X-RAY FLUORESCENCE (XRF) SPECTROMETRY AND ITS TYPES and limitations.

1. X-RAY FLUORESCENCE (XRF)
SPECTROMETRY AND ITS TYPES
Name: Hamza Suharwardi
Roll No: MM-03
Course: Advanced Material Characterization Technique MM-(505)
DEPARTMENT OF MATERIALS ENGINEERING

2. INTRODUCTION:-
• X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or
fluorescent)
• X-rays from a material that has been excited by being bombarded with high-
energy X-rays or gamma rays.
• The phenomenon is widely used for elemental analysis and chemical analysis,
particularly in the investigation of metals, glass, ceramics and building
materials, and for research in geochemistry, forensic science, archaeology and
art objects such as paintings.
• Most of the XRF instruments in use today fall into two categories: energy-
dispersive (ED) and wavelength-dispersive (WD) spectrometers.
• Within these two categories is a tremendous variety of differing
configurations, X-ray sources and optics, and detector technologies

3. PRINCIPLE:-
• XRF is based on the principle that individual atoms, when
excited by an external energy source, emit X-ray photons
of a characteristic energy or wavelength. By counting the
number of photons of each energy emitted from a sample,
the elements present may be identified and quantities.

4. THEORY:-
• When an electron beam of high energy strikes a material, one of the results
of the interaction is the emission of photons which have a broad continuum
of energies. This radiation, called braking radiation, is the result of the
declaration of the electron inside the material.

5. • Another result of the interaction between
the electron beam and the material is the
ejection of photoelectrons from the inner
shells of the atoms making up the
material.
• These photoelectrons leave with a kinetic
energy which is the difference in energy
between that of the incident particle and
the binding energy of the atomic
electron.
• This ejected electron leaves a "hole" in
the electronic structure of the atom, and
after a brief period, the atomic electrons
rearrange, with an electron from a higher
energy shell filling the vacancy.
• By way of this relaxation the atom
undergoes fluorescence, or the emission
of an X-ray photon whose energy is
equal to the difference in energies of the
initial and final states.
• Detecting this photon and measuring its
energy allows us to determine the
element and specific electronic transition
from which it originated.

6. AUGER ELECTRON:-
• The Auger effect is a physical phenomenon in which the filling of an inner-shell
vacancy of an atom is accompanied by the emission of an electron from the
same atom. When a core electron is removed, leaving a vacancy, an electron from a
higher energy level may fall into the vacancy, resulting in a release of energy.

8. SCHEMATIC DIAGRAM OF WAVELENGTH OF DISPERSIVE X-RAY
FLUORESCENCE

9. WDXRF:-
• The WD-XRF analyzer uses a x-ray source to excite a sample. X-rays that have
wavelengths that are characteristic to the elements within the sample are emitted and they
along with scattered source x-rays go in all directions.
• A crystal or other diffraction device is placed in the way of the x-rays coming off the
sample.
• A x-ray detector is position where it can detector the x-rays that are diffracted and scattered
off the crystal.
• Depending on the spacing between the atoms of the crystal lattice (diffractive device) and
its angle in relation to the sample and detector, specific wavelengths directed at the detector
can be controlled.
• The angle can be changed in order to measure elements sequentially, or multiple crystals
and detectors may be arrayed around a sample for simultaneous analysis
Wavelength-dispersive X-ray spectroscopy is based on known principles of,
 how the characteristic x-rays are generated by a sample
 and how the x-rays are measured.

10. X-RAY GENERATIONS:-
• X-rays are generated when an electron
beam of high enough energy dislodges
an electron from an inner orbital within
an atom or ion, creating a void. This
void is filled when an electron from a
higher orbital releases energy and drops
down to replace the dislodged electron.
The energy difference between the two
orbitals is characteristic of the electron
configuration of the atom or ion and
can be used to identify the atom or ion.
• The lightest
elements, hydrogen, helium, lithium, Be
ryllium up to atomic number 5, do not
have electrons in outer orbitals to
replace an electron displaced by the
electron beam and thus cannot be
detected using this technique.

11. X-RAY MEASUREMENT:-
• According to Bragg's law, when an X-ray beam of wavelength "λ" strikes the surface of a
crystal at an angle and the crystal has atomic lattice planes a distance "d" apart,
then constructive interference will result in a beam of diffracted x-rays that will be emitted
from the crystal at angle if nλ = 2d sin Θ, where n is an integer.
• This means that a crystal with a known lattice size will deflect a beam of x-rays from a
specific type of sample at a pre-determined angle.
• The x-ray beam can be measured by placing a detector (usually a scintillation counter or
a proportional counter in the path of the deflected beam and, since each element has a
distinctive x-ray wavelength, multiple elements can be determined by having multiple
crystals and multiple detectors.
• To improve accuracy the x-ray beams are usually collimated by parallel copper blades called
a Soller collimator The single crystal, the specimen, and the detector are mounted precisely
on a goniometer with the distance between the specimen and the crystal equal to the distance
between the crystal and the detector.
• It is usually operated under vacuum to reduce the absorption of soft radiation (low-energy
photons) by the air and thus increase the sensitivity for the detection and quantification of
light elements (between boron and oxygen. The technique generates a spectrum with peaks
corresponding to x-ray lines. This is compared with reference spectra to determine the
elemental composition of the sample.

