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

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Even, WD-XRF has the advantage due to the resolution. If a peak is one tenth as wide it has one tenth the background. ED-XRF counters with filters and targets that can reduce the background intensities by a factor of ten or more. 4. Excitation Efficiency: Usually expressed in PPM per count-per-second (cps) or similar units, this is the other main factor for determining detection limits, repeatability, and reproducibility. The relative excitation efficiency is improved by having more source x-rays closer to but above the absorption edge energy for the element of interest. a. WDXRF generally uses direct unaltered x-ray excitation, which contains a continuum of energies with most of them not optimal for exciting the element of interest. b. EDXRF analyzers may use filter to reduce the continuum energies at the elemental lines, and effectively increasing the percentage of X-rays above the element absorption edge. Filters may also be used to give a filter fluorescence line immediately above the absorption edge, to further improve excitation efficiency. Secondary targets provide an almost monochromatic line source that can be optimized for the element of interest to achieve optimal excitation efficiency.
SECTION V SAMPLE PREPARATION XRF analysis is a physical method which directly analyses almost all chemical elements of the periodic system in solids, powders or liquids. These materials may be solids such as lass, ceramics, metal, rocks, coal, plastic or liquids, like petrol, oils, paints, solutions or blood. With XRF spectrometer both very small concentrations of very few ppm and very high concentrations of up to 100 % can directly be analyzed without any dilution process. Therefore XRF analysis is a very universal analysis method, which, based on simple and fast sample preparation, has been widely accepted and has found a large number of users in the field of research and above all in industry. The quality of sample preparation in X-ray fluorescence analysis is at least as important as the quality of measurements. An ideal sample would be prepared so that it is: • Representative of the material; • Homogeneous; • Thick enough to meet the requirements of an infinitely thick sample; • Without surface irregularities; • Composed of small enough particles for the wavelengths to be measured. The care taken to determine the best method of sample preparation for a given material, and the careful adherence to that method, will often determine the quality of results obtained. It is safe to say that sample preparation is likely the single most important step in an analysis. A wide variety of sample types may be analyzed by X-ray spectrometer; hence, a wide variety of sample preparation techniques is required (Figure V.1). Samples are often classified into two types based upon their thickness as measured by the attenuation of X-rays. Infinitely thick samples are those which completely attenuate Xrays emitted from the back side of the sample before they emerge from the sample. Further increase in the thickness yields no increase in observed X-ray intensity. Clearly, the critical value for infinite thickness will depend upon the energy of the emitted X-radiation and the mass absorption coefficient of the sample matrix for those X-rays. On the other hand, a thin sample has been defined as one in which m⋅µm ≤ 0.1, where m is the mass per unit area (g/cm 2 ) and µm is the sum of the mass absorption coefficient for the incident and emitted X-radiation. Although there are many advantages to thin samples, it is rarely feasible to prepare them for routine samples. Many samples fall between these two cases and require extreme care in preparation.
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X-Ray Fluorescence Analytical Techn
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II.4 Energy Resolution III. Spectru
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Module: Title: X-Ray Fluorescence A
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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
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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: When using other counting gases (Ne
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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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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