High-Energy Radiography in the 6- to 30-Mev Range

The dynamic interest in the radiography of very thick steel sections and solid rocket-propellant motors has become the basis for exploring in detail the radiographic characteristics of high-energy X-rays. Furthermore, new types of particle accelerators capable of producing X-rays in the multi-Mev region have become developed to practicality within the past few years (1–4). These two new factors, combined with the scattered and sketchy information on high-energy radiography in the literature, justify a consolidation of known data, corroboration of theoretical extrapolations, and reporting of new techniques of value in this particular field of radiography. This paper attempts to collect much of the available information of importance in the supervoltage and high-energy radiographic ranges. In addition, it is hoped that this report can form the third part of a series of papers discussing in detail the radiographic characteristics of 0.5 to 2.5-Mev X-rays (5), and of 2-to 6-Mev X-rays (6). The present paper will extend the same lines of reasoning into the 6- to 30-Mev X-ray range. In the 0.5- to 6-Mev range, the Van de Graaff and resonant transformer types of X-ray equipment have been capable of providing the intensity and penetrating power necessary for high-quality radiography in the steel thickness range up to 10 in. Above about 3 Mev, however, and for heavier steel sections, these two direct acceleration methods become impractical for flexible industrial use. In their stead, the betatron and microwave linear electron accelerator (linac) become the radiation producers of greatest practicality.