PURPOSE:To improve the detection sensitivity and to simplify the detection method by using the correction members of specified structure. CONSTITUTION:A pair of correction members 7 are prepared. They consist of circular arc 7a equal to the outer circumference of CV cable 1, the material to be tested, and straight line part 7b. They posses a certain thickness in case perfectly fitted to CV cable 1, namely, the transmit routing length (2x) and are made of same material as the insulating layer of CV cable 1 or the material having the same line absorption coefficient for magnetic waves. And a pair of correction members 7 are arranged against the X-ray transmit route holding CV cable 1 between them off or in contact with, so as to make the straight line part 7b be perpendicular to the projecting X-ray. Thereby, when X-ray integrating sphere 4 and photomultiplier counter 6 are moved relatively against CV cable 1 and the defect detection is performed with the strength variation of transmit X-ray 5', then, the apparent transmit routing length can be easily made equal, thus, the expected purpose is attained.
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