Measurements of x-ray emission from zinc and molybdenum transition radiators

This article describes the measurements of x-ray power, spatial and spectral distributions from transition radiators whose spectra are narrowed by the foil material’s K-shell photoabsorption edge. We used two foil stacks, one composed of 15 foils of 3-μm-thick Zn and the other composed of 15 foils of 4-μm-thick Mo. At low average currents, the x-ray spectrum produced by transition radiation was measured by pulse height analysis to be between 5 and 9.7 keV for the Zn radiator and between 10 and 20.0 keV for the Mo radiator. These measurements compared well with calculations. The x-ray spatial distribution from the Zn radiator was measured using a silicon linear diode array. The x rays generated by the Zn radiator were found to be emitted in a forward-directed cone with half angle of ∼1.9 mrad with the center of the expected annulus filled. The power density in the peak of the annulus was found to be 50 mW/(mA cm2). At a high average electron-beam current of 12.5 μA, the x-ray power produced by a stack of ten Zn foils was measured in the spectral range between 5 and 9.66 keV to be 1.54 mW with the peak power in the 1 μs macropulse to be 8.5 W. Electron-beam energies between 249 and 282 MeV were used in these experiments.