An assembly of components for constructing a bulk material analyzer of the type that is used to analyze bulk material transported on a conveyor belt through an activation region located in a tunnel between at least one radiation source and at least one radiation detector within the bulk material analyzer, said assembly comprising: a radiation-source box for disposition either above the activation region or below the conveyor belt; a radiation-detector box for disposition either below or above the radiation source box on the opposite side of the activation region and the conveyor belt from the radiation-source box; and characterised in that the assembly further comprises: a set of stackable structural beams (14, 15, 16, 17, 18, 19) predominantly containing radiation shielding material and configured for stacking about the activation region, the radiation-source box and radiation-detector box to prevent unwanted radiation being generated and transported to the radiation-detector box when said boxes (11, 12) are disposed on opposite sides of the activation region and the conveyor belt from each other; and a frame for supporting the ends of at least some of the structural beams (14, 15, 16, 17, 18, 19) when the beams (14, 15, 16, 17, 18, 19) are so stacked; wherein the frame is adapted for mounting on an existing conveyor support structure (34, 35, 36), without removing or substantially modifying any part of the existing conveyor support structure (34, 35, 36). a radiation-source box for disposition either above the activation region or below the conveyor belt; a radiation-detector box for disposition either below or above the radiation source box on the opposite side of the activation region and the conveyor belt from the radiation-source box; and characterised in that the assembly further comprises: a set of stackable structural beams (14, 15, 16, 17, 18, 19) predominantly containing radiation shielding material and configured for stacking about the activation region, the radiation-source box and radiation-detector box to prevent unwanted radiation being generated and transported to the radiation-detector box when said boxes (11, 12) are disposed on opposite sides of the activation region and the conveyor belt from each other; and a frame for supporting the ends of at least some of the structural beams (14, 15, 16, 17, 18, 19) when the beams (14, 15, 16, 17, 18, 19) are so stacked; wherein the frame is adapted for mounting on an existing conveyor support structure (34, 35, 36), without removing or substantially modifying any part of the existing conveyor support structure (34, 35, 36). a set of stackable structural beams (14, 15, 16, 17, 18, 19) predominantly containing radiation shielding material and configured for stacking about the activation region, the radiation-source box and radiation-detector box to prevent unwanted radiation being generated and transported to the radiation-detector box when said boxes (11, 12) are disposed on opposite sides of the activation region and the conveyor belt from each other; and a frame for supporting the ends of at least some of the structural beams (14, 15, 16, 17, 18, 19) when the beams (14, 15, 16, 17, 18, 19) are so stacked; wherein the frame is adapted for mounting on an existing conveyor support structure (34, 35, 36), without removing or substantially modifying any part of the existing conveyor support structure (34, 35, 36).