Measuring the Lorentz factors of energetic particles with transition radiation

Transition radiation detectors can be used for the measurements of the high energy cosmic ray nuclear composition up to Lorentz factors ∼ 10 5 if the X-ray yields can be increased beyond those of present designs. The state of the art of current and recently proposed detectors is briefly reviewed, and the considerations are discussed governing the dependence of the transition radiation signal on particle energy. It is shown that the incident particle energy range accessible to transition radiation, and the total intensity produced, can be increased using foils with large plasma frequency. Graphene radiator foils are proposed as a potential high energy radiator.