XRF X-RAY FLUORESCENCE EMISSION -THEORY AND APPLICATION

1. Introduction to XRF
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Introduction toIntroduction to
X-RayX-Ray
FluorescenceFluorescence
AnalysisAnalysis

2. Introduction to XRF
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DR. HARSH MOHAN
DEPARTMENT OF PHYSICS
M.L.N. COLLEGE
YAMUNA NAGAR
(HARYANA

3. Introduction to XRF
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Electromagnetic Radiation
1Hz - 1kHz 1kHz - 1014Hz
1014Hz - 1015Hz
1015Hz - 1021Hz
Extra-Low
Frequency
(ELF)
Radio Microwave Infrared
Visible Light
X-Rays,
Gamma Rays
Ultraviolet
Low energy High energy

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Theory
 A source X-ray strikes an
inner shell electron. If at
high enough energy (above
absorption edge of
element), it is ejected it
from the atom.
 Higher energy electrons
cascade to fill vacancy,
giving off characteristic
fluorescent X-rays.
 For elemental analysis of
Na - U.

5. Introduction to XRF
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6. Introduction to XRF
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How can we create core holes?
•X-rays, Electrons, Ions whichX-rays, Electrons, Ions which
have higher energy than the corehave higher energy than the core
electron ionization energies.electron ionization energies.
•Electrons and ions produces manyElectrons and ions produces many
peaks with multiple excitations. X-peaks with multiple excitations. X-
ray excitation is preferable.ray excitation is preferable.
•Now, X-ray fluorescence analysisNow, X-ray fluorescence analysis
by X-ray excitation is a standardby X-ray excitation is a standard
technique for trace elementtechnique for trace element
analysisanalysis

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The Hardware
• SourcesSources
• OpticsOptics
• Filters & TargetsFilters & Targets
• DetectorsDetectors

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Sources
•X-Ray Tubes
•Radioisotopes
•Other Sources
–Scanning Electron Microscopes
–Synchrotrons
–Positron and other particle beams

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X-Ray Tubes
•X-ray tubes work on the principle:
• Accelerating electrons in an electrical field
and decelerating them in a suitable anode
material.
•The region of the electron beam in which
this takes place must be evacuated in order
to prevent collisions with gas molecules.
• Hence there is a vacuum within the
housing

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•The technical means of achieving this is
to apply high voltage between a heated
cathode (e.g. a filament) and a suitable
anode material.
• Electrons emanate from the heated
cathode material and are accelerated
towards the anode by the applied high
voltage
X-Ray Tubes

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X-Ray Tubes
• They strike the anode material and lose their
energy through deceleration.
• Only a small proportion of their energy loss
(approx.1-2%, depending on the anode material)
is radiated in the form of X-rays.
•The greatest amount of energy contributes to
heating up the anode material.
• Consequently the anode has to be cooled which
is achieved by connection to a water-cooling
system.

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X-Ray Tubes
•The proportion of the electron energy loss
emitted in the form of an X-ray can be between
zero and the maximum energy that the electron
has acquired as a result of the acceleration in the
electrical field
•The X-rays escape from the housing at a
special point that is particularly transparent
with a thin beryllium window

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Side Window X-Ray Tube

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•In side-window tubes, a negative high voltage is
applied to the cathode.
•The electrons emanate from the heated cathode
and are accelerated in the direction of the anode.
•The anode is set on zero voltage and
thus has no difference in potential to the
surrounding housing material and the laterally
mounted beryllium exit window
Side Window X-Ray Tube

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Side Window X-Ray Tube
• For physical reasons, a proportion of the electrons
are always scattered on the surface of the anode.
• The extent to which these backscattering electrons
arise depends, among other factors, on the anode
material and can be as much as 40%.
•In the side-window tube, these backscattering
electrons contribute to the heating up of the
surrounding material, especially the exit window.

