that is protected by clothing and the outermost dead layer of the skin. However, when these same alpha-emitting radionuclides are taken into the body, their emissions can directly irradiate nearby cells of tissues in which they are deposited and may cause cellular changes. Such changes may result in adverse health effects in the short or long term, depending on the nature of the changes. Alpha-emitting radionuclides may be encountered in contamination created by intentional or accidental dispersion of nuclear weapon-source materials (e.g., plutonium-239) or as a result of a nuclear detonation. Alpha-emitting radionuclides, such as radium in soil and radon in air, are also naturally occurring sources of radiation and contribute to normal background levels.

In comparison to alpha radiation, fast-moving electrons, which are known as beta particles, have much smaller mass and electric charge, are more deeply penetrating, and dissipate their energy over a larger volume of tissue. Even high-energy beta particles, however, will transfer most of their energy and come to a stop within about 1 centimeter of plastic, 1 to 2 centimeters of tissue, or 4 to 5 meters of air. Therefore, beta particles that strike the outside of the body will penetrate only a short distance, but they may travel far enough to damage the actively dividing cells of the skin. Beta-emitting radionuclides are of most concern after they have entered the body and can transfer their energy to nearby cells of internal organs. Beta-emitting radionuclides may be found in contamination consisting of fission products from a nuclear detonation or resulting from the dispersion of nuclear reactor waste or radiotherapy sources (e.g., cesium- 137 and cobalt-60).

Gamma rays and x rays, which are emitted from radionuclides as well as produced by machines, are the most penetrating forms of ionizing radiation and consist of electromagnetic energy. While randomly colliding with electrons in the body along a scattered path length, gamma rays may give up all or part of their energy in tissue or, although it is unlikely, they may pass all the way through the body without interacting. Therefore, exposure to gamma or x rays from sources outside the body may cause ionizations in tissues at any location in their path. Gamma rays are characteristic of a wide variety of radioactive contaminants associated with nuclear weapons and nuclear waste and also with radioactive sources used in medicine and industry, whereas x rays are most commonly encountered in the use of radiation-producing equipment used in medical applications (including those in combat medical facilities).

Radiation Units and Measurements

Radiation Units

The energy of ionizing radiation is measured and described in a number of ways. One can use a survey meter or other device to measure exposure-ionization in air caused by radiation. Exposure is measured in coulombs per kilogram

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