摘要:

Two‐dimensional X‐ray diffraction patterns may be recorded quantitatively by means of X‐ray‐to‐electron converters which are scanned in a television‐type raster scan. Detectors of this type are capable of operating over the whole range of counting rates from very low to higher than those with which other types of converters can deal. The component parts of an X‐ray television detector are examined and the limits to the precision of the measurements

ISSN:1600-5767    

DOI:10.1107/S0021889879011663

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

The diffractometer measurement of twinned and clustered crystals requires an accurate knowledge ofQi=UiBimatrices of single‐crystal individuals contained in the sample. A determination of theQimatrix is best done from several accurately centered orienting reflections diffracted by theith single‐crystal individual. The assignment of the orienting reflections to the individuals is easy for well resolved reciprocal lattices; for closely superimposed ones a method is presented which facilitates this assignm

ISSN:1600-5767    

DOI:10.1107/S0021889879011675

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

A formula giving the correction for counting losses due to the dead‐time effect in single‐crystal X‐ray diffractometry has been obtained by least‐squares fit of theoretical formulae with either a Gaussian or a Lorentzian doublet taken as the shape of the diffraction peaks. The fit has been achieved with corrected data obtained for three different crystal types by step scanning. It is shown that this correction, easily applicable during the data reduction, is quantitatively satisfying and is necessary for any study in accurate X‐ray crysta

ISSN:1600-5767    

DOI:10.1107/S0021889879011687

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

X‐ray holography schemes are analyzed. It is shown that they have a very low aperture ratio, and this limits the size of objects from which a hologram can be recorded. It is indicated that holography schemes can be constructed on the basis of the methods of X‐ray diffraction opt

ISSN:1600-5767    

DOI:10.1107/S0021889879011699

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

A simple modification of the jig proposed by the IUCr Commission on Crystallographic Apparatus for the measurement of polarization ratios for X‐rays allowing the full rotation of the detector arm permits cancellation of the first‐order errors by averaging pairs of measurements differing by 180° around the rotation axis of the detector arm. The plot ofImeasas a function of cos2Φ, whereΦis the angle between the detector arm and one of the principal directions of polarization in the beam gives a reliable value of the polarization ratioK. The experimental results are: MoKα0.969 ± 3, 0.970 ± 3; CuKα0.908 ± 5, 0.897 ± 5 for a 0.42° and a 0.60° FWHM graphite monochromato

ISSN:1600-5767    

DOI:10.1107/S0021889879011705

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

Model calculation based on parallel cylindrical fibrils with a distribution of radii are used to derive fibrillar radii obtained from the transverse intensity profile of the small‐angle X‐ray scattering (SAXS) peaks. The results are expressed in terms of moments of the distribution function of the radii. The traverse integral breadth of the peak leads to (/), the initial slope gives (/)1/2, the asymptotic slope in the transverse wings yields or (/)1/2and the analysis of the characteristic function gives (/). The first two methods are applied to the SAXS patterns of well oriented samples of nylon 6, for which it is found that a positively skewed distribution of fibrillar radii. The relation between these analyses of uniaxially oriented systems and other SAXS and wide‐angle diffraction methods is consi

ISSN:1600-5767    

DOI:10.1107/S0021889879011717

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

X‐ray diffraction data for three aqueous solutions of MgCl2were analyzed. It is shown that in a very concentrated solution the structure and correlation functions can be reproduced almost completely by using a nearest‐neighbor model of ionic hydration, whereas in the more dilute solutions a certain number of interactions between the hydrated cation and external water molecules must also be considered. The mean coordination geometry for the close hydration was found to be octahedral both for cation and anion with mean cation–water distances (2.10–2.12 Å) and mean anion–water distances (3.11–3.14 Å) in accordance with results fou

ISSN:1600-5767    

DOI:10.1107/S0021889879011729

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

A computation method is presented which allows a rapid indexing of any unknown spot pattern obtained by back‐reflection or transmission Laue methods. The Cartesian coordinates ofnspots are measured in an orthonormal frame referred to the photographic film. Two spots 1 and 2 separated by a wide angular distanceαmare carefully chosen. Their indices are assumed to be less than 5. The set (E) of all the pairs of planes (h1k1l1) and (h2k2l2) making an angleαclose toαmis then computed. Since the pair of reflecting planes related to spots 1 and 2 belongs to (E), each computed pair of planes is tried, in order to determine the orientation of the crystal and to check whether the coordinates of the (n−2) other spots can be matched to dense planes of indices less than 8. If the uncertainty of the measurements is high or ifnis too low, this method gives the possible orientations for the crystal. Plane indices less than 8 have been identified in cubic, tetragonal and orthorhombic cr

ISSN:1600-5767    

DOI:10.1107/S0021889879011730

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

The Fourier transform values are obtained by multiplying the integrated intensities by the correction factorC(h). The problem of calculating the correction factor for biological specimens which have a multilayered structure is treated. Allowance is made for the transverse size of the specimen, the disorientation in the specimen (ω), the divergence of the X‐ray beam (ɛ), the size of the repeating unit and the curvature of the sphere of reflection. The correction factorC(h) is given byC(h) =Ω[1 + 2γh2]1/2exp (πδ2)exp (−Ω2[1 + 2γh2]), whereγ= (ω2+ɛ2)/2(Ω2d2) and whereΩis the diameter of thehth order disc whenω=ɛ= 0. The formula forC(h) applies to specimens which remain stationary during th

ISSN:1600-5767    

DOI:10.1107/S0021889879011742

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY

摘要:

Measurements of lattice parameters and birefringence of PbTiO3single crystals are described as a function of temperature. The anomalous rise in birefringence with temperature is interpreted in terms of lattice strain and dielectric polarization.

ISSN:1600-5767    

DOI:10.1107/S0021889879011754

出版商:International Union of Crystallography    

年代:1979

数据来源: WILEY