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Because of their large mass alpha particles have a short range of only a few centimeters in air, and can be stopped by a sheet of paper. They have a strongly ionizing effect on the molecules that they strike, and are therefore capable of damaging living cells. Alpha particles traveling in a vacuum are deflected slightly by magnetic and electric fields.
Beta Decay.
Beta particle electrons are ejected with great velocity from a radioactive atom that is undergoing spontaneous disintegration. Beta particles do not exist in the nucleus but are created on disintegration, beta decay, when a neutron converts to a proton to emit an electron. .
Beta particles are more penetrating than alpha particles, but less so than gamma radiation; they can travel several meters in air, but are stopped by 2-3 mm of aluminum. They are less strongly ionizing than alpha particles and, like cathode rays, are easily deflected by magnetic and electric fields.
Gamma Radiation.
Gamma radiation is a very high-frequency electromagnetic radiation, similar in nature to X-rays but of shorter wavelength, emitted by the nuclei of radioactive substances during decay or by the interactions of high-energy electrons with matter. Cosmic gamma rays have been identified as coming from pulsars, radio galaxies, and quasars, although they cannot penetrate the earth's atmosphere. Gamma rays are stopped only by direct collision with an atom and are therefore very penetrating. They are less ionizing in their effect than alpha and beta particles, but are dangerous nevertheless because they can penetrate deeply into body tissues such as bone marrow. They are not deflected by either magnetic or electric fields. Gamma radiation is used to kill bacteria and other microorganisms and sterilize medical devices.
The Concept Half Life.
In theory, the decay process is never complete and there is always some residual radioactivity. For this reason, the half-life of a radioactive isotope is measured, rather than the total decay time.
