Note - XRF - Introduction to X-Ray Fluorescence Analysis M84-E06001

BRUKER ADVANCED X-RAY SOLUTIONS

USER’S MANUAL

INTRODUCTION TO

X-RAY FLUORESCENCE

ANALYSIS (XRF)

TRAINING

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In case you need more information than this user's manual can supply, you can get additional help from our service group in oneof the following ways:

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Please include in the subject line one of the following shorthand expressions in order to indicate the prod-uct line.

XRF: Questions concerning Spectrometry

XRD: Questions concerning Diffractometry

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Authors: Dr. Reinhold Schlotz, Dr. Stefan Uhlig. Layout: Ingrid Tremmel

Order No. M84-E06001. Issue: July 13, 2004

© 2000 - 2004 Bruker AXS GmbH, Karlsruhe, West Germany.

All trademarks and registered trademarks are the sole property of their respective owners. Printed in the Federal Republic of Germany.

Introduction to X-Ray Fluorescence Analysis (XRF) Table of Contents

DOC-M84-E06001 July 2004 i

Introduction to X-ray Fluorescence Analysis (XRF)

Table of Contents

Fundamental Principles............................................................................................1Electromagnetic Radiation, Quants ..............................................................................................1

The Origin of X-rays...................................................................................................................2Bohr's Atomic Model ..................................................................................................................2Characteristic Radiation.............................................................................................................4

Nomenclature ..................................................................................................................................4Generating the Characteristic Radiation ......................................................................................5

X-ray Tubes, Bremsspektrum ....................................................................................................6Tube Types, the Generator........................................................................................................7

Side-window Tubes ............................................................................................................8End-window Tubes .............................................................................................................9Generator..........................................................................................................................10

Excitation of Characteristic Radiation in Sample Material .......................................................10Layer Thickness, Saturation Thickness ...................................................................................14Secondary Enhancement.........................................................................................................14

Tube-spectrum Scattering at the Sample Material ....................................................................15Measuring X-rays ..........................................................................................................................16

Detectors, Pulse Height Spectrum...........................................................................................16Gas Proportional Counter .................................................................................................17Scintillation Counters ........................................................................................................18

Pulse Height Analysis (PHA), Pulse Height Distribution..........................................................19The Counter Plateau................................................................................................................22

Diffraction in crystals ...................................................................................................................23Interference..............................................................................................................................23Diffraction .................................................................................................................................24

Table of Contents Introduction to X-Ray Fluorescence Analysis (XRF)

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X-ray Diffraction From a Crystal Lattice, Bragg's Equation..................................................... 25Reflections of Higher Orders................................................................................................... 29Crystal types............................................................................................................................ 30Dispersion, Line Separation .................................................................................................... 32Standard Types, Multilayers.................................................................................................... 33Special Crystals....................................................................................................................... 36Curved Crystals....................................................................................................................... 43

Instrumentation....................................................................................................... 45The Multichannel Spectrometer MRS......................................................................................... 45

Scanners for MRS 400, MRS 404 and MRS 4000.................................................................. 47The Sequential Spectrometers SRS 3X00 and S4..................................................................... 48

The End-window Tube and Generator .................................................................................... 51The Primary Beam Filter ......................................................................................................... 51Sample Cups, the Cup Aperture ............................................................................................. 54The Vacuum Seal.................................................................................................................... 54Collimator Masks..................................................................................................................... 55Collimators, the Soller Slit ....................................................................................................... 55The Crystal Changer ............................................................................................................... 56The Flow Counter.................................................................................................................... 56The Sealed Proportional Counter............................................................................................ 57The Scintillation Counter ......................................................................................................... 58

Electronic Pulse Processing ....................................................................................................... 59The Discriminator .................................................................................................................... 59Main Amplifier, Sine Amplifier ................................................................................................. 59Dead Time Correction ............................................................................................................. 60Line-shift Correction ................................................................................................................ 62

Appendix A.............................................................................................................. 63Supplementary Literature............................................................................................................ 63

Books....................................................................................................................................... 63Tables...................................................................................................................................... 65Journals................................................................................................................................... 65

Introduction to X-Ray Fluorescence Analysis (XRF) Table of Contents

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Appendix B ..............................................................................................................67Sources of Standard Samples .....................................................................................................67

Appendix C ..............................................................................................................69Sample Preparation Catalog for XRF Analysis ..........................................................................69

Introduction ..............................................................................................................................69Preparation of solid samples....................................................................................................74

Metals ...............................................................................................................................74Pressed pellets .................................................................................................................75Fused beads .....................................................................................................................76

Preparation of liquid samples...................................................................................................77Preparation of filter samples .............................................................................................78

Sample preparation equipment for XRF Analysis .....................................................................78Crushing...................................................................................................................................78Grinding....................................................................................................................................79Pelletizing.................................................................................................................................92

Accessories for pressing...................................................................................................99Desiccator and accessories............................................................................................101

Milling .....................................................................................................................................102Fusing ....................................................................................................................................103

Accessories for fusing.....................................................................................................115Fluxes .............................................................................................................................115

Liquid sample measurement accessories..............................................................................115Liquid cups......................................................................................................................115Foils for liquid cups .........................................................................................................116Foils for liquid cells..........................................................................................................116Paper filters.....................................................................................................................117Pipettes and accessories................................................................................................117

Index.......................................................................................................................119

Introduction to X-Ray Fluorescence Analysis (XRF) Fundamental Principles

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Fundamental Principles

Electromagnetic Radiation, Quants

From a physical point of view, X-rays are of the same nature as visible light. Visible light can be de-scribed as electromagnetic wave radiation whose variety of colours (e.g. the colours of the rainbow) we interpret as different wavelengths. The wavelengths of electromagnetic radiation reach from the kilometre range of radio waves up to the picometre range (10-12 m) of hard gamma radiation (Table 1).

Tab. 1: Energy and wavelength ranges of electromagnetic radiation

Energy range (keV) Wavelength range Name

< 10-7 cm to km Radio waves (short, medium, long waves)

< 10-3 µm to cm Microwaves

< 10-3 µm to mm Infra-red

0,0017 - 0,0033 380 to 750 nm Visible light

0,0033 - 0,1 10 to 380 nm Ultra-violet

0,11 - 100 0,01 to 12 nm X-rays

10 - 5000 0,0002 to 0,12 nm Gamma radiation

In the following text, the unit nanometre (nm = 10-9 m) is used for the wavelength, (= Lambda), and the unit kiloelectronvolts (keV) for energy, E.

Comment In literature the unit Angström (Å) is often stated for the wavelength:

1 Å = 0,1 nm = 10-10 m

Fundamental Principles Introduction to X-Ray Fluorescence Analysis (XRF)

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The following relationship (conversion formula) exists between the units E (keV) and (nm):

)(

24.1)(

nmkeVE or

)(

24.1)(

keVEnm

The X-ray fluorescence analysis records the following range of energy or wavelengths:

E = 0,11 - 60 keV

= 11.3 - 0,02 nm

Apart from the wave properties, light also has the properties of particles. This is expressed by the term ”photon”. In the following we will be using the term quants or X-ray quants for this. The radiation in-tensity is the number of X-ray quants that are emitted or measured per unit of time. We use the num-ber of X-ray quants measured per second, cps (= counts per second) or KCps (= kilocounts per sec-ond) as the unit of intensity.

The Origin of X-rays

Electromagnetic radiation can occur whenever electrically charged particles, particularly electrons, lose energy as a result of a change in their state of motion, e.g. upon deceleration, changing direction or moving to a lower energy level in the atomic shell. The deceleration of electrons and the transition from an energy level in the atomic shell to a lower one play an important part in the creation of X-rays in the field of X-ray analysis. To understand the processes in the atomic shell we must take a look at the Bohr's atomic model.

Bohr's Atomic Model

Bohr's atomic model describes the structure of an atom as an atomic nucleus surrounded by electron shells (Fig. 1):


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Fig. 1: Bohr's atomic model, shell model

The positively charged nucleus is surrounded by electrons that move within defined areas (”shells”). The differences in the strength of the electrons‘ bonds to the atomic nucleus are very clear depending on the area or level they occupy, i.e. they vary in their energy. When we talk about this we refer to energy levels or energy shells. This means: A clearly defined minimum amount of energy is required to release an electron of the innermost shell from the atom. To release an electron of the second inner-most shell from the atom, a clearly defined minimum amount of energy is required that is lower than that needed to release an innermost electron. An electron’s bond to an atom is weaker the further away it is from the atom’s nucleus. The minimum amount of energy required to release an electron from the the atom, and thus the energy with which it is bound to the atom, is also referred to as the binding energy of the electron to the atom.

The binding energy of an electron in an atom is established mainly by determining the incident. It is for this reason that the term absorption edge is very often found in literature:

Energy level = binding energy = absorption edge

The individual shells are labelled with the letters K, L, M, N, ...., the innermost shell being the K-shell,the second innermost the L-shell etc. The K-shell is occupied by 2 electrons. The L-shell has three


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sub-levels and can contain up to a total of 8 electrons. The M-shell has five sub-levels and can contain up to 18 electrons.

Characteristic Radiation

Every element is clearly defined by its atomic number Z in the periodic system of elements or by the number of its electrons in a neutral state. The binding energies or the energy levels in every element are different and characteristic for every element as a result of the varying number of electrons (nega-tive charges) or the number Z of the positive charges in the atomic nucleus (= atomic number).

If an electron of an inner shell is now separated from the atom by the irradiation of energy, an electron from a higher shell falls into this resultant “hole” which releases an amount of energy equivalent to the difference between the energy levels involved.

The energy being released can be either be emitted in the form of an X-ray or be transferred to an-other atomic shell electron (Auger effect). The probability of an X-ray resulting from this process is

called the fluorescence yield . This depends on the element’s atomic number and the shell in which

the “hole” occurred. is very low for light elements (approx. 10-4 for boron) and almost reaches a value of 1 for the K-shell of heavier elements (e.g. uranium).

However, decisive is that the energy or wavelength of the X-ray is very characteristic for the element from which it is emitted; such radiation is called characteristic X-rays.

This provides the basis for determining chemical elements with the aid of X-ray fluorescence analy-sis.

Nomenclature

The energy of an X-ray corresponds to the difference in energy of the energy levels concerned. K-radiation is the term given to the radiation released when replenishing the K-shell, L-radiation to that released when replenishing the L-shell etc. (Fig. 2).

Also needed for the full labelling of the emitted X-ray line is the information telling us which shell the electron filling the “hole” comes from. The Greek letters , , , ... are used for this with the numbering 1, 2, 3, ... to differentiate between the various shells and sub-levels.


