Journal of Applied Crystallography

Mittal, R; Chaplot, S.L; Lalla, N.P; Mishra, R.K

doi: 10.1107/S0021889899008109pmid: N/A

Temperature-dependent X-ray diffraction measurements are reported for ZrMo2O8 in the trigonal phase from 80 to 925 K. The measurements reveal highly anisotropic thermal expansion coefficients with average values of -3.9 x 10-6 and 52 x 10-6 K-1 for the a and c cell parameters, respectively.

Weber, S

doi: 10.1107/S0021889899009140pmid: N/A

Weber, S.

doi: 10.1107/S0021889899009140pmid: N/A

Thorkildsen, Gunnar; Mathiesen, Ragnvald H.; Larsen, Helge B.

doi: 10.1107/S0021889899007347pmid: N/A

By parametrizing the conic surfaces spanned by the reciprocal‐lattice vector under the action of the rotation axes, a new procedure for angle calculations for a κ diffractometer is presented. It is applied to obtain angle settings in various modes for a newly developed six‐circle diffractometer.

Brodersen, D.E; Jenner, L.B; Andersen, G.R; Nyborg, J

doi: 10.1107/S0021889899006056pmid: N/A

XAct is a stand-alone application for Microsoft Windows 95/98 that, through a spreadsheet-like interface, allows the user to construct crystallization experiments in a highly flexible way. The object-oriented data structure helps to maintain an overview of many experiments and provides reusable stock and tray objects. The program features a hardware interface that enables automatic setup of experiments by use of a Gilson 222 autosampler (Gilson Inc., Wisconsin, USA). Additionally, experimental information can be imported from external spreadsheets and World Wide Web applications.

Pan, H.Y; Du, K; Wang, Y.M; Zhu, J; Li, S.Y; Ye, H.Q

doi: 10.1107/S0021889899007402pmid: N/A

The microdiffraction from a single translation domain boundary (TDB) in -Ni3Nb has been recorded by using a Hitachi HF-2000 field emission gun transmission electron microscope, while high-resolution transmission electron microscopy images were used to assist the analysis. The diffraction splitting effect of a TDB is well explained by the kinematics and dynamic calculations, and complex diffraction characteristics have been studied by using dynamics simulation.

Haga, Y.K; Kumazawa, S; Niimura, N

doi: 10.1107/S0021889899005701pmid: N/A

The energy dependence of gamma-ray sensitivity of a neutron imaging plate (NIP) has been measured. The gamma-ray sensitivity is equivalent to one half that of a thermal neutron at a gamma-ray energy less than 300 keV, and 1/40 at greater than 300 keV. The shielding of the NIP, by lead, from gamma rays in the experimental hall of the reactor JRR-3M of the Japan Atomic Energy Research Institute (JAERI) was measured. It was found that lead of thickness 40 mm is sufficient to reduce the gamma-ray background to 1/10 on a normalized scale. Covering the NIP with lead foil of thickness 1 mm results in a decrease of the gamma-ray background without reduction of the neutron signal.

Ida, T.; Kimura, K.

doi: 10.1107/S0021889899008894pmid: N/A

The effect of transparency and finite thickness of the sample on the peak profile in powder diffractometry with Bragg–Brentano geometry is treated as a convolution with an asymmetric aberration function. The formula of the aberration function and a practical method for numerical calculation of the convolution are proposed. The model function for the total profile is given by triple convolution of the pseudo‐Voigt function with asymmetric functions based on vertical (axial) divergence, horizontal (equatorial) divergence and sample transparency. The validity of the model profile function is examined by fitting the Cu Kα X‐ray diffraction profile of diluted lanthanum hexaboride (LaB6) standard samples (SRM660) of 0.5 mm thickness, the transparency of which is varied by mixing with different amounts of starch; all the parameters that may affect the shape of the profile function are treated as fixed parameters. Even in the case of heavily distorted profiles of highly transparent samples with the inverse linear absorption coefficients μ−1 = 0.34 and 1.19 mm, experimental profiles are fairly well reproduced by the model function, typically within several % in R factor. It is also demonstrated that the lattice constants of the transparent samples are precisely evaluated by applying this model function.

McMahon, P. J.; Moss, S. D.

doi: 10.1107/S0021889899008559pmid: N/A

Small‐angle X‐ray scattering (SAXS) is often used to study porous and aggregated fractal materials. Typically when q is small or when large primary‐beam intensities are required, the small‐angle geometry employed introduces infinite‐slit‐height smearing into the experimental data. Herein, simple derivations for infinite‐slit‐height‐smeared SAXS from porous surface and mass fractals are presented, including an approximation for aggregated mass fractals. The models allow rapid analysis of background‐subtracted data without the need for deconvolution. An equation is derived that allows analysis of normalization from deconvolution routines applied to porous‐fractal data. This model is tested using simulated and experimental SAXS data.

Riboldi‐Tunnicliffe, A.; Hilgenfeld, R.

doi: 10.1107/S0021889899008584pmid: N/A

A method is described that permits the cooling of protein crystals without the use of conventional cryoprotective agents. Covering the crystal completely with highly liquid dry paraffin oil (Merck) prevents ice formation. It is suggested that this method, because of its simplicity, be tried as a first choice in cryocrystallography, since it does not require the growth or soaking of crystals in solvents which could disturb the packing by diffusing into the crystal.