Small-angle Scattering Of X-rays Research Articles

A study of carbon black Corax N330 with small-angle scattering of neutrons and X-rays.

Carbon black Corax N330 (hereinafter called CB) is used as a filler in elastomers. The properties of the surface are important for the binding of the elastomer to the carbon black particles. Porod's law requires the intensity to satisfy I(q) approximately q(-alpha) with alpha = 4 for large q. Rieker et al. observed alpha = 3.7 +/- 0.1 for small-angle X-ray scattering (SAXS) data and concluded that the particle surface is fractally rough. Ruland critized this and suggested that the observed deviation is due to fluctuations of the spacing of the graphitic layer planes ("graphenes") which contribute a component I(q)fluc = 1Cflucq(-2) to the intensity component satisfying Porod's law. We studied CB by nitrogen adsorption, high-resolution transmission electron microscopy, synchroton SAXS, and small-angle neutron scattering (SANS). Our SAXS experiments with samples of high transmission (Tr = 0.96) confirmed the form of the scattering curves published by Rieker et al., but the correction for I(q)fluc restored Porod's law. SANS experiments were performed with a sample of low transmission in order to analyze the high q-range for scattering from voids and isolated graphenes. We found I(q) approximately q(-beta) with beta approximately 2 at q > 2.5 nm(-1) and will show that this intensity component requires graphenes consisting of about 12 benzene rings. The contrast matching technique revealed the presence of inaccessible voids. The SANS data for a sample with Tr = 0.363 satisfy Porods law, in contrast to the SAXS data for the high transmission samples. The latter discrepancy is likely due to the lower resolution of the SANS measurements because of wavelength smearing and multiple scattering. A SANS sample with Tr = 0.97 shows a minor deviation from Porod's law only (alpha = 3.9). The original SANS data and the SAXS data corrected for the fluctuation component indicate that the CB surface is essentially smooth.

How Bacterial Ribosomal Protein L20 Assembles with 23 S Ribosomal RNA and Its Own Messenger RNA

In bacteria, the expression of ribosomal proteins is often feedback-regulated at the translational level by the binding of the protein to its own mRNA. This is the case for L20, which binds to two distinct sites of its mRNA that both resemble its binding site on 23 S rRNA. In the present work, we report an NMR analysis of the interaction between the C-terminal domain of L20 (L20C) and both its rRNA- and mRNA-binding sites. Changes in the NMR chemical shifts of the L20C backbone nuclei were used to show that the same set of residues are modified upon addition of either the rRNA or the mRNA fragments, suggesting a mimicry at the atomic level. In addition, small angle x-ray scattering experiments, performed with the rRNA fragment, demonstrated the formation of a complex made of two RNAs and two L20C molecules. A low resolution model of this complex was then calculated using (i) the rRNA/L20C structure in the 50 S context and (ii) NMR and small angle x-ray scattering results. The formation of this complex is interesting in the context of gene regulation because it suggests that translational repression could be performed by a complex of two proteins, each interacting with the two distinct L20-binding sites within the operator.

SAXS study on the microstructure of Fe 2O 3 nanocrystal

The aim of this work is to investigate the microstructure development of Fe 2O 3 nanocrystal, prepared in sol–gel process, as a function of annealing temperature in air. Combined with the TEM and XRD patterns, small-angle scattering of X-rays (SAXS) reveals that the size of Fe 2O 3 nanocrystal increases and Fe 2O 3 structure changes from maghemite to hematite (γ to α) by increasing annealing temperature. SAXS also indicates that the growth of Fe 2O 3 nanocrystal follows fractal. When the annealing temperature is increased, fractal property of Fe 2O 3 nanocrystal changes from volume fractal to surface fractal, corresponding to the formation of Fe 2O 3 network.

