. Turn off all the lights and use a high intensity LED flashlight to observe the tracks. Angle the light so that you can see the rain of alcohol droplets in the chamber as they fall into the supersaturated zone.

By following the steps in the instructable with the slight changes I suggest here, I was able to observe tracks for over an hour with minimal frosting and good viewing. Again, thank you for such an excellent instructable!

Kranthi Gunthoti (author)PaulA662015-10-16


BuildingTheBest (author)2015-10-16

Though you could make it more neater.

BuildingTheBest (author)2015-10-16

Not bad....not bad....

BuildingTheBest (author)2015-10-16

Not bad....not bad....

VincentZ3 (author)2015-08-10

something tells me when you grow up you will be important

sarrocks (author)2015-07-12

wow great


neosarchizo (author)2015-06-29

Awesome! And she is so cute and genious!

Thank you!

kelseymh (author)2015-06-22

Awesome project! Congratulations on getting an article on the MAKE Magazine blog (

Thank you!

brightled (author)2015-06-10

I did this along time ago great work,also try to control the flight of the vapor trails using some magnets from an old hard drive....WCH

Thanks for the suggestion.

impied (author)2015-06-04

This is awesome!!! The cloud chamber is one of my favorite exhibits at the Exploratorium in San Francisco and it would be so cool to have my own for on demand hypnotic viewing pleasure :) :)

Kranthi Gunthoti (author)impied2015-06-05


Kiteman (author)2015-06-03

Oh, very cool, well done (rather than photographing the tracks, video is better, because you can take screen-grabs of any moment you like).

Kranthi Gunthoti (author)Kiteman2015-06-04

Thank you!

sypher (author)2015-06-04

How long does this last?

Kranthi Gunthoti (author)sypher2015-06-04

approximately 10 minutes

Edbed (author)2015-06-03

This is Amazing! I need to make one!

seamster (author)2015-06-03

This is really cool! I need to make this with my kids. They would love it, thank you!

Thank you!

About This Instructable




More by Kranthi Gunthoti:How to extract your own DNA at homeMeasuring the speed of sound with Arduino microcontroller and ultrasonic sensorKitchen Physics - Measure the speed of light with chocolate!
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