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Side Window X-Ray Tube
•As a consequence, the exit window must withstand
high levels of thermal stress and cannot be selected with
just any thickness.
•The minimum usable thickness of a beryllium window
for side-window tubes is 300 μ m.
•This causes an excessively high absorption of the low-
energy characteristic L radiation of the anode material in
the exit window .
•Thus a restriction of the excitation of lighter elements
in a sample.

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End Window X-Ray Tube

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End Window X-Ray Tube
•The distinguishing feature of the end-window tubes is that
the anode has a positive high voltage and the beryllium exit
window is located on the front end of the housing
•The cathode is set around the anode in a ring (annular
cathode) and is set at zero voltage. The electrons emanate
from the heated cathode and are accelerated towards the
electrical field lines on the anode.
•Due to the fact that there is a difference in potential between
the positively charged anode and the surrounding material,
including the beryllium window, the backscattering electrons
are guided back to the anode and thus do not contribute to the
rise in the exit window’s temperature.

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End Window X-Ray Tube
•The beryllium window remains “cold” and can therefore be
thinner than in side-window tubes. Windows are used with a
thickness of 125 μm and 75 μm.
• This provides a prerequisite for exciting light elements with
the characteristic L radiation of the anode material (e.g.
rhodium).
•Due to the high voltage applied, non-conductive, de ionized
water must be used for cooling. Instruments with end-window
tubes are therefore equipped with a closed, internal circulation
system containing deionized water that cools the tube head as
well.

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Duane–Hunt law
•The Duane–Hunt law, named after the
American physicists William Duane and
Franklin Hunt
• It gives the maximum frequency of X-
rays that can be emitted by
Bremsstrahlung in an X-ray tube by
accelerating electrons through an
excitation voltage V into a metal target.

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Duane–Hunt law
•In an X-ray tube, electrons are accelerated in a vacuum by
an electric field and shot into a piece of metal called the
"target". X-rays are emitted as the electrons slow down
(decelerate) in the metal.
• The output spectrum consists of a continuous spectrum of
X-rays, with additional sharp peaks at certain energies
•The continuous spectrum is due to bremsstrahlung, while
the sharp peaks are characteristic X-rays associated with
the atoms in the target.

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Characteristic X-RaysBremsstrahlung X-Rays and

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Duane–Hunt law
•The maximum frequency νmax is given by
which corresponds to a minimum wavelength

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Duane–Hunt law
where h is Planck's constant, e is the charge of the
electron, and c is the speed of light. This can also be
written as:
The process of X-ray emission by incoming electrons is
also known as the inverse photoelectric effect.

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X-ray tube emission
λ0
λ0 = 12,398/V
Duane-Hunt Law
•Independent of material
•Related to acceleration
voltage  E
Continuum Spectra: Results from
Collisions between the electrons and the
atoms of target materials
Ee = E’e + hν
At λo, E’e = 0
hν0 = hc/λo = Ve
V: accelerating voltage
e: charge on e-

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Line spectra is possible!
Line Spectrum of a Molybdenum target
λ0
•Atomic number>23
•2 line series K and L ,
E K> EL
Atomic number < 23 ,K
only
L
From electron transitions
involving inner shells
A minimum acceleration voltage required for each element increases
with atomic number
λ0

27. Introduction to XRF
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Radioisotopes
Isotope Fe-55 Cm-244 Cd-109 Am-241 Co-57
Energy (keV) 5.9 14.3,
18.3
22, 88 59.5 122
Elements (K-
lines)
Al – V Ti-Br Fe-Mo Ru-Er Ba - U
Elements (L-
lines)
Br-I I- Pb Yb-Pu None none
 While isotopes have fallen out of favor they are still useful for
many gauging applications.

28. Introduction to XRF
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Other Sources
Several other radiation sources are capable of
exciting material to produce x-ray fluorescence
suitable for material analysis.
Scanning Electron Microscopes (SEM) – Electron beams excite the
sample and produce x-rays. Many SEM’s are equipped with an EDX
detector for performing elemental analysis
Synchotrons - These bright light sources are suitable for research
and very sophisticated XRF analysis.
 Positrons and other Particle Beams – All high energy particles
beams ionize materials such that they give off x-rays. PIXE is the
most common particle beam technique after SEM.