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Fig. 2: X-ray line labelling

Examples:

K Electron from sub-level LIII to the K-shell (K )

K Electron from sublevel LII to the K-shell (K )

K if neither line is resolved by the spectrometer: KK 1 Electron from sublevel M to the K-shell (K 1)L Electron from sublevel M to the L-shell (L )

Generating the Characteristic Radiation

The purpose of X-ray fluorescence is to determine chemical elements both qualitatively and quantita-tively by measuring their characteristic radiation. To do this, the chemical elements in a sample must be caused emit X-rays. As characteristic X-rays only arise in the transition of atomic shell electrons to


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lower, vacant energy levels of the atom, a method must be applied that is suitable for releasing elec-trons from the innermost shell of an atom. This involves adding to the inner electrons amounts of en-ergy that are higher than the energy bonding them to the atom.

This can be done in a number ways:

Irradiation using elementary particles of sufficient energy (electrons, protons, -particles, ...) that transfer the energy necessary for release to the atomic shell electrons during collision processes

Irradiation using x- or gamma rays from radionuclides

Irradiation using X-rays from an X-ray tube

Using an X-ray tube here proves to be the technically most straightforward and, from the point of view of radiation protection, the safest solution (an X-ray tube can be switched off, a radionuclide cannot).

X-ray Tubes, Bremsspektrum

In an X-ray tube, electrons are accelerated in an electrical field and shot against a target material where they are decelerated. 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. There 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.

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. If 30 kV (Kilovolt) are applied between the anode and cathode, the electrons acquire 30 keV from passing through this voltage (kiloelectron volts) (Definition: 1 eV = the energy that an electron acquires when passing through a potential of 1 Volt).

A maximum X-ray energy of 30 keV can be acquired from deceleration in the anode material, i.e. the distribution of the energies of numerous X-rays is between zero and the maximum energy. If the inten-sity of this type of X-ray is applied depending on the energy, the result is the Bremsspektrum (= con-tinuum) of the tube.


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Fig. 3: A Bremsspektrum (= continuum) with characteristic radiation of the anode material

In addition to the Bremsspektrum, an X-ray tube of course emits the characteristic radiation of the anode material as well which is of major importance for the X-ray fluorescence analysis (Fig. 3).

Tube Types, the Generator

All X-ray tubes work on the same principle: accelerating electrons in an electrical field and decelerat-ing 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


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housing. The X-rays escape from the housing at a special point that is particularly transparent with a thin beryllium window.

The main differences between tube types are in the polarity of the anode and cathode and the ar-rangement of the exit window. The two most significant types are the end-window tubes and the side-window tubes.

Side-window Tubes

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 volt-age and thus has no difference in potential to the surrounding housing material and the laterallymounted beryllium exit window (Fig. 4).

Fig. 4: The principle of the side-window tube

For physical reasons, a proportion of the electrons are always scattered on the surface of the anode. The extent to which these back-scattering electrons arise depends, amongst other factors, on the anode material and can be as much as 40%. In the side-window tube, these back-scattering electrons


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contribute to the heating up of the surrounding material, especially the exit window. As a conse-quence, the exit window must withstand high levels of thermal stress any cannot be selected with just any thickness. The minimum usable thickness of a beryllium window for side-window tubes is 300 µm. This causes an excessively high absorption of the low-energy characteristic L radiation of the anode material in the exit window and thus a restriction of the excitation of lighter elements in a sample.

End-window Tubes

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 (Fig.5).

Fig. 5: The principle of the end-window tube


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The cathode is set around the anode in a ring (anular cathode) and is set at zero voltage. The elec-trons 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 back-scattering electrons are guided back to the anode and thus do not contribute to the rise in the exit window’s temperature. The beryl-lium window remains “cold” and can therefore be thinner than in the side-window tube. Windows are used with a thickness of 125 µm and 75 µm. This provide 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-ionised water must be used for cooling. Instru-ments with end-window tubes are therefore equipped with a closed, internal circulation system con-taining de-ionised water that cools the tube head as well.

End-window tubes have been implemented by all renowned manufacturers of wavelength dispersive X-ray fluorescence spectrometers since the early 80‘s.

Generator

Current and high voltage for the X-ray tubes as well as the heating current for the cathode are pro-duced in a so-called X-ray generator. The generators available today supply a maximum tube current of 150 mA and a maximum high voltage of 60 kV at a maximum output of 4 kW, i.e. current and volt-age must be selected in such a way that 4 kW is not exceeded. The architecture of modern control electronics and software ensures that damage to the tube resulting from maladjustment is impossible. The reason for restricting the maximum excitation power to 1 kW is that cooling with external coolant can be dispensed with which simplifies installation requirements.

Excitation of Characteristic Radiation in Sample Material

The Bremsstrahlung and the characteristic radiation of the X-ray tube’s anode material are used to excite the characteristic radiation of the elements in the sample material. It is very important to know that a chemical element in the sample can only be made to emit X-rays when the energy of the incident X-ray quants is higher than the binding energy (absorption edge) of the element’s inner elec-trons. If the sample is irradiated with a tube high-voltage of e.g. 20 kV, the maximum energy of the quants emitted from the tube is 20 keV. Hence, it is impossible, for example, to excite the K radiation of the elements that have an atomic number Z > 43 as their K binding energy is greater than 20 keV. Excitation of the K radiation of heavier elements is achieved with a generator setting of 60 kV.


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All renowned manufacturers use rhodium (Rh) as the standard anode material as the characteristic energies of this element are simultaneously suitable for exciting both heavy and light elements.

Energies and wavelengths of rhodium’s characteristic lines, and the heaviest element that can be ex-cited with the appropriate line in each case, are listed in Table 2.

Tab. 2: Rhodium’s characteristic lines

Line Energy Wavelength Heaviest element

Rh Ka1 20,214 keV 0,0613 nm Molybdenum (Mo)

Rh Ka2 20,072 keV 0,0617 nm Molybdenum (Mo)

Rh Ka1 22,721 keV 0,0546 nm Ruthenium (Ru)

Rh La1,2 2,694 keV 0,4601 nm Sulphur (S)

Rh La1 2,834 keV 0,4374 nm Chlorine (Cl)

The following can be extracted from Table 2:

The K lines of the heavy elements from rhodium to tantalum (Ta) can, on principle, only be excited with the Bremsstrahlung of the rhodium tube as the energy of the rhodium lines is insufficient to do it. A generator setting of 60 kV is recommended for such cases.

The elements as far as molybdenum are excited by the Rh K radiation. The Rh-K 1 radiation can even excite the element ruthenium but is of lower intensity than the K-alpha radiation.

The light elements up to sulphur are excited very effectively by the Rh L radiation.

The Rh-L 1 radiation can excite the element chlorine but is of a lower intensity. Decisive for the available intensity of the Rh L radiation is the thickness of the tube’s beryllium exit window.

Instead of rhodium, other elements can be used as an anode material for special applications. Tung-sten (W) and gold (Au) are particularly suitable for exciting heavier elements with the Bremsspektrum. Chromium (Cr) was often used in side-window tubes for exciting lighter elements. Molybdenum (Mo) was frequently used for the interference-free measurement of rhodium and, for example, cadmium.

The use of the rhodium end-window tube as a “universal tube” is justified as the light elements can be excited far more effectively with the Rh L radiation than with the K radiation of a chromium anode.


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Moreover, instrument technology is so advanced nowadays that measuring rhodium itself (or cad-mium) presents no problem. Please also refer to the tecnique of the primary beam filter, page 51.

Absorption, the Mass Attenuation Coefficient Passing through matter weakens the intensity of X-rays. The degree of this weakening depends on both the radiation energy and the chemical composition of the absorbing material (e.g. the sample). Heavier elements absorb better than light ones: 1 mm of lead absorbs practically all of the higher-energy radiation occurring during X-ray fluorescence, 1 mm of polypropylene (hydrocarbon) is more or less permeable to X-rays. Low-energy X-ray quants are absorbed more readily than quants with higher energy (= short wavelengths): the quants emitted by the element boron, for example, have a very low energy of 0,185 keV (= 67 nm) and are practically completely absorbed by even 6 µm of polypropylene foil.

If an X-ray with quants of energy E and an intensity of Io pass through a layer of material, e.g. 1 mm sheet of pure iron (Fe), the ray emerging from behind the iron layer will only be left with the intensity I < Io as a result of the absorption. The relationship between I and Io after the transition through the layer thickness x is described by the law of absorption:

xeII 0

µ = linear absorption coefficient

The linear absorption coefficient has the dimension [1/cm] and is dependent on the energy or the wavelength of the X-ray quants and the special density (in [g/cm3]) of the material that was passed through.

If the iron sheet in the above example is replaced by a 1 mm layer of iron powder, the absorption is less because the density of the absorber is lower. Therefore, it is not the linear absorption coefficient that is specific to the absorptive properties of the element iron, but the coefficient applicable to the density of the material that was passed through

/ = mass attenuation coefficient

The mass attenuation coefficient has the dimension [cm2/g] and only depends on the atomic number of the absorber element and the energy, or wavelength, of the X-ray quants.

Fig. 6 illustrates the schematic progression of the mass attenuation coefficients depending on the en-ergy or wavelength.


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Fig. 6: Schematic progression of the mass attenuation coefficient of energy or wavelength

Fig. 6 supplies the following:

The overall progression of the coefficient decreases as energy increases, i.e. the higher the en-ergy of the X-ray quants, the less they are absorbed.

The rapid changes in the mass attenuation coefficient reveal the binding energies of the electrons in the appropriate shells. If an X-ray quant has a level of energy that is equivalent to the binding energy of an atomic shell electron in an appropriate shell, it is then able to transfer all its energy to this electron and displace it from the atom. In this case, absorption increases sharply. Quants whose energy is only slightly below the absorption edge are absorbed far less readily.

Example:The K radiation of iron (Fe) is absorbed less by its neighbouring element manganese (Mn) than by the element chromium (Cr) as Fe K 1,2 is below the absorption edge of Mn but above that of Cr.


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Layer Thickness, Saturation Thickness

The more readily the radiation of an element in the sample material is absorbed, the smaller is the layer of the sample from which the measurable radiation comes. A K-alpha quant from the element molybdenum (Mo K 1, 17.5 keV) has a far greater chance of being measured at a depth of 0,5 mm from the analysis surface of a steel sample than a quant from carbon (C K 1,2, 0,282 keV). As a con-sequence, a specific layer thickness is analysed for each element which depends on the specific en-ergy of the used element line. The analysis of very light elements e.g. in solids (such as Be, B, C, .... , for example) is comparable with a plain surface analysis as their radiation originates from few atomic layers. Practically all the radiation from deeper layers is fully absorbed within the sample.

A sample is referred to as being infinitely thick for a radiation component if it is sufficiently thick to practically completely absorb the radiation from the rear. Thus, a 1mm thick sample of cement is prac-tically infinitely thick for Fe K 1,2 radiation as the radiation from the rear of the sample is almost fully absorbed in the sample material. The thickness of a sample that is sufficient to absorb the radiation of an element line to a high degree (e.g. 90%) is called the saturation thickness.

