Single crystals were examined at approximately 100 kHz over the temperature range 4.2-300 K. The specimens were oriented near the centre of the stereographic triangle and were deformed in tension at 156 K and 450 K. Increasing the magnitude of the applied strain amplitude was found to increase the background damping in all specimens and to produce an alpha peak in some instances. The occurrence of the alpha relaxation peak was found to depend on the presence of an optimum dislocation configuration, internal stresses, and applied strain amplitude. The optimum dislocation configuration appears to be one of edge type segments present after small amounts of deformation and under the influence of locally high internal stresses. Other segments apparently achieve this or other optimum configurations after much larger amounts of plastic deformation when the overall internal stress level is higher. The results are interpreted in terms of the depinning of kinks trapped by point defects as the likely mechanism of the alpha peak.