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Thomson scattering is the elastic scattering of electromagnetic radiation by a free charged particle, as described by classical electromagnetism. It is the low-energy limit of Compton scattering : the particle's kinetic energy and photon frequency do not change as a result of the scattering. [ 1 ]
The classical electron radius appears in the classical limit of modern theories as well, including non-relativistic Thomson scattering and the relativistic Klein–Nishina formula. Also, is roughly the length scale at which renormalization becomes important in quantum electrodynamics. That is, at short-enough distances, quantum fluctuations ...
In some cases it is convenient to express the classical electron radius in terms of the Compton wavelength: = ¯ = /, where is the fine structure constant (~1/137) and ¯ = / is the reduced Compton wavelength of the electron (~0.386 pm), so that the constant in the cross section may be given as:
Thomson scattering is the classical elastic quantitative interpretation of the scattering process, [26] and this can be seen to happen with lower, mid-energy, photons. The classical theory of an electromagnetic wave scattered by charged particles, cannot explain low intensity shifts in wavelength.
In either unit system, the power radiated by a single electron can be expressed in terms of the classical electron radius and electron mass as: = One implication is that an electron orbiting around a nucleus, as in the Bohr model , should lose energy, fall to the nucleus and the atom should collapse.
In any case, the context and/or unit of the gas constant should make it clear as to whether the universal or specific gas constant is being referred to. [ 10 ] In case of air, using the perfect gas law and the standard sea-level conditions (SSL) (air density ρ 0 = 1.225 kg/m 3 , temperature T 0 = 288.15 K and pressure p 0 = 101 325 Pa ), we ...
The units of the structure-factor amplitude depend on the incident radiation. For X-ray crystallography they are multiples of the unit of scattering by a single electron (2.82 m); for neutron scattering by atomic nuclei the unit of scattering length of m is commonly used.
The absorption coefficient is fundamentally the product of a quantity of absorbers per unit volume, [cm −3], times an efficiency of absorption (area/absorber, [cm 2]). Several sources [2] [12] [3] replace nσ λ with k λ r, where k λ is the absorption coefficient per unit density and r is the density of the gas.