An alpha particle is a type of subatomic particle that consists of two protons and two neutrons, making it identical to a helium nucleus. It is emitted during the process of radioactive decay, particularly from heavy elements like uranium and radium. Alpha particles carry a positive charge and have relatively low penetration power, meaning they can be stopped by a sheet of paper or even human skin. Due to their positive charge, alpha particles can ionize nearby atoms, which can lead to chemical changes. While they are not very penetrating, they can be harmful if ingested or inhaled, as they can cause significant damage to biological tissues at close range.