A method and device construction for detecting of hiding places with smuggled materials in the extremely heavy railway loads transporting iron ore by the means of neutron beam are disclosed. Upon the scanning of the iron ore load with neutrons the searched cavities or leaden containers with contraband are expressed by reducing of the flow of passing neutrons. The outline width of the scanned load is measured by dimension detectors. Values of differences between the scanned widths of the load and the outline widths are measures of the cavity dimensions with smuggled materials and said measures are included into the neutron radiographic image.