7.4 Exposure to radiation

Several different forms of radiation are emitted during the radioactive decay of radionuclides (alpha particles, beta particles and positrons, gamma rays and x-rays). Each form has different biological interaction mechanisms. Alpha particles have very low penetration of tissue but cause considerable cell damage over a short range. Therefore, radionuclides that emit alpha particles are only a hazard if they are taken into the body (internal irradiation). Beta particles are more penetrating than alpha particles but on external exposure do not penetrate to internal organs. Gamma radiation and x-rays, on the other hand, are highly penetrating and radioactive sources of these types of radiation are an external radiation hazard.

Humans are exposed to radiation internally if they ingest radioactive substances in food and water or inhale radioactive components in air. Radionuclides that enter the body in this way can remain in a particular organ or tissue for a long time, resulting in exposure over many months or, in some cases, years.