Guidance for Radiation Accident Management

Basics of Radiation

What is radiation?

Radiation is energy that comes from a source and travels through some material or through space. Light and heat are types of radiation. The kind of radiation discussed on this site is called ionizing radiation because it has enough energy to remove an electron from an atom, making that atom an ion.

In order to reach stability, these atoms give off, or emit, the excess energy or mass in the form of radiation. The two types of radiation are electromagnetic (like light) and particulate (i.e., mass given off with the energy of motion). Gamma radiation and X-rays are examples of electromagnetic radiation. Beta and alpha radiation are examples of particulate radiation. Ionizing radiation can also be produced by devices such as X-ray machines.

Irradiation refers to exposure to radiation. Irradiation occurs when all or part of the body is exposed to radiation from a source. Irradiation does not make a person radioactive.

Contamination occurs when radioactive material is deposited on skin, clothing, or any place where is it not desired. It is important to remember that radiation does not spread or get "on" or "in" people; rather it is radioactive contamination that can spread. A person contaminated with radioactive materials will be irradiated until the source of radiation (the radioactive material) is removed.

  • A person is externally contaminated if radioactive material is on skin or clothing.
  • A person is internally contaminated if radioactive material is breathed in, swallowed, or absorbed through wounds.
  • The environment is contaminated if radioactive material is spread about or uncontained.

Alpha radiation

Radiation is energy, in the form of particles or electromagnetic rays, released from radioactive atoms. The three most common types of radiation are alpha particles, beta particles, and gamma rays.

  • Alpha radiation is not able to penetrate skin.
  • Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed, or absorbed through open wounds.
  • A variety of instruments have been designed to measure alpha radiation. Special training in use of these instruments is essential for making accurate measurements.
  • Instruments cannot detect alpha radiation through even a thin layer of water, blood, dust, paper, or other material, because alpha radiation is minimally penetrating.
  • Alpha radiation travels a very short distance through air.
  • Alpha radiation is not able to penetrate turnout gear, clothing, or a cover on a probe. Turnout gear and clothing can keep alpha emitters off of the skin. Personal protective equipment should be worn to protect clothing and otherwise uncovered skin from contamination of all types.

Beta radiation

  • Beta radiation may travel meters in air and is moderately penetrating.
  • Beta radiation can penetrate human skin to the innermost layer of the epidermis where new skin cells are produced. If 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. Some beta emitters, however, produce very low energy, poorly penetrating radiation that may be difficult or impossible to detect. Examples of these are carbon-14, tritium, and sulfur-35.
  • Clothing and turnout gear provide some protection against most beta radiation.Personal protective equipment should be worn to protect clothing and otherwise uncovered skin from contamination of all types.

Gamma radiation

  • Gamma radiation and X-rays are electromagnetic radiation like visible light, radio waves, 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.
  • Gamma radiation is able to travel many meters in air and many centimeters in human tissue. It readily penetrates most materials.
  • X-rays are like gamma rays. They can also travel over long distances in both air and human tissue.
  • Radioactive materials that emit gamma radiation and X-rays constitute both an external and internal hazard to humans.
  • Dense materials are needed for shielding from gamma radiation. Clothing and turnout gear provide little shielding from penetrating radiation but will prevent contamination of the skin by radioactive materials.
  • Gamma radiation is detected with survey instruments, including civil defense instruments. Low levels can be measured with a standard Geiger counter.
  • Gamma radiation or X-rays frequently accompany the emission of alpha and beta radiation.
  • Instruments designed solely for alpha detection will not detect gamma radiation.
  • Pocket chamber (pencil) dosimeters, film badges, thermoluminescent, and other types of dosimeters can be used to measure accumulated exposure to gamma radiation.

Basics of Radiation - Shielding Alpha, Beta, Gamma

The following list provides a selection of general terms that are used to describe aspects of radiation.

Alpha particle
A Energetic helium nuclei (two protons and two neutrons) emitted by some radionuclides with high atomic numbers (e.g., plutonium, radium, uranium). It has low penetrating power and short range. Alpha particles will generally fail to penetrate the skin. Alpha-emitting atoms can cause health effects if introduced into the lungs or wounds.
The smallest piece of an element that cannot be divided or broken up by chemical means.
Background radiation
The radiation in man's natural environment, including cosmic rays and radiation from the naturally radioactive elements, both outside and inside the bodies of humans and animals. It is also called natural radiation. Man-made sources of radioactivity contribute to total background radiation levels.
The SI unit of activity 1 disintegration per second; 37 billion Bq = 1 curie. (See conversion factors in the Measuring Radiation section.)
Beta particle
A small particle ejected from a radioactive atom. It has a moderate penetrating power and a range of up to a few meters in air. Beta particles will penetrate only a fraction of an inch of skin tissue.
Controlled area
An area where entry, activities, and exit are controlled to help ensure radiation protection and prevent the spread of contamination.
Cosmic rays
High-energy radiation that originates outside the earth's atmosphere.
Deposition of radioactive material in any place where it is not desired, particularly where its presence can be harmful.
A unit of measure used to describe the amount of radioactivity in a sample of material.
The reduction or removal of contaminating radioactive material from a structure, area, object, or person.
A device that is sensitive to radiation and can produce a response signal suitable or measurement or analysis. A radiation detection instrument.
A general term for the quantity of radiation or energy absorbed.
Dose rate
The dose delivered per unit of time. It is usually expressed as rads per hour or in multiples or submultiples of this unit such as millirads per hour. The dose rate is commonly used to indicate the level of hazard from a radioactive source.
A small, pocket-sized device used for monitoring radiation exposure of personnel.
Electromagnetic radiation
Types of electromagnetic radiation range from those of short wavelength, like x rays and gamma rays, through the ultraviolet, visible, and infrared regions, to radar and radio waves of relatively long wavelengths.
A quantity used to indicate the amount of ionization in air produced by x- or gamma-ray radiation. The unit is the roentgen (R). For practical purposes, one roentgen is comparable to 1 rad or 1 rem for X ray and gamma radiation. The SI unit of exposure is the coulomb per kilogram (C/kg). One R = 2.58 x 10-4 C/kg.
Gamma rays, or gamma radiation
Electromagnetic radiation of high energy. Gamma rays are the most penetrating type of radiation and represent the major external hazard.
Geiger counter or G-M meter
An instrument used to detect and measure radiation.
The SI unit of absorbed dose; 1 gray = 100 rad
Inverse square law
The relationship that states that electromagnetic radiation intensity is inversely proportional to the square of the distance from a point source.
Production of charged particles in a medium.
Ionizing radiation
Electromagnetic (X-ray and gamma) or particulate (alpha, beta) radiation capable of producing ions or charged particles.
Exposure to ionizing radiation.
Determining the amount of ionizing radiation or radioactive contamination present. Also referred to as surveying.
The unit of radiation absorbed dose.
Energy traveling through space.
The spontaneous emission of radiation from the nucleus of an unstable atom. As a result of this emission, the radioactive atom is converted, or decays, into an atom of a different element that might or might not be radioactive.
A measure of radiation dose related to biological effect.
The unit of exposure from X or gamma rays (see types of radiation exposure).
Sealed source
A radioactive source, sealed in a container that has sufficient mechanical strength to prevent contact with a dispersion of the radioactive material under the conditions of use and wear for which it was designed.
The SI unit of dose equivalent; 1 Sv = 100 rem.
Penetrating electromagnetic radiation whose wavelengths are shorter than those of visible light.