ULTRA SMALL-ANGLE SCATTERING OF NEUTRONS FROM VANADIUM HYDROGEN SYSTEMS

Perfect crystal small-angle scattering with channel-cut crystals is used for investigations of the alpha <-- --> (alpha + beta) phase transition in V-H and V-D systems. Characteristic hysteresis effects of several degrees are observed between the heating and cooling cycles. The thickness of the plate-shaped hydride precipitates is of the order of mu-m. From the beam attenuation in the forward direction, the total scattering cross section is deduced. It can be described by an anisotropic harmonic oscillator model for the motion of hydrogen and deuterium in the vanadium lattice.