Introduction to XRF

Introduction to

X-Ray fluorescence

Analysis

Dr. Aseel B. AL-

Zubaydi

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Introduction to XRF

When an element is placed in a beam of x-

rays, the x-rays are absorbed. The

absorbing atoms become ionized (e.g. due

to the x-ray beam ejects the electron in the

inner shell).

An electron from higher energy shell (e.g.,

the L shell) then fall into the position

vacated by dislodged inner electron and

emit x-rays or characteristic wavelength.

This process is called x-ray fluorescence. 2

Introduction to XRF

The wavelength of fluorescence is characteristic of the element being excited, measurement of this wavelength enable us to identify the fluorescing element.

The intensity of the fluorescence depends on how much of that element is in x-ray beam.

Hence measurement of the fluorescence intensity makes possible the quantitative determination of an element.

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Introduction to XRF

The process of detecting and analyzing the

emitted x-rays is called “X-ray

Fluorescence Analysis.”

In most cases the innermost K and L shells

are involved in XRF detection.

A typical x-ray spectrum from an irradiated

sample will display multiple peaks of

different intensities.

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Introduction to XRF

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Introduction to XRF

The characteristic x-rays are labeled as K, L, M or N to denote the shells they originated from.

Another designation alpha (α), beta (β) or gamma (γ) is made to mark the x-rays that originated from the transitions of electrons from higher shells.

Hence, a Kα x-ray is produced from a transition of an electron from the L to the K shell, and a Kβ x-ray is produced from a transition of an electron from the M to a K shell, etc.

Since within the shells there are multiple orbits of higher and lower binding energy electrons, a further designation is made as α1, α2 or β1, β2, etc. to denote transitions of electrons from these orbits into the same lower shell.

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Introduction to XRF

The X-Ray Fluorescence Process

Example: Titanium Atom (Ti = 22)

1) An electron in the K shell is

ejected from the atom by an

external primary excitation

x-ray, creating a vacancy.

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Introduction to XRF

2) An electron from the L

or M shell “jumps in” to

fill the vacancy. In the

process, it emits a

characteristic x-ray

unique to this element

and in turn, produces a

vacancy in the L or M

shell.

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Introduction to XRF

3) When a vacancy is created

in the L shell by either the

primary excitation x-ray or by

the previous event, an

electron from the M or N shell

“jumps in” to occupy the

vacancy. In this process, it

emits a characteristic x-ray

unique to this element and in

turn, produces a vacancy in

the M or N shell.

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Introduction to XRF

“Auger” Electron

The excitation energy from

the inner atom is

transferred to one of the

outer electrons causing it

to be ejected from the

atom. This process is a

competing process to the

XRF.

The second ejected

electron is called an Auger

electron

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Introduction to XRF

X-ray Spectra

X-rays are generated and caught by detectors

Introduction to XRF

• X-ray fluorescence's spectroscopy provides a means of identification of an element, by measurement of its characteristic X-remission length or energy

• The method allows the quantification of a given element by first measuring the emitted characteristic line intensity and then relating this intensity to elemental concentration

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Introduction to XRF

• The energy of the peaks leads to the

identification of the elements present in

the sample (qualitative analysis),

• while the peak intensity provides the

relevant or absolute elemental

concentration (semi-quantitative or

quantitative analysis).

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Introduction to XRF

Advantages of X-ray Fluorescent Analysis

1. Rapid analysis

2. Nondestructive analysis

3. No spectrum is affected by chemical bonding

4. Easily analysis of the element among the same family elements

5. High accurate analysis (5B to 92U can be analysis)

6. Easy qualitative analysis

7. Easy sample preparation

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Introduction to XRF

• Can analyzed oxygen but Consequently

oxides content is estimated result because

XRF can only determine elements.

• Elemental carbon and sulfur can also be

analyzed but not CO3=, SO4

=, SO3= .