29. Introduction to XRF
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Source Modifiers
Several Devices are used to modify the shape
or intensity of the source spectrum or the
beam shape
 Source Filters
 Secondary Targets
 Polarizing Targets
 Collimators
 Focusing Optics

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Source Filters
Filters perform one of two functions
–Background Reduction
–Improved Fluorescence
DetectorDetector
X-RayX-Ray
SourceSource
Source FilterSource Filter

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Filter Transmission Curve
%
T
R
A
N
S
M
I
T
T
E
D
ENERGY
Low energy x-rays
are absorbed
Absorption
Edge
X-rays above the absorption
edge energy are absorbed
Very high energy
x-rays are transmitted
Ti Cr
Titanium Filter transmission curve
The transmission curve shows the parts of the source
spectrum are transmitted and those that are absorbed

32. Introduction to XRF
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Filter Fluorescence Method
ENERGY (keV)
Target peakWith Zn Source filter
Fe
Region
Continuum
Radiation
The filter fluorescence method decreases the background and
improves the fluorescence yield without requiring huge amounts of
extra power.

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Filter Absorption Method
ENERGY (keV)
Target peak
With Ti Source filter
Fe
Region
Continuum
Radiation
The filter absorption Method decreases the background while
maintaining similar excitation efficiency.

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Secondary Targets
Improved Fluorescence and lower background
The characteristic fluorescence of the custom line
source is used to excite the sample, with the
lowest possible background intensity.
It requires almost 100x the flux of filter methods
but gives superior results.

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Secondary Targets
Sample
X-Ray Tube
Detector
Secondary Target
A. The x-ray tube excites the secondary target
B. The Secondary target fluoresces and excites the
sample
C. The detector detects x-rays from the sample

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Secondary Target Method
ENERGY (keV)
Tube
Target
peak
With Zn Secondary
Target
Fe
Region
Continuum
Radiation
Secondary Targets produce a more monochromatic
source peak with lower background than with filters

37. Introduction to XRF
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Secondary Target Vs Filter
Comparison of optimized direct-filtered excitation with secondary
target excitation for minor elements in Ni-200

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Polarizing Target Theory
a) X-ray are partially polarized whenever they scatter off a
surface
b) If the sample and polarizer are oriented perpendicular to
each other and the x-ray tube is not perpendicular to the
target, x-rays from the tube will not reach the detector.
c) There are three type of Polarization Targets:
– Barkla Scattering Targets - They scatter all source energies
to reduce background at the detector.
– Secondary Targets - They fluoresce while scattering the
source x-rays and perform similarly to other secondary
targets.
– Diffractive Targets - They are designed to scatter specific
energies more efficiently in order to produce a stronger peak
at that energy.

39. Introduction to XRF
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Collimators
Collimators are usually circular or a slit and restrict the size or
shape of the source beam for exciting small areas in either
EDXRF or uXRF instruments. They may rely on internal
Bragg reflection for improved efficiency.
Sample
Tube
Collimator sizes range from 12
microns to several mm

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Focusing Optics
Because simple collimation blocks unwanted x-rays
it is a highly inefficient method. Focusing optics like
polycapillary devices and other Kumakhov lens
devices were developed so that the beam could be
redirected and focused on a small spot. Less than 75
um spot sizes are regularly achieved.
Source Detector
Bragg reflection
inside a Capillary

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Detectors
• Si(Li)
• PIN Diode
• Silicon Drift Detectors
• Proportional Counters
• Scintillation Detectors

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Detector Principles
2
E
n
e
n = number of electron-hole pairs produced
E = X-ray photon energy
e = 3.8ev for Si at LN temper
where :
atures
=
A detector is composed of a non-conducting or semi-conducting
material between two charged electrodes.
X-ray radiation ionizes the detector material causing it to become
conductive, momentarily.
The newly freed electrons are accelerated toward the detector
anode to produce an output pulse.
In ionized semiconductor produces electron-hole pairs, the
number of pairs produced is proportional to the X-ray photon
energy

