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Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or "decays" into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two.
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay.
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. [5] They are generally produced in the process of alpha decay but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α.
The following are among the principal radioactive materials known to emit alpha particles. 209 Bi , 211 Bi , 212 Bi , 213 Bi 210 Po , 211 Po , 212 Po , 214 Po , 215 Po , 216 Po , 218 Po
The four most common modes of radioactive decay are: alpha decay, beta decay, inverse beta decay (considered as both positron emission and electron capture), and isomeric transition. Of these decay processes, only alpha decay (fission of a helium-4 nucleus) changes the atomic mass number ( A ) of the nucleus, and always decreases it by four.
Uranium emits alpha particles through the process of alpha decay. External exposure has limited effect. External exposure has limited effect. Significant internal exposure to tiny particles of uranium or its decay products, such as thorium-230, radium-226 and radon-222 , can cause severe health effects, such as cancer of the bone or liver.
The 4n decay chain of 232 Th, commonly called the "thorium series" Thorium-232 has a half-life of 14 billion years and mainly decays by alpha decay to radium-228 with a decay energy of 4.0816 MeV. [3] The decay chain follows the thorium series, which terminates at stable lead-208. The intermediates in the thorium-232 decay chain are all ...
The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay.