FIU CHM 4130 - CHAPTER 12_Xiao_X_Ray_Spectrometry_2018 (82 pages)

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Atomic X Ray Spectroscopy Chapter 12 X ray range 10 5 to 100 Used 0 1 to 25 Atomic X Ray Spectrometry Atomic X Ray Spectrometry Emission absorption scattering fluorescence and diffraction Emission absorption scattering fluorescence and diffraction Fundamentals Instruments Fundamentals X ray Fluorescence Instruments X rayFluorescence Absorption X ray X rayAbsorption diffraction X ray X ray diffraction 8 1 8 1 Making X rays 1 By bombardment of a metal target with a beam of high energy electrons 2 By expose of a substance to a primary beam of X rays to generate a secondary beam of Xray fluorescence 3 By use of a radioactive source whose decay process results in X ray emission 4 From a synchroton radiation source Formation of X Rays emission Bombardment of a metal target with a beam of high energy electrons Formation of X Rays fluorescence Exposure of a substance to x ray radiation absorption and then secondary fluorescence Formation of X Rays decay synchroton Radioactive decay X ray emission common in medicine Synchrotron source radiation accelerated particles very few of these available X Rays are just like any kind of electromagnetic radiation Two different atomic processes to produce X ray photons Bremsstrahlung K shell emission Bremsstrahlung braking radiation X rays are generated by interactions encountered by free electrons Tungsten is the best element a high melting point and a good heat conducting The same bremsstrahlung pattern for most of heavy elements A range of photons emitted X ray A simplified diagram of a water cooled X ray tube X ray tube emission Continuum Spectra Results from Collisions between the electrons and the atoms of target materials Ee E e h At o E e 0 h 0 hc o Ve V accelerating voltage e charge on electron 0 12 398 V Duane Hunt Law Independent of material Related to acceleration voltage E 0 K shell emission X rays are generated by electrons changing energy levels within an atom K shell knock out on Innermost electron K shell spectrum depends on the target element Line spectra is possible From electron transitions involving inner shells Atomic number 23 0 L 2 line series K and L E K EL Atomic number 23 K only Line Spectrum of a Molybdenum target A minimum acceleration voltage required for each element increases with atomic number Line spectra 0 Bohr s atomic model shell model X ray line labeling Electron Transitions X Rays 1 Transitions that involve the innermost atomic orbitals 2 Energy difference between the L and K levels that between the M and L levels 3 Energy difference between the transitions labeled 1 and 2 as well as those between 1 and 2 are so small single lines 4 Energy difference between the levels increase regularly with atomic number 5 Energy of characteristic X ray lines are independent of the physical and chemical state of the element Relationship between X ray emission frequency and atomic number for K 1 and L 1 Line spectra from fluorescent