An alpha particle is a type of radiation consisting of two protons and two neutrons, identical to the nucleus of a helium atom. Due to its composition, it carries a positive charge of +2 and possesses a relatively high mass. When emitted during radioactive decay, these particles travel slower than gamma rays or beta particles, and their large mass and high charge result in a low penetrating power. Consequently, alpha radiation can be easily stopped by a sheet of paper or the outer layer of skin, making it relatively shielded compared to other forms of ionizing radiation.