2005/07/08 | 韧致辐射[Bremsstrahlung]
类别(Ω〖物理〗) | 评论(0) | 阅读(170) | 发表于 21:19
Electromagnetic radiation that occurs when charged particles with energies large compared to their rest energies are decelerated over a very short distance. Since electrons are much lighter than protons, electron bremsstrahlung is the most common. In bremsstrahlung, a continuous spectrum with a characteristic profile and energy cutoff (i.e., wavelength minimum) is produced. In addition, lines can appear super imposed, corresponding to the ejection of K and L shell electrons knocked out of atoms in collisions with the high-energy electrons.

For the continuous bremsstrahlung spectrum, equate the quantities
[
(1)

where is the charge on the electron, V is the voltage change, h is Planck's constant, c is the speed of light, and is the minimum possible wavelength of radiation. Solving for then gives
[
(2)

The cross section for an electron to be observed in a solid angle is given by


(2)

where and are the initial and final velocities, respectively and is the range of wavenumbers. In the soft-photon limit, , and for scattering angle . In this limit, each of the last two integrals are given by

(4)

The first integral can be reduced to




(5)

This can be expanded in a series as
[
(6)

so combining ,,and gives
[
(7)

in the nonrelativistic limit (Bjorken and Drell 1964, pp. 126-127).

A line spectrum occurs when electrons are knocked out from low shells and electrons from higher shells drop down.
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