Metal-metal nanolayered structures for generation of hard x-ray radiation

Our new research effort is aimed at developing a new X-ray source for medical applications, using low-energy electrons. Generation of intense narrow-band X-ray transition radiation (TR) by few-MeV electrons traversing solid multilayer structures, initially proposed for by us $\sim$ 1 keV photons, changes dramatically at energies of interest to medicine, 30-50 keV, because of significant changes in dielectric constants. In particular, the choice of the materials for the multilayer target proposed by us for soft X- ray generation, is no longer applicable. In particular, our original approach was based on choosing a layer of a high-Z material as a ``radiator'' with a chosen $K$-shell transition, and the layer of low-Z material as a neutral ``spacer.'' However, in the 30-50 keV range, TR spectra with such pairs show a spectral $dip$, not a peak,at the chosen $K$-shell. Our new theoretical investigations have shown that the optimal spacer now, as a rule, should have higher Z than the radiator. One example of such combination is Mo/Ag; we predict that its X-ray TR spectrum contains a strong, 1\% wide peak at the K-edge of Mo, $\sim$20 KeV. We present our recent theoretical results of the subject, as well as our experimental results for the Mo/Ag target.