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Si(Li) Detector
Window
Si(Li)
crystal
Dewar
filled with
LN2
Super-Cooled Cryostat
Cooling: LN2 or Peltier
Window: Beryllium or Polymer
Counts Rates: 3,000 – 50,000 cps
Resolution: 120-170 eV at Mn K-alpha
FET
Pre-Amplifier

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Si(Li) Cross Section

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PIN Diode Detector
Cooling: Thermoelectrically cooled (Peltier)
Window: Beryllium
Count Rates: 3,000 – 20,000 cps
Resolution: 170-240 eV at Mn k-alpha

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Silicon Drift Detector- SDD
Packaging: Similar to PIN Detector
Cooling: Peltier
Count Rates; 10,000 – 300,000 cps
Resolution: 140-180 eV at Mn K-alpha

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Proportional Counter
Anode Filament
Fill Gases: Neon, Argon, Xenon, Krypton
Pressure: 0.5- 2 ATM
Windows: Be or Polymer
Sealed or Gas Flow Versions
Count Rates EDX: 10,000-40,000 cps WDX: 1,000,000+
Resolution: 500-1000+ eV
Window

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Scintillation Detector
PMT (Photo-multiplier tube)
Sodium Iodide Disk Electronics
Connector
Window: Be or Al
Count Rates: 10,000 to 1,000,000+ cps
Resolution: >1000 eV

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Spectral Comparison - Au
Si(Li) Detector
10 vs. 14 Karat
Si PIN Diode Detector
10 vs. 14 Karat

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Polymer Detector WindowsPolymer Detector Windows
♦ Optional thin polymer windows compared
to a standard beryllium windows
♦ Affords 10x improvement in the MDL for sodium (Na)

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Detector Filters
Filters are positioned between the sample and
detector in some EDXRF and NDXRF systems
to filter out unwanted x-ray peaks.
SampleSample
DetectorDetector
X-RayX-Ray
SourceSource
Detector FilterDetector Filter

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Detector Filter Transmission
%
T
R
A
N
S
M
I
T
T
E
D
ENERGY
Low energy x-rays
are absorbed
EOI is transmitted
Absorption
Edge
X-rays above the absorption
edge energy are absorbed
Very high energy
x-rays are transmitted
S Cl
A niobium filter absorbs Cl and other higher energy
source x-rays while letting S x-rays pass. A detector
filter can significantly improve detection limits.
Niobium Filter Transmission and Absorption

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Filter Vs. No Filter
Unfiltered Tube
target, Cl, and Ar
Interference Peak
Detector filters can dramatically improve the element of interest
intensity, while decreasing the background, but requires 4-10 times
more source flux. They are best used with large area detectors that
normally do not require much power.

54. Introduction to XRF
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Ross Vs. Hull Filters
 The previous slide was
an example of the Hull
or simple filter method.
 The Ross method
illustrated here for Cl
analysis uses intensities
through two filters, one
transmitting, one
absorbing, and the
difference is correlated
to concentration. This is
an NDXRF method
since detector resolution
is not important.

55. Introduction to XRF
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Wavelength Dispersive XRF
Wavelength Dispersive XRF relies on a diffractive device
such as crystal or multilayer to isolate a peak, since the
diffracted wavelength is much more intense than other
wavelengths that scatter of the device.
SampleSample
Detector
X-Ray
Source
Diffraction Device
Collimators

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Diffraction
The two most common diffraction devices used in WDX
instruments are the crystal and multilayer. Both work
according to the following formula.
nλ = 2d × sinθ
n = integer
d = crystal lattice or
multilayer spacing
θ = The incident angle
λ = wavelength Atoms

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Multilayers
While the crystal spacing is based on the natural atomic
spacing at a given orientation the multilayer uses a
series of thin film layers of dissimilar elements to do
the same thing.
Modern multilayers
are more efficient
than crystals and can
be optimized for
specific elements.
Often used for low Z
elements.

