[en] The SANS diffractometer LOQ at the ISIS pulsed neutron source is described. Data from neutron wavelength of 2.0-9.8 A are combined to give a simultaneous Q range of 0.006-0.22 A^-1 at a sample-detector distance of 4.4 m. 6 figs

[en] The document is a users' guide to COLETTE, the data reduction program for the LOQ Small-Angle Neutron Scattering (SANS) instrument at the ISIS Spallation Neutron Source. COLETTE runs on top of and incorporates GENIE (the graphics program) in order to handle the two-dimensional datasets, which are an essential feature of operation in processing SANS data. However to ensure speed and ease of use COLETTE functions independently of GENIE, with its own command set, and data input and output routines. (UK)

[en] In this paper, metallographic sectioning and non-destructive small angle neutron scattering (SANS) are used to map the level of creep cavitation around a surface breaking crack in a stainless steel pressure vessel. The cracking developed during 65,000 h service at an operating temperature of around 525 deg. C and was promoted by the accumulation of creep strain resulting from relaxation of tensile residual stresses associated with a nozzle attachment weld. The distribution and evolution of the cavities is discussed in terms of existing models of creep cavitation failure based on a ductility exhaustion model in which the corresponding multi-axial creep ductility, expressed as the von Mises strain at failure, is a function of the strain rate and stress state. An empirical approach has been adopted for describing the effects of stress state on ductility, which takes into account cavity nucleation as well as cavity growth by creep deformation, and is similar to local approach models for ductile crack growth. Crack initiation is conceded when the creep damage parameter D_c≥1. The measured creep cavitation results are found to be in reasonable accordance with such a model

[en] The formalism of Cooper and Nathans is used to discuss the resolution characteristics of the Constant Q Spectrometer for neutron inelastic scattering described in a previous paper. Expressions are derived for the parameters of the ellipsoid describing the resolution function. The theory is compared with measurements of the resolution function made on a prototype spectrometer on the old Harwell linac. An appendix derives the resolution function analytically for the case of a perfect analyser crystal. (orig.)

[en] Short communication

[en] Calcium carbonate dispersions stabilized by an adsorbed surfactant layer are used to regulate the acidity of lubricating oils for internal combustion engines. Three typical commercial samples have been examined using a combination of X-ray and neutron scattering techniques. The solid active material was extracted from the samples and redispersed in heptane and mixtures of toluene and toluene-d₈ and n-octane and n-octane-d₁₈. The results were in broad agreement with the core/shell model. The core radius was obtained from SAXS data. The total particle radius (∝20-50A) and hence the shell thickness were obtained by model fitting to the deuterated-solvent and 65% deuterated solvent SANS data with the core radius from the X-ray data. In determining the best fit, the core density, amount of solvent in the shell and polydispersity were also adjusted to give fits with a shell-to-core-volume ratio and a volume fraction that agreed with the expected values. The SANS data were weaker than expected assuming a simple monodisperse core/shell model with a calcite core. This is consistent with the observed polydispersity and in addition implies diffuse boundaries. Although WAXS (wide-angle X-ray scattering) confirmed that the cores were non-crystalline the best model fits were obtained with a core scattering density not much less than that calculated for calcite. The absolute intensities suggested that some solvent was incorporated into the shells of all the samples and one sample showed a preference for uptake of octane as compared to toluene. (orig./GSCH)

[en] Two different small-angle neutron scattering (SANS) facilities, the D11 camera at the Institut Laue-Langevin (ILL, Grenoble, France) and the LOQ time-of-flight diffractometer at the Rutherford Appleton Laboratory (RAL, Didcot, Oxon, England), were used in the investigations of δ'-Al₃Li precipitation at 463 K in Al-Li 3% alloy. The results obtained from the steady-state reactor and from the pulsed source by using two different data-acquisition techniques and two different procedures for data analysis are compared. The SANS curves for the same set of samples investigated using the two different instruments are in good agreement within the experimental uncertainties. A check was also made on the metallurgically relevant quantities, namely the average size and the size-distribution function of the δ' precipitates at the various stages of the ageing process, obtained from the two sets of SANS curves by applying the same numerical method. Good agreement was found between the results from the two data sets. (orig.)

[en] The ability of the triple-axis spectrometer to perform scans as a function of energy transfer at a fixed scattering vector Q has given the instrument a vital role in neutron scattering. A spectrometer which can provide this same role on a pulsed neutron source is described. It depends on the simultaneous observation of scattering at several different scattered neutron energies using a Multi Angle Reflecting Crystal (MARC) analyser. A prototype spectrometer installed on the Harwell electron linac is described and as assessment given of its capabilities and limitations. Some consideration is given to the possible forms of optimised practical spectrometers. (Auth.)

[en] The structures of the ion conducting glasses LiCl-Li₂O-2B₂O₃, (AgI)_0.6-(Ag₂O-B₂O₃)_0.4, CsI-4AgPO₃, and PbI₂-9AgPO₃ have been investigated using small- and wide-angle neutron diffraction experiments. We have applied the reverse Monte Carlo modeling method to the experimental data with the aim to reveal the intermediate-range structure on a length scale of 5-50 A. The (AgI)_0.6-(Ag₂O-B₂O₃)_0.4 glass shows exceptionally high scattering intensity at low Q values (<0.5 A-1) due to the existence of chemical inhomogeneities on length scales up to at least 50 A. Both the salt ions and the network atoms are inhomogeneously distributed. The first diffraction peak, located at 0.46 A-1 in the total structure factor, is caused by a characteristic distance between B-O segments separated by salt ions. The LiCl-Li₂O-2B₂O₃ glass shows inhomogeneities only in the distribution of salt ions, where particularly the chlorine ions are very inhomogeneously distributed. The ion concentration fluctuations occur on a wide range of length scales. In contrast to the investigated borate glasses, the two phosphate glasses show only minor structural inhomogeneities on length scales above 10 A

[en] Gemini surfactants consist of two hydrophobic chains and two hydrophilic head groups covalently connected by a hydrophobic or hydrophilic spacer. This paper reports the small-angle neutron scattering (SANS) measurements from newly synthesized bis-cationic C₁₆H₃₃N⁺(CH₃)₂-CH₂-(CH₂-O-CH₂)_p- CH₂-N⁺(CH₃)₂C₁₆H₃₃,2Br^- gemini surfactants composed of hydrophilic polyethylene oxide spacer, referred to as 16-CH₂-p-CH₂-16,2Br^-, for spacer lengths p = 1-3. The micellar structures of these surfactant are compared with the earlier studied C₁₆,H₃₃N⁺(CH₃)₂-CH₂)_m-CH₂-N⁺ (CH₃)₂C₁₆H₃₃,2Br^- gemini surfactants composed of hydrophobic poly methylene spacer, referred to as 16-m-16,2Br^-. It is found that 16-CH₂-p-CH₂-16,2Br^- micelles are ellipsoidal for all the values of p 1-3. The micelles are however large in comparison to those of 16-m-16,2Br^-for similar spacer lengths. This is connected with the fact that in 16-CH₂-p-CH₂-16,2Br^- micelles the spacer is more hydrated as compared to that in the 16m-16,2Br^-. An increase in the hydration of the spacer increases the screening of the Coulombic repulsion between the charged head groups and the screening effect increases with an increase in the length of the hydrophilic spacer. (author)