Critical scattering of neutrons by Fe: study of the hydrodynamic and critical regions

In the present work we describe the latest experiments on the critical magnetic scattering of neutrons by iron just above the Curie temperature, performed at the Centre d'Etudes Nucleaires at Saclay. In these experiments we have tried to explore the 'hydrodynamical region' as defined by the 'scaling laws' and to determine the temperature dependence of the diffusion constant. These experiments yield a verification of the recent theoretical calculations made by P. Resibois and C. Piette. These calculations and several measurements which we have conducted show the existence of an intermediate region between the 'critical' and the 'hydrodynamical' regions, which we call the 'quasi-hydrodynamical' region. In the hydrodynamical region, whose borders are well defined by the calculations of Resibois and Piette, our results confirm the theoretical predictions concerning this region. (author)