No abstract

Absolute calibration forms a valuable diagnostic tool in small-angle scattering experiments and allows the parameters of a given model to be restricted to the set which reproduces the observed intensity. General methods which are available for absolute scaling of small-angle X-ray scattering (SAXS) data are reviewed along with estimates of the degree of internal consistency which may be achieved between the various standards. In order to minimize the time devoted to calibration in a given experimental program, emphasis is placed on developing a set of precalibrated strongly scattering standards for the SAXS facilities of the National Center for Small-Angle Scattering Research (Oak Ridge). Similar standards have been developed previously for calibration of small-angle neutron scattering (SANS) data. Particular attention is given to standards which can be used for either SAXS or SANS experiments where each sample has been independently calibrated for both types of radiation. These calibrations have been tested via the theoretical relationships between the two cross sections. It has been found that specimens best suited for such intercalibration purposes are a glassy carbon specimen where the scattering arises from voids in a carbon matrix and a perdeuterated polyethylene where the scattering arises from periodic arrangement of the crystalline lamellae. In only these two cases could the identical specimen be used for both the neutron and X-ray scattering experiments.

No abstract

A precise study of fluxoid-line lattice (FLL) in the intermediate

Aluminium foils (99.99% purity) and single crystals (99.999% purity) were charged with hydrogen using a gas plasma method and electrochemical methods, resulting in the introduction of a large amount of hydrogen. X‐ray diffraction measurements indicated that within experimental error there was a zero change in lattice parameter after plasma charging. This result is contradictory to almost all other face‐centred cubic (f.c.c.) materials, which exhibit a lattice expansion when the hydrogen enters the lattice interstitially. It is hypothesized that the hydrogen does not enter the lattice as an interstitial solute, but instead forms an H–vacancy complex at the surface that diffuses into the volume and then clusters to form H2 bubbles. Small‐ and ultra‐small‐angle neutron scattering (SANS, USANS) and small‐angle X‐ray scattering (SAXS) were primarily employed to study the nature and agglomeration of the H–vacancy complexes in the Al–H system. The SAXS results were ambiguous owing to double Bragg scattering, but the SANS and USANS investigation, coupled with results from inelastic neutron scattering, and transmission and scanning electron microscopy, revealed the existence of a large size distribution of hydrogen bubbles on the surface and in the bulk of the Al–H system. The relative change in lattice parameter is calculated from the pressure in a bubble of average volume and is compared with the experimentally determined value.