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 mass and charge, alpha particles can cause significant damage to biological tissues if ingested or inhaled. They are used in various applications, including smoke detectors and certain types of cancer treatments, where their ability to deliver localized radiation can help target tumors effectively.