Common types of ionizing radiation

Alpha rays

Are comparatively large, slow particles emitted from the nucleus of an atom, containing two protons and two neutrons, identical to the nucleus (without the electrons) of a helium atom, but lack the two electrons that make helium stable.

They are high-energy particles which can be easily stopped, but can cause great damage if the chemicals emitting them are inhaled or ingested.

Beta particle

A high-speed particle (at close to the speed of light), identical to an electron, emitted from the nucleus of an atom. They are smaller and faster than alpha particles and are far more penetrating. Elements that emit beta particles can be very dangerous when inhaled or ingested into the body, same as alpha-emitters.

Are neutral particles that are normally contained in the nucleus of all atoms and may be removed by various interactions or processes like collision and fission. These processes cause the unsticking of the "binding energy" in the atom's core. The resulting disequilibrium causes neutron particles to be shot out in a way that makes them capable of penetrating solid steel walls.

When neutrons strike atoms of elements that are not fissionable, they can render them radioactive by changing their atomic structure. Several feet of water or concrete are required to stop most of them.

Because of their tremendous penetrating ability, neutrons can be very damaging to the human body.

Gamma rays are electromagnetic waves or photons emitted from the nucleus of an atom, when it undergoes transformations. They are a very high energy form of radiation, similar to X-rays, and can penetrate steel and concrete.

X Rays are electromagnetic waves or photons not emitted from the nucleus, but normally emitted by energy changes in electrons. These energy changes are either in electron orbital shells that surround an atom or in the process of slowing down such as in an X-ray machine.

Because X rays can expose film after passing through some substances -such as human flesh and some building materials- they have been widely used in medicine and some industrial processes.

It is believed by many that because they are directly applied to the human body, medical X rays are at present the single greatest source of external exposure to human-made radiation.

Radiation (at a typical rate of 60-100 mrem per year) coming from space or from the earth. It can be both natural and man-made.