Caution is advised with sample materials that are composed of light elements such as liquids or plas-tics (hydrocarbons). Here, for the high-energy radiation of heavier elements, high saturation thick-nesses that cannot be used in practice (e.g. 10 cm) are easily attainable. Hence, where these material groups are concerned, it must be ensured that identical sample quantities are used for quantitative analysis as the measured intensity may depend on the thickness of the sample.

Applying liquid sample materials to filter paper is a method of almost completely preventing the ef-fects of absorption. The term for this is infinitely thin samples.

Nowadays, the calculation of those layer thicknesses in defined samples that contribute to the analysis is integrated into modern software packages.

Table 1 of the sample preparation catalogue contains a list of the various layer thicknesses, from which 90% of the fluorescence radiation originates, for different types of materials.

Secondary Enhancement

Secondary enhancement, i.e. those X-ray quants that are produced as a result of the effect of the sample elements‘ absorbed radiation, is closely linked to produced X-rays‘ absorption in the sample.

Example:

An Si K 1 quant is produced in a sample by the effect of an X-ray tube’s radiation. Inside the sample, it can be absorbed again by transferring its energy to an Al K electron. This can then emit an X-ray


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quant itself. The silicon radiation thus contributes to the X-ray emission of the aluminium. This is re-ferred to as secondary enhancement (Fig. 7).

In quantitative analyses, the effects of absorption and secondary enhancement may have to be cor-rected. Modern software packages offer a selection of correction models (matrix correction or inter-element correction) for this purpose.

Fig. 7: Secondary enhancement

Tube-spectrum Scattering at the Sample Material

The purpose of X-ray fluorescence spectrometry is the qualitative and quantitative determination of the elements in a sample by measuring their characteristic radiation. As the sample is exposed to a beam of X-ray quants from a tube, a proportion of these X-rays also reach the detector in the form of radia-tion background as a result of physical scattering processes. While the scattered Bremsstrahlung proportion generally produces a continuous background, the scattered characteristic radiation of the anode material contributes towards the line spectrum. Besides the lines of elements from the sample, the anode material’s lines and the scattered Bremsspektrum usually appear as well as a background .

The intensity of the scattering depends on the composition of the sample: for samples who are mainly composed of light elements (light matrix), the proportion of scattered radiation is high. Where sam-ples are concerned that comprise mainly heavy elements (heavy matrix), the scattered proportion is relatively low.


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Background and characteristic scattering can be very effectively reduced by inserting a suitable absorption material between tube and sample (cf. primary beam filter, page 51).

There are two types of scattering whose physical scattering processes differ from each other and are referred to in literature as follows:

Rayleigh scattering = elastic scattering = classic scattering

Compton scattering = inelastic scattering

We will use the bold terms from now on and elaborate upon the effects of scattered characteristic radiation of the anode material.

Rayleigh scattering The Rh quants coming from the tube change their direction in the sample material without losing en-ergy and can thus enter the detector and be measured. The peaks of the anode material (e.g. rho-dium) appear in the line spectrum. If the element rhodium in the sample material is to be analysed using an Rh tube then the characteristic radiation coming from the tube must be absorbed by a pri-mary beam filter before it reaches the sample (cf. Fig. 2, page 52).

Compton scattering The Rh quants coming from the tube strike the sample elements‘ electrons. In this process, some a quant’s energy is transferred to an electron. The X-ray quant therefore loses energy. The intensity of the quants scattered by the Compton effect depends, amongst other factors, on the tube radiation’s angle of incidence to the sample and on the take-off angle of the radiation in the spectrometer. As these angle settings are fixed in a spectrometer (cf. beam path), a somewhat wider peak appears on the low-energy side of the appropriate Rh peak. These peaks are called “Compton peaks” (cf. Fig. 2, page 53).

Measuring X-rays

Detectors, Pulse Height Spectrum

When measuring X-rays, use is made of their ability to ionize atoms and molecules, i.e. to displace electrons from their bonds by energy transference. In suitable detector materials, pulses whose strengths are proportional to the energy of the respective X-ray quants are produced by the effect of X-rays. The information about the X-ray quants‘ energy is contained in the registration of the pulse heigth. The number of X-ray quants per unit of time , e.g. pulses per second (cps = counts per second,


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KCps = kilocounts per second), is called their intensity and contains in a first approximation the in-formation about the concentration of the emitting elements in the sample. Two main types of detectors are used in wavelength dispersive X-ray fluorescence spectrometers: the gas proportional counterand the scintillation counter.

The way these quant counters function is described in the following:

Gas Proportional Counter

The gas proportional counter comprises a cylindrical metallic tube in the middle of which a thin wire (counting wire) is mounted. This tube is filled with a suitable gas (e.g. Ar + 10% CH4). A positive high

voltage (+U) is applied the wire. The tube has a lateral aperture or window that is sealed with a mate-rial permeable to X-ray quants (Fig. 8).

Fig. 8: A gas proportional counter

An X-ray quant penetrates the window into the counter’s gas chamber where it is absorbed by ionizing the gas atoms and molecules. The resultant positive ions move to the cathode (tube), the free elec-trons to the anode, the wire. The number of electron-ion pairs created is proportional to the energy of the X-ray quant. To produce an electron-ion pair, approx. 0.03 keV are necessary, i.e. the radiation of the element boron (0.185 keV) produces approx. 6 pairs and the K-alpha radiation of molybdenum (17.5 keV) produces approx. 583 pairs. Due to the cylinder-geometric arrangement, the primary elec-trons created in this way “see” an increasing electrical field on route to the wire. The high voltage in


DOC-M84-E06001 July 2004 18

the counting tube is now set so high that the electrons can obtain enough energy from the electrical field in the vicinity of the wire to ionize additional gas particles. An individual electron can thus create up to 10.000 secondary electron-ion pairs.

The secondary ions moving towards the cathode produce a measurable signal. Without this process of gas amplification, signals from boron, for example, with 6 or molybdenum with 583 pairs of charges would not be able to be measured as they would not be sufficiently discernible from the electronic “noise”. Gas amplification is adjustable via high voltage in the counting tube and is set higher for measuring boron than for measuring molybdenum. The subsequent pulse electronics supply pulses of voltage whose height depends, amongst other factors, on the energy of the X-ray quants.

There are two models of gas proportional counters: the flow counter (“FC”) and the sealed propor-tional counter (“PC”). The flow counter is connected to a continuous supply of counting gas (Ar + 10% CH4) and has the advantage of being able to be equipped with a very thin window (< 0,6 µm). The FC is therefore also suitable for measuring the very light elements and is very stable. The propor-tional counter, on the other hand, has a closed volume a requires a thick window normally made of beryllium. The absorption in this "thick" beryllium window prevented the measurement of the very light elements (Be to Na).

Since innovative, highly transparent organic materials have been in use, there has now been success in developing sealed proportional counters that are just as sensitive to the very light elements (Be to Na) as flow counters are.

Scintillation Counters

The scintillation counter, “SC”, used in XRF comprises a sodium iodide crystal in which thallium atoms are homogeneously distributed 'NaI(Tl)'. The density of the crystal is sufficiently high to absorb all the XRF high-energy quants. The energy of the pervading X-ray quants is transferred step by step to the crystal atoms that then radiate light and cumulatively produce a flash. The amount of light in this scin-tillation flash is proportional to the energy that the X-ray quant has passed to the crystal. The resulting light strikes a photocathode from which electrons can be detached very easily. These electrons are accelerated in a photomultiplier and, within an arrangement of dynodes, produce so-called secondary electrons giving a measurable signal once they have become a veritable “avalanche” (Fig. 9). The height of the pulse of voltage produced is, as in the case of the gas proportional counter, proportional to the energy of the detected X-ray quant.


DOC-M84-E06001 July 2004 19

Fig. 9: Scintillation counter including photomultiplier

Pulse Height Analysis (PHA), Pulse Height Distribution

If the number of the measured pulses (intensity) dependent on the pulse height are displayed in a graph, we have the “pulse height spectrum”. Synonymous terms are: “pulse height analysis or “pulse height distribution”. As the height of the pulses of voltage are proportional to the X-ray quants’ energy, it is also referred to as the energy spectrum of the counter (Fig. 10a, Fig. 10b). The pulse height is given in volts, scale divisions or in “%” (and could be stated in keV after appropriate calibration). The “%”-scale is defined in such a way (SPECTRAplus) that the peak to be analysed appears at 100%.


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Fig. 10a: Pulse height distribution (S) Gas proportional counter

Fig. 10b: Pulse height distribution (Fe) Scintillation counter

If argon is used as the counting-gas component in gas proportional counters (flow counters or sealed counters), an additional peak, the escape peak (Fig. 11), appears when X-ray energies are irradiated that are higher than the absorption edge of argon.


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Fig. 11 Pulse-height distribution (Fe) with escape peak

The escape peak arises as follows:

The incident X-ray quant passes its energy to the counting gas thereby displacing a K electron from an argon atom. The Ar atom can now emit an Ar K 1,2 X-ray quant with an energy of 3 keV. If this Ar-fluo-rescence escapes from the counter then only the incident energy minus 3 keV remains for the meas-ured signal. A second peak, the escape peak that is always 3 keV below the incident energy, appears in the pulse height distribution. Please refer to Fig. 10a: In this case no escape peak appears as the incident energy of sulphur radiation (S K 1,2) is lower than the absorption edge of argon.

When using other counting gases (Ne, Kr, Xe) instead of argon, the escape peaks appear with an energy difference below the incident energy that is equivalent to the appropriate emitted fluorescence


DOC-M84-E06001 July 2004 22

radiation (Kr, Xe). Using neon as the counting-gas component produces no recognisable escape peak as the Ne K-radiation, with an energy of 0,85 keV, is almost completely absorbed in the counter. Also, the energy difference to the incident energy of 0,85 keV and the fluorescence yield are very small.

The Counter Plateau

Every counter has a high-voltage area within which it can be optimally adapted to the appropriate ap-plication (operating range). It has already been mentioned that the gas amplification must be set somewhat higher for measuring light elements than for the K-radiation of heavier elements by chang-ing the high voltage of the gas proportional counter. The high-voltage area that can be used for the application is called the "plateau" of the counter. This applies for the gas counter as well as for the scintillation counter with an integrated photomultiplier. Generally, the counter plateau is determined by irradiating X-ray energy typical for the application into the counter and measuring the intensity under increasing high voltage.

Fig. 11b illustrates the example of a counter plateau for a gas proportional counter with Ar + 10% CH4 as counting gas and Fe K 1 as the radiation source (Fig. 11a). The number of pulses has been ap-plied whose pulse height (Volt) exceeds a lower electronic discriminator threshold (e.g. 100 mV). If the high voltage is too low, the electrical field strength is not sufficient for producing a gas amplification; the pulse heights are too low to pass the threshold.

