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

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II.3.3 Crystal Types Figure IV.8: Second order reflection (n = 2). The wavelength dispersive X-ray fluorescence technique can detect every element above the atomic number 4 (Be). The wavelengths cover the range of values of four magnitudes: 0.01 – 11.3 nm. As the angle θ can theoretically only be between 0° and 90° (in practice 2° to 75°), sinθ an only accept values between 0 and +1. When Bragg’s equation is applied: nλ 0< = sinθ
Ge InSb PET AdP TIAP OVO-55 OVO-N OVO-C OVO-B Germanium Indiumantimonide Pentaerythite Ammoniumdihydrogenphosphate Thalliumhydrogenphthalate Multilayer [W/Si] Multilayer [Ni/BN] Multilayer [V/C] Multilayer [Mo/B4C] II.3.4 Dispersion, Line Separation P, S, Cl Si Al – Ti Mg F, Na O – Si (C) N C B (Be) 0.653 0.7481 0.874 1.0648 2.5760 5.5 11 12 20 The extent of the change in angle ∆θ upon changing the wavelength by the amount ∆λ (thus: ∆θ/∆λ) is called “dispersion”. The greater the dispersion, the better is the separation of two adjacent or overlapping peaks. Resolution is determined by the dispersion as well as by surface quality and the purity of the crystal. Mathematically, the dispersion can be obtained from the differentiation of the Bragg equation: ∆θ n = ∆λ 2dcosθ . (IV.4) It can be seen from this equation that the dispersion (or peak separation) increases as the lattice plane distance ‘d’ declines. II.3.5 Synthetic Multilayers Multilayers are not natural crystals but artificially produced ‘layer analyzers’. The lattice plane distances ‘d’ are produced by applying thin layers of two materials in alternation on to a substrate (Figure IV.9). Multilayers are characterized by high reflectivity and a somewhat reduced resolution. For the analysis of light elements the multilayer technique presents an almost revolutionary improvement for numerous applications in comparison to natural crystals with large lattice plane distances (e.g. RbAp, PbST, KAP). Figure IV.9: Diffraction in the layers (here: Si/W) of a multilayer.
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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 and 18: e neglected provided that momentum
Page 19 and 20: In higher atomic number materials,
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: II.3.2 Reflections of Higher Orders
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
Page 69 and 70: The mechanism of the enhancement ef
Page 71 and 72: Mineralogical effect were discussed
Page 73 and 74: In general this equation is referre
Page 75 and 76: from sugar, but then this involved
Page 77 and 78: I. (The Photon Concept) EXERCICES A
Page 79 and 80: I. Solution SOLUTIONS An FM radio s
Page 81 and 82: charge = 15× 10 Cs second −3 -1
Page 83: h ∆λ = ( 1 − cosθ ) = 2λ c =
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