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The two-axis diffractometer SPN-100 at the Center of Accelerators and Nuclear Analytical Methods (CANAM) in Řež, is a neutron diffraction instrument dedicated to residual stress analyses in polycrystalline materials, it has recently been equipped with a new two-dimensional position sensitive detector (2D-PSD) and a six-axis robotic arm for sample positioning. Recent results of strain/stress distribution measurements with the upgraded tools are presented. The measured materials are made of C-Mn unalloyed steel used for spherical storage tank. Welding-induced residual stresses have direct influence on ductility and toughness of both weld metal and heat affected zone of the weld area, which affect the service life time of structures. Normal, transversal and longitudinal components of the stresses obtained in the vicinity of the butt weld from a spherical storage tank were measured by neutron diffraction at CANAM.

The neutron diffraction properties of a double-crystal (+n,-m) setting, which contains a bent perfect Si(311) crystal in the fully asymmetric diffraction (FAD) geometry with output beam expansion and a bent perfect Si(220) crystal in the symmetric diffraction geometry, are presented. Generally, there are two possibilities for the FAD geometry: either with output beam compression or with output beam expansion. In this case, attention has been focused on the latter. The properties of the (+n,-m) double-bent-crystal arrangement of a bent perfect crystal FAD Si(311) geometry, in combination with a bent Si(220) crystal slab in the symmetric diffraction geometry, were studied. It was found that, after beam expansion, this FAD geometry can provide a monochromatic beam of rather large cross section but very small divergence. [ABSTRACT FROM AUTHOR]

Residual strains measured by neutron diffraction near sample boundaries can be biased by the surface effect as a result of incomplete filling of the instrumental gauge volume. This effect is manifested as anomalous shifts of diffraction lines, which can be falsely interpreted as a lattice strain unless appropriate data corrections are made. A new analytical model for the surface effect has been developed, which covers a broad variety of instrumental arrangements, including flat mosaic and bent perfect crystal monochromators, narrow slits, and Soller and radial collimators. This model permits the spurious peak shifts to be predicted quantitatively, and also allows the optimum configuration parameters, such as curvature of a focusing monochromator, which lead to suppression of the surface effect, to be calculated. The model has been thoroughly validated by comparisons with Monte Carlo simulations and experiments on a stress-free calibration sample. Predictions of the model proved to be very accurate, often within the interval of experimental errors, which makes it suitable for use in data analysis. [ABSTRACT FROM AUTHOR]

Multiple Bragg reflections (MBRs), which can be realized in a bent perfect crystal (BPC) slab and are mutually in dispersive diffraction geometry, provide a monochromatic beam of excellent resolution. After identifying many MBR effects in a BPC Si crystal by using the method of θ-2θD scanning, we have turned our attention to the study of selected effects using the method of azimuthal rotation of the crystal lattice around the scattering vector of the primary reflection for a fixed chosen wavelength. In this paper, several azimuthal scans with the intention of possible practical exploitation for very high resolution diffractometry are presented. [ABSTRACT FROM AUTHOR]