Subatomic particle tracks Coloured bubble chamber photograph showing tracks left by subatomic particles from a particle accelerator at CERN the European particle physics laboratory at Geneva A bubble chamber is a container filled with liquid hydrogen which is superheated momentarily raised above its normal boiling point by a sudden drop in pressure in the container Any charged particle passing through the liquid in this state leaves behind a trail of tiny bubbles as the liquid boils in its wake The bubbles are seen as fine tracks which show the characteristic paths of different types of particle and which are curved due to an intense applied magnetic field