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:''For "attenuation coefficient" as it applies to electromagnetic theory and telecommunications see propagation constant. For the "mass attenuation coefficient", see the article mass attenuation coefficient. Attenuation coefficient or narrow beam attenuation coefficient of the volume of a material characterizes how easily it can be penetrated by a beam of light, sound, particles, or other energy or matter. A large attenuation coefficient means that the beam is quickly "attenuated" (weakened) as it passes through the medium, and a small attenuation coefficient means that the medium is relatively transparent to the beam. The SI unit of attenuation coefficient is the reciprocal metre (m−1). Extinction coefficient is an old term for this quantity,〔 but still used in meteorology and climatology 〔(【引用サイトリンク】title=2nd Edition of the Glossary of Meteorology )〕 ==Overview== Attenuation coefficient describes the extent to which the radiant flux of a beam is reduced as it passes through a specific material. It is used in the context of *X-rays or Gamma rays, where it is denoted ''μ'' and measured in cm−1; *neutrons and nuclear reactors, where it is called ''macroscopic cross section'' (although actually it is not a section dimensionally speaking), denoted ''Σ'' and measured in m−1; *ultrasound attenuation, where it is denoted ''α'' and measured in dB·cm−1·MHz−1;〔ISO 20998-1:2006 "Measurement and characterization of particles by acoustic methods"〕〔Dukhin, A.S. and Goetz, P.J. "Ultrasound for characterizing colloids", Elsevier, 2002〕 *acoustics for characterizing particle size distribution, where it is denoted ''α'' and measured in m−1. The attenuation coefficient is called the extinction coefficient in the context of *solar and infrared radiative transfer in the atmosphere, albeit usually denoted with another symbol (given the standard use of for slant paths); A small attenuation coefficient indicates that the material in question is relatively transparent, while a larger value indicates greater degrees of opacity. The attenuation coefficient is dependent upon the type of material and the energy of the radiation. Generally, for electromagnetic radiation, the higher the energy of the incident photons and the less dense the material in question, the lower the corresponding attenuation coefficient will be. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Attenuation coefficient」の詳細全文を読む スポンサード リンク
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