1911 – cloud chamber

Expanding on earlier work done by John Aitken, Charles Wilson invented the first cloud chamber in 1911. Cloud chambers are used to detect and study particles that leave trails of ionization visibly displayed by vapor formation. Alpha particles (a helium nucleus) and beta particles (electrons) will leave trails of water vapor, much like a miniature jet contrail, in the bubble chamber under the right conditions.

cloud chamber

cloud chamber

The Cloud Chanber

When there was no ionising radiation present Wilson found that the clouds showed a uniform distribution of droplets.

When the chamber was ionised with alpha-particles clear, straight tracks were emitted from the radium source. Wilson said his photographs gave ‘a poor idea of the really beautiful appearance of these clouds’..

Beta-particles produced ‘two or three absolutely straight thread-like lines’ from the direction of an impure radium salt source. The tracks produced by beta-particles were less clear than those produced by alpha-particles. Less energetic particles would spiral in the earth’s field.

We now know that beta-particles are electrons and alpha-particles are atomic nuclei of the element helium. Beta-particles are negatively charged while alpha-particles have a positive charge of twice the magnitude. Alpha-particles are more ionising than beta-particles.

Leave a Reply

You must be logged in to post a comment.