Transition radiation - Definition and Overview

Transition radiation is produced by relativistic charged particles when they cross the interface of two media of different dielectric constants. The total energy loss of a charge particle on the transition depends on its Lorentz factor <math>\gamma = E/mc^2<math> and mostly directed forward, peaking at an angle <math>o(1/\gamma)<math> relative to the particle's path. The intensity of the emitted radiation is roughly proportional to the particle's energy <math>E<math>.

The characteristics of this electromagnetic radiation makes it suitable for particle discrimination, particularly of electrons and hadrons in the momentum range between <math>1 GeV/c<math> and <math>100 GeV/c<math>. The transition radiation photons produced by electrons have wavelengths in the X-ray range, with energies typically in the range from <math>5<math> to <math>15 keV<math>. However, the number of produced photons per interface crossing is very small: for particles with <math>\gamma = 2\times 10^3<math>, about <math>0.8<math> X-ray photons are detected. Usually several layers of alternating materials or composites are used to collect enough transition radiation photons for an adequate measurement --- for example, one layer of inert material followed by one layer of detector (e.g. microstrip gas chamber), and so on.

See also

• External article on transition radiation: http://rkb.home.cern.ch/rkb/PH14pp/node194.html