Analytical techniques based on photon-matter interactions

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Analytical techniques based on photon-matter
interactions
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Photon-matter interactions
IR-vis-UV molecular bonds

• No strict bondaries in between wavelength
  domains
• Inner electronic shells on light elements may be
  involved in molecular bonds
• Hard X-rays may reach either heavier elements
  inner electronic shells or lighter elements
  nucleii

X-rays inner electronic shells
g-rays nucleus
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Type of interactions

• Fluorescence
• Incident photon is absorbed. Target is excited.
  Target relaxes with emitting a new photon,
  usually with energy lost.
• Scattering
• Incident photon is deviated with energy lost
  (inelastic) or without energy lost (elastic)
• Resonance
• Photon is absorbed by target. Target is excited.
  Target relaxes through emission of a photon
  without energy lost. Emitted photon excites a
  neighbour of the target
• Absorption
• Incident photon is absorbed by the target. Photon
  flux after the target decreases. What happens
  during target relaxation is not of interest.
• Attenuation
• Incident photons do not reach detector behind the
  sample. Wether they are absorbed or not by the
  target is not of interest.
• Emission
• Target is excited by incident beam. Energy lost
  necessary for relaxation is done by emission of a
  particle (usually photon or electron)
• Interference
• Pattern due to addition or subtraction of two
  waves of identical wavelengths.

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Type of information accessible

• Molecular
• IR photon absorption
• Raman photon scattering
• UV fluorescence photon emission
• Atomic
• UV fluorescence photon emission
• X-ray fluorescence photon emission
• Auger electrons electron emission
• Photoelectrons electron emission
• Structural
• X-ray Absorption spectroscopy absorption
• Diffraction interference of scattered photons
  (elastic)
• Mössbauer nuclear resonance
• Density
• Compton scattering X-ray inelastic scattering
• Absorption imaging attenuation of incident beam
• Morphology
• Absorption imaging attenuation of incident beam
• Phase contrast imaging interference of
  transmitted beam

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X-ray attenuation
Elastic scattering
Photoelectric effect
Inelastic scattering
Pair creation
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XRD photon-matter interaction

• ACCD2d/sin(q)
• AB ADcos(q)
• 2d/tan(q)cos(q)
• 2d/sin(q)cos²(q)
• Phase shift ACAD-AB
• 2d/sin(q)(1- cos²(q))
• 2dsin(q)

• If phase shift nl ? photon contributions are
  added
• If phase shift nl/2 ? photon contributions are
  subtracted
• ? apparition of patterns for sample orientation
  at angles 2dsin(q) nl
• ? patterns can provide crystal plane distances

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Photoelectric effect and relaxation
Photoelectric effect
XRF
Transition probability
Auger
Atomic number
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Synchrotron radiation
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Synchrotron radiation

• Synchrotron facility
• A facility in which charged particles are
  orbiting at relativistic velocities, thus
  emitting electromagnetic waves each time they are
  deflected (lateral acceleration) to maintain
  their trajectory.
• Synchrotron radiation
• The radiation produced at deflection points.
• Synchrotron radiation facilities
• First generation synchrotron science was a
  by-product of bending magnets used in particle
  accelerators to maintain particles in their
  vacuum tube.
• Second generation were facilities designed to
  enhance synchrotron radiation using technologies
  developed for particle accelerators.
• Third generation are facilities use straight
  sections between bending magnets to produce
  radiation with wigglers or insertion devices.
• Future X-FEL, tabletop synchrotrons

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Brilliance
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Synchrotron radiation facility general layout
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Photon production
X-ray emission
Electrons injection and acceleration
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Bending magnet, wiggler, insertion device,
Bending magnet
Wiggler
Insertion device
Free electron laser
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Synchrotron radiation characteristics

• Photon emission is concentrated in a narrow cone
  centred on the tangent of the electron trajectory
  (isotropic in the electron coordinates)
• Photon emission covers a large electromagnetic
  spectrum
• Photons are polarised
• Synchrotron radiation is at most partially
  coherent. It is not a laser. Coherence has to be
  built using optical devices

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Synchrotron radiation based analytical techniques

