Neutron diffraction evidence for the spin-reorientational transition in FeBO3 at high pressures

The spin-reorientational transition from the state with “easy-plane” anisotropy to the state with “easy-axis” anisotropy—a pressure analogue of the Morin temperature transition in hematite— was detected in iron borate at a pressure of P～17 kbar at room temperature by the neutron diffraction method.     

Direct observation of anomalous Kossel lines

Anomalous Kossel lines corresponding to the yield of X rays from a germanium crystal under the conditions of strongly asymmetric diffraction have been observed in the simplest experimental scheme with the use of characteristic Mo K _α radiation and a germanium crystal analyzer. In agreement with the results of a previous theoretical analysis, such lines are narrow collimated beams of radiation in the form of a ridge in a narrow angular range near a given direction whose intensity is one or two orders of magnitude higher than the background with a divergence of about several seconds of arc in the diffraction plane and of about 10′ along the Kossel line. The possible applications of this effect, in particular, for solving the problems of X-ray holography, are discussed.     

Phase relations in analysis of glancing incidence X-ray rocking curves from superlattices

Nontrivial features of the formation of glancing incidence x-ray rocking curves from superlattices are revealed and analyzed for the magnetic digital alloy GaSb/15(Mn/GaSb)/GaAs. The qualitative analysis of the shape of the experimental curve in the framework of specific phase relations in the reflection amplitude makes it possible not only to describe these features, in particular, the two-humped profile of the first Bragg peak and to reconstruct the real structure of the alloys under investigation, but also to develop the general scheme for analyzing x-ray rocking curves from imperfect superlattices.     

Laser-Synchrotron Facility of the National Research Centre “Kurchatov Institute”

Crystallography Reports - The laser-synchrotron facility (LSF) of the National Research Centre “Kurchatov Institute” (NRC KI) is a unique research complex that combines unprecedented...     

Source focusing and coherent imaging of a microscopic object at weak spatial coherence of the synchrotron radiation beam

Experimental results are presented on the measurement of a holographic (phase-contrast) image of a boric fiber (100-μm-diameter boric cylinder with a 20-μm-diameter tungsten core) and on radiation focusing by Fresnel zone plates using the Kurchatov synchrotron radiation source. By comparison of the obtained hologram with theoretically calculated data, the vertical size of the source was determined to be 325 ± 25 μm. This value was also confirmed by measuring the half-width of the direct image of the source. Features of image recording on a photographic film are discussed.     

Determination of the electron beam size at the Kurchatov Synchrotron Radiation Source using an edge screen

The electron beam size of the 2.5-GeV storage ring of the Kurchatov Synchrotron Radiation Source was measured using a fixed edge screen. The obtained vertical beam size of 190 μm and the corresponding calculated value of 198 μm (for 2% betatron coupling) almost coincide within the experimental error.     

X-Ray “knife” as a submicrometer tool for studying focusing lens quality

A mobile x-ray “knife” developed by the authors is described. The device is intended for determining the profile of the spatial intensity distribution in the ionizing radiation beam. Its automated motion system combines two actuator types. Significant displacements are performed using a goniometric module with a piezoelectric actuator. The angular step of this module is 1 arc second, which corresponds to a linear displacement of 0.97 μm. As a “fine” drive, a rotating module with a piezoelectric column is used. Its linear step can be varied from 0.01 to 1 μm at a total number of steps of 1000. The x-ray knife was experimentally tested at the Kurchatov Center of Synchrotron Radiation for diagnostics of the parameters of a short-focus x-ray lens at a photon energy of 18 keV. In the vertical direction, the width of the profile for the intensity distribution in the beam formed by the lens was 2.4 μm.     

Microanalysis station at the Kurchatov synchrotron radiation source

The REFRA station developed, fabricated, and put into operation at the Kurchatov Synchrotron Radiation Center is described. The station is placed on beamline 5.6 of the big storage ring. The station consists of a vertical beam position monitor, an operating shutter, vertical and horizontal slits for the white beam, a monochromator, an alignment stage, an intensity monitor, an EXAFS spectrometer unit, a diffractometer unit, detectors, and a data control and acquisition system. The station operating energy range is 5–30 keV. The station is fully-automated and has been operating with the SR beam since spring 2005. The station units can be reproducibly mounted on the SR beam to provide various research configurations.     

Nontrivial role of the resolution function in the formation of double-crystal X-ray rocking curves

A theoretical analysis of the shape of the resolution function of an X-ray diffractometer in the double-crystal nondispersive scheme for measuring rocking curves has been performed. It is shown that this function, along with the strong narrow central line (corresponding to the characteristic line to which the collimator crystal and slits in the experimental scheme are tuned) always contains an additional weak satellite, corresponding to the neighboring characteristic line. This feature manifests itself in experimental curves as an additional pseudopeak, whose intensity is comparable with the corresponding diffraction scattering intensity from a sample in the fundamental characteristic line, and whose shape and exact position are set by the resolution function in a specific experimental scheme. It is shown that the exact allowance for the angular and spectral distribution of incident radiation in the double-crystal scheme makes it possible to precisely determine the parameters of the structures studied.     

Observation of standing x-rays in Bragg diffraction on high-T c superconducting crystals Nd1.85Ce0.15CuO4−δ

Curves of the secondary-fluorescence yield from the constituent elements of high-T _c superconducting crystals Nd_1.85Ce_0.15CuO_4−δ are measured in the dynamic x-ray diffraction regime. The form of the curves attests to the appearance of a standing x-ray wave in the crystal. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 9, 703–706 (10 May 1997)