Radiation is a very general term used to describe energy emitted from a source ( Fig 90.10 ) Ionizing radiation, for example x-ray radiation, deposits a large amount of energy in a small volume of tissue, and energy is sufficient to strip electrons from atoms Nonionizing radiation, for example visible light and microwave radiation, is less energetic, of longer wavelength, and primarily deposits heat in tissue Ionizing radiation can be further subdivided into types of radiation that have no associated mass (nonparticulate ) and those that have mass (particulate ) X-rays and gamma rays are nonparticulate types of radiation and can penetrate deeply into the body and affect radiation-sensitive tissues, for example, bone marrow and the lining of the GI tract X-rays are emitted by excited electrons, whereas gamma rays are emitted by excited or unstable nuclei (radioisotopes or radionuclides) Once x-rays or gamma rays have been emitted, they are indistinguishable Particulate radiation can be further divided into charged and uncharged particles Neutrons, a type of uncharged particulate radiation, can penetrate the body to depths similar to x-rays and gamma rays Because neutrons deposit their energy in a more concentrated area, they cause more biologic damage than x-rays or gamma rays