The Compton effect

A high energy photon can knock an electron out of an atom. In this photograph, taken in the CERN 2m bubble chamber filled with liquid hydrogen, the highlighted spiralling track is produced by such a `Compton electron’.

As it turns in the applied magnetic field it loses energy:

• partly by ionizing hydrogen atoms and leaving a trail of bubbles
• but more by emitting electromagnetic radiation (accelerated charges radiate; for more details click here).