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
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