X-Ray Fluorescence Analytical Techniques - CNSTN : Centre ...

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Figure I.10: Coherent scattering of an X-ray by an atom. III.7.4 Competitive Interactions The energy at which interactions change from predominantly photoelectric to Compton is a function of the atomic number of the material. The Figure I.11 shows this crossover energy for several different materials. At the lower photons energies, photoelectric interactions are much more predominant than Compton. Over most of the energy range, the probability of both decreases with increased energy. However, the decrease in photoelectric interactions is much greater. This because the photoelectric rate changes in proportion to (1/E 3 ), whereas Compton interactions are much less energy dependent. Figure I.11: Comparison of Photoelectric and Compton interaction rates for different materials and photon energies.
In higher atomic number materials, photoelectric interactions are more probable, in general, and they predominate up to higher photon energy levels. The conditions that cause photoelectric interactions to predominate over Compton are the same conditions that enhance photoelectric interactions, hat is, low photon energies and materials with high atomic numbers. III.8 <strong>Fluorescence</strong> Yield When an electron is ejected from an atomic orbital by the photoelectric process, there two possible results: X-ray emission, or Auger electron ejection (Figure I.12). One of these two events occurs for each excited atom, but not both. Therefore, Auger electron production is a process which is competitive with X-ray photon emission from excited atoms in a sample. The faction of the excited atoms which emits X-rays is called the Fluorescent yield. This value is a property of the element and the X-ray line under consideration. Figure I.13 shows a plot of X-ray fluorescent yield versus atomic number of the elements for the K and L lines. It is an unfortunate fact that low atomic number elements also have low fluorescent yield. Figure I.12: The excitation energy from the inner atom is transferred to one of the outer electrons causing it to be ejected from the atom (Auger electron). Figure I.13: Fluorescent yield versus atomic number for K and L lines.
Page 1 and 2: X-Ray Fluorescence Analytical Techn
Page 3 and 4: II.4 Energy Resolution III. Spectru
Page 5 and 6: Module: Title: X-Ray Fluorescence A
Page 7 and 8: very high resolution and X-ray phot
Page 9 and 10: where: c = speed of light (2.99782
Page 11 and 12: Figure I.2: Bohr’s atomic model,
Page 13 and 14: decelerated as they penetrate the m
Page 15 and 16: The mass attenuation coefficient ha
Page 17: e neglected provided that momentum
Page 21 and 22: Figure I.14: A Bremsstrahlung (Cont
Page 23 and 24: filters but more often with pulse h
Page 25 and 26: SECTION II ENERGY DISPERSIVE X-RAY
Page 27 and 28: just above the absorption edges of
Page 29 and 30: energy. Electronic noise is minimiz
Page 31 and 32: E is the photon energy, ε is the a
Page 33 and 34: IV.2 Compton Edge Figure II.8: Esca
Page 35 and 36: The relative error resulting from a
Page 37 and 38: Figure II.11: Schematic diagram of
Page 39 and 40: factor of 2, because also the refle
Page 41 and 42: IV. Instrumentation The major compo
Page 43 and 44: One of the inherent advantages in T
Page 45 and 46: Figure III.6: Sample preparation me
Page 47 and 48: III.1 gives an overview of various
Page 49 and 50: crystal mounted on a 2θ goniometer
Page 51 and 52: Figure IV.4: Collimators with diffe
Page 53 and 54: II.3.2 Reflections of Higher Orders
Page 55 and 56: Ge InSb PET AdP TIAP OVO-55 OVO-N O
Page 57 and 58: II.4.2 Scintillation Counters The s
Page 59 and 60: When using other counting gases (Ne
Page 61 and 62: SECTION V SAMPLE PREPARATION XRF an
Page 63 and 64: eground and pressed or cast as a di
Page 65 and 66: SECTION VI QUANTITATIVE ANALYSIS Th
Page 67 and 68: Cr 1.2 16 Sn 4.8 (Lα) 8 Mn 2.6 12
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The mechanism of the enhancement ef
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Mineralogical effect were discussed
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In general this equation is referre
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I. (The Photon Concept) EXERCICES A
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I. Solution SOLUTIONS An FM radio s
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charge = 15× 10 Cs second −3 -1
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