alpha decay Certain radionuclides (radioactive nuclides) decay by the spontaneous emission of alpha particles from their nuclei. The alpha particle is composed of two protons and two neutrons and has a charge of +2. It also has an appreciable mass and its ejection from the nuclide creates a certain amount of recoil energy in the nucleus. The total energy (E_x) created by alpha decay is, therefore, the sum of the kinetic energy of the particle, the recoil energy given to the new nucleus and the total energy of any emitted gamma rays. See also RADIOACTIVE DECAY.

alpha decay The decay of a radionuclide (radioactive nuclide) by the spontaneous emission from its nuclei of alpha particles. An alpha particle is composed of two protons and two neutrons and has a charge of +2. It also has an appreciable mass and its ejection from the nuclide creates a certain amount of recoil energy in the nucleus. The total energy (E_x) created by alpha decay is, therefore, the sum of the kinetic energy of the particle, the recoil energy given to the new nucleus, and the total energy of any emitted gamma rays.