If the high voltage is increased in increments, at first the pulses produced by the Fe K-peak will exceed the discriminator threshold’s voltage height and be registered. If the power is increased further, the escape peak will pass the threshold, too. So, by increasing the counter high-voltage the radiation source’s peaks are pushed over the discriminator threshold.

After a steep increase in intensity, a relatively flat high-voltage area takes shape. This is the counter’s plateau or operating range. At the end of the plateau, the intensity increases sharply again due to counter pulses that do not primarily originate from the incident source. No measurements are to be taken in this area. Fig. 11b shows a form of plateau that occurs as a result of the integral measure-ment of all pulses over the discriminator threshold. If the pulses are pushed over a discriminator win-dow with a lower and upper threshold, the intensity drops once more as the peaks are pushed out of the window again.


DOC-M84-E06001 July 2004 23

Fig. 11b: A gas proportional counter plateau

Diffraction in crystals

Interference

Electromagnetic radiation displays interference and diffraction effects due to the nature of its waves. “Interference” is the property of waves to overlap each other and, under certain circumstances, to cancel out or amplify each other.

Amplification always takes place, for example, when waves of identical wavelength have zero phase difference (coherence), i.e. when "wave maxima" and "wave minima" overlap in such a way that min-ima meets minima and maxima meets maxima. This is precisely the case when the phase difference

is zero or a multiple of the wavelength , i.e.:

n n = 0, 1, 2, ....

“n” is referred to as the “order” (Fig. 12):


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Fig. 12 Amplification resulting from the effects of interference

Where the phase difference is one half of the wavelength: n = 1/2, 3/2, 5/2, ...... wave maxima coin-cide with wave minima resulting in total cancellation (Fig. 13). When a number of waves of the same wavelength propagating in the same direction interfere with each other under continuous phase shift, only the coherent among them will be amplified. In total, the rest will almost completely cancel each other out.

Fig. 13: Cancellation resulting from the effects of interference

Diffraction

From what we experience every day we know that light generally travels in straight lines. This corre-sponds with the image of light as a beam of particles (photons, quants). We know from waves that


DOC-M84-E06001 July 2004 25

when a wave series (e.g. water waves) travels through a hole smaller than the wavelength, the waves exiting the hole spread out to the sides. Light displays the same characteristics due to its nature of waves. The deviation of light from its travel in a straight line is called diffraction, also when it is not reflected or refracted.

There are numerous applications for the effects of diffraction. In wavelength dispersive XRF we are mainly interested in diffraction in reflection grids. Often used in the optical range ( = 380 - 750 nm) are mirror lattices produced by spacing grooves at equal distances in reflecting metal surfaces. This is no longer possible in the X-ray field for technical reasons as the wavelengths involved are around 2 to 5 orders of magnitude smaller ( = 0,02 - 11 nm). Very much smaller lattice distances such as are found in natural crystals, are required for X-ray diffraction in the reflexion grid.

The effects of diffraction are a prerequisite for wavelength dispersive XRF. After excitation of the ele-ments in the sample (by X-rays), a blend of element-characteristic wavelengths (fluorescence radia-tion) leaves the sample. There are now two methods ( or procedures) in XRF of identifying these vari-ous wavelengths. The energy dispersive XRF calls on the assistance of an energy dispersive detec-tor that is able to resolve the different energies. Wavelength dispersive XRF utilises the diffraction effects to split up (or separate) the various wavelengths in an analyzer crystal. The detector subse-quently determines the intensity of a particular wavelength. The procedure will be covered in detail in the following sections.

X-ray Diffraction From a Crystal Lattice, Bragg's Equation

Crystals consist of a periodic arrangement of atoms (molecules) that form the crystal lattice. In such an arrangement of particles you generally find numerous planes running in different directions through the lattice points (=atoms, molecules), and not only horizontally and vertically but also diagonally. These are called lattice planes. All of the planes parallel to a lattice plane are also lattice planes and are at a defined distance from each other. This distance is called the lattice plane distance 'd'.

When parallel X-ray light strikes a lattice plane, every particle within it acts as a scattering centre and emits a secondary wave. All of the secondary waves combine to form a reflected wave. The same occurs on the parallel lattice planes for only very little of the X-ray wave is absorbed within the lattice plane distance 'd'. All these reflected waves interfere with each other. If the amplification condition "phase difference = a whole multiple of the wavelength" ( = n ) is not precisely met, the reflected wave will interfere such that cancellation occurs. All that remains is the wavelength for which the am-plification condition is met precisely. For a defined wavelength and a defined lattice plane distance, this is only given with a specific angle, the Bragg angle (Fig. 14).


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Fig. 14 Bragg's Law

To Fig. 14 :

Under amplification conditions, parallel, coherent X-ray light (1,2) falls on a crystal with a lattice plane distanced 'd' and is scattered below the angle (theta) (1', 2'). The proportion of the beam that is scat-tered on the second plane has a phase difference of 'ACB' to the proportion of the beam that was scat-tered at the first plane. Following the definition of the sine:

sin''

d

AC or sin'' dAC

The phase difference 'ACB' is twice that, so:

sin2'' dACB

The amplification condition is fulfilled when the phase difference is a whole multiple of the wavelength , so:

nACB''

This results in Bragg's Law:

n =2d sin Bragg's equation

n = 1, 2, 3 ... Reflection order


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Fig. 15a: 1st order reflection: = 2d sin 1

Fig. 15b: 2nd order reflection: 2 = 2d sin 2


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Fig. 15c: 3rd order reflection: 3 = 2d sin 3

Fig. 15a, 15b, 15c (page 27) illustrate Bragg's Law for the reflection orders n = 1, 2, 3.

On the basis of Bragg's Law, by measuring the angle you can determine either the wavelength ,and thus chemical elements, if the lattice plane distance 'd' is known or, if the wavelength is known, the lattice plane distance 'd' and thus the crystalline structure.

This provides the basis for two measuring techniques for the quantitative and qualitative determination of chemical elements (XRF) and crystalline structures (molecules, XRD), depending on whether the wavelength or the 2d-value is identified by measuring the angle (Table 3).:

Table 3: Wavelength dispersive X-ray techniques

Known Sought Measured Method Instrument type

d X-ray fluorescence Spectrometer d X-ray diffraction Diffractometer


DOC-M84-E06001 July 2004 29

In X-ray diffraction (XRD) the sample is excited with monochromatic radiation of a known wavelength ( ) in order to evaluate the lattice plane distances as per Bragg's equation.

In XRF, the 'd'-value of the analyzer crystal is known and we can solve Bragg's equation for the ele-ment-characteristic wavelength ( ).

Reflections of Higher Orders

Fig. 15a-c illustrate the reflections of the 1st, 2nd, and 3rd order of one wavelength below the different angles Here, the total reflection is made up of the various reflection orders (1, 2, .... n). The

higher the reflection order, the lower the intensity of the reflected proportion of radiation generally is. How great the maximum detectable order is depends on the wavelength, the type of crystal used and the angular range of the spectrometer.

It can be seen from Bragg's equation that the product of reflection order 'n = 1, 2, ...' and wavelength ' ' for greater orders, and shorter wavelengths ' * < ' that satisfy the condition ' * = /n', give the same result.

Accordingly, radiation with one half, one third, one quarter etc. of the appropriate wavelength (using the same type of crystal) is reflected below an identical angle ' ':

1 = 2( /2) = 3( /3) = 4( /4) = ...........

As the radiation with one half of the wavelength has twice the energy, the radiation with one third of the wavelength three times the energy etc., peaks of twice, three times the energy etc. can occur in the pulse height spectrum (=energy spectrum) as long as appropriate radiation sources (elements) exist. (Fig. 16).

Fig. 16 shows the pulse height distribution of the flow counter using the example of the element haf-nium (Hf) in a sample with a high proportion of zircon. The Zr K 1 – peak has twice the energy of the Hf L 1 – peak and appears, when the Hf L 1 – peak is set, at the same angle in the pulse height spec-trum.


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Fig. 16: 2nd order reflection (n=2)

Crystal types

The wavelength dispersive X-ray fluorescence technique can detect every element above the atomic number 4 (Be). The wavelengths cover the range of values of four magnitudes: 0,01 - 11.3 nm (cf. Table 1). As the angle can theoretically only be between 0° and 90° (in practice 2° to 75°), 'sin 'only accepts values between 0 and +1. When Bragg's equation is applied:

1sin2

0d

n


DOC-M84-E06001 July 2004 31

this means that the detectable element range is limited for a crystal with a lattice plane difference 'd'. Therefore a variety of crystal types with different '2d' values is necessary to detect the whole element range (from atomic number 4). Table 4 shows a list of the common crystal types.

Lithiumfluoride crystals which also state the lattice planes (200, 220, 420) are identical to the following names:

LiF(420) = LiF(210)

LiF(220) = LiF(110)

LiF(200) = LiF(100)

Besides the 2d-values, the following selection criteria must be considered when a particular type of crystal is to be used for a specific application:

resolution

reflectivity (-- intensity)

Further criteria can be:

temperature stability

suppression of higher orders

crystal fluorescence


DOC-M84-E06001 July 2004 32

Table 4: Crystal types

Crystal Name Element range 2d-value (nm)

LiF(420) Lithiumfluoride > Co K 1 0.1801

LiF(220) Lithiumfluoride > V K 1 0.2848

LiF(200) Lithiumfluoride > K K 1 0.4028

Ge Germanium P, S, Cl 0.653

InSb Indiumantimonide Si 0.7481

PET Pentaerythite Al - Ti 0.874

AdP Ammoniumdihydrogenphosphate Mg 1.0648

TlAP Thalliumhydrogenphthalate F, Na 2.5760

OVO-55 Multilayer [W/Si] O - Si (C) 5.5

OVO-N Multilayer [Ni/BN] N 11

OVO-C Multilayer [V/C] C 12

OVO-B Multilayer [Mo/B4C] B (Be) 20

Dispersion, Line Separation

The extent of the change in angle upon changing the wavelength by the amount (thus: is called “dispersion”. The greater the dispersion, the better is the separation of two adjacent or over-lapping peaks. Resolution is determined by the dispersion as well as by surface quality and the purity of the crystal.

Mathematically, the dispersion can be obtained from the differentiation of the Bragg equation:

cos2d

n

d

d

It can be seen from this equation that the dispersion (or peak separation) increases as the lattice plane distance 'd' declines.


DOC-M84-E06001 July 2004 33

Examples: (cf. Table 5)The 2 -values of the K 1-peaks of vanadium (V) and chromium (Cr) are further apart when measuring with LiF(220) than when measuring with LiF(200).

The 2 values of the K 1-peaks of sulphur (S) and phosphorus (P) are further apart when measuring with the Ge crystal than when doing so with the PET crystal (cf. e.g.: Bruker AXS table-top periodic table).

