X1-Experiment : Transition Radiation (TR)


   Smith Purcell




Experiments with TR show that a hard x-ray beam with photon energies up to about 35 keV can be produced from a stack of 30 beryllium foils [1,2]. The spectral brilliance should reach, at 855 MeV and 0.1 mA, that of the most powerful synchrotron radiation sources from bending magnets. A highly oriented pyrolytic graphite crystal has been used to prepare a quasi-monochromatic 33 keV photon beam. At the K-absorption edge of titanium at 4.96 keV narrow band transition radiation is emitted from a stack of four foils originating from effects of the anomalous dispersion. A novel type of interferometer has been developed with which the real part of the refrective index decrement of thin self-supporting foils can be measured in the hard X-ray region [8,9]. It consists of two foils at which the low emittance 855 MeV electron beam of the Mainz Microtron MAMI produces transition radiation, a single crystal spectrometer with a flat crystal in Bragg geometry, and a pn CCD X-ray detector. Distinct interference oscillations have been observed as function of both, the photon emission angle and the distance between the foils. The dw of a 2 µm thick nickel sample foil has been measured at X-ray energies around the K-absorption edge at 8333 eV and at 9930 eV with an accuracy of better than 1.5%.
TR Production Mechanism

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