Abstract: A sensing apparatus including a plurality of sensing units having an energy source for transmitting a beam of electromagnetic radiation through a subject article and a detector for receiving the beam emerging from the subject article, and a controller, in which the detectors are arranged in a dispersed configuration, in which the sensing units include multiple groups. The controller sends a first activation signal to an individual group and a second activation signal to the next group at separate times and subsequent signals to further groups. In the dispersed configuration each detector of each group is spaced from each other detector of each other group a greater distance than it is spaced from the nearest detector of the next sequential group.