Exposure of children to ionizing radiation most commonly is from the environment, chiefly through cosmic rays and radon, or from medical technology. Medical radiation exposure occurs during diagnosis, therapy, and dental radiography. More is known about the biological effects of exposure to ionizing radiation than to nonionizing radiation from microwaves, radiowaves, and the electrical fields of other electrical appliances. This review applies only to sources of ionizing radiation and does not include the potential risks of indoor radon. The effects on children of ionizing radiation have been studied from war activities and environmental accidents. Protections are mode from that data to help pediatricians evaluate risk from radiation when ordering radiographs.
High-energy electromagnetic waves (x-rays, gamma rays)
Particles (alpha particles, beta particles, neutrons)
Alpha particles are energetic helium nuclei emitted by some radionuclides with high atomic numbers (eg, plutonium, radium, uranium); they cannot penetrate skin beyond a shallow depth (< 0.1 mm).
Beta particles are high-energy electrons that are emitted from the nuclei of unstable atoms (eg, cesium-137, iodine-131). These particles can penetrate more deeply into skin (1 to 2 cm) and cause both epithelial and subepithelial damage.
Neutrons are electrically neutral particles emitted by a few radionuclides (eg, californium-252) and produced in nuclear fission reactions (eg, in nuclear reactors); their depth of tissue penetration varies from a few millimeters to several tens of centimeters, depending on their energy. They collide with the nuclei of stable atoms, resulting in emission of energetic protons, alpha and beta particles, and gamma radiation.
Gamma radiation and x-rays are electromagnetic radiation (ie, photons) of very short wavelength that can penetrate deeply into tissue (many centimeters). While some photons deposit all their energy in the body, other photons of the same energy may only deposit a fraction of their energy and others may pass completely through the body without interacting.
Because of these characteristics, alpha and beta particles cause the most damage when the radioactive atoms that emit them are within the body (internal contamination) or, in the case of beta-emitters, directly on the body; only tissue in close proximity to the radionuclide is affected. Gamma rays and x-rays can cause damage distant from their source and are typically responsible for acute radiation syndromes (ARS—see Radiation Exposure and Contamination : Acute radiation syndromes (ARS)).
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