Bremsstrahlung

Bremsstrahlung, from the German braking radiation, is electromagnetic radiation produced when a charged particle is decelerated or deflected by the Coulomb field of another charged body, most commonly a nucleus in matter. The most familiar case involves fast electrons passing through a material. As the electron accelerates or changes direction in the nuclear field, it can emit a photon. In quantum electrodynamics the process is described as electron plus nucleus scatter to electron plus nucleus plus photon. The emitted photon energy can range continuously from near zero up to nearly the incident electron energy, yielding a continuous X-ray spectrum rather than discrete lines.

Bremsstrahlung intensity increases with the square of the nuclear charge and with material thickness, so high-Z materials and thick absorbers maximize emission. At high electron energies, bremsstrahlung is often the dominant mechanism for energy loss in matter, contributing to the continuous X-ray output of X-ray tubes and to heating and shielding concerns in radiation facilities. The angular distribution is strongly forward-peaked, especially at high energies, and the spectrum is influenced by atomic screening and the electron’s initial energy.

Bremsstrahlung is also a key radiative process in astrophysical and laboratory plasmas, where free-free emission acts as an important cooling mechanism. Related processes include inverse bremsstrahlung, in which photons are absorbed by free electrons, and the line emissions that accompany bremsstrahlung in real materials, such as characteristic X-rays from atomic transitions.