They are stopped by:Therefore, alpha emitters are not too dangerous unless ingested.
Articles by others on the same topic
An alpha particle is a type of subatomic particle that consists of two protons and two neutrons, making it identical to the nucleus of a helium-4 atom. It is emitted during a type of radioactive decay known as alpha decay, which occurs in some heavy unstable atomic nuclei (like uranium or radium) as they seek to become more stable.