Radioactivity — Definition

Definition

Radioactivity is the spontaneous transformation of unstable atomic nuclei, accompanied by emitted radiation. It differs from ordinary chemical reactions, which chiefly rearrange electrons and bonds. Isotopes share a proton number but differ in neutron number, and not every isotope is radioactive.

Half-life describes the statistical decline of a parent-nuclide population rather than an exact expiry time for an individual nucleus. Activity is measured in becquerels, while absorbed dose is energy deposited per mass and is measured in gray.

Radiation is a broader category than radioactivity: electromagnetic radiation can also be generated by processes that do not involve radioactive decay.