Radioactive decay is a fundamental physical process involving the spontaneous transformation of an unstable atomic nucleus, resulting in the emission of radiation. This process occurs because the nucleus possesses excess energy, which is released over time as the constituent particles stabilize. Decay can manifest through several forms, including alpha decay, where a helium nucleus is emitted; beta decay, involving the conversion of a neutron to a proton and the emission of an electron; and gamma decay, which involves the emission of high-energy photons. The rate of decay is characterized by the concept of the half-life, which is defined as the time required for exactly half of the initial sample of the radioactive substance to undergo decay. The decay of radioactive isotopes is governed by statistical probabilities and is a core subject in nuclear physics.