Table 5: Explanatory details for dispersion

Crystal type 2d-value (nm) 2 (El1) (degrees) 2 (El2) (degrees) Difference (degrees)

LiF(220) 0.2848 107.11 (Cr) 123.17 (V) 16.06

LiF(200) 0.4028 69.34 (Cr) 76.92 (V) 7.58

Ge 0.653 110.69 (S) 141.03 (P) 30.34

PET 0.874 75.85 (S) 89.56 (P) 13.71

The following describes the characteristics of the individual crystal types divided into “standard crys-tals”, “multilayers” and “special crystals”.

Standard Types, Multilayers

LiF(200), LiF(220), LiF(420)

LiF crystal types exist in a variety of lattice planes (200/220/420). In the sequence (200) -- (220) --(420), resolution increases and reflectivity decreases (Fig. 17).


DOC-M84-E06001 July 2004 34

Fig. 17: Intensities of the crystals Lif(220) and Lif(420) in relation to Lif(200). (Intensity LiF(200) = 1)

LiF(200): A universally usable crystal for the element range atomic number 19 (K) onwards; high reflectivity, high sensitivity (HS).

LiF(220): Lower reflectivity than the LiF(200) but higher resolution (HR); can be used for the element range atomic number 23 (V) onwards; particularly suitable for better peak separation where peaks overlap.

Examples for the application of the LiF(220) for reducing peak overlaps:

Cr K 1,2 - V K 1

Mn K 1,2 - Cr K 1

U L 1 - Rb K 1,2


DOC-M84-E06001 July 2004 35

LiF(420):

One of the special crystals; can be used for the element range atomic number 28 (Ni or Co K 1) on-wards; best resolution but low reflectivity;

Fig. 17 shows a reflectivity of only 10% of that of the Lif(200) for the Lif(420) in the energy range around 10 keV.

PET:A universal crystal for the elements Al to Ti (K-peaks) and Rb to I (L-peaks).

ATTENTION

The PET is the crystal with the greatest heat-expansion coefficients, i.e. temperature fluctuations are most noticeable here.

Multilayers OVO-55, OVO-160, OVO-N, OVO-C, OVO-B Multilayers are not natural crystals bur artificially produced 'layer analyzers'. The lattice plane dis-tances 'd' are produced by applying thin layers of two materials in alternation on to a substrate (Fig. 18). Multilayers are characterized by high reflectivity and a somewhat reduced resolution. For the analysis of light elements the multilayer technique presents an almost revolutionary improvement for numerous applications in comparison to natural crystals with large lattice plane distances (e.g. RbAP, PbST, KAP).


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Fig. 18: Diffraction in the layers (here: Si/W) of a multilayer

OVO-55: The most commonly used multilayer with a 2d-value of 5.5 nm for analysing the elements N (C) to Si; standard application for measuring the elements F, Na, Mg.

Special Crystals

The term 'special crystals' refers to crystal types and multilayers that are not used universally but are employed in special applications.

LiF(420): Cf. 'standard types', description of the LiF crystals (200, 220, 420).


DOC-M84-E06001 July 2004 37

Ge:A very good crystal for measuring the elements S, P, Cl. In comparison to PET, Ge is characterised by a higher dispersion and a more stable temperature behaviour. Ge suppresses the peaks of the 2nd and 4th order, in particular.

Ge is especially suitable for differentiating between sulphide/sulphate e.g. in samples of cement.

AdP:In practice, AdP is only used for the analysis of Mg and has a higher resolution with a significantly lower reflectivity compared to the multilayer OVO-55. AdP is therefore required where interference peaks can occur such as in the case of low Mg concentrations in an Al matrix.

TlAP:TlAP has high resolution but low reflectivity and is recommended for analysing F and Na if the resolu-tion of OVO-55 is insufficient (e.g. where Na is overlapped by the Zn-L peaks in Zn-rich samples).

DANGER

Disadvantages are the limited lifetime, toxicity, and high price.

InSb:InSb is a very good crystal for analysing Si in traces as well as in higher concentrations (e.g. glass). It replaces PET and is used wherever high precision and great stability is required. The disadvantages are the limited use (only Si) and the high price.

OVO-C:OVO-C is a multilayer with a 2d value of 12 nm, specially optimized for carbon.

OVO-N:OVO-N is multilayer with a 2d-value of 11 nm, specially optimized for nitrogen.

OVO-B:OVO-B is multilayer with a 2d-value of 20 nm, specially optimized for boron and is equally suitable for the analysis of Be.


DOC-M84-E06001 July 2004 38

Which multilayer crystal is the most suitable for analysing the very light elements? Fig. 19a shows that the OVO-B is the best one for analysing Boron (B), naturally with the correspond-ing coarse collimator (at least 2° opening). A compromise for analysing Boron can be the OVO-160 when Carbon (C) should be also measured with the same crystal.

For the analysis of Carbon (C) the OVO-C provides a sharper peak and a better ratio of the peak / background intensities, which means that better sensitivies can be achieved (Fig. 19b). To apply the OVO-55 for analysing Carbon should be exceptional in case of having no OVO-C or OVO-160. Only very high concentrations (several tens of per cent) of Carbon can be determined with the OVO-C. In case of determining Carbon with the OVO-55 using the „standardless“ precalibrated XRF routine, please don´t forget to select a very slow scanning speed (long measuring time) for Carbon or to select the peak/background measurement mode.

Nitrogen (N) is best analysed using the OVO-N. If needed, the OVO-55 can be applied also (Fig. 19c). OVO-B, OVO-C and OVO-160 are not suitable to analyse Nitrogen.

Oxigen (O) and all further „heavier“ light elements have to be analysed with the OVO-55 which gives the best resolution and the best peak/background ratio (Fig. 19d).


DOC-M84-E06001 July 2004 39

B KA1,2 in BN (OVOs; 2,0°; 20kV/50mA)

05 (#) - B - - - - - -

Operations: Import [004]

Immediate Measurement - Crystal: OVO-N - 2Th.0: 5


Immediate Measurement - Crystal: OVO-C - 2Th.0: 4


Immediate Measurement - Crystal: OVO-160 - 2Th.0


Immediate Measurement - Crystal: OVO-B - 2Th.0: 1

Lin

(KC

ps)

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SqE - Scale7,025 7,03 7,04 7,05 7,06 7,07 7,08 7,09 7,10

SqE - Scale

7,025 7,03 7,04 7,05 7,06 7,07 7,08 7,09 7,10

OVO-B

OVO-160

OVO-C

OVO-N

Fig. 19a: OVO-B is the best multilayer crystal for analysing Boron (B).


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C KA1,2 in Graphite (OVOs; 1,0°; 20kv/50mA)

06 (#) - C - - - - - -


Immediate Measurement - Crystal: OVO-55 - 2Th.0:









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(KC

ps)

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SqE - Scale6,90 6,91 6,92 6,93 6,94 6,95 6,96 6,97 6,98 6,99 7,00 7,01 7,02 7,03

SqE - Scale

6,90 6,91 6,92 6,93 6,94 6,95 6,96 6,97 6,98 6,99 7,00 7,01 7,02 7,03

OVO-160

OVO-C

OVO-N

OVO-55

OVO-B

Fig. 19b: The OVO-C multilayer crystal is suitable for the determination of Carbon.


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N KA1,2 in NOPS (OVOs; 1,0°; 20kV/50mA)

07 (#) - N - - - - - -











Sqr

(KC

ps)

0

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SqE - Scale6,837 6,84 6,85 6,86 6,87 6,88 6,89 6,90 6,91

SqE - Scale

6,837 6,84 6,85 6,86 6,87 6,88 6,89 6,90 6,91

OVO-N

OVO-55

OVO-B

OVO-C

OVO-160

Fig. 19c: Nitrogen (N) is best analysed using the OVO-N.


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O KA1,2 in NOPS (OVOs; 0,46°; 20kV/50mA)

08 (#) - O - - - - - -









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6,712 6,72 6,73 6,74 6,75 6,76 6,77 6,78 6,79 6,80 6,81 6,82

OVO-C

OVO-160

OVO-N

OVO-55

Fig. 19d: Oxigen (O) and all further „heavier“ light elements have to be analysed with the OVO-55.


DOC-M84-E06001 July 2004 43

Curved Crystals

Whereas flat crystals are used in sequence spectrometers, multichannel spectrometers principally employ curved crystals (cf. instrumentation, Fig. 21 - 23).

The curvature of the crystals is selected in such a way that by applying a slit optics the X-ray entrance slit is focussed by the curved crystals onto the exit slit. This allows higher intensities in a space-saving geometric arrangement.

Different types of crystal curvature are used for focussing. The most commonly used are the curva-tures that follow a logarithmic spiral (Fig. 20a) and the Johansson curvature (including grinding) (Fig. 20b).

Fig. 20a: Logarithmic spiral curvature Fig. 20b: Johansson curvature

Introduction to X-Ray Fluorescence Analysis (XRF) Instrumentation

DOC-M84-E06001 July 2004 45

Instrumentation

The following explains the instrumentation in the Bruker AXS X-ray fluorescence spectrometer. The first three sections contain brief summaries on the multichannel X-ray spectrometer MRS, the older side-window sequential spectrometer SRS 200 and the SRS 30X. The fourth section deals in detail with the technology of the sequential spectrometers SRS 3X00 and S4.

The Multichannel Spectrometer MRS

The multichannel spectrometer MRS can measure up to 28 elements simultaneously. A multichannel spectrometer is always required where short measuring periods are necessary when analysing large numbers of elements, or a high throughput of samples (e.g. 600 samples per day) must be dealt with as in industrial quality and production control processes.

An individual measuring channel incorporating crystal, detector and electronics module must be in-stalled for each element line. As there are limited possibilities for the geometric arrangement of 28 channels in close proximity to the sample, so-called monochromators with slit-optics are used. A monochromator comprises an arrangement of entry slit, curved focussing crystal and an exit slit (Fig. 21, Fig. 22). The crystals are curved in a logarithmic spiral and focus the desired wavelength of the beam passing through the entry slit on to the exit slit. The detector is located behind the exit slit. Scintillation counters or gas proportional counters are used depending on the element line. Flow counters as well as sealed proportional counters can be used as gas proportional counters. Sealed proportional counters can be equipped with a 25 µm Be or an SHT (Super-High Transmission) win-dow. The 25 µm thin Be window is used for the elements Al - Fe. The new SHT window is used for the elements Be to Mg.

All monochromators are located in a large vacuum chamber. The beam is applied from above. The fixed channels are used exclusively for quantitative analyses. A scanner can be employed for qualita-tive analysis.

Instrumentation Introduction to X-Ray Fluorescence Analysis (XRF)

DOC-M84-E06001 July 2004 46

As all elements are measured simultaneously, a generator setting (kV/mA) must be selected that pro-vides the best compromise in each case for the components to be measured. The measurement pe-riod depends on statistical accuracy requirements of the element with the lowest intensity and is typi-cally around 20 – 60 seconds. No background positions can be measured as the monochromators are at a fixed setting to the angle of the appropriate line.

