Transition radiation detectors

 Transition radiation is a radiation in the X-ray region, that arises when ultrarelativistic particles cross a boundary between 2 media with different dielectric constants. It depends strongly on the relativistic $\gamma$ factor of the particle which makes it usable for particle identification at energies where time of flight methods or detection of Cherenkov radiation no longer work. As an example, the large mass difference between electrons and pions makes it possible to separate electrons from pions in an energy interval from 0.5 GeV to 200 GeV.

To build a detector based on transition radiation is far from easy though since the number of X-ray photons from a single boundary are of the order $\alpha$ , the fine structure constant.

The theory here is mainly based on the review articles [32] and [33] and the section on applications to detectors on [34] and [35].