Nuclear Energy Radiation Types

Alpha Decay

• Some radioactive isotopes, such as uranium-238, emit particles comprising two protons and two neutrons. Some physicists refer to such particles as helium nuclei because their composition is identical to that of helium atoms without the electrons surrounding the nucleus. Alpha particles represent the most massive of the radioactive particles. As such, alpha particles do not penetrate well and will not travel more than a few centimeters in air.
  
  

Beta Decay

• Beta decay occurs when an isotope emits a single electron as a neutron metamorphoses into a proton. The emitted electron, however, does not represent one of the electrons in the cloud surrounding the nucleus--it originates from the nucleus itself as a byproduct of the metamorphosis. Tritium, or 3H, for example, contains one proton and two neutrons, which creates an unstable configuration. To become stable, one of the neutrons transforms to a proton, but in doing so, the atom now becomes helium, or 3He, because the number of protons in the nucleus determines the identity of the atom.
  
  

Gamma Decay

• Unlike alpha and beta decay, gamma decay releases a photon--an energy packet--rather than a particle. The emission occurs as the nucleus of an isotope transitions from a high-energy state to a low-energy state. Also unlike alpha and beta decay, gamma decay does not alter the chemical identity of the isotope. Dysprosium-152, for example, remains dysprosium-152 before and after emission of a gamma photon. Gamma photons possess significant energy--sufficient to penetrate most materials and damage or destroy living cells.
  
  

Other Radiation Types

• Although alpha, beta and gamma decay represent the most common radioactive decay pathways, nuclear scientists have elucidated several other less-common mechanisms. The electron capture pathway occurs when a nucleus captures one of its own emitted electrons and then emits a neutrino--a particle with zero charge and zero mass. Positron decay represents a variation of beta decay in which the emitted particles exhibit a positive instead of a negative charge. Finally, the internal conversion pathway occurs when energy emitted from the nucleus subsequently results in the ejection of one of the atom's orbital electrons.