Because of the relatively large particle size, alpha particles are easily stopped by dead skin, clothing, or a single sheet of paper. Alpha radiation produces little risk to exposed humans as long as the radioactive source is located outside the body. This is because the radioactive particle gives up all of its energy when it hits a persons clothing and produces no injury to the person inside. However, if the source of the radiation is inside the body, the cells immediately surrounding the source will absorb massive amounts of energy and may mutate into cancerous growths. Nuclear weapons grade plutonium is an example of a highly hazardous alpha emitter if taken internally.
Beta radiation is composed of a single particle comparable to an electron.
Because of the smaller size, beta radiation will penetrate most clothing and up to one inch if tissue. It takes about one half inch of aluminum to stop a beta particle. Beta particles are of equal danger whether the source is located on the inside or the outside of the body, with tissue burns a typical result of exposure. Gamma radiation is a photon level electromagnetic radiation and penetrates the human body with relative ease. While not commonly used in industry, gamma radiation is difficult to protect against and may cause extensive cellular and genetic damage during human exposure events.