Radiation
The term radiation broadly applied to a class of physical phenomena that share a characteristic loss of energy in the radiating body or system that results in a propagation of particles and/or waves that carry the ability to do work and thus change the energy state of an impacted body or system.
Radiation is a catch-all name given to several different types of energetic phenomena. In particular, we think of the entire electromagnetic spectrum as being radiation of graduating wavelengths. Heat and visible light, being parts of the spectrum, were among the first forms of electromagnetic radiation recognized by scientists. Electromagnetic radiation is now understood to encompass a broad spectrum of electromagnetic radiation form gamma rays to radio waves that differ only in wavelength and frequency.
Radiation also aptly describes phenomena specifically related to blackbodies that are described by Planck's law, Kirchhoff's law, Wien's law, and the Stefan-Boltzmann law.
Another form of radiation is the particulate emissions from natural radioactive decay, or from induced atomic disruption. In either case, unstable atoms emit protons, neutrons, electrons and neutrinos at varying energy levels. Alpha particles are heavy, positively-charged emissions with low penetrating capabilities; they rarely travel more than a few centimeters from their source and have difficulty penetrating clothes or even skin. Beta particles are high-energy electrons with much greater penetrating power.
The primary biological danger of particulate radiation, as well as gamma radiation, is their ionizing effect. Ionizing radiation, creating ions in impacted bodies or systems, that can often result in a break down of molecular structure. This breakdown can bring about a variety of physiological effects, depending on the tissues and organs exposed, and the duration and intensity of exposure.
Radiation can propagate in different ways depending on circumstances. Radiation moving through a vacuum tends to take the form of waves. When interacting with matter, however, radiation (even non-particulate radiation) generally exhibits particle-like behavior. This variance in behavior is called the wave-particle duality and is one of the bases of quantum theory.
We are continuously exposed to radiation from solar and cosmic sources. In addition to extraterrestrial sources, there are naturally occurring terrestrial radiation sources (e.g., radioactive elements such as uranium). The decay of uranium deep in the rock strata can also release radon, a radioactive gas that can seep into basements and underground structures.
Radiation can also be generated artificially. A common way of doing this is to bombard a heavy metal such as tungsten with electrons to stimulate x rays. Radiation is also produced by the series of high-energy isotope conversions that take place during and after nuclear fission. The medical dangers of radiation are still being sorted out. One of the reasons for this is that the effects are to some degree governed by probability. The same duration and intensity of radiation exposure can result in widely varying physical effects. Although extreme levels of radiation can be harmful or even fatal, radiation in the form of diagnostic x rays and radiation therapy is routinely used in medical diagnosis and treatment (e.g., in cancer treatment).
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