A Basic Overview Theory and Applications

1. X-RAY FLUORESECENCE
A Basic Overview
Theory and Applications
AHMED ABD ELGHANY
Egyptian petroleum research institute

2. PRESENTATION OUTLINE
 INTRODUCTION
 BASICS OF XRF
 XRF THEORY
 XRF INSTRUMENTS
 XRF HARDWARE
 SAMPLE PREPARATION
 ADVANTAGE OF XRF
 APPLICATIONS OF XRF

3. INTRODUCTION
X-ray fluorescence (XRF) spectrometry is an elemental
analysis technique with broad application in science and
industry.
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
quantitated.

4. Basics of XRF
• In XRF, X-rays produced by a source irradiate the
sample.
• The elements present in the sample will emit
fluorescent X-ray radiation with discrete energies
(equivalent to color in optical light) that are
characteristic for these elements.

5. • By measuring the intensities of emitted energies (colors) it
is possible to determine how much of each element is
present in sample.
• This step is called quantitative analysis

6. What are X-rays
X-rays can be seen as electromagnetic waves with their associated
wavelengths, or as beams of photons with associated energies.
The X-rays have wavelengths and energies between gamma rays
and ultra violet light.
The wavelengths of X-rays are in range from 0.01 to 10 nm, which
corresponds to energies in the range from 0.125 to 125 KeV.

7. Principle of the excitation by X-Rays
 An Incoming X-Ray photon strikes an electron, the
electron breaks free and leaves the atom.
 This leaves a void that must be filled by an electron from
an outer shell.
 The excess energy from the new electron is released
(fluorescence) in the form of an x-ray photon.

8. THEORY OF XRF
 A source X-ray strikes an inner shell electron. If it has
a high energy (above absorption edge of element), it is
ejected from the atom.
 Higher energy electrons cascade to fill vacancy, giving
off characteristic fluorescent X-rays.

9. K shell, n=1, 2 electrons, 1 level
L shell , n=2, 8 electrons, 3 sublevels
M shell, n=3 , 18 electrons, 5 sublevels
N shell , n=4, 32 electrons, 7 sublevels
ELECTRON SHELLS
Shells have specific names (i.e., K, L, M) and
only hold a certain number of electrons
X-rays typically affect only inner shell (K, L) electrons
n = principal quantum number
2n2= number of electrons
2n-1 = number of sublevels

10. HOW XRF WORKS
The basic concept for XRF work , the X-rays irradiates
sample and detector measure the radiation coming from
sample.
There are three main interactions when X-rays contact
matter:
1. Fluorescence refer to absorbed fraction from X-ray
photons.
2. Compton (incoherent) Scatter : fraction scattering with
a loss of energy

11. 3- Rayleigh (coherent) Scatter: fraction scattering without
a loss of energy
the fluorescence and the scatter depend on Thickness,
Density and Composition of material.

12. THE XRF SPECTROMETER
Spectrometer are generally divided into two main groups:
1- Energy Dispersive system (EDXRF).
EDXRF spectrometers have a detector that is able to
measure different energies of the characteristic radiation
coming directly from the sample.

13. 2- Wavelength Dispersive system (WDXRF).
WDXRF spectrometers use an analyzer crystal to disperse
the different energies.

14. XRF HARDWARE
XRF spectrometers consist of four main parts
1- Source 2- Sample 3- Detector 4- MCA
1- SOURCE
The source in most cases is an X-ray tube, it contains
filament (wire) and anode (target) placed in a vacuum
housing.
Tubes divided into two types
 End Window X-Ray Tubes
 Side Window X-Ray Tubes

15. End Window
X-Ray Tube
Side Window
X-Ray Tube

16. 2- SAMPLE
XRF spectrometer have ability to measure any phase of
samples like solid, powder and liquid or other form.
3- DETECTOR
Different types of detectors are used in XRF.
I. EDXRF mainly uses Solid state Detector, which have
wide-range and measure all elements from Na up to U.

17. II. WDXRF uses two types of detectors
1- Gas filled Detector, measure elements from Be up to Cu
2- Scintillation Detector, range of measuring from Cu to U

18. HOW DETECTORS WORK
All of these detectors produce an electrical pulse when an
X-ray photon enters the detector, and the height of this
pulse is proportional to the energy of the incoming photon.
4- Multi channel analyzer (MCA)
The (MCA) count how many pulses are generated in each
height interval. The number of pulses of certain height
gives the intensity of corresponding energy. The ability of
the detector and MCA to distinguished between different
energies is called the resolution

19. SAMPLE PREPARATION
 Powder sample:
1- Grinding (<400 mesh if possible).
2- Pressing (hydraulically or manually) into tablet.
A binding material is sometimes added to improve the
quality of the tablet.
 Solid Sample:
Polishing surfaces will also minimize scatter affects.
Flat samples are optimal for quantitative results.

20.  Liquid sample:
Liquids are poured into special cups with supporting films.
Samples should be fresh and analysed with short analysis
time - if sample is evaporative.
Sample should not contain precipitants/solids.

21. ADVANTAGE OF XRF ANALYSIS
• Non-destructive analysis
• Rapid analysis – results in minutes
• Easy sample preparation
• Clean analysis (No wet chemistry – no acids, no reagents).
• Wide range of measuring (Na11 to U92 ).
• High accurate analysis
• Used with all material forms solids, liquid and powders etc
• Qualitative, semi-quantitative, to full quantitative analysis

22. APPLICATIONS OF XRF
XRF spectrometry is very widely applied in many industries
and scientific fields.
• Petroleum Industry (e.g., sulfur content of crude oils and
other petroleum products)
• Geological, Mining and Mineralogical Exploration
(qualitative and quantitative analysis of soil, rocks and ore
assessment etc.
• Cement production Ceramic and Glass industry
• Metallurgy and Chemical Industry: quality control of raw
materials, production processes and final products