The process by which an unstable particle transforms into other particles, emitting energy.Decay is the spontaneous transformation of an unstable particle into other particles, accompanied by the release of energy. This process is fundamental to nuclear physics, particle physics, and cosmology, explaining phenomena from radioactivity to the eventual fate of matter. Decay occurs when a particle's mass exceeds the sum of the masses of its possible decay products, allowing the excess energy to be converted into kinetic energy and new particles.
Radioactive decay was discovered by Henri Becquerel in 1896, and the term 'decay' was later extended to elementary particles with the development of quantum field theory in the mid-20th century.
Decay is governed by quantum mechanics and the fundamental forces. For example, in beta decay, a neutron transforms into a proton, an electron, and an antineutrino via the weak nuclear force. The probability of decay per unit time is characterized by a half-life, which is exponential and independent of the particle's history. The specific decay channels depend on conservation laws, such as energy, momentum, and charge.
Decay is used in radiometric dating (e.g., carbon-14), medical imaging (PET scans), and nuclear power generation, where controlled decay of uranium releases heat.
A free neutron decays with a half-life of about 15 minutes, but when bound in an atomic nucleus, it can be stable for billions of years.