When measuring trace and major elements simultaneously, the generator is normally set so that the trace elements can be measured with the highest possible intensity. This means that the major ele-ments are usually of very high intensity that cannot be processed by the detectors. For cases such as these, the MRS can be fitted with absorbers (attenuator) for the major elements whose intensities are reduced sufficiently for them to then lie in the operational range of the detectors.

Fig. 21: Beam entry in the MRS


DOC-M84-E06001 July 2004 47

Fig. 22: Monochromator with absorber and flow counter

Scanners for MRS 400, MRS 404 and MRS 4000

In addition to the fixed channels, a scanner can be installed in the vacuum chamber of multichannel spectrometer. The scanner is a 'move-able channel' (linear spectrometer) enabling sequential cover-age of a large element range. As only a single curved crystal (LiF(200) or PET) is fitted, several ele-ments in the periodic table must be measured in the 2nd reflection order as the scanner's 2 -angular range is limited (30 - 120 degrees). A flow counter or a sealed proportional counter serves as a detec-tor.

The scanner works on the physical principle of the Rowland-Circle, i.e. the crystal and detector move in such a way that the entry slit, crystal and exit slit lie on a fixed-radius circle that changes its position (Fig. 23).

The scanner can be used for qualitative as well as quantitative analyses.


DOC-M84-E06001 July 2004 48

Fig. 23: The scanner principle, the Rowland-Circle

The Sequential Spectrometers SRS 3X00 and S4

The heart of the spectrometer is a high-precision goniometer with two independent stepper motors for separate drive.

Several microprocessors control and monitor the functions and processes inside the spectrometer. A master processor coordinates the internal flow of information and communicates with the external analysis computer (PC). Having its own service interface enables the master processor be remote-diagnosed by the Bruker AXS-Service-Centers via Teleservice, without being able to access security-relevant data in the analysis computer. This concept optimizes the diagnosis possibilities and rapid fault location.

The various measuring parameters are set exclusively via the analysis computer’s software and pro-vides the user with great flexibility.


DOC-M84-E06001 July 2004 49

Besides extending the adjustment parameters of the primary beam filter, the crystal and collimator changer beyond those possible on the SRS 303, the detector high-voltages, too, are set via the analy-sis computer.

The separate goniometer drive with two independent stepper motors allows a precise angle alignment via the analysis computer’s software.

The flow counter is situated inside the spectrometer chamber and has an angle scope of 2° to 148°. Located behind the flow counter and outside the chamber, separated by a 0.1 mm Al foil, is the scintil-lation counter with an angle scope of 2° to 110°. Both detectors can be used individually or in tandem. In tandem operation, the intensity in the flow counter is measured as well as the radiation that passes through the flow counter and the radiation that is absorbed by the scintillation counter.

Tandem operation was excluded from the S4 EXPLORER and the S4 PIONEER to save space and the scintillation counter located in the spectrometer chamber next to the proportional counting tube.

Integrating temperature measuring points allows this stability-relevant factor to be checked in the in-strument. Furthermore, the temperature of the water in the internal deionised cooling system is kept constant.

An optional protractable/retractable foil screen can be installed between the sample chamber and the spectrometer chamber for measuring, for example, liquids in an He atmosphere.

Fig. 24 shows the beam path and the adjustable factors of the S4 basically contains the same compo-nents.

A flexible, modifiable sample changer with a robot arm that moves in the directions X and Y allows fully automatic transport of:

sample cups with a grab

'bare samples' with a suction unit

combinations of both

steel rings with a magnetic holder

to the instrument’s entry position. The SRS 3000 was the first X-ray spectrometer with an X-Y-sample magazine thereby setting the standard for all of the manufacturer’s subsequent developments as well as for those of competitors. An internal 2-sample changer enables rapid processing of samples in


DOC-M84-E06001 July 2004 50

stack operation without time-loss through transporting samples, i.e. while one sample is being meas-ured, the next is being inserted into the pre-vacuum chamber.

Fig. 24 Beam path in the S4

Problem-free docking on to a conveyor belt allows easy integration into an automated environment.

The function and possible settings for the various parameters will now be described in the order they are encountered by the beam propagating from the tube to the scintillation counter.

X-ray Tube

Primary Beam Filters

SampleVacuum Seal

Collimators

Analyzer Crystals

ScintillationCounter

Proportional Counter


DOC-M84-E06001 July 2004 51

The End-window Tube and Generator

The tube and generator are designed for a permanent output of 4 kW (S4 PIONEER) at a maximum high voltage of 60 kV and a maximum tube current of 100 mA or 150 mA. The combination of high voltage and tube current must not exceed 4 kW, e.g. at 4 kW max.:

27 kV / 150 mA = 4,05 kW

30 kV / 134 mA = 4,02 kW

40 kV / 100 mA = 4,00 kW

50 kV / 80 mA = 4,00 kW

60 kV / 67 mA = 4,02 kW

Minimum settings: 20 kV / 5 mA = 0,1 kW

NOTE

The control and analysis software SPECTRA AT / SPECTRA 3000 / SPECTRAplus checks the settings and prevents the maximum permissible values being exceeded.

Rhodium is used as the standard anode material. The light elements Be to Cl are effectively excited by the Rh-L beam’s high transmission rate through the 75 µm Be tube window. The characteristic Rh-K radiation excites the elements up to Mo (Ru) (cf. also Table 2, page 9). The elements from Rh on-wards are excited by the Bremsstrahlung’s high-energy “tail”.

4 kW-Tubes with other anode materials can be used for special applications (e.g. Mo, W, Au, Cr)

The Primary Beam Filter

The primary beam filter is seated on a changer for 10 positions (including vacant positions) and is equipped with a selection of absorber foils. It is located between the tube and the sample and serves the purpose of filtering out undesirable or interfering components of the tube radiation for certain applications and improves the signal-to-noise ratio. Al and Cu foils, for example, are used in a variety


DOC-M84-E06001 July 2004 52

of thickness as absorbers. The one fitted can be selected to suit individual requirements when pur-chasing the instrument.

When measuring Rh K with the Rh tube, the characteristic Rh radiation coming from the tube must be filtered out because it would otherwise be measured as a result of elastic scattering on the sample (cf. page 15). By using a 0.2 mm-thick Cu filter, the characteristic Rh tube radiation is largely absorbed prior to reaching the sample. The measurement must be taken with a tube high-voltage of 60 kV as the Rh in the sample is only excited by the high-energy Bremsstrahlung.

Fig. 25 illustrates the tube spectrum acting on the sample without a primary beam filter and tube high-voltage of 60 kV.

Fig. 26 shows the reduction in Rh radiation scattering on a plant sample using different primary beam filters made of copper or aluminium.

Fig. 25: Cd- and Rh-peak without a copper primary beam filter


DOC-M84-E06001 July 2004 53

Fig. 26: Cd- and Rh-peak with 0.2 or 0.3 copper primary-beam filter

Fig. 27: The effect of the aluminium primary beam filter for optimizing the peak-background ratio


DOC-M84-E06001 July 2004 54

When analysing a sample of very pure graphite, peaks of the elements Cr, Fe, Ni und Cu can occur and in the 2 -spectrum although the sample contains none of the elements. The Cu peak originates from the excitation of the collimator material that mainly consists of copper.

The Cr, Fe and Ni peaks are called “spectral impurities” of the tube. If the elements Cr, Fe and Ni are to be measured as traces, it may be advantageous to use the 0.2 mm Al filter to absorb these compo-nents.

Sample Cups, the Cup Aperture

In the S4, the sample to be measured is first of all fed into the 2-sample changer’s prevacuum cham-ber and subsequently into the measuring position where it rotates up to 30 revs per minute, depending on the application, to even out sample inhomogenity. In the S4 EXPLORER, the S4 collimator mask’s optimized screening allows steel apertures to be used in the majority of cases. Other aperture diame-ters and materials are available on request.

Depending on type of sample magazine, the samples have to be placed in the cups manually (maga-zine with grab) or the magazine is designed for “bare samples” (magazine with sucker) or steel rings (magazine with magnet) which put the sample into the cup automatically. When using thin filters for measurements it must be ensured that an anti-background scattering cup is used to eliminate the fix-ing plate radiation.

The Vacuum Seal

When measuring (liquid) samples in a helium atmosphere, the vacuum can be maintained in the spec-trometer volume by inserting a thin separating, or sealing, foil between the sample chamber and the spectrometer chamber. This causes the separating foil to absorb less radiation than would be the case if the spectrometer chamber were filled with helium.

For alternate measurements of samples in a vacuum and helium, this technique considerably quickens the change from one operating mode to another as a result of the smaller sluicing volume and reduces the helium consumption.


DOC-M84-E06001 July 2004 55

Collimator Masks

The collimator masks are situated between the sample and collimator and serve the purpose of cutting out the radiation coming from the edge of the cup aperture. The size of the mask is generally adapted to suit of the cup aperture being used. The SRS 3X00’s changer has 4 positions, the SRS 300/303 is equipped with a 3-position changer. The S4 EXPLORER employs a new collimator mask that is set very close to the sample and therefore optimally screens the sample cup aperture.

Collimators, the Soller Slit

Collimators consist of a row of parallel slats and select a parallel beam of X-rays coming from the sample and striking the crystal. The spaces between the slats determine the degree of parallelism and thus the angle resolution of the collimator.

The SRS 3X00 and the S4 EXPLORER are fitted with a 4-position changer. Besides the standard collimators with aperture angles of 0.15° and 0.46° (S4: 0.23 and 0.46) two additional collimators can be installed to optimize the measurement parameters, depending on the application. A 0. 077° collima-tor is available for high-resolution measurements (e.g. with LiF(420)). Collimators with a low resolution (e.g. 1.5 – 2.0°) are advantageous for light elements such as Be, B and C as the OVO-Multilayer’s angle resolution is limited. Using a collimator with a low resolution increases then intensity signifi-cantly. This enables intensity to be increased without a loss in angle resolution when analysing the light elements (Fig. 28).


DOC-M84-E06001 July 2004 56

Fig. 28: The influence of collimator resolution on the intensity for light elements

The Crystal Changer

The SRS 3X00‘s and S4 EXPLORER’s crystal changer can hold up to 8 crystals and be custom-equipped to suit the requirements of specific fields of application.

The Flow Counter

The flow counter is located inside the vacuum chamber and has an entrance window made of a thin, aluminium-coated foil that be selected with a thickness of 0.6 µm or 0.3 µm.

This allows optimum measurement of the light elements Be to Na. Fig. 29 illustrates the permeability for a variety of counting-tube foils that were used in older instruments (SRS 200 / 300). It can be seen from the transmission curve, for example, that the permeability of the 1 µm polypropylene foil for Na is around twice that of the 2 µm Makrofol-foil.


