thermal emission


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thermal emission

(thermal radiation; thermal bremsstrahlung) Electromagnetic radiation resulting from interactions between electrons and atoms or molecules in a hot dense medium. The term usually refers to thermal emission from ionized gas (but see also thermal black-body radiation). Free electrons in the ionized gas radiate when they are deflected in passing near protons. The electrons are unbound to a nucleus before and after each encounter and the radiation is therefore also known as free-free emission. The radiation has a continuous spectrum, which at low frequencies has the spectral index, α, of a thermal black-body radiator, i.e.
S ∝ ν–α; α = –2
where S is the flux density and ν the frequency. At higher frequencies the spectrum flattens to a spectral index of α = 0. The emission measure of an ionized region of length l containing a density n e of free electrons is given by
EM = l 0 n e 2 ds
where ds is an element of the path through the region. Compare nonthermal emission.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
On the validity of Kirchhoff's law of thermal emission. IEEE Trans.
Finally, a value of 0.1 magnitudes is added to the H filter value to account for thermal emission (Vernazza et al.
Thermal emission of alkali metal ions from natural MM is observed at temperatures higher than 770 K under used sensitivity of mass spectrometer [10.sup.-17] A.
These thermal emissions produce pressure changes in the gas phase present above the sample that creates acoustic signal.
During the raising of T, according to exp(-[E.sub.t]/kT) dependence of the thermal emission rate, as long as T is too low for significant thermal emission until [t.sub.2], the difference in (2) is zero.
We used the ARCHEOPS and IRIS 100 [micro]m maps to characterize the dust thermal emission model.
The storage time of 1.6 s was the result of an emission process limited by pure thermal emission, as thermally-assisted tunnel emission was not involved.
In order to prove the hypothesis experimental research and simulation of the structure behavior applying thermo graphic and thermal emission methods was performed.
The video is a compilation of images taken by the Advanced Spaceborne Thermal Emission and Radiometer (whew, what a mouthful) on NASA's Terra satellite.
The Aqua satellite, equipped with an atmospheric infrared sounder, and Terra, equipped with a thermal emission and reflection radiometer, have identified 636 forest fires in Russia.
This environment- friendly facility has a zero rate in terms of environment pollution and thermal emission. Lesser electricity consumption and easy and environmentfriendly operation are the hallmarks of this facility.
The digital images were created by a specially designed piece of technology called the Advanced Space-borne Thermal Emission and Reflection Radiometer, or ASTER.

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