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Ionizing radiation
  • Ionizing radiation consists of alpha particles, beta particle, gamma rays, and X-rays.

The two types of ionizing radiation are particulate (alpha, beta, neutrons) and electromagnetic (X-rays, gamma rays) radiation.

Alpha particles

Alpha particles are energetic, positively charged particles consisting of two protons and two neutrons. Alpha particles are commonly emitted in the radioactive decay of the heaviest radioactive elements such as uranium-238, radium-226, and polonium-210. Even though they are highly energetic, the high mass of alpha particles means they move slowly through the air. The health effects of alpha particles depend heavily upon how exposure takes place. External exposure (external to the body) is of far less concern than internal exposure, because alpha particles lack the energy to penetrate the outer dead layer of skin. Internally alpha particles can be very harmful. If alpha emitters are inhaled, ingested (swallowed), or absorbed into the blood stream, sensitive living tissue can be exposed to alpha radiation.

Beta particles

Beta particles are fast-moving electrons emitted from the nucleus during radioactive decay. Humans are exposed to beta particles from man-made and natural radiation sources, such as tritium, carbon-14, and strontium-90. Beta particles are more penetrating than alpha particles but are less damaging over equally traveled distances. They travel considerable distances in air but can be reduced or stopped by a layer of clothing or by a few millimeters of a substance, such as aluminum. Some beta particles are capable of penetrating the skin and causing radiation damage, such as skin burns. However, as with alpha-emitters, beta-emitters are most hazardous when they are inhaled or ingested.

Gamma rays

Like visible light and x-rays, gamma rays are weightless packets of energy called photons. Gamma rays often accompany the emission of alpha or beta particles from a nucleus. They have neither a charge nor a mass and are very penetrating. Several feet of concrete or a few inches of lead may be required to stop gamma rays. One source of gamma rays in the environment is naturally occurring potassium-40. Man-made sources include cobalt-60 and cesium-137. Gamma rays are a radiation hazard for the entire body. While gamma rays can easily pass completely through the human body, a fraction will always be absorbed by tissue.

X-rays

X-rays are high-energy photons produced by the interaction of charged particles with matter. X-rays and gamma rays have essentially the same properties but differ in origin. X-rays are either produced from a change in the electron structure of the atom or are machine produced. They are emitted from processes outside the nucleus, while gamma rays originate inside the nucleus. They also are generally lower in energy and therefore less penetrating than gamma rays. A few millimeters of lead can stop X-rays. Literally thousands of X-ray machines are used daily in medicine and industry for examinations, inspections, and process controls. Because of their many uses, X-rays are the single largest source of man-made radiation exposure.