beta particle

Electron ejected with great velocity from a radioactive atom that is undergoing spontaneous disintegration. Beta particles are created in the nucleus on disintegration, beta decay, when a neutron converts to a proton (the atomic number increases by one while the atomic mass stays the same) by emitting an electron. The mass lost in the change is converted into kinetic energy of the beta particle. Strontium-90 (⁹⁰Sr) is an example of a material that emits beta particles.

Beta particles are more penetrating than alpha particles, but less so than gamma radiation; they can travel several metres in air, but are stopped by 2-3 mm/0.08-0.1 in of aluminium. They are less strongly ionizing than alpha particles. Owing to their low mass, beta particles, like cathode rays, are easily deflected by magnetic and electric fields. Beta decay is caused by the weak nuclear force.