Opacity Definition and Characteristics
- Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light.
- It describes the absorption and scattering of radiation in a medium.
- An opaque object is neither transparent nor translucent.
- Light striking an interface between substances can be reflected, absorbed, scattered, or transmitted.
- Opacity depends on the frequency of the light being considered.
- The word 'opacity' originated from the Late Middle English term 'opake.'
- The current spelling was influenced by the French form.
- The spelling became more common in the 19th century.
- Radiopacity is used to describe the opacity of X-rays.
- Radiodense substances do not allow X-rays or similar radiation to pass through.
- Radiodense contrast media revolutionized radiographic imaging.
- Radiopacity is a key consideration in the design of medical devices used during radiological intervention.
- It allows the tracking of devices during procedures.
- Opacity has a specific, quantitative definition used in astronomy, plasma physics, and other fields.
- It is synonymous with the mass attenuation coefficient or mass absorption coefficient.
- Opacity is measured at a particular frequency of electromagnetic radiation.
- In air pollution work, opacity refers to the percentage of light blocked.
- Opacity can vary from 0% light blocked to 100% light blocked.
Planck and Rosseland Opacities
- Planck opacity uses the normalized Planck black-body radiation energy density distribution as the weighting function.
- Rosseland opacity uses the temperature derivative of the Planck distribution as the weighting function.
- Photon mean free path is the inverse of the Rosseland opacity.
- The Rosseland opacity is derived in the diffusion approximation to the radiative transport equation.
- The mean opacity for Thomson electron scattering and nonrelativistic thermal bremsstrahlung can be calculated.
Opacity (optics) Data Sources