Radioactivity, also known as radioactive decay, is the process by which an unstable atomic nucleus loses energy by emitting ionizing radiation. This radiation can take the form of alpha particles, beta particles, or gamma rays. Radioactive decay occurs naturally in certain elements and isotopes, and can also be induced through nuclear reactions.

The process of radioactivity occurs when the nucleus of an atom is unstable and spontaneously breaks down into a lighter, more stable nucleus. During this process, energy is released in the form of radiation, which can interact with nearby atoms and molecules. This interaction can cause ionization, or the removal or addition of electrons, which can alter chemical reactions and potentially cause damage to living tissue.

Different types of radioactive decay include alpha decay, where an atom emits an alpha particle consisting of two protons and two neutrons; beta decay, where a neutron is converted into a proton and an electron is emitted; and gamma decay, where an atom releases energy in the form of a gamma ray.

Radioactivity has many applications in science and technology, including in medicine (radiation therapy, medical imaging), energy production (nuclear power plants), and scientific research (carbon dating, radiometric dating). However, due to its potential hazards, the use and transportation of radioactive materials is strictly regulated to minimize the risk of exposure to human health and the environment.