Cloud chambers are setup in a way such that any charged particle passing through will
leave behind a trail. Typically this is done by permeating the space with a gas in a supersaturated state,
such that any charged particle will ionise and reliquify the gas to form droplets.
In the absence of a radioactive sources, cloud chambers detect cosmic rays and their products from cosmic
showers. By placing the cloud chamber in a magnetic field, the particles' mass and charge reveal themselves
through the radius of its cycloidal motion. This is how the first anti-particle was discovered when Blackett
and Anderson saw an electron veering in the wrong direction! Cloud chambers also discovered the muon and
the anti-muon.
In particular, the electron has mass \(m_e\simeq 0.5\,\mathrm{MeV}\) while
the muon has \(m_{\mu}\simeq 100\, \mathrm{MeV}\). What does this tell us about their trajectory's radius in
the chamber? (Hint: Think radially!)
If you want to build your own cloud chamber for cheap, for example I recommend
this video.