A method and apparatus for performing a radiation scan of a structure involve arranging a source of penetrating radiation and a radiation detector at opposed ends of a radiation path through the structure, oriented in such a way that the source emits radiation along the path through the structure and the detector is capable of detecting the radiation after it has passed through the structure and monitoring the radiation emitted from the source that is detected by the detector. At least one continuous loop of a cable is mounted on the structure between at least two fixed locations on the structure so that the cable is movable along its length relative to the structure, and the at least one of the source of penetrating radiation and the radiation detector are fixed to the cable.