The radiography of polythene in submarine cable systems

Polythene is very transparent to X-rays, and unless it is several inches thick it requires special equipment for X-ray testing. An X-ray tube with a window of very low absorption is needed, so that radiation generated in the range 10¿20kV can be used. The performances of various types of tube have been investigated. Fluoroscopic inspection is unsuitable with such low operating voltages and film recording is much preferable. It gives considerably enhanced image contrast, allows critical inspection of the image with a lens, and provides a permanent record of the test. X-ray examination of joints in polythene submarine cable core and of cable-entry glands of submerged repeaters is illustrated. When these parts are being checked, exposures from various angles are required because in any one view some of the polythene is hidden by metal. It is desirable to make systematic tests from known angles and to record them side by side on a single film to help locate features of interest. An example of equipment designed for the field testing of cable joints is described.