[en] Radial distributions of fast neutrons in aluminium, stainless steel, beryllium and water reflectors have been experimentally investigated. The experiments are conducted using a critical assembly consisting of one or three sections of a sectional type research and test reactor. The measurements have been carried out with ²³⁷Np fission chambers in cadmium sheath. Presented are basic parameters of the assemblies, experimental and calculated neutron relaxation lengths. The calculations are performed in terms of the Psub(I)-approximation using a one-dimensional 18-group code. The measurements have proved the additivity property of neutron fluences from several sources. The experimental lengths weakly depend on the core height and are in a good agreement with the calculated ones for the reflector materials