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Soller Collimators
Soller and similar types of collimators are used to
prevent beam divergence. The are used in WDXRF to
restrict the angles that are allowed to strike the
diffraction device, thus improving the effective
resolution.
Sample
Crystal

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Cooling and Temperature Control
The diffraction technique is relatively inefficient and WDX
detectors can operate at much higher count rates, so WDX
Instruments are typically operated at much higher power
than direct excitation EDXRF systems. Diffraction devices
are also temperature sensitive.
Many WDXRF Instruments use:
•X-Ray Tube Coolers, and
•Thermostatically controlled instrument coolers

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Chamber Atmosphere
Sample and hardware chambers of any XRF instrument may be
filled with air, but because air absorbs low energy x-rays from
elements particularly below Ca, Z=20, and Argon sometimes
interferes with measurements purges are often used. The two
most common purge methods are:
Vacuum - For use with solids or pressed pellets
Helium - For use with liquids or powdered materials

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Changers and Spinners
Other commonly available sample handling
features are sample changers or spinners.
Automatic sample changers are usually of the circular or
XYZ stage variety and may have hold 6 to 100+ samples
Sample Spinners are used to average out surface features
and particle size affects possibly over a larger total surface
area.

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Typical PIN Detector InstrumentTypical PIN Detector Instrument
This configuration is most commonly used in higher
end benchtop EDXRF Instruments.

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Typical Si(Li) Detector InstrumentTypical Si(Li) Detector Instrument
This has been historically the most common laboratory
grade EDXRF configuration.

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Energy Dispersive
Electronics
Fluorescence generates a current in the detector. In a detector
intended for energy dispersive XRF, the height of the pulse produced is
proportional to the energy of the respective incoming X-ray.
DETECTOR
Signal to Electronics
Element
A
Element
C
Element
B
Element
D

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Multi-Channel Analyser
• Detector current pulses are translated into counts (counts per
second, “CPS”).
• Pulses are segregated into channels according to energy via
the MCA (Multi-Channel Analyser).
Signal from Detector
Channels, Energy
Intensity
(# of CPS
per Channel)

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WDXRF Pulse Processing
 The WDX method uses the diffraction device and
collimators to obtain good resolution, so The
detector does not need to be capable of energy
discrimination. This simplifies the pulse processing.
 It also means that spectral processing is simplified
since intensity subtraction is fundamentally an
exercise in background subtraction.
Note: Some energy discrimination is useful since it allows for rejection of low
energy noise and pulses from unwanted higher energy x-rays.

67. How to analyze X-Ray FluorescenceHow to analyze X-Ray Fluorescence
Wavelength-dispersive vs. energy-dispersiveWavelength-dispersive vs. energy-dispersive
Wavelength-dispersive
solar-slit solar-slit
crystal
gas/scintillation
detector
Energy
2dsinθ=λ
Energy-dispersive
electronic
signal
processing
MCA
Energy
semiconduct
or/
superconduct
or detector

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From Energy-dispersive to Wavelength-dispersiveFrom Energy-dispersive to Wavelength-dispersive
SpectrometerSpectrometer
To further upgrade signal to background ratioTo further upgrade signal to background ratio
Energy-dispersive TXRFEnergy-dispersive TXRFEnergy-dispersive TXRFEnergy-dispersive TXRF
Sample
Si(Li)
Detector
Substrate
X-ray
Wavelength-dispersive TXRFWavelength-dispersive TXRFWavelength-dispersive TXRFWavelength-dispersive TXRF
Large solid angle (High detection efficiency)Collecting
whole XRF spectra simultaneously
Large solid angle (High detection efficiency)Collecting
whole XRF spectra simultaneously
Low energy-resolution
Limitation of counting-rate
Scattering background
Low energy-resolution
Limitation of counting-rate
Scattering background
AdvantagesAdvantages
Disadvantage
s
Disadvantage
s
High energy-resolution
Good signal to background ratio
High energy-resolution
Good signal to background ratio
AdvantagesAdvantages
Low detection-efficiencyLow detection-efficiency
Disadvantage
s
Disadvantage
s
Analyzing
Crystal
(Johansson)
Sample
Substrate
X-
ray
Scintillator
detector