SAXS experiments on absolute scale with Kratky systems using water as a secondary standard

For small-angle scattering, of X-rays (SAXS) and neutrons (SANS), the importance of absolute calibration has been recognized since the inception of the technique. The work reported here focuses on SAXS measurements using Kratky slit systems. In former days, only molecular weights or scattering per particle were determined, but today absolute calibration implies the use of the unit of cm−1for the scattering curve. It is necessary to measure the so-called absolute intensity, which is the ratio of the scattering intensity to the primary intensityP0. Basically there are two possible ways to determine the absolute intensity. The first one is the direct method, which involves the mechanical attenuation of the primary beam by a rotating disc or a moving slit. The second is the indirect method, using secondary standards. Water is well suited as a calibration standard because of the angle-independent scattering. The essential advantage is that the scattering of water only depends on the physical property of isothermal compressibility. Before presenting an example of the practical performance of this method, the most important theoretical equations for an SAS experiment on the absolute scale are summarized. With the slit collimation system, the scattering curve of water can be measured with high enough statistical accuracy. As a first example, the scattering curve of the protein lysozyme on the absolute scale is presented. The second example is the determination of the aggregation number of a triblock copolymer P94 (EO17–PO42–EO17). Taking into account that at least 10% of the polymer sample consists of diblocks, the accuracy of around 10% for the determined aggregation number is rather good. The data of P94 are also considered on the particle scale in order to obtain the radial scattering-length density distribution.

Phase Formation Kinetics in a Glass Ceramic Studied by Small-Angle Scattering of X-rays and Neutrons and by Visible-Light Scattering

The kinetics of the primary phase formation in a glass ceramic base glass near the cordierite composition in the MgO–Al2O3–SiO2 system, with additions of ZrO2 and TiO2 as nucleating agents, have been investigated by combining different small-angle scattering techniques. Phase formation in the base glass heated isothermally at 1093 K has been studied in order to elucidate the structural processes that take place during controlled nucleation before volume crystallization begins. Complementary results of X-ray diffraction, transmission electron microscopy and electron microprobe analysis reveal that in the final stages of annealing, different crystalline phases, which are dispersed in the residual glassy phase, are developed. The largest particles have sizes of the order of several hundreds of nanometers and consist of magnesium petalite as well as a high-quartz solid solution. Besides these crystals, two populations of smaller particles, the sizes of which can be resolved by small-angle scattering, were detected and found to be enriched with TiO2 and/or ZrO2. The growth of particles of intermediate size was studied in situ. The radius, R, of each of these particles increases with increasing treatment time, t, according to the power law R ∝ t1/2, indicating diffusion-limited independent growth. The scattering patterns are modified by diffusion zones surrounding the growing particles. The characteristics of the diffusion zones are evaluated by fitting appropriate model scattering curves to the experimental scattering data. The structural arrangement of the Ti and Zr ions was studied by contrast variation with the help of anomalous small-angle X-ray scattering and small-angle neutron scattering. As revealed by the contrast variation experiments, Ti ions are concentrated in the interface between the intermediate-sized particles and the glass matrix, whereas Zr is homogeneously distributed in these particles. Additionally, the Zr ions participate in the formation of the smallest particles, which are crystallites enriched with ZrO2. Finally, the catalyzing effect of TiO2 and ZrO2 on the nucleation and volume crystallization of the glass ceramic is discussed.

SAXS/WAXS study on the formation of precursors and crystallization of silicalite

The formation of colloidal aggregates which can act as precursors in zeolite crystallization has been studied using small-angle scattering of X-rays (SAXS). In the same experiment the onset of crystallization and the increase of crystallinity were measured using wide-angle scattering of X-rays (WAXS). To perform in situ time-resolved combined SAXS WAXS measurements high brilliance synchrotron radiation was applied. The influence of silica, template, and OH+ concentrations on the synthesis of silicalite (MFI structure) from a clear solution was studied. The alkalinity of the synthesis mixture appeared to be decisive for the formation of colloidal aggregates. At relatively low alkalinity colloidal aggregates were formed prior to the onset of the crystallization. At higher alkalinities no colloidal aggregates could be observed at any time during the synthesis, suggesting that nucleation and crystal growth occurred directly from the solution.

