Transition radiation in the x-ray region from a low emittance 855 MeV electron beam

A quasi-monochromatic hard x-ray beam with a photon energy of 33 keV has been produced from transition radiation (TR) at the Mainz Microtron MAMI. The radiator was a stack of 30 polyimide foils of 25 μm thickness and 75 μm separation and the monochromator a highly-oriented pyrolytic graphite crystal. The intrinsic bandwidth was measured with a critical absorption technique to be 100 eV. On the basis of these experiments a photon flux of 4⋅109/mm2s over an illuminated area of 5.7×125 mm2 can be expected from an optimized beryllium radiator at a beam current of 100 μA. At the K-absorption edge of titanium at 5 keV narrow band transition radiation has been observed from a stack of four foils of 6 μm thickness and 294 μm separation originating from constructive interference in the region of anomalous dispersion. A new method is being developed with which the complex refractive index of thin foils in the x-ray region can be studied using such interference phenomena in the generation of transition radiation.