• Virtually any technique based on photon-matter
  interactions
• FTIR (Fourier Transform Infra-Red)
• UV (Ultra Violet)
• Raman spectroscopy
• XRF (X-Ray Fluorescence)
• XRD (X-Ray Diffraction)
• XAS (X-ray absorption spectroscopy)
• Nuclear resonance
• Auger
• X-ray tomographies absorption, phase contrast,
  holography, topography,
• X-ray techniques privileged because X-rays
  cannot be conditioned with alternate sources
  monochromatization, focusing, divergence

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XRD experimental setup single crystal

• Single crystal turned in the beam to solve its
  structure
• Mainly required for protein studies

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XRD experimental setup microfocus

• Sample is put in the beam and diffraction
  pattern is recorded at a micrometer scale.
• 2D scans are possible to build diffraction maps

Powder diffraction-like data processing
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Data processing for XRD mapping
A pattern in each pixel
Sample
A diffractogram from each pattern
Several diffraction images
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Example coupled XRF XRD on sample from IODP
Ca
Fe
Br
One diffraction peak

• Thin section from oceanic gabbro sampled on the
  Mid-Atlantic Ridge Kane Fracture (MARK)
• In each pixel of the map
• A full fluorescence spectrum
• A diffraction pattern which is converted into a
  diffractogram
• Both type of data are taken in the same pixel
  (simultaneous techniques)
• Both techniques integrate the signal over the
  full sample thickness

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Full field imaging from 2D to 3D

• Reconstruction of 3D geometries with absorption
  images
• Web corner for understanding backprojection
  reconstructions
• http//www.colorado.edu/physics/2000/tomography/au
  to_rib_cage.html

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Full field imaging experimental setup
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Full field imaging case study

• Compaction of salt samples and porosity evolution
• Compaction (e) corresponds to a decrease of the
  volume of halitesolution.
• It decreases by 18.2 (compaction e) in 82.8h
• Porosity (grey parts) decreases with compaction
  (e)
• What about permeability?

Renard et al., Geophysical Research Letters, 31,
L07607 (2004)
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Full field imaging case study

• Grain indentation
• grains are displaced
• Strengthening of the halite skeleton

• Pore throat closure
• grains do not move
• Disconnection of porosity

Renard et al., Geophysical Research Letters, 31,
L07607 (2004)
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Full field imaging what if no contrast ?
Phase imaging
Absorption imaging

• z0 pure absorption
• Near field refraction creates interferences
  fringes enhancing edge between phases
• Fresnel region interferences fringes dominate
  and image loses resemblance with the object
• Fraunhofer region Fourier transform of the object

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Full field imaging what if no contrast ?
Ludwig, School on X-ray Imaging Techniques at the
ESRF, (2007) http//www.esrf.eu/events/conferences
/past-conferences-and-workshops/xray-imaging-schoo
l
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Synchrotron radiation strenghts in-situ

• Photons are no-mass no-charge particles
• ? Limited interactions with matter penetration
  in sample, windows,
• ? Sample container possible specific T and P
  conditions
• ? Gas filling control possible oxiding medium or
  hygrometric control
• ? Particularly adapted to in-situ experiments
  see previous example on salt compaction, see also
  Pascal Philippot talk

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Synchrotron radiation strengths multitechnique

• X-rays are hard to condition (energy selection,
  focusing, divergence,)
• ? Large devices required
• ? Long focal distances (cm to meters)
• ? Large space available around the sample
  compared to other techniques
• Very well adapted to combination of techniques.
  Without setup change it is possible to
• ? combine techniques (IODP example,
  XRFXASXRDimaging on fluid inclusions
  illustrated in next talk by Pascal Phillipot)
• ? Perform point analysis as well as imaging using
  pencil-beam

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Conclusions (1)

• Bright source
• Narrow divergence of the beam
• Large facility, space around the sample
• ? beam conditioning becomes possible
• Monochromatisation
• Focalisation (small divergent beam)
• Collimation (large parallel beam)
• Large facility, space around the sample
• Photons used as excitation beam penetrate easily,
  use of windows possible
• ? in-situ technique feasible
• Temperature or pressure conditions
• Controlled fluid medium (liquid, gas or vacuum)

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Conclusions (2)

• It is hard to be granted beamtime
• ? synchrotron has to be used when other
  techniques cannot be applied
• Sample preservation (laser-ablation, electron or
  particle probes)
• Detection limits (other X-ray sources)
• Spot size (other X-ray sources)
• Depth of penetration in the sample (electron or
  particle probes)
• ? usually no replicate can be measured

