High-power x-ray generation using transition radiation

摘要

Abstract: In experiments using targets consisting of many thin metal foils, we have demonstrated that a narrow, forward-directed cone of transition radiation in the 0.8 to 60 keV spectral range can be generated by electron beams with moderate energies (between 17 and 500 MeV). We have measured the spectral and spatial photon densities of these radiators using low current electron beams. Using high currents, we have measured the total power of these radiators. A total power of 15.2 mW was measured from a beryllium radiator, 8.1 mW from the aluminum radiator, 4.8 mW from the titanium radiator, and 3.6 mW from the copper radiator. These values matched calculated predictions within experimental error. Both x-ray lithography for the production of integrated circuits and Laue diffraction for the study of biological materials are possible applications of this radiation. In particular, using the Al and Be radiators we have exposed photoresist-coated silicon wafers. Exposure times of the bare resist were as short as 120 s for 5 cm$+2$/ of wafer area (this resist had a 230 mj/cm$+2$/ energy dose per unit area). The shortest time for mask/wafer exposure was 180 seconds for 5 cm$+2$/. Using an Intel mask, we obtained lithographs with features of 0.5 $mu@m. In addition, we have calculated that the quasi-monochromatic bandwidth of transition radiation would be feasible for Laue diffraction of biological crystals. By designing transition radiators to emit x rays at the foil material's K-, L-, or M-shell photo-absorption edge, the x-ray spectrum is narrowed. The sources is then quasi-monochromatic and uses an electron beam whose energy is considerably lower than that needed for synchrotron sources.!32