DOC-M84-E06001 July 2004 57

ATTENTION

As the plastic foils have a high proportion of carbon, the absorption of the nitrogen radiation close to the C absorption edge is very high. This means that even the 1 µm foil only has an approx. 10% per-meability. For this reason, the measured intensities for the element N are relatively low. The newer 0.6 µm and especially the 0.3 µm foils are more permeable to nitrogen radiation.

Generally, Ar + 10% CH4 is used as the counting gas (P10). The flow of counting gas is held constant in the instrument as a fluctuating counting-gas density in the counting tube would cause fluctuations in the absorption depth as well as fluctuations in the gas amplification and thus in the position of the peaks in the pulse height spectrum, too (cf. Fundamental Principles: The gas proportional counter Fig. 8).

The high voltage at the counting wire is set higher for light elements (OVO Multilayer) than for measur-ing the K-radiation (e.g. LiF crystals) of medium and heavy elements. In sequential spectrometers the detector high voltage is set separately for each element range (energy range) and thus for each in-stalled crystal (cf. also Fig. 8 ).

The Sealed Proportional Counter

The S4 EXPLORER is the first device in XRF to utilise a sealed proportional counter thus enabling even the very light elements (Be – Na) to be determined effectively as with a flow counter. The basis for this is provided by the newly developed window material with very high transmission (SHT win-dow).


DOC-M84-E06001 July 2004 58

Fig. 29: X-ray transmission for various counting-tube foils

The Scintillation Counter

The scintillation counter is positioned behind the flow counter outside the vacuum chamber. The ra-diation measured inside it must pass through the flow counter, a 0.1 mm thick vacuum-chamber seal-ing foil and a 0.2 mm Be entrance window. It therefore makes sense to use the scintillation counter for energies above

approx. 4.5 keV (Cr K 1) as the lower ones are absorbed mainly in the flow counter (cf. Fundamental Principle: The scintillation counter Fig. 9).

The SC’s angle scope ranges from 4° to 110° (SRS 30X: 4° to 90°).


DOC-M84-E06001 July 2004 59

In the S4 EXPLORER the scintillation counter is directly beside the proportional counter in the spec-trometer chamber and can be moved from 0° to 115°.

Electronic Pulse Processing

The pulses produced in the detectors by X-rays are processed and counted by subsequent electronic processing. The flow counter’s signals are electronically amplified in a preamplifier, shaped and further processed as voltage pulses in a main amplifier (sine amplifier) and discriminator. After the photomul-tiplier, the scintillation counter’s signals are fed directly into a main amplifier and discriminator.

The Discriminator

Depending on the application, higher order peaks or other sources of interference appear in the pulse height distribution, or the detectors‘ energy spectrum (cf. also Fig. 10a, b and Fig. 11) with different levels of energy. A discriminator window is used to set a lower and an upper pulse-height threshold. Only the pulse heights that lie within these limits are counted In this way, higher order peaks or inter-ference radiation with pulse heights beyond the window are supressed (cf. Fig. 16). Discriminating undesirable pulses reduces the background.

Main Amplifier, Sine Amplifier

After the preamplifier (flow counter and proportional counter), or photomultiplier (scintillation counter), the pulses are further enhanced electronically in a main amplifier. As the detectors' high voltage is set separately for each crystal, i.e. as the gas amplification in the flow counter and proportional counter, or the photomultiplier’s amplification, depends indirectly on the crystal, the electronic additional ampli-fication must also be made dependent on the crystal used.

X-ray energies, for example, of 3.3 keV to 30 keV (potassium to iodine) are detectable with LiF(200). To have each one of the set peaks in the pulse height spectrum always appear in the same place (= identical pulse height), the electronic amplification must be linked to the goniometer’s angle setting. This is achieved by making the main amplifier’s amplification factor V for the appropriate crystal (2d value) and the selected reflection order (n) dependent on the sine of the adjustment angle:

V sin


DOC-M84-E06001 July 2004 60

This is the only way of ensuring that a discriminator window once set for a crystal will be applicable for all detectable energies (element peaks).

A main amplifier coupled in this way is called a sine amplifier.

Dead Time Correction

The electronics need a certain amount of time to process a pulse during which no other pulse can be registered. This period is called counter channel dead time for an individual pulse. As the pulse forma-tion is different for the flow counter and the scintillation counter, the dead times (ca. 300 to 400 ns) are also different for both detectors. The total dead time is the result of an individual pulse multiplied by the pulse rate. As the measured pulses occur statistically distributed over time, the proportion of pulses occurring during the processing period of a previously registered pulse depends on the inten-sity of the radiation, i.e. the total dead time increases due to the increase of the intensity. This results in a non-linear rise of the measured intensity with the intensity irradiated in the detector. The greater the incident intensity, the greater the losses during measurement. Fig. 30 illustrates how the dead time is dependent on the increasing incident intensity (increasing generator current). The curve flattens out distinctly at high measured intensities.

A correction of the measured intensities is necessary to produce a linear relationship between incident and measured intensities. A dead time correction can be made in the analysis computer. Fig. 31 shows the dead time corrected measurement points. A useful correction can be obtained in tandem operation up to an incident intensity of approx. 1.200 KCps per detector. Greater intensities are not worthwhile.

For routine operation it is recommended not to exceed an intensity of approx. 400 KCps per detector.


DOC-M84-E06001 July 2004 61

Fig. 30: The dead time effect

Fig. 31: Dead time corrected readings


DOC-M84-E06001 July 2004 62

Line-shift Correction

Line-shift correction is only important for the flow counter and the proportional counter at high intensi-ties. It makes itself noticeable when the peak in the pulse height spectrum shifts to lower values at high counting rates. The reason for this is that high counting rates in the detector volume between the flow counter’s cathode and counting wire build up a space charge that causes a temporary reduction of the effective high voltage and thus the reduction of gas amplication.

This shift of pulse heights to lower values is automatically corrected by the electronics. The correction can be switched on and off in the software (SPECTRA 3000 / SPECTRAplus).

Introduction to X-ray Fluorescence Analysis (XRF) Appendix A: Literature

DOC-M84-E06001 July 2004 63

Appendix A

Supplementary Literature

Books

Eugene P. Bertin Introduction to X-Ray Spectrometric Analysis Plenum Press, New York - London, 1978

L.S. Birks X-Ray Spectrochemical Analysis Interscience Publishers, New York Second Edition 1969

Blokhin Methods of X-Ray Spectroscopic Research Pergamon, New York, 1965

Victor E. Burke, A practical guide for the preparation of specimens for Ron Jenkins, X-ray fluorescence and X-ray diffraction analysis Deane K. Smith Wiley-VCH, 1998, 333 pp. (Eds.) ISBN 0-471-19458-1

Harry Bennet, XRF Analysis of Ceramics, Minerals and allied materials Graham J. Oliver John Wiley & Sons, 1992 ISBN 0-471-93457-7

Appendix A: Literature Introduction to X-ray Fluorescence (XRF) Analysis

DOC-M84-E06001 July 2004 64

Dekker Handbook of X-ray Spectrometry, 1993, 704 pp. ISBN 0-8247-8483-9

P. Hahn-Weinheimer Röntgenfluoreszenzanalytische A. Hirner Methoden, Grundlagen und praktische Anwendung in den Geo-, K. Weber-Diefenbach Material- und Umweltwissenschaften Friedrich Vieweg & Sohn, Braunschweig / Wiesbaden 1995 ISBN 3-528-06579-6

Ron Jenkins An Introduction to X-Ray Spectrometry Heyden, London - New York - Rheine, 1974

Jenkins and de Vries Practical X-Ray Spectrometry MacMillan, London, 1976

Rudolf O. Müller Spektrochemische Analysen mit Röntgenfluoreszenz R. Oldenburg, München - Wien, 1967

Rolf Plesch Auswerten und Prüfen in der Röntgenspektrometrie G-I-T Verlag Ernst Giebeler, Darmstadt, 1982 ISBN 3-921956-23-4

Joachim Urlaub Röntgenanalyse Band 1: Röntgenstrahlen und Detektoren SIEMENS AG, Berlin - München, 1974 ISBN 3-8009-1193-0

Helmut Erhardt Röntgenfluoreszenzanalyse (Hrsg.) Anwendung in Betriebslaboratorien Springer Verlag ISBN 3-540-18641-7, ISBN 0-387-18641-7

Introduction to X-ray Fluorescence Analysis (XRF) Appendix A: Literature

DOC-M84-E06001 July 2004 65

Tables

J. Leroux Revised Tables of X-Ray Mass Attenuation Coefficients T. Ph. Thinh Corporation Scientifique Claisse Inc. Quebec 1977

R. Theisen Tables of X-Ray Mass Attenuation Coefficients D. Vollath Verlag Stahleisen m.b.H. Düsseldorf 1967

X-Ray Absorption Wavelengths and Two-Theta Tables Second Edition ASTM Data Series DS37A, published by the American Society for Testing and Materials 1916 Race Street Philadelphia, PA 19103 Heyden, London - New York - Rheine, 1973

Journals

XRS X-Ray Spectrometry ISSN 0049-8246 John Wiley & Sons Limited Baffins Lane, Chichester, Sussex PO19 1UD England

Introduction to X-ray Fluorescence Analysis (XRF) Appendix B: Sources of standard samples

DOC-M84-E06001 July 2004 67

Appendix B

Sources of Standard Samples

NBS U.S Department of Commerce National Bureau of Standards Washington, DC 20234, USA Tel.: (301) 921-2045

BAS Bureau of Analyzed Samples Ltd. Newham Hall, Newsby Middlesbrough, Cleveland, TS8 9EA England

CANMET Canadian Certified Reference Materials 555 Booth Street Ottawa, Ontario, K1A OG1 Canada

MBH MBH Analytical Ltd. Certified Reference Materials Holland House, Queens Road, Barnet, Herts EN5 4DJ England

Appendix B: Sources of standard samples Introduction to X-ray Fluorescence Analysis (XRF)

DOC-M84-E06001 July 2004 68

BNF Analytical Reference Materials Grove Laboratories Denchworth Road Wantage, Oxon, OX12 9BJ England

BCR Reference Materials Commission of the European Communities Community Bureau of Reference Vertrieb: Herr Ornigg Siemens Societe Anonyme Chaussee de Charleroi 116 B-1060 Bruxelles

ALCOA Spectrochemical Standards for Analysis of Aluminium and its Alloys Aluminium Company of America Alcoa Laboratories Alcoa Center, Pennsylvania 15069 USA

ALCOA European sales: Alcoa of Great Britain Ltd. Droitwich, Worcestershire, P.O. Box 15 England

Breitländer Eichproben und Labormaterial GmbH Postfach 8046 D-59035 Hamm Tel.: 02381-404000

Introduction to X-ray Fluorescence Analysis (XRF) Appendix C: Sample Preparation Catalog

DOC-M84-E06001 July 2004 69

Appendix C

Sample Preparation Catalog for XRF Analysis

Introduction

X-ray fluorescence (XRF) analysis is a fast, non-destructive and environmentally friendly analysis method with very high accuracy and reproducibility. All elements of the periodic system from beryllium to uranium can be measured qualitatively, semiquantitatively and quantitatively in powders, solids and liquids. Concentrations of up to 100 % are analysed directly and without any dilution – with reproduci-bilities better than ± 0.1 %. Typical limits of detection are from 0.1 to 10 ppm. Most modern X-ray spectrometers with modular sample changer concepts enable a fast, flexible sample handling and adaptation to customer specific automation processes without any problems.

