  X-ray transition radiation can be used to measure the Lorentz factor of
relativistic particles. At energies approaching gamma = E/mc^2 = 10^5,
transition radiation detectors (TRDs) can be optimized by using thick (sim 5 -
10 mil) foils with large (5-10 mm) spacings. This implies X-ray energies >100
keV and the use of scintillators as the X-ray detectors. Compton scattering of
the X-rays out of the particle beam then becomes an important effect. We
discuss the design of very high energy detectors, the use of metal radiator
foils rather than the standard plastic foils, inorganic scintillators for
detecting Compton scattered transition radiation, and the application to the
ACCESS cosmic ray experiment.