12. SPECTRAL LINES BY WDXRF:-

13. DETECTORS:-
• Detectors used for wavelength dispersive spectrometry need to have high
pulse processing speeds in order to cope with the very high photon count
rates that can be obtained. In addition, they need sufficient energy
resolution to allow filtering-out of background noise and spurious photons
from the primary beam or from crystal fluorescence. There are four
common types of detector:
• gas flow proportional counters
• sealed gas detectors
• scintillation counters
• semiconductor detectors

15. SCHEMATIC DIAGRAM OF ENERGY OF DISPERSIVE X-RAY
FLUORESCENCE

16. EDXRF:-
• The ED-XRF analyzer also uses an x-ray source to excite the sample but it may be
configured in one of two ways.
• The first way is direct excitation where the x-ray beam is pointed directly at the
sample. Filter made of various elements may be placed between the source and
sample to increase the excitation of the element of interest or reduce the
background in the region of interest.
• The second way uses a secondary target, where the source points at the target, the
target element is excited and fluoresces, and then the target fluorescence is used to
excite the sample.
• A detector is positioned to measure the fluorescent and scattered x-rays from the
sample and a multichannel analyzer and software assigns each detector pulse an
energy value thus producing a spectrum
• The peak positions are predicted by the moseley's law with accuracy much better
than experimental resolution of a typical edx instrument

18. COMPONENTS OF EDX
• Four primary components of the EDS setup are
• the excitation source (electron beam or x-ray beam)
• the X-ray detector
• the pulse processor
• the analyzer.
 X-ray beam excitation is used in X-ray fluorescence (XRF) spectrometers.
 A detector is used to convert X-ray energy into voltage signals; this information is
sent to a pulse processor, which measures the signals and passes them onto an
analyzer for data display and analysis.
 The most common detector used to be Si(Li) detector cooled to cryogenic
temperatures with liquid nitrogen.
 Now, newer systems are often equipped with silicon drift detectors (SDD)
with Peltier coolings ystems.

19. SILICON DRIFT DETECTOR:-
• There is a trend towards a newer EDS detector, called the silicon drift
detector (SDD). The SDD consists of a high-resistivity silicon chip where
electrons are driven to a small collecting anode. The advantage lies in the
extremely low capacitance of this anode, thereby utilizing shorter
processing times and allowing very high throughput. Benefits of the SDD
include:
• High count rates and processing,
• Better resolution than traditional Si(Li) detectors at high count rates,
• Lower dead time (time spent on processing X-ray event),
• Faster analytical capabilities and more precise X-ray maps or particle data
collected in seconds,
• Ability to be stored and operated at relatively high temperatures,
eliminating the need for liquid nitrogen cooling

20. WAFER DETECTORS:-
• More recently, high-purity silicon wafers with low conductivity have become
routinely available.
• Cooled by the Peltier effect, this provides a cheap and convenient detector,
although the liquid nitrogen cooled Si(Li) detector still has the best resolution (i.e.
ability to distinguish different photon energies).
• The pulses generated by the detector are processed by pulse-shaping amplifiers.
• It takes time for the amplifier to shape the pulse for optimum resolution, and there is
therefore a trade-off between resolution and count-rate: long processing time for good
resolution results in "pulse pile-up" in which the pulses from successive photons
overlap.
AMPLIFIER:-

21. COMPARISON BETWEEN EDXF AND
WDXF:-

22. APPLICATIONS OF XRF:-
• It is a method of elemental (metal and Non metal ) analysis with atomic number
greater than 12.
• Quantitative analysis can be carried out by measuring the intensity of
fluorescence at the wavelength characteristics of the element being determined,
especially applicable to most of the element in the periodic table.
• In medicine ,
 Direct determination of sulfur in protein. The sulfur content of each of the many
different forms in which protein exists in human blood varies considerably.
 XRF indicates protein distribution and provides a diagnostic link for the
medical practitioner.
 Determination of chloride in blood serum.
 Determination of strontium in blood serum and bone tissue.
 Elemental analysis of tissues, bones and body fluids.
 It is used for detection of pesticides on fruits and herbal drugs

24. Hamza Suharwardi
Researcher
Slow and steady win the race.
Any questions?
You can find me at:
● hamzaahmed0696@gmail.com
• https://www.researchgate.net/profile/Hamza
-Suharwardi-2