In 1885, Wilhelm Conrad Röntgen, a German physicist, discovered x-rays, which are electromagnetic radiation with a wavelength range of 0.01-100 Å, corresponding to frequencies in the range of 30 PHz-300 EHz. Figure 5.1a denotes that the spectral range of electromagnetic waves and x-rays are longer than γ-rays but shorter than ultraviolet (UV) rays. Although x-rays cannot be seen because they have a shorter wavelength than visible light of about 400-700 nm, they have been used for diagnostic radiography and crystallography, covering an extremely wide area. When x-rays are applied to such materials as human bodies and steel, the intensity of transmitted x-rays is governed by the thickness and nature of the materials. The fracture position and the cracking of steels are therefore determined by radiographic examinations; results from such radiographic findings have been the most reliable basis for diagnosis. However, since x-rays have a harmful effect on body tissues, the x-ray path should be shielded with lead (Pb) and the amount of exposure should be measured by installing a dosimetry radiation badge containing x-ray-sensitive film. In fact, long-term overexposure to radiation may result in loss of hair, redness and inflammation of the skin, blood count change, cell atrophy, ulcerations, sterility, genetic damage, cancer, leukemia, and death. These types of biological damage depend on exposure dose, and sievert (Sv) is the SI-derived unit of dose equivalent. X-ray diffraction (XRD) performed at 45 kV and 30 mA is able to provide an exposure dose of about 1 Sv for 1 min. Hair loss and blisters may result from the exposure dose of about 1-3 and 5-12 Sv, respectively. Accordingly, proper safety precautions must be observed by all persons working in or near an area where x-rays are being generated.