Reflecting properties of a double-crystal (DC) monochromator consisting of two elastically bent perfect silicon crystals in the parallel non-dispersive (1, -1) setting were experimentally treated. Using an unconventional fully asymmetric geometry, the effective mosaicity may be significantly enhanced up to the value of about 10 -2 rad. Test experiments were performed on the 111 and 400 reflections for wavelengths of 0"2 nm and 0.157 nm, respectively. The experimental results obtained are found to be in good agreement with the theoretical predictions published in a previous paper I- Mikula, Kulda, Vrfina & Chalupa (1984). J. Appl. Cryst. 17,[189][190][191][192][193][194][195].
Theoretical considerations concerning the δE/E resolution of perfect and elastically bent silicon single crystals for the case of backscattering geometry are introduced. It is shown, that in the case of horizontal divergence of the incident beam being of the order 10−2 red, one can significantly gain in the integrated reflectivity corresponding to higher‐order reflections by means of bending the perfect crystals having a negligible influence on the total δE/E resolution. Simultaneously the dependences of the integrated reflectivity on the radius of bending experimentally obtained by the TOF method for 220 and 440 reflections of silicon crystal are presented.
Diffraction of neutrons by a longitudinally vibrating quartz single-crystal bar was investigated for thicknesses of 3 and 13 mm. The 1st, 3rd and 5th harmonic frequencies were excited in the bar. The observed increase of the integrated intensity of diffracted neutrons as a function of the vibration amplitude of longitudinal vibrations of the quartz bar is compared with that calculated from an approximate theory considering the possibility of secondary reflexions of neutrons during their flight across the sample.
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