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How a cloud chamber works

You still can't see radiation but you can see where it goes

A cloud chamber lets you see where radiation goes because it forms clouds along the paths that particles take.

Try Why Do Astronauts Float by Julian Hamm

Super-cooling is the key

One way to make a cloud chamber is to use super-cooled alcohol in normal air.

Alcohol at the top of the chamber at around room temperature.  It cools and falls to the bottom of the chamber which has dry ice under it.  This is called super-cooling because the alcohol would normally form little liquid droplets when it's that cold.

The ions act as centres for drop formation

When an alpha particle, say, passes through the super-cooled alcohol it causes lots of ionizations, normally of the air molecules.  Charged things attract uncharged things so the ions tend to attract little clusters of alcohol molecules.  These grow to tiny droplets of alcohol liquid, millions of which make up the clouds you can see.

back to Lesson 11: Ionization and Detection