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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 Radiation

    Alpha 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 Radiation

    Beta 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 Radiation

    Gamma 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.
The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.
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