Alpha Decay
Alpha decay is a type of nuclear decay in which an unstable atomic nucleus emits an alpha particle – a particle consisting of two protons and two neutrons.
Alpha decay takes its name from the first letter of the Greek alphabet, α. The symbol for an alpha particle is α. Alpha particles are also called alpha rays or alpha radiation.
An Example of Alpha Decay
Radium-223 is an isotope of radium that undergoes alpha decay to radon-219. The nuclear equation below represents this process.
$$_{88}^{223}\textrm{Ra} \, \rightarrow \, _{86}^{219}\textrm{Rn} + \alpha$$
Because an alpha particle contains two protons, when a nucleus emits an alpha particle, its atomic number decreases by two. Because an alpha particle also contains two neutrons, making for a total of four nucleons, when a nucleus emits an alpha particle, its mass number decreases by four.