# Bremsstrahlung

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Bremsstrahlung (German pronunciation: [ˈbʁɛmsˌʃtʁaːlʊŋ]  ( listen), from bremsen "to brake" and Strahlung "radiation", i.e. "braking radiation" or "deceleration radiation"), is electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. The term is also used to refer to the process of producing the radiation. Bremsstrahlung has a continuous spectrum, which becomes more intense and shifts toward higher frequencies when the energy of the accelerated particles is increased.

Strictly speaking, bremsstrahlung refers to any radiation due to the acceleration of a charged particle, which includes synchrotron radiation; however, it is frequently used in the more narrow sense of radiation from electrons stopping in matter.

Bremsstrahlung emitted from plasma is sometimes referred to as free-free radiation. This refers to the fact that the radiation in this case is created by charged particles that are free both before and after the deflection (acceleration) that causes the emission.

## Contents

### Dipole approximation

Suppose that a particle of charge q experiences an acceleration $\vec{a}$ which is collinear with its velocity $\vec{v}$ (this is the relevant case for linear accelerators). Then, the relativistic expression for the angular distribution of the bremsstrahlung (considering only the dominant dipole radiation contribution), is