ASNT

Yale University, in January 1896. This was quickly followed by X-ray work at other universities. Introduction of Additional Radiation Sources In 1898, Marie Sklodowska Curie (Figure 15) and her husband, Pierre Curie, published research showing the discovery of two new radioactive elements — polonium and radium — laying the foundation for gamma radiography. The early X-ray tubes were partially evacuated glass bulbs. Metal targets and curved cathodes were quickly added to increase X-ray output. Neverthe- less, it was a challenge to operate these early gas tubes consistently. The gas pressure changed because of outgassing of the walls and other heating effects. One of the first X-ray-related patents was for a technique of controlling the tube gas pressure (issued March 1896 to Siemens). Among the early uses of radioscopy, f luoroscopes (Figure 16) similar to those at today’s airports were used during World War I to inspect packages for contraband (St. John and Isenburger 1934). It was in this background that William D. Coolidge (Figure 17a) of General Electric introduced the hard vacuum, hot cathode X-ray tube, truly a significant advance in X-ray technology (ASNT 1944). This new X-ray tube concept brought much improved reproducibility and ease of operation to X-ray technology and prepared the way for high-energy X-ray use. The patent for this landmark X-ray development was issued in 1916 (Coolidge 1916).

X-RAYS FOR NONDESTRUCTIVE TESTING X-ray Diffraction Röntgen’s early X-ray work included unsuccessful attempts to show diffraction effects by directing the rays through a fine slit. This effect was successfully shown later following the 1909 work of Bernhard Walter and Robert Pohl (Ewald 1962). It was Max von Laue who first thought of using the regular order of a crystal to diffract X-rays. Experimen- tal confirmation of this now-important and widespread use of X-rays came from Laue’s work with Walter Friedrich and Paul Knipping (Friedrich, Knipping, and Laue 1912; Friedrich, Knipping, and Laue 1913) and from the pioneering work of the father and son Bragg team, composed of William Henry and William Lawrence Bragg (Bragg and Bragg 1913a; Bragg and Bragg 1913b). Now X-ray diffraction is a widely used to identify and analyze materials (Ewald 1962). Some idea of the impact that X-ray diffraction has had on science is given by noting that twenty Nobel physics prizes have been awarded for achievements in crystallography (Hasek 1989). Radiography Early advances in X-ray nondestructive testing were being made in many countries around the world. Documentation of early X-ray work in the United Kingdom and in Germany describes work going

Figure 16 Radioscopic system for detection of contraband (circa 1910).

Figure 15 Marie Sklodowska Curie (1928).

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Part 2