Influence of the doping level on the microstructure of P-type porous silicon studied by small-angle X-ray scattering

Small-angle scattering of X-rays (SAXS) can lead to a better understanding of the microstructure of porous silicon because the pore radii range (2–10 nm) corresponds to the small-angle scattering investigation range (1–100 nm). A recent SAXS study performed by some of the present authors on porous layers prepared on lightly doped and heavily doped silicon wafers revealed strong differences according to the dopant type. Here the dependence of the microstructure of P-type porous silicon on its doping level is focused upon. In nondegenerate P-type silicon, the porous structure is an apparently random distribution of voids. The scattering pattern obtained in that case is isotropic. In degenerately doped P-type silicon (P+), the porous film structure consists of many long voids running perpendicular to the surface, with small `buds' on their sides. SAXS experiments carried out with a two-dimensional detector revealed the anisotropic character of the P+ microstructure.

Grazing-incidence X-ray scattering study of the microstructure of tungsten–carbon films

The microstructure of a coating deposited onto a tungsten carbide layer by cathodic sputtering assisted by chemical vapour deposition (CVD) has been analysed by small-angle scattering of X-rays (SAXS) with a conventional laboratory set-up specially adapted for grazing incidence. Anomalous-scattering measurements have also been performed at LURE, the French synchrotron-radiation facility at Orsay with the aim of characterizing the structure of phases present in the coating. SAXS results reveal the existence of very small precipitates; the size of these precipitates determined from the use of the Guinier approximation is about 16 Å, the correlation length deduced from the position of the peak in the small-angle scattering pattern is about 36 Å. The value of the experimental integrated intensity and the variation of the observed intensities with photon energy lead to the conclusion that these nanocrystals are highly enriched in tungsten and embedded in a carbon-based matrix having a weak electronic density. Electron diffraction results support the assumption of the presence of β-WC1 − x, an unstable high-temperature phase. Furthermore, the low electronic density of the matrix is in agreement with face-centred-cubic carbon recently proposed in the literature.

On the estimation of the locations of subunits within macromolecular aggregates from neutron interference data

Neutron interference methods are currently being used to determine the positions of the centers of mass of subunits in macromolecular aggregates, e.g. Langer, Engelman & Moore [J. Mol. Biol. (1978). 119, 463–485] and May et al. [Fourth International Conference on Small-Angle Scattering of X-rays and Neutrons, Gatlinberg, Tennessee, 1977. Abstract F-2. Unpublished]. Subunit positions are found by triangulation from distances estimated from data sets which relate subunits pairwise. A serious limitation of the method as it has been applied so far is that only an approximate value for the distance between a pair of subunits can be obtained from its corresponding data. The errors in distances which result from these approximations lead in turn to inaccuracies in subunit positions. This paper presents a method for analyzing the whole set of data obtained for a structure which eliminates the need for approximating distances from individual data sets and leads, therefore, to unbiased estimates of subunit locations. This method of analysis also yields information about subunit radius of gyration in situ.

Fourth International Conference on Small-Angle Scattering of X-rays, and Neutrons, Gatlinburg, Tennessee, USA, 3-7 October 1977

Fourth International Conference on Small-Angle Scattering of X-rays, and Neutrons, Gatlinburg, Tennessee, USA, 3-7 October 1977

Small-Angle Scattering of Soft X-Rays by Use of Synchrotron Radiation

Small-Angle Scattering of Soft X-Rays by Use of Synchrotron Radiation

Small-Angle Scattering of Celestial X-Rays by Interstellar Grains.

Small angle scattering of X-rays by interstellar grains in light of neutron star discoveries

Small-Angle Scattering of X-Rays from Deformed Natural Graphite

Examinations of deformed metals using x-ray smallangle scattering techniques were stimulated by the development of theories and experiments on defects in crystals. Some results of the examinations of natural graphite are presented. The graphite was deformed by either rolling, extruding, pressing, or Lamellar compounding. The determination of scattering was achieved by exposure, under constant operating conditions, on the same photographic film. Representative scattering curves are plotted, showing that scattering is almost linear over the range of angles observed and is approximately parallel for different deformations. The angular dependence of the scattered intensity was compared with that of stressed copper and aluminum in the same angular range. (B.O.G.)

