Radioactive decay and ionizing radiation

As radioactive isotopes decay they emit ionizing radiation (detected with a Geiger counter, photographic film etc.) and may inflict a level of biological damage that depends on total exposure. Natural radiatioactive isotopes include ²³⁸U and ²³²Th that have long half-lives that are comparable to the age of the Earth.

Three types of ionizing radiation are identified.

Alpha particles - high energy helium nuclei emitted by unstable nuclei, including uranium and thorium.

Beta particles - high energy electrons (±) emitted by isolated neutrons and tritium atoms etc.

Gamma rays - high energy photons emitted by the decay of excited nuclei in most, but not all, nuclear decay events.

Radiation in the environment is mostly due to cosmic rays, atmospheric radon, and radiation within animal bodies (including ourselves) from the decay of ⁴⁰K, a long lived isotope of potassium. The several sources contribute to what is called background radiation.

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