Research group Analytical X-ray Physics X-ray Fluorescence Spectrometry Wolfgang
and BLiX
Team
Our Current Activities 3D Micro-XRF 3D Micro-XANES High resolution X-ray emission spectroscopy Characterisation of X-ray optics and sources Analytic for photovoltaics Laser-Plasma-Sources for the soft X-ray regime X-ray microscopy with laser-plasma-source Profesional courses fields of application: cultural heritage, solar cells, geology, bio-medical
X-rays as a probe
Selection rules and emission line energy shells quantum numbers n l j 1 0 1/2 K Kα1 Kα2 Kβ1 Kβ2 2 2 0 1/2 1 1/2 LIII 2 1 3/2 MI 3 3 3 0 1/2 1 1/2 1 3/2 MV selection rules l=± 1 j = 0, ± 1 satellites LI LII Kα2: Siegbahn Notation K-L3: IUPAC Notation
Outline - Survey on XRF Instrumentation and Methods - Quantitative X-ray Fluorescence Analysis - An Application of Micro-XRF
Scheme of a XRF-spectrometer detector source beam conditioner geometry
X-ray detectors Wavelength Dispersive Spectrometer - Crystal or multilayer source - proportional counter, scintillation counter detector - Quantitative analysis - Light element analysis beam conditioner Energy Dispersive Spectrometer - Solid state detector (Si, Ge) - Small, leightweight detectors (SDD, PIN)geometry - Qualitative and quantitative analysis - Range: (B) Na - U
X-ray sources Syncrotron radiation source - High brillance - Mikro/Nano-XRF (< 1µm) detector X-ray tubes - Micro focus X-ray tubes beam conditioner beam conditioner - Brillance optimised - Miniature X-ray tubes - Portable instrumentation (Handheld) geometry Other - Radioactive sources
Spectrometer geometry source Standard: Ψ 45 detector Gracing Incidence XRF - Surface sensitive Gracing Exit XRF beam conditioner - Surface sensitive Total reflection XRF geometry
Outline - Survey on XRF Instrumentation and Methods - Quantitative X-ray Fluorescence Analysis - An Application of Micro-XRF
Why is quantification an issue? Intensity plots for a 2-element sample 1. No matrix effects 2. Apsorption by matrix dominates 3. Absorption by analyte dominates 4. Analyte line is enhanced by matrix
Routes and Steps of Quantification Primärintensität Peakidentifikation Selbstabsorption Peaküberlagerung Leichte Matrix Untergrund Sekundärfluoreszenz Detektoreffekte n e tr n k e Sp uatio l a v e Spektrum Netto intensitäten Fun d Par ament ame ale ter M. Em p M. irische Zusammensetzung der Probe
Spectrum evaluation Spectra of solid state det. And of wavelength systems detail
Solid State Detectors spectrum fitting
Enhanced uncertainty due to overlap with escape peak
Routes and Steps of Quantification Primärintensität Peakidentifikation Selbstabsorption Peaküberlagerung Leichte Matrix Untergrund Sekundärfluoreszenz Detektoreffekte n e tr n k e Sp uatio l a v e Spektrum Netto intensitäten Fun d Par ament ame ale ter M. Em p M. irische Zusammensetzung der Probe
X-ray fluorescence intensity of bulk samples Complex radiation transport is simplified to primary fluorescence intensity + secondary fluorescence intensity
Sherman s approach for intensity calculation Equation di, monochromatic Ω dn i = wiε i 4 π Model for X-ray fluorescence production Integration over sample thickness µ S ( E0 ) ρx µ S ( Ei ) ρx τi ρdx jiωi pi N I 0 exp sin Ψ0 sinψ 0 sinψ det
Sherman s approach for intensity calculation Equation di, monochromatic Integration over excitation spectrum NIo Sample is flat and homogeneous τi N i = wi K i * N I 0 µi with µ = w * i j ( µ0 j j sinψ 0 + µ ij sinψ det )
Use of Sherman s equation for quantification wi = K iτ i N I0 µ i* Ni (1 + S i ) but µ = f (w ) * i Initial guess for w Iterative solution
Stratified materials Sketch primary intensity ( ) 1 exp µ Q N i = wi K i τ i N I0 * µi * i
Stratified materials Primary fluorescence intensity + intra-layer enhancenment + inter-layer enhancenment
Use of Sherman s equation What is the information depth of my sample? Is the homogeneity of my sample sufficient?
Information depth Equation di Definition effective mass absorption coefficient Example figures Definition of information depth: Half of the total intensity comes from above Simplifications: * Only consider attenuation of fluorescence line * 1/2 1/e Mean free path length 1/µρ is an estimate for the information depth
Information depth Equation di Definition effective mass absorption coefficient Example figures Mean free path in µm Fe Sn SiO2 (2 g/cm3) 70 3,500 O (1 g/cm3) 440 19,000
Calculation of transmission http://henke.lbl.gov/optical_constants/filter2.html
Sample inhomogeneity Respective LambertBeer equations exp( ( wa µ A + wb µ B )Q ) Use Q = exp( wa µ A Q ) exp( wb µ BQ ) exp( wa µ A Q ) + exp( wb µ BQ ) Q = ρd
Sample inhomogeneity particle size «particle mean free path length information depth» sample mean free path length
Routes and Steps of Quantification Primärintensität Peakidentifikation Selbstabsorption Peaküberlagerung Leichte Matrix Untergrund Sekundärfluoreszenz Detektoreffekte n e tr n k e Sp uatio l a v e Spektrum Netto intensitäten Fun d Par ament ame ale ter M. Em p M. irische Zusammensetzung der Probe
Empirical methods for quantification Standard addition, internal standard, etc. Fingerprint Influence coefficients method
Influence coefficients ( ) + m N (1 + m I ) wi = w0i + mi N i 1 + j α ij w j wi = w0i i i j ij j Best precision achievable (< 1%) Two reference materials per coefficient Applied in analysis of steel, gold, concrete production
Fin Part 1