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.
- 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
- 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.
- 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,
- Clothing provides some protection against beta radiation.
Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35.
- 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
- 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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