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During residual stress measurements by neutron diffraction additional information becomes available through the accompanying high-energy prompt capture gamma radiation, which in turn produces positrons within the bulk of the specimen. Plastic deformation will increase the dislocation density within the material. This leads to an increase in the mosaic spread of the diffraction reflections and to changes of the lineshape of the positron annihilation radiation. The correlation between the width of the Bragg reflections and the S-parameter, which describes the shape variation of the annihilation line was investigated as a function of the degree of plastic deformation. The experimental work was performed at the FRG-I research reactor of GKSS.

A tensile specimen was machined from heat treated ferritic steel, with a small volume fraction of carbon in the form of cementite. In situ measurements of the strain response of multiple hkl lattice planes to an applied uniaxial tensile load were made using neutron diffraction, to macroscopic plastic strains of around 3%. The experimental results are compared with predictions from a self-consistent Hill–Hutchinson model modified to take into account the presence of the second phase. Good agreement was obtained between model and experimental data. The interpretation of residual stress measurements, for both single peak and Rietveld measurements is considered in light of these results.

The influence of phase errors on the accuracy of the neutron diffraction peak parameters is discussed. It is shown that a constant phase error leads to both a distortion of the shape and a shift of the center of gravity of a reflection peak. A method was developed which takes the phase error into account and corrects for the peak shift.

Three different modes of operation have been realized for the Fourier-RTOF diffractometer FSS at the GKSS Research Center which produce peak shapes that are either a Gaussian or the first or second derivative of it. The triangular shape of the modulation function of the neutron intensity as well as the rectangular shape of the optical pickup signal cause deviations from the ideal shapes of the reflection peaks. Distortions caused by the constraints on the upper limit of the modulation frequency cause specific oscillations, which are superimposed on the diffraction peaks. The characteristic properties of the three modes of operation are discussed.

The quality of a neutron time-of-flight diffractometer can be significantly improved by setting up its detectors in time-focusing geometry. In order to fully exploit the time-focusing method, the nominal resolution of the spectrometer must be thoroughly investigated by analysing the contributions of several different factors. In this paper analytic formulae are given, which describe the different components contributing to the resolution function and the conditions which optimize the resolution are derived. It is shown how the analytic integral equations can be solved numerically. The programs allow iterative computations to optimize a detector system composed of many individual detector elements, considering the specimen size and instrumental resolution. The flow diagram of the programs to calculate numerically the detector system is briefly discussed and the precision of the individual optimal detector position coordinates is given.

The first successful application of a new method to investigate phase transformations in real time, like the decomposition of austenite into bainite in grey iron, is described. During the ongoing transformation, transmission spectra of thermal neutrons, which contain Bragg edges corresponding to the crystal structure of the transforming phases, are recorded. By evaluating the height of these Bragg edges, which is a measure of the volume fraction of the phase, at different transformation times, the transformation can be followed in-situ in a time resolved manner. The method is compared to other previously used methods (micrographs, dilatometry, diffraction techniques); also a summary and an outlook are given.

Integrated substructure analysis in polycrystals is often based on the interpretation of physical diffraction-line broadening. In the present work the case of high-resolution neutron diffraction by means of RTOF is considered in comparison with the angular-dispersive neutron diffractometry. First experimental results indicate that RTOF can successfully be used for the determination of physical line-broadening.

Low-energy neutron transmission diffraction has been successfully demonstrated to be a powerful experimental method to investigate changes in crystal structure development down to the millisecond range. Bragg edge diffraction measurements thus can be the basis for future experiments like strain radiography, determination of the strain-rate dependent elastic properties of engineering materials, temporal development of phase changes, structural properties of materials under extreme environmental conditions like high pressure or temperature states. At high instantaneous neutron bursts current-mode detection can be used, which enables both transient and stroboscopic measurements. Progress has been made in rapid data acquisition and analysis as well as temperature measurement by resonance doping.

The Kiel University fast-chopper has been simulated by a Monte Carlo model taking into account the geometric outlines of the system, neutron leakage through rotor edges and neutron beam divergence. The calculated results have been verified by experimental investigations. Special emphasis was laid on the very sensitive dependence of the measured neutron time-of-flight spectra on the rotor displacement from the collimator axis, which is also well reproduced by the calculations. Therefore the model is regarded to be authentic to derive a better estimate for the resolution function of the spectrometer, which is needed for measurement tasks like neutron resonance spectroscopy and shape analysis. The FORTRAN programs permit achievement of the best spectrometer adjustment to a given experimental problem. They may be modified to calculate different system geometries.

A lithium glass detector bank for the fast chopper facility at the Geesthacht research reactor (FRG-1) is described.