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Evaluating Spectra
• K & L Spectral Peaks
• Rayleigh Scatter Peaks
• Compton Scatter Peaks
• Escape Peaks
• Sum Peaks
• Bremstrahlung
In addition to elemental peaks, other peaks
appear in the spectra:

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K & L Spectral Lines
 K - alpha lines: L shell e-
transition to fill vacancy in K
shell. Most frequent
transition, hence most intense
peak.
 K - beta lines: M shell e-
transitions to fill vacancy in K
shell.
L Shell
K Shell  L - alpha lines: M shell e-
transition to fill vacancy in L
shell.
 L - beta lines: N shell e-
transition to fill vacancy in L
shell.
K alpha
K beta
M Shell
L alpha
N Shell
L beta

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K & L Spectral Peaks
Rh X-ray Tube
L-lines
K-Lines

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Scatter
Some of the source X-
rays strike the sample
and are scattered back
at the detector.
Sometimes called
“backscatter”
Sample
SourceDetector

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Rayleigh Scatter
• X-rays from the X-ray tube or
target strike atom without
promoting fluorescence.
• Energy is not lost in collision. (EI =
EO)
• They appear as a source peak in
spectra.
• AKA - “Elastic” Scatter
EI
EO
Rh X-ray Tube

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Compton Scatter
• X-rays from the X-ray tube or
target strike atom without
promoting fluorescence.
• Energy is lost in collision. (EI >
EO)
• Compton scatter appears as a
source peak in spectra, slightly
less in energy than Rayleigh
Scatter.
• AKA - “Inelastic” Scatter
EI
EO
Rh X-ray Tube

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Sum Peaks
 2 photons strike the detector at the same
time.
 The fluorescence is captured by the
detector, recognized as 1 photon twice
its normal energy.
 A peak appears in spectra, at: 2 X
(Element keV).

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Escape Peaks
• X-rays strike the sample and
promote elemental fluorescence.
• Some Si fluorescence at the
surface of the detector escapes,
and is not collected by the
detector.
• The result is a peak that appears
in spectrum, at: Element keV - Si
keV (1.74 keV).
Rh X-ray Tube
1.74 keV

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Brehmstrahlung
Brehmstrahlung (or Continuum) Radiation:
German for “breaking radiation”, noise that appears in
the spectra due to deceleration of electrons as they strike
the anode of the X-ray tube.

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Interferences
Spectral Interferences
Environmental Interferences
Matrix Interferences

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Spectral Interferences
• Spectral interferences are peaks
in the spectrum that overlap the
spectral peak (region of interest)
of the element to be analyzed.
• Examples:
– K & L line Overlap - S & Mo, Cl
& Rh, As & Pb
– Adjacent Element Overlap - Al
& Si, S & Cl, K & Ca...
• Resolution of detector
determines extent of overlap.
220 eV Resolution
140 eV Resolution
Adjacent Element Overlap

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Environmental Interferences
• Light elements (Na - Cl) emit
weak X-rays, easily attenuated by
air.
• Solution:
– Purge instrument with He
(less dense than air = less
attenuation).
– Evacuate air from analysis
chamber via a vacuum pump.
• Either of these solutions also
eliminate interference from Ar
(spectral overlap to Cl). Argon
(Ar) is a component of air.
Air Environment
He Environment
Al Analyzed with Si Target