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Introduction to XRF

• Schematic figure of an x-ray fluorescence

spectrophotometer

sin.2dn BASIC PRINCIPLE: 16

Introduction to XRF

X-ray generator

Sample chamber

collimator

Analyzing crystal

collimator

To counting and recording part

To spectrometer part

X-ray generator part

Spectrometer Part

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Introduction to XRF

X-RAY GENERATOR • X-ray tube for XRF spectrometer is a

diode (vacuum tube) consist of the

filament generating thermo- electron and

the anode (target) generating x-rays.

• Near the target, there is a window to pass

x-rays through to the outside tube. The

window material, Beryllium, is employed

because of its nature for having the

excellent transmission (penetration) of x-

rays. 18

Introduction to XRF

There are two types of x-ray

tubes:

1.End Window Type X-ray Tube

target end-window type x-ray tube has the

features that since it is effectively sensitive

to the element less than the atomic

number 16 (S) and it can also obtain

relatively the good sensitivity to the heavy

elements.

2.Side Window Type X-ray Tube

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Introduction to XRF

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Introduction to XRF

• The diffraction phenomenon of x-ray

through the single crystal is utilized for the

dispersion of x-rays. This crystal is called

the (analyzing crystal.)

Analyzing crystal

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Introduction to XRF

• Diffracting angles (θ) are measured and λ

of each element is determined using

Bragg’s law.

• By determining the elemental spectra

recorded on a chart, we can learn the

name of elements containing in the

specimen.

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Introduction to XRF

Example of a qualitative measurement

result.

Fluorescent spectrum recording of a stainless steel 23

Introduction to XRF

Sample Preparation

1.Powders:

Grinding (<400 mesh if possible) can minimise

scatter affects due to particle size.

Additionally, grinding insures that the

measurement is more representation of the

entire sample, vs. the surface of the sample.

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Introduction to XRF

2.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.

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Introduction to XRF

3. Liquids:

Samples should be fresh when analysed and

analysed with short analysis time - if

sample is evaporative.

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Introduction to XRF

XRF Application

1. Ecology and environmental measurement of heavy metals in soils.

2. Geology and mineralogy: Metallurgy and chemical industry: quality control of raw materials.

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Introduction to XRF

XRF Application

6. Jewelry: measurement of precious metals concentrations

7. Fuel industry: monitoring the amount of contaminants in fuels

8. Food chemistry: determination of toxic metals in foodstuffs

9. gardening: trace metals analysis in soils and agricultural products

10. Archaeology and archaeometry Art Sciences: study of paintings, sculptures etc.

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Introduction to XRF

Introduction to XRF

Introduction to XRF

Introduction to XRF

Introduction to XRF

QUIZ :What is the difference between xrd

& xrf? XRF and XRD measure different things, each giving different information about the same

sample.

XRF, or X-Ray Fluorescence analysis, measures the intensity of x-rays flouresced by individual elements in a sample, irrespective of the different compounds present that may contain those elements. eg. in cement the XRF analysed Ca percentage is the total Ca contributed by all calcium compounds in the cement.

XRD, or X-Ray Diffraction analysis, measures the intensity of crystal diffraction peaks due to the individual chemical compounds in the sample. ie CaCO3, CaO, CaSO4 etc. The result is estimated percentages for each compound of interest.

One method is not necessarily better than the other, they are simply complementary techniques which, when combined, give the total picture.

XRD is becoming more popular because it can estimate the quantity of clinker minerals more accurately than the traditional Bogue equations. which use the XRF chemical results. And XRD can also quickly analyse important compounds such as Free lime which are time consuming to analyse by any other method. With advances in computer power and programming sofware the complex calculations required to estimate clinker phases have become faster and more accurate, enabling this method to be used in on-line analysers for both clinker and cement.

Lastly, the formulae for calculating clinker phases can allow for free lime by simply subtracting the free lime from the XRF CaO value and using that value in the equation.