Structural studies on fluid Hg and fluid Se at high temperatures and high pressures by means of X-ray diffraction and small angle X-ray scattering

X-ray diffraction (XRD) and small angle X-ray scattering (SAXS) measurements for fluid Hg and fluid Se up to the supercritical region have been carried out using synchrotron radiation at SPring-8. We obtained the structure factor, $S\left(Q\right)$, including a small angle region, and the pair distribution function, $g\left(r\right)$, for both fluids from the liquid to the dense vapor region. Change of the local structure and medium-range correlations at the metal-insulator transition in fluid Hg were revealed. On the other, the average coordination number of two was preserved at the semiconductor-metal transition in fluid Se. From a SAXS experiment of fluid Se in 2012, SAXS spectra near the semiconductor-metal transition region show the Ornstein–Zernike profile and the SAXS intensity is reduced with increasing pressure. These results indicate difficulties of separating fluctuations intrinsic to the semiconductor-metal transition from those arising from the liquid-vapor critical point in fluid Se, although fluctuations intrinsic to the electronic transitions are largely expected in both fluids.

Application of small-angle scattering to study the effects of moisture content on a native soy protein

The nano- and microstructure of glycinin, a soybean protein, has been investigated as a function of moisture for moisture contents between 4 and 21 wt%. Glycinin exhibits peaks in the small-angle region whose positions show minimal change with X-rays for samples up to 13% moisture. However, the use of neutron scattering, and the associated enhancement in contrast, results in the Bragg peaks being well resolved up to higher moisture contents; the associated shift in peak positions between 4 and 21% moisture are consistent with the expansion of a hexagonal unit cell as a function of moisture content. A Porod slope of ∼−4 indicates that the interface between the `dry' protein powder and the surrounding medium at a length-scale of at least 3 µm down to ∼20 nm is smooth and sharp. Scanning electron microscopy indicates that the powders, with low moisture content, have a porous appearance, with the porosity decreasing and microstructure expanding as the moisture content increases.

The use of multiple-scattering data to enhance small-angle neutron scattering experiments

Multiple scattering of neutrons by the inhomogeneities responsible for small-angle neutron scattering (SANS) during the passage of the beam through the specimen can be used to provide valuable information about the shape of the objects and the absolute value of the contrast between the scattering particles and the matrix. The neutrons emerging from the specimen are classified into those that have been scattered n times. The index n ranges from zero to infinity. The remnant of the incident beam is the group of neutrons for which n equals zero. Each group contributes separately to the scattering profile. The small-angle scattering cross section is independent of the neutron wavelength for n = 1 only. Thus collection of data as a function of specimen thickness and of neutron wavelength will provide a number of different profiles describing the same physical situation. Simultaneous analysis of these profiles provides absolute values of the cross section for scattering into the small-angle region and of the cross section for removal of neutrons from the small-angle region. So that the method can be used generally, a profile function that is a very good approximation to those in the literature is introduced. The implications for time-of-flight SANS are discussed.

Untersuchung der kristallinen Strukturen in Depotfetten von Tieren mittels Röntgenbeugungsmethoden / Investigation of Crystalline Structures in Fats of Animals by X-Ray Scattering

Fat-praeparates of cow and pork have been investigated by small-angle X-ray scattering methods. Dependent on the temperature these fats show distinct X-ray interference patterns in the small-angle region. Hence complete phasediagrams of the fats in the temperature region between -20 °C and 55 °C could be estimated. Using the intensity distribution of the X-ray scattering the electron-density distribution along one direction of the ground-cells of the fat crystals were calculated.

Dispersion of Solid State Excitations

The addition of an electron spectrometer to an electron microscope extends the capabilities not only of the microscope but also of the electron spectrometer. Operation of the electron microscope in the high angular resolution, small angle scattering mode (see, for example, Wade and Silcox) extends the angular scattering range of the electron spectrometer into an interesting small angle region (<10−4 radians) hitherto inaccessible. The dispersion of many solid state excitations in the energy range leV to 20eV is strongly affected by the light line w = ck where the energy loss ΔE = ђw and the momentum transfer is ђk. These effects can be observed directly by the electron microscope/spectrometer combination at scattering angles <10-4 radians.