Beta radiation is emitted during the radioactive decay of many beta-active, unstable nuclides.
Examples of pure beta-emitters are the radionuclides Strontium-90 with a half-life of 27.7 years and tritium 12.3 years.
The beta particle, which is an electron, is emitted when a neutron in a nucleus is transformed into a proton.
The beta particle is very light. Its mass is about 1/2000 that of the proton.
Beta particles ionize less easily than do the heavy particles and therefore they have a much longer range. Their path is very crooked. The range in air can be several metres. In tissue or water, the range is several millimetres. Spectacles or thick clothing are often sufficient to stop beta radiation.
Unprotected skin exposed to very strong beta radiation may burn as a result of a large skin dose.
For beta-emitters too, the greatest risk is associated with ingestion with food, or inhalation.