To the theory of three- and four-crystal X-ray spectrometers

The resolution was studied of the following types of X-ray spectrometers: a three-crystal spectrometer with all crystals in antiparallel position, a three-crystal spectrometer with first two crystals in quasiparallel position (i.e. these crystals are set in the parallel position and then slightly misaligned) and a four-crystal spectrometer with two pairs of quasiparallel crystals. The shape and width of smearing function were calculated and compared with the calculations for double-crystal spectrometer. (author)