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

In this new tube thermal electrons emitted from a hot

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a gas-filled discharge tube. In this new tube, thermal electrons emitted from a hot filament hit the target, which was an emission source of X-rays (1913) [8]. Following the investigation of the properties of X-rays by Barkla, Mose- ley studied characteristic X-rays in an exchange of communications with W.L. and W.H. Bragg. He put target samples into a gas-filled discharge tube, which were then irradiated with electrons for the generation of char- acteristic x-rays. The narrow collimated characteristic X-rays hit the cleaved surface of a K 4 Fe(CN) 6 · H 2 O crystal and the third-order lines of Bragg re- flection X-rays were obtained, which were shown in the famous photograph taken in 1913 [9]. Moseley elucidated the relationship between the character- istic X-rays and the measured elements, and communicated his experimental results to Bohr [10]. Siegbahn produced an X-ray spectrometer for a wider range of characteris- tic X-rays. He measured the wavelengths of characteristic X-rays precisely and classified them into α , β , γ . . . according to the X-ray intensities in the respec- tive series. X-ray spectroscopy was established with these works (1913–1923). In the next advances, Hadding tried to analyze rare earth elements using the X-ray method. His work was supported by Siegbahn. Due to the establishment of the structure of atoms, it became possible to predict the existence of elements that had yet to be discovered. This was based on the assumption that undiscovered elements belonging to the same family of elements in the periodic table have the same chemical features. In this respect, hafnium was isolated by von Hevesy and Coster (1923) [11] and rhenium by Noddack and Tacke with the support of Berg (1925). During the initial stage of the use of X-ray spectroscopy for chemical analysis, the samples being analyzed were modified (or even destroyed) when electron excitation was applied, leading to changes in the X-ray intensities. Hadding, Glocker, and Frohnmayer pointed out the analytical problems of inter-element effects in quantitative analysis. When electron excitation was used, Coster and Nishina noticed sample evaporation because of the induced heat in the sample (1925), and Glocker and Schreiber found concentration changes in the constituent elements (1928). For the emission of character- istic X-rays in X-ray spectrochemical analysis, the X-ray excitation method was adopted as a non-destructive analysis method. Although the relative dis- tance between the X-ray source and sample was reduced to increase the pri- mary X-ray intensity, the resultant X-ray intensity was still insufficient to be measured [12]. On the positive side background X-rays became lower and, as a result for quantitative analysis, low intensity peaks could be measured easily. For the measurement of X-ray intensities an ionization chamber or a pho- tographic plate had been used. Perrin invented the ionization chamber in 1896, which was used in Barkla’s works and adopted in Bragg spectrometers.
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  • Spring '14
  • MichaelDudley

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