Animated particle tracks showing the interactions of neutrons with atoms. Neutron have no electric charge, and are therefore not visible in cloud chambers or bubble chambers. Their presence can be inferred by their effect on other, charged particles. In this animation, a narrow beam of neutrons enters from left. The cloud chamber is filled with hydrogen gas saturated with a mixture of ethyl alcohol and water. Three neutrons induce transmutations of oxygen and carbon atoms in the alcohol, give rising to three stars. The tracks of the subatomic particles produced in these transmutations have been coloured blue, green and red, according to which star they belong to.