Alpha radiation consists of alpha particles, which are essentially the nuclei of helium-4 atoms, composed of two protons and two neutrons. They carry a charge of +2e and have a relatively large mass. Alpha particles are emitted during a type of radioactive decay known as alpha decay, primarily by heavy atomic nuclei attempting to achieve greater stability.
Common naturally occurring alpha emitters include isotopes found in the Uranium Decay Series and Thorium Decay Chain. Notable examples include Uranium-238, Radium-226, Radium-228, and Radon-222. These processes are characterized by specific half-lives, with some chains demonstrating Secular Equilibrium.
Due to their large mass and charge, alpha particles interact very strongly with matter. They cause significant ionization over a short range, depositing a large amount of energy within a small volume. This characteristic is quantified by their high Linear Energy Transfer (LET). The energy deposition profile of alpha particles as they slow down in matter is described by the Bragg Curve. Their short range means they can be stopped by a thin sheet of paper or the outer layer of human skin.
While externally alpha radiation poses little threat, internal contamination (e.g., inhalation or ingestion of alpha-emitting radionuclides) is extremely hazardous. This is due to their high LET, which causes severe localized damage to tissues. Many industries, especially those dealing with naturally occurring radioactive materials (NORM) such as Mineral sand mining (involving minerals like Monazite, Ilmenite, and Zircon) or Uranium - undeground mining, must manage potential alpha exposure.
Compared to beta radiation and gamma radiation, alpha particles are the least penetrating but most damaging internally. Protection measures often involve containment and preventing inhalation/ingestion, alongside monitoring with specialized equipment that can detect highly ionizing radiation, though Personal Dosimeters are generally designed for external exposure.