[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

Many instrumental improvements led to high grade

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Many instrumental improvements led to high-grade medical treatment that was founded on the present X-ray machine [3]. On November 8, 1895, Wilhelm Conrad R¨ ontgen discovered X-rays in his laboratory at the physics institute of Julius-Maximilians University of W¨urzburg in Bavaria. He had studied cathode rays using an air-filled Hittorf- Crooks tube, which was shaded with a black paper. The tube wall was hit by electrons and emitted light. In his darkened room, he noticed a weak lumi- nescence which radiated from a fluorescent screen located near the tube. He recognized “eine neue Art von Strahlen” (a new type of rays), which originated from the tube. After changing the experimental and surrounding conditions, he was able to observe the emission of weak rays of light on the fluorescent screen. He announced the new experimental results. It was immediately recog- nized that this discovery might be used to look into the structure of a living human body and the interior of constructed materials [4, 5]. After the announcement by R¨ ontgen, two further important discoveries were made: radioactivity from uranium by Becquerel (1896) as well as radium and polonium by Marie and Pierre Curie (1898). Using an aluminum filter method for the separation of X-rays and an ion- ization chamber for X-rays detection, Barkla studied the nature of X-rays relative to the atomic structure. Observing the secondary X-rays which were radiated from a target sample, he discovered the polarization of X-rays (1906), the gaps in atomic absorption (1909), and the distinction between contin- uous and characteristic X-rays, which consisted of several series of X-rays, named the K, L, M . . . series (1911). The intensity and distribution of con- tinuous X-rays were dependent on the number of electrons in an atom, and the characteristic X-rays were related to the electron energy configuration in the atom [6]. In succession to Barkla’s works, the wave properties of X-rays were investigated by von Laue, who exhibited X-rays diffraction from a single crystal, which was composed of a three-dimensional structure with a regularly repeating pattern (1912). The experimental results showed the comparability of the wavelength of X-rays with the atomic distances and confirmed the wave properties of X-rays. W. H. Bragg, who derived the famous Bragg’s formula, was interested in von Laue’s experiments. Using a Bragg spectrometer, the X-ray reflection patterns from single crystals of NaCl and KCl were observed to be the regular patterns of an isometric system showing differences in the X-ray intensity when comparing sodium and potassium. This was the starting point of crystal structure analysis with X-rays [7]. For the expansion of radiographic technology, the need for a heavy-duty X-ray tube emerged. After the tungsten filament (1908) and the tungsten incandescent lamp (1911) were invented, Coolidge developed a new type of tube setting, successfully solving the problem of low power and instabilities of
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1 Introduction 3 a gas-filled discharge tube. In this new tube, thermal electrons emitted from a
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