HIGH-RESOLUTION MONOCHROMATOR FOR SOFT AND HARD X-RAYS

An x-ray monochromator for the range from 800 eV to 10 keV has been designed, constructed, and tested at LNLS. The high resolution is achieved by a four-crystal scheme where two nondispersive double crystals (or channel-cut crystals) are arranged in the dispersive configuration. Each double crystal is installed on the axis of a precision-machined cylindrical plate. Synchronized counterrotation of both plates is achieved by a single high precision translation stage connected to them by thin metallic tapes or wires. This mechanical design makes it very stable and easy to implement as a compact ultrahigh-vacuum unit, since only one translation has to be transmitted into the monochromator vessel. To characterize the prototype we used the Cu K lines of a conventional x-ray tube and two Si(422) channel-cut crystals, yielding an angular acceptance of 2.6 arcsec and an energy resolution of 10(-5). The stability of the whole system turned out to be better than 0.6 arcsec for several hours. We swept several times the angle from Cu K-alpha1,2 to Cu K-beta (about 5.6-degrees) and the position was reproduced within the same accuracy of 0.6 arcsec.