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Synchrotron radiation X-ray Fluorescence theory
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XRF

• Detailed principle
• Strength a limited number of possible X-ray
  lines, a number of tables for fluroescence
  cross-section calculations
• Fluorescence spectra deconvolution overlapping
  peaks, sum peaks, escape peaks, background
  signal, scattering peaks
• Quantifications, two main methods
• Fundamental parameters
• Monte-Carlo
• Heterogeneous samples multi-layer model
• Pencil beam mapping and fluorescence tomography

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XRF a relaxation mode of the photoelectric effect
Photoelectric effect
XRF
Transition probability
Auger
Atomic number
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XRF a relaxation mode of the photoelectric effect

• The fluorescence photon has a characteristic
  energy equal to the difference in energy of the
  initial and final orbital

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XRF allowed electronic transitions

• Quantum physics
• n principal quantum number
• l angular quantum number (n-1 to zero)
• m magnetic quantum number (-l to l)
• s spin quantum number (½)
• J total momentum of an electron l s
• Dn 1
• Dl 1
• DJ 0 or 1

• Each element has a limited number of X-ray line
• Each X-ray line energy is known
• A single line does not evolve with external
  conditions

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Irradiation detection requirements
XRF XRD XAS
Irradiation White to monochromatic White to monochromatic Monochromatic
Detection Multi channel of precise dE (EDX, WDX) No energy resolution (CCD camera) Single channel of large DE (Photodiode, EDX)
or
or
dE
dE
E
E
dE
DE
E
dEi
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Experimental setup
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Data analysis sum spectrum
A full fluorescence spectrum in each pixel

A sum spectrum for the entire image


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Data analysis calibration
From channels

• Each channel has an energy resolution of 10 eV
• Measured with a Gresham Si(Li) solid state
  detector (EDX)

to keV
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Data analysis peak identification
Fluorescence line energies in eV
http//xdb.lbl.gov/xdb.pdf
Analysis performed with EDX detector of 140 eV
resolution
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Data analysis ROI imaging
As-Ka Pb-La
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Data analysis spectrum fitting

• Fluorescence peaks
• Background
• Scattering
• Escape peaks
• Pile-up peaks
• Detector response
• ? various fitting programs PyMca, Axil, Gupix,
  GeoPIXE (soon),
• ? Example with PyMca freeware
• download http//pymca.sourceforge.net/
• Ref for publications Solé, et al., Spectrochim.
  Acta Part B 62 (2007) 63-68.

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Data analysis imaging with fitted spectra
As-Ka Pb-La
As-Ka
Pb-La
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Qualitative analysis ROI vs. Peak fitting
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Are XRF signal and concentration proportional?

• Regions of interest provide qualitative data if
  no peak overlap.
• Regions of interest may be misleading if peak do
  overlap
• Concentrations cannot be calculated from regions
  of interest, peak area are required
• Peak area is proportional to elemental
  concentration provided
• No detector saturation
• Measurements are corrected from absorption
• Measurements are corrected from secondary and
  higher order fluorescence
• Internal geometry of the sample can be
  approximated using a multilayer model

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Heterogeneous samples multilayer approximation
Rock
Fluid inclusion
Capillary
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Quantification two families of procedures

• Fundamental parameters peak area are used to
  calculate concentrations in taking into account
  all absorption corrections inside the sample
• Monte-Carlo simulations from the sample
  geometry, beam characteristics, detector response
  and a first guess in sample composition, a
  spectrum is simulated. The result of the
  simulation is compared to the measured spectrum
  to better estimate concentrations.

