Overgangsradiussen

Overgangsradiussen, or transition radiation in English, is electromagnetic radiation produced when a charged particle passes from one medium into another with different electromagnetic properties, such as a boundary between materials with different dielectric constants or refractive indices. The effect is rooted in the way the particle’s electromagnetic field must re-adjust to the new medium, and it is a classical phenomenon that becomes increasingly important for highly relativistic particles. The amount of radiated energy grows with the particle’s Lorentz factor, making transition radiation more readily observable for fast electrons than for heavier charged particles.

The emission can occur at a single boundary, but the effect is enhanced when the particle traverses a stack of many thin interfaces (a radiator). In such radiators, radiation from successive boundaries can interfere, producing a characteristic spectrum that is shifted toward higher frequencies. For relativistic electrons, the emitted photons are typically in the X-ray region, with the exact spectrum depending on gamma, the spacing and thickness of the layers, and the materials used.

Applications of overgangsradiussen are most prominent in particle physics. Transition radiation detectors use many thin foils and an X-ray detector to identify high-velocity electrons by detecting the characteristic transition-radiation photons. These detectors help distinguish electrons from pions and other hadrons in collider experiments, contributing to particle identification and event reconstruction. The concept, proposed by Ginzburg and Frank in 1946, remains a standard tool in experimental high-energy physics and has influenced detector design and calibration.