Scanning instrument

A sub-sea pipeline scanning apparatus for measuring the attenuation of gamma radiation passing from a source of gamma radiation along a radiation path through a sub-sea pipeline to a radiation detector comprising:

• a) the source of gamma radiation;
• b) the radiation detector, which is capable of detecting gamma radiation emitted by said source and passed through the sub-sea pipeline,
• wherein the sub-sea pipeline scanning apparatus is configured to rotate the source and the at least one radiation detector around the sub-sea pipeline while maintaining the source and the at least one radiation detector in a fixed relationship to each other;
• c) a data processor associated with said at radiation detector configured to calculate a property of a material present in a linear radiation path between said source and said radiation detector;
• wherein said sub-sea pipeline scanning apparatus further comprises:
• a first spacer mounted in a fixed relationship with respect to the source and positioned, between the source and the sub-sea pipeline to be scanned;
• and
• a second spacer mounted in a fixed relationship with respect to the radiation detector and positioned, between the radiation detector and the sub-sea pipeline;
• wherein said first and second spacers are rotatable around the sub-sea pipeline with the source and the radiation detector, and said first and second spacers each define a space which is capable of excluding water and have an average density which is less than 1 gcm−3.