Scanning instrument

摘要

A scanning apparatus 10 for measuring the attenuation of radiation passing through a pipe 12 comprises a source of radiation 18; at least one radiation detector 20 capable of detecting radiation emitted by said source; a data processor associated with said at least one radiation detector for calculating a property of material present in a linear radiation path 22 between said source and said detector; and a spacer 26, 28 arranged between said source and said at least one detector. The spacer defines a space which is capable of excluding water and has an average density which is less than 1 gcm-3. The provision of a spacer in the radiation path enables more radiation to be passed along the radiation path because water in a gap 24 can be replaced with a material which is less attenuating to radiation.