Sherman, Spectrochimica Acta, 7 283-306
(1955) Sherman, Spectrochimica Acta, 15 466
(1959) Lachance and Claisse , Quantitative X-ray
fluorescence analysis. Theory and application
(1995)
Gardner and Hawthorne, X-ray spectrometry, 4,
138-148 (1975) Vincze et al., Spectrochimica Acta
part B, 48, 553-573 (1993) Vincze et al.,
Spectrochimica Acta part B, 50, 127-148
(1995) Vincze et al., Analytical Atomic
Spectrometry, 14, 529-533 (1999) Vekemans et al.,
NIM B, 199 396-401 (2003)
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Fundamental parameters
Peak areas
Detector efficiency
Fluorescence reaching the detector
Absorption from sample to detector
Fluorescence exiting the sample
Absorption in the sample
Fluorescence generated in the sample
Incident flux Absorption of incident photons in
the sample Fluorescence cross-sections Sample
geometry
Concentrations
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Monte-Carlo
Incident flux Beam characteristics Sample geometry
Estimation of the sample composition
Modelling of photons trajectories and
interactions with matter in the sample and on the
way to the detector
Detector response
Simulation of a fluorescence spectrum
Fitting
Iterations
Simulated peak areas
Measured peak areas
D areas
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HT-HP cells a multilayer sample

• Above simplified equation valid if
• No secondary or higher order fluorescence
  (diluted sample)
• Windows do not contain elements that have to be
  quantified in the sample
• Sample is homogeneous
• Windows are homogeneous

Ménez et al., Modern Research and Educational
Topics in Microscopy, accepted
50
HT-HP cells a multilayer sample
Incident monochromatic flux
Solid angle of detection
Efficiency of the detector at the energy of the
fluorescence line
Fluorescence cross section of the target element
Density of the sample
Ménez et al., Modern Research and Educational
Topics in Microscopy, accepted
51
HT-HP cells a multilayer sample
absorption of incident X-rays in top window
absorption of incident X-rays in the sample
absorption of fluorescent X-rays in exit window
absorption of fluorescent X-rays in the sample
Ménez et al., Modern Research and Educational
Topics in Microscopy, accepted
52
HT-HP cells a multilayer sample
Ménez et al., Modern Research and Educational
Topics in Microscopy, accepted
53
HT-HP cells a multilayer sample
Ménez et al., Modern Research and Educational
Topics in Microscopy, accepted
54
Fluorescence mapping depth issue

• Fluorescence mapping provides qualitative maps of
  elemental distributions.
• Quantitative maps can be calculated demanding in
  time and computer resource. Geometrical and
  density parameters must be known or approximated
  in each pixel
• Mapping do not discriminate deep and surface
  contributions photons penetrate deeply in the
  sample

? Depth location problem solved using
fluorescence tomography
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Fluorescence tomography geometrical solution
Ca-rich solid inclusion in diamonds from mantle
xenoliths
3D Sr, Th, Y/Zr image

• Using focused detection with a microbeam,
  fluorescence is detected from a well defined
  volume (5 to 15mm in each dimension)
• Motor position help positioning fluorescence
  signal in the sample
• Reconstructing from the sample surface enables
  correcting for absorption with increasing depths

Vincze et al., Anal. Chem 76, 6786-6791
(2004) Brenker et al., EPSL 236, 578-587
(2005) Susini, School on X-ray Imaging Techniques
at the ESRF, (2007) http//www.esrf.eu/events/conf
erences/past-conferences-and-workshops/xray-imagin
g-school
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Fluorescence tomography computed solution

• Use of backprojection algorithms developped for
  computed tomography
• Absorption corrections require much more
  complicated data treatment
• Combination of techniques usually necessary
• Absorption tomography sample internal geometry
• Compton tomography sample internal density for
  light element contributions to fluorescence
  absorption
• Fluorescence tomography elemental repartitions
  inside the sample

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Sinograms helical scannig
Sinograms Si Ge As Rb
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From sinograms tp 3D imaging
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Conclusions

• Technique allows 1D, 2D or 3D quantitative
  analysis. 3D imaging program now available at a
  user friendly level
• Sample preparation is minimal operation in air
  or any medium
• Technique allows installation of space consuming
  devices for controlled PTX conditions
• Fluorescence is compatible with a wide range of
  other techniques (X-ray absorption, X-ray
  absorption spectroscopy, X-ray diffraction,
  Compton,) and benefits from these complementary
  data
• Quantitative analysis requires inputs from
  experts users and use of specific programs
• A freely available software (PyMca) provides
• Spectrum fitting
• Batch fitting
• ROI imaging
• Non-iterative fundamental parameters based
  quantification
• Focalisation (small divergent beam)
• Collimation (large parallel beam)
• Same program should provide in the near future
• Monte-Carlo quantification plugins
• Iterative fundamental parameters quantification