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Matrix Interferences
• Absorption: Any element can absorb or scatter
the fluorescence of the element of interest.
• Enhancement: Characteristic x-rays of one
element excite another element in the sample,
enhancing its signal.
Influence Coefficients, sometimes called alpha
corrections are used to mathematically correct for
Matrix Interferences
Absorption/Enhancement Effects

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Absorption-Enhancement Affects
 Incoming source X-ray fluoresces Fe.
 Fe fluorescence is sufficient in energy to fluoresce Ca.
 Ca is detected, Fe is not. Response is proportional to concentrations of
each element.
Red = Fe, absorbed
Blue = Ca, enhanced
Source X-ray
X-Ray Captured
by the detector.
Sample

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Software
• Qualitative Analysis
• Semi-Quantitative Analysis (SLFP, NBS-
GSC.)
• Quantitative Analysis (Multiple intensity
Extraction and Regression methods)

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Qualitative Scan Peak ID
 This spectrum also contrasts the resolution of a PIN diode detector
with a proportional counter to illustrate the importance of detector
resolution with regard to qualitative analysis.
Automated Peak identification programs are a useful
qualitative examination tool
Element Tags

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Semi-Quantitative Analysis
• The algorithm computes both the
intensity to concentration relationship
and the absorption affects
• Results are typically within 10 - 20 %
of actual values.
SLFP
Standardless Fundamental
Parameters
FP (with Standards)
NBS-GSC, NRLXRF, Uni-Quant,
TurboQuant, etc…
 The concentration to intensity
relationship is determined with
standards, while the FP handles the
absorption affects.
• Results are usually within 5 - 10 %
of actual values

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Quantitative AnalysisConcentration
Intensity
XRF is a reference method,
standards are required for
quantitative results.
Standards are analysed,
intensities obtained, and a
calibration plot is generated
(intensities vs. concentration).
XRF instruments compare the
spectral intensities of unknown
samples to those of known
standards.

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Standards
 Standards (such as certified reference materials) are
required for Quantitative Analysis.
 Standard concentrations should be known to a better
degree of precision and accuracy than is required for
the analysis.
 Standards should be of the same matrix as samples to be
analyzed.
 Number of standards required for a purely empirical
method, N=(E+1)2
, N=# of standards, E=# of Elements.
 Standards should vary independently in concentration
when empirical absorption corrections are used.

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Sample Preparation
Powders:
Grinding (<400 mesh if possible) can minimise scatter affects due to particle size.
Additionally, grinding insures that the measurement is more representative of the entire
sample, vs. the surface of the sample.
Pressing (hydraulically or manually) compacts more of the sample into the analysis
area, and ensures uniform density and better reproducibility..
Solids:
Orient surface patterns in same manner so as minimise scatter affects.
Polishing surfaces will also minimise scatter affects.
Flat samples are optimal for quantitative results.
Liquids:
Samples should be fresh when analysed and analysed with short analysis time - if sample
is evaporative.
Sample should not stratify during analysis.
Sample should not contain precipitants/solids, analysis could show settling trends with
time.

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ADVANTAGES AND
DISADVANTAGES
Advantages of X-Ray SpectrometryAdvantages of X-Ray Spectrometry
* Simple spectra
* Spectral positions are almost independent of the chemical
state of the analyte
* Minimal sample preparation
* It is non-destructive
* Applicable over a wide range of concentrations
* Good precision and accuracy

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Disadvantages of X-Ray Spectrometry
* X-ray penetration of the sample is limited to the top 0.01 -
0.1 mm layer
* Light elements (below 22
Ti) have very limited sensitivity
although C is possible on new instruments
* Inter element (MATRIX) effects may be substantial and
require computer correction
* Limits of detection are only modest
* Instrumentation is fairly expensive

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XRF Applications
XRF analyze almost all chemical elements and application
includes –
􀃆 Mineral, ceramic, cement, rock composition
􀃆 S, Cl & Pb in petroleum products
􀃆 Additives to polymers & paints
􀃆 Alloy identification for ferrous & non-ferrous materials
􀃆 Trace metals in alloys & solutions

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