Structure in Vitreous Silicate Fibers as Shown by Small-Angle Scattering of X-Rays

The relation of the x-ray diagram at small angles to the preparation conditions of glass fibers from molten silicates is studied. The composition Na2O·MgO·3SiO2 is studied extensively, and fibers are also studied in which K2O replaces Na2O, and CuO and PbO replace MgO. Most of the diagrams are characterized by very intense, shaped, diffuse scattering. Also, fibers which had certain thermal histories show intense, unshaped diffraction maxima. The diffuse scattering is interpreted as due to voids which are elongated by the spinning process. The discrete diffraction corresponds to a Bragg spacing of about 30 A but is not associated with short-range order. It is concentrated on the surface or accessible to liquid penetration from the surface. It is either frozen in by quenching, produced by quenching, or produced by a combination of quenching and reaction with the atmosphere. No interpretation of the structure responsible for it is given.

Small Angle Scattering of X-Rays by Plastically Deformed Single Crystals

The small angle scattering of x-rays from single crystals of magnesium plastically deformed in simple shear has been measured in the angular range of 4′ to 5°. The crystals were subjected to both unidirectional and cyclic shear stresses applied along the [112̄0] direction. Thin slices of the deformed single crystals were prepared using strain-free cutting and polishing techniques. The thin slices had orientations such that the slip direction was either parallel or perpendicular to the incident x-ray beam in order to observe any anisotropy in the scattering that might be due to dislocations. It was found that those samples which contained deformation twins within the irradiated volume produced rather large scattered intensity. This scattered intensity is interpreted as being due to double Bragg scattering. The scattered intensity from other specimens was attributed to surface scattering. No evidence for small angle scattering by dislocations was found.

Small-Angle Scattering of X-Rays and Neutrons from Deformed Metals

X-rays or thermal neutrons may be scattered at small angles from deformed metals due both to ``true'' small-angle scattering and to double Bragg reflections. These two effects are discussed theoretically and compared to see how one may be distinguished from the other in the results of experimental observations. Experiments are described on the small-angle scattering of x-rays from polycrystalline copper and single grains of aluminum deformed by cold-work or fatigued in pulsating tension. The results show in a direct and conclusive way that almost all of the scattering is due to double Bragg reflections. No surface scattering has been observed. Double Bragg reflections have been eliminated in experiments on the small-angle scattering of cold neutrons from cold-worked and fatigued copper and aluminum. The results, which indicate the magnitude of the ``true'' scattering, are consistent with scattering from dislocations. Hence there is no direct evidence of the existence of cavities in cold-worked or fatigued metals as the result of small-angle scattering experiments with either x-rays or neutrons.

Small-Angle Scattering of X-Rays from Neutron Irradiated Copper

The scattering of x-rays at small angles from polycrystalline copper is found to increase when the recrystallized metal is bombarded with fast neutrons. The observed effects above 2° are due to double Bragg reflections; below about 1½° they can be explained in terms both of double reflections and ``true'' small-angle scattering. The results indicate that either small coherent regions (of diameter about 100 A) or severe strains are present in the irradiated metal. The results are consistent with other measurements (particularly of mechanical properties) on irradiated metals.

Small Angle Scattering of X-rays by Deuteron-irradiated Germanium Crystal

The angular intensity distribution of scattered x rays from an irradiated germanium crystal is given. (auth)

Small-Angle Scattering of X-Rays in Aqueous Solutions of Sodium Salts of Conjugated and Unconjugated Bile Acids.

Small-Angle Scattering of X-Rays in Aqueous Solutions of Sodium Salts of Conjugated and Unconjugated Bile Acids.

Small-Angle Scattering of X-Rays.

Small-Angle Scattering of X-Rays.