Abstract :
To obtain maximum sensitivity of flaw detection in the radiographic examination of thick specimens encountered in heavy engineering, several aspects of the X-ray equipment must be considered. The most important factors are the energy of the radiation and the size of the source, while in order to obtain reasonably short exposure times a large X-ray output is required. The paper shows that, due to the complex process involved, the absorption of radiation at first decreases as energy is increased, but reaches a minimum and thereafter rises to some asymptotic value. The energy for minimum absorption depends on the absorbing substance, but for the materials used in engineering it will be some few MeV. Since the inherent unsharpness of the photographic image increases with energy, it can be shown that optimum results may be expected with equipment operating at an energy of the order of 4 MeV. The development of the travelling wave linear accelerator, which is briefly described, has made possible compact equipments to operate at such an energy, and the results of investigations into the suitability of such equipments for industrial radiography are given.
