Transition radiation detectors in particle astrophysics

Transition radiation detectors (TRDs) have been used for three decades to study highly relativistic cosmic rays. Their relatively low weight but large sensitive area makes them particularly suitable for measurements above the atmosphere, on balloons or in space. A review is given of the different requirements and experimental solutions for threshold detectors and energy-measuring devices, and the astrophysical significance of the measurements is briefly summarized. Finally, the importance of TRD devices for future works is discussed.