How to see cosmic rays

Create a cloud chamber and watch subatomic particles zoom through the air in front of you

1. Prepare your tank

First, you’ll need to find a large, rectangular tank – like a fish tank. Cut out a piece of felt the same size at the top and stick it inside the tank, then soak it in isopropyl alcohol.

2. Add dry ice

Now ask an adult to put on some thick gloves and place some dry ice in a large, well-insulated base. Dry ice is solidified carbon dioxide, and it needs to be very cold to stay solid, so be careful.

3. Cool the base

Now take the lid of your fish tank – ideally one that’s dark in colour – and place it on top of the dry ice. Let it sit there until it cools to the temperature of the dry ice.

4. Seal it off

If you have any excess alcohol in your fish tank, pour it out in a rectangle on the cooled base. When you place the fish tank on top, it should form a seal with the liquid.

5. Waiting game

Place the fish tank onto the lid and turn the lights out. We now need to wait for the room- temperature alcohol to evaporate into the air inside the fish tank.

6. Watch it cool

As the evaporated alcohol reaches the bottom of the fish tank, the dry ice begins to cool it. As it cools, it wants to form a liquid – so tiny droplets form into a cloud.

7. Lights out

Shine a torch in through the side of the fish tank. You should see the cloud, but you should also see lines appearing in the cloud. These are particles!

(Illustrations by Ed Crooks)


Particles from space are constantly bombarding the Earth, passing through us on their journey through the universe. As they zoom through the cloud chamber, they cause disturbances in the gas, ionising the gas molecules. This makes them clump together to form tiny droplets. Different types of particles form different kinds of tracks.

This article was originally published in How It Works issue 134, written by Steve Ashby

For more science and technology articles, pick up the latest copy of How It Works from all good retailers or from our website now. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, subscribe today!