What Types of Radiation Are There?

The radiation one typically encounters is one of four types: alpha
radiation, beta radiation, gamma radiation, and x radiation. Neutron
radiation is also encountered in nuclear power plants and high-altitude
flight and emitted from some industrial radioactive sources.

1. Alpha RadiationAlpha radiation is a heavy, very short-range particle and is actually
   an ejected helium nucleus. Some characteristics of alpha radiation are:
   • Most alpha radiation is not able to penetrate human skin.
   • Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed, or absorbed through open wounds.
   • A variety of instruments has been designed to measure alpha
     radiation. Special training in the use of these instruments is
     essential for making accurate measurements.
   • A thin-window Geiger-Mueller (GM) probe can detect the presence of alpha radiation.
   • Instruments cannot detect alpha radiation through even a thin layer
     of water, dust, paper, or other material, because alpha radiation is
     not penetrating.
   • Alpha radiation travels only a short distance (a few inches) in air, but is not an external hazard.
   • Alpha radiation is not able to penetrate clothing.

   Examples of some alpha emitters: radium, radon, uranium, thorium.

2. Beta RadiationBeta radiation is a light, short-range particle and is actually an ejected electron. Some characteristics of beta radiation are:
   • Beta radiation may travel several feet in air and is moderately penetrating.
   • Beta radiation can penetrate human skin to the “germinal layer,”
     where new skin cells are produced. If high levels of beta-emitting
     contaminants are allowed to remain on the skin for a prolonged period
     of time, they may cause skin injury.
   • Beta-emitting contaminants may be harmful if deposited internally.
   • Most beta emitters can be detected with a survey instrument and a
     thin-window GM probe (e.g., “pancake” type). Some beta emitters,
     however, produce very low-energy, poorly penetrating radiation that may
     be difficult or impossible to detect. Examples of these
     difficult-to-detect beta emitters are hydrogen-3 (tritium), carbon-14,
     and sulfur-35.
   • Clothing provides some protection against beta radiation.

   Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35.

3. Gamma and X RadiationGamma radiation and x rays are highly penetrating electromagnetic radiation. Some characteristics of these radiations are:
   • Gamma radiation or x rays are able to travel many feet in air and
     many inches in human tissue. They readily penetrate most materials and are sometimes called “penetrating” radiation.
   • X rays are like gamma rays. X rays, too, are penetrating radiation.
     Sealed radioactive sources and machines that emit gamma radiation and x
     rays respectively constitute mainly an external hazard to humans.
   • Gamma radiation and x rays are electromagnetic radiation like
     visible light, radiowaves, and ultraviolet light. These electromagnetic
     radiations differ only in the amount of energy they have. Gamma rays
     and x rays are the most energetic of these.
   • Dense materials are needed for shielding from gamma radiation.
     Clothing provides little shielding from penetrating radiation, but will
     prevent contamination of the skin by gamma-emitting radioactive
     materials.
   • Gamma radiation is easily detected by survey meters with a sodium iodide detector probe.
   • Gamma radiation and/or characteristic x rays frequently accompany
     the emission of alpha and beta radiation during radioactive decay.

   Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and technetium-99m.

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