Last modified on April 12, 2017, at 11:50

Alpha particle

An alpha particle is a positively charged particle (a Helium-4 nucleus) made up of two neutrons and two protons. It is the least penetrating of the three common forms of radiation, being stopped by a sheet of paper. It is not dangerous to living things unless the alpha-emitting substance is inhaled or ingested or comes into contact with the lens of the eye.[1]


  1. Glencoe Physics, Principles and Problems, Teacher Edition.