A variable-geometry backscatter inspection system has a radiation detector array including one or more backscatter radiation detectors. The position of a second backscatter radiation detector is variable with respect to the position of a first backscatter radiation detector, so that the size of the detector array may be varied by moving the second radiation detector into or out of a predefined alignment with the first radiation detector. The system may include a movable base, and at least one of the detectors is movable with respect to the base. Methods of inspecting an object include forming a detector array by moving a second radiation detector into a predefined alignment with a first radiation detector, illuminating the object with a pencil beam of penetrating radiation, and detecting backscattered radiation with the detector array.