XRF analysis is a physical method which directly analyses almost all chemical elements of the periodic system in solids, powders or liquids. These materials may be solids such as glass, ceramics, metal, rocks, coal, plastic or liquids, like petrol, oils, paints, solutions, blood or even wine. With an X-ray fluo-rescence spectrometer both very small concentrations of very few ppm and very high concentrations of up to 100 % can directly be analysed without any dilution process. Therefore XRF analysis is a very universal analysis method, which, – based on simple and fast sample preparation – has been widely accepted and has found a large number of users in the field of research and above all in industry. Especially in the extremely complex environmental analysis and in production and quality control of intermediate and end products, there are increasing possibilities for XRF analysis.

The quality of sample preparation in X-ray fluorescence analysis is at least as important as the quality of measurements.

An ideal sample would be prepared so that it is:

representative of the material

homogeneous

Appendix C: Sample Preparation Catalog Introduction to X-ray Fluorescence Analysis (XRF)

DOC-M84-E06001 July 2004 70

thick enough to meet the requirements of an infinitely thick sample

without surface irregularities

composed of small enough particles for the wavelengths to be measured

Elemental analysis using XRF provides a non-destructive and environmentally friendly analysis method without having to bring solid samples into solution and without having to dispose of solution residues, as is the case with all wet-chemical methods. Basic prerequisite for an exact and reproduci-ble analysis is a plane, homogeneous and clean analysis surface. For analysis of very light elements, e.g. beryllium, boron and carbon, the fluorescence radiation to be analysed originates from a layer, whose thickness is of only a few atom layers up to a few tenths of micrometer and which strongly de-pends on the sample material (Tab. 1). Therefore especially for analysis of light elements, sample preparation has to be carried out extremely carefully.


DOC-M84-E06001 July 2004 71

Tab. 1: Layer thickness (in m), where 90 % of the fluorescence radiation originate from

Sample matrix Graphite Glass Iron Lead

Line

U L 1

Pb L 1

Hg L 1

W L 1

Ce L 1

Ba L 1

Sn L 1

Cd K 1

Mo K 1

Zr K 1

Sr K 1

Br K 1,2

As K 1

Zn K 1,2

Cu K 1,2

Ni K 1,2

Fe K 1,2

Mn K 1,2

Cr K 1,2

Ti K 1,2

Ca K 1,2

K K 1,2

Cl K 1,2

S K 1,2

h_(90%, m)

28000

22200

10750

6289

1484

893

399

144600

60580

44130

31620

18580

17773

6861

5512

4394

2720

2110

1619

920

495

355

172

116

48.9

h_(90%, m)

1735

1398

709

429

113

71.3

44.8

8197

3600

2668

1947

1183

1132

466

380

307

196

155

122

73.3

54.3

40.2

20.9

14.8

16.1

h_(90%, m)

154

125

65.6

40.9

96.1

61.3

30.2

701

314

235

173

106

102

44.1

36.4

29.8

164

131

104

63

36.5

27.2

14.3

10.1

4.69

h_(90%, m)

22.4

63.9

34.9

22.4

6.72

4.4

3.34

77.3

36.7

28.9

24.6

55.1

53

24

20

16.6

11.1

9.01

7.23

4.52

3.41

3.04

2.19

4.83

2.47


DOC-M84-E06001 July 2004 72

Sample matrix Graphite Glass Iron Lead

Si K 1,2

Al K 1,2

Mg K 1,2

Na K 1,2

F K 1,2

O K 1,2

N K 1,2

C K 1,2

B K 1,2

31.8

20

12

3.7

1.85

0.831

13.6

4.19

10.5

7.08

5.56

1.71

2.50

1.11

0.424

0.134

3.05

1.92

1.15

0.356

0.178

0.08018

0.03108

0.01002

1.7

1.13

0.728

0.262

0.143

0.07133

0.03124

0.01166

Massive materials, such as rocks, soils, slags and similar samples have to be crushed, e.g. in a crush-ing device. The crushed material, as well as pieces thereof, are afterwards very finely pulverized in a vibrating disk mill or planetary ball mill in order to be suitable for analysis. The grain size diameter should then be inferior to 50 m. In earlier times, in the cement industry, milling in suspension was preferred (nowadays – in fully automatic sample preparation – it is dry milling using milling and binding agents), in order to reach grain sizes smaller than 15 m. The smaller and more equally grain-sized the sample, the more homogeneous the pressed powder sample will be. Through pressing under 10 to 20 t with pressing times of 5 to 10 seconds, the sample powder is pressed into aluminium cups, steel rings or directly freely with or without a binding agent. By rotating the sample holder in the spectrome-ter (with 30 r/min), inhomogeneities of the sample can be compensated.

Important for XRF analysis of powder samples is the homogeneity and the fineness of the sample powder, not only in the case of very light elements, but also e.g. for analysis of Si in samples contain-ing quartz. At the same time, reproducibility of the samples is very important, as XRF analysis is a comparing analysis method; this means that all unknown samples measured in comparison to a cali-bration curve should show the same grain size distribution as the standard samples used for calibra-tion. The importance of this requirement is often easily underestimated.

With high requirements in respect to sample homogeneity, fused beads are produced from the sample powder at 1100 up to 1200 °C. The melting process of the sample powder is supported by melting agents (e.g. lithium tetraborate) and, if necessary, also by oxidation agents, which are mixed into the sample in different ratios. In earlier times, the melting method was preferred, because of the de-


DOC-M84-E06001 July 2004 73

creased influence of the matrix effects due to the dilution of the sample matrix with the “lighter” melting agents. Nowadays very efficient PC programs are available for calculation of the correction coeffi-cients (“theoretical alphas”) for matrix correction, these, too, are successfully used for pressed pellets.

For this reason, only the excessive requirement for a very high analytical accuracy nowadays speaks against quicker and more inexpensive pressing of sample powder. With careful sample preparation (milling), a sufficient accuracy even with pressed pellets can often be reached. For this reason, sample preparation systems should be selected very carefully.

Since X-ray spectrometry is essentially a comparative method of analysis, it is vital that all standards and unknown samples are presented to the spectrometer in a reproducible and identical manner. Any method of sample preparation must give specimens which are reproducible and which, for a certain calibration range, have similar physical properties including mass absorption coefficient, density and particle size. In addition, the sample preparation method must be rapid and inexpensive and must not introduce extra significant systematic errors, for example, the introduction of trace elements from con-taminants in a diluent.


DOC-M84-E06001 July 2004 74

Preparation of solid samples

Metals

The preparation must be simple, rapid and reproducible. Usually, metallic samples are prepared as solid disks by conventional methods of machining: cutting, milling and polishing; grinding is used in the case of hard alloys and brittle materials such as ceramics.

The best polishing operation requires very fine abrasives to produce the scratch-free surfacing neces-sary for most analyses, and a mirror-like surface if the sample is to be analysed for light elements. The surface finish is of prime importance, because the polishing striations give rise to the so-called shield-ing effect which results in a decrease in fluorescence intensities. As expected, the decrease in inten-sity is more important for lighter elements when the primary radiation is perpendicular to the striations and weaker when they are parallel to them. For that reason, modern spectrometers are equipped with spinning sample holders to smooth out the influence of sample orientation, resulting in observed in-tensities on samples and standards that are reproducible.

However, the shielding effect may still be present; sample rotation will compensate for it only if the magnitude of the effect is the same for standards and production samples; this requires that the stria-tion be of the same size and that the sample composition be similar (same effective wavelength).

In practice, striation depths of 100 m are acceptable for elements with characteristic lines of short wavelengths, but striations deeper than few m may impair significantly the accuracy of Si, Al and Mg determinations.

Very fine grits of Al2O3, SiC, B6C (80 to 120 grits) are commonly used to obtain the desired surface finish for most metals (Fe, Ni and Co bases).

Mechanical polishing may be undesirable for soft, malleable, multiphase alloys because of smearing of the softer components; the intensities of the elements in softer phases increase while those of the harder phases decrease. In such cases, special precautions must be taken even during milling and especially in the final polishing operation (Pb, Cu, Al, Zn and Sn bases).

Polishing may be the source of contamination since currently used abrasives, SiC and Al2O3, contain two elements that are often determined in commercial alloys. Sample surface cleaning may be neces-sary to remove contamination as well as grease stains and handling residue.


DOC-M84-E06001 July 2004 75

Pressed pellets

Where powders are not affected by particle size limitations, the quickest and simplest method of preparation is to press them directly into pellets of equal density, with or without the additional use of a binder. In general, provided that the powder particles are less than about 50 m in diameter, the sam-ple will pelletize at around 10 to 30 t. Where the self-bonding properties of the powder are poor, higher pressure may have to be employed or in extreme cases a binder will be used. It is sometimes neces-sary to add a binder before pelletizing and the choice of the binding agent must be made with care. As well as having good self-bonding properties the binder must be free from significant contaminant ele-ments and must have low absorption. It must also be stable under vacuum and irradiation conditions and it must not introduce significant interelement interferences. Of the large number of binding agents which have been successfully employed probably the most useful are wax and ethyl cellulose.

The analysis of powder is invariably more complex than that of metallic samples, since the addition to interelement interferences and macroscale heterogeneity, particle size effects are also important. Al-though inhomogeneity and particle size can often be minimized by grinding and pelletizing at high pressure, often the effects cannot be completely removed because the harder compounds present in a particular matrix are not broken down. These effects produce systematic errors in the analysis of spe-cific type of material, e.g. siliceous compounds in slags, sinters and certain minerals.

Analytical data for longer wavelengths will sometimes be improved if a finely ground powder is com-pacted at higher pressures (say up to 30 t), thus a 40 ton press should be considered if light element analysis is required in pressed powder samples. A good quality die set is required to produce good quality pressed powder samples. A choice can be made between pressing into aluminium cups or steel rings. Alternatively boric acid backing can be used, or free pressing if a binder is used.

Sample preparation with the binding agent Moviol

Preparation of the solution Over a mild heat mix 100 ml aqua dest. with 2 g Moviol flakes. Stir the solution for approx. 15 to 20 min and, afterwards, transfer to a container to cool. If necessary, allow the undissolved parts to settle (cloudiness) and draw off the clear liquid. Transfer the solution to a PE dropper bottle and label it. The solution is now usable and can be kept for approx. 2 years.

Use of the binding agent A prerequisite is a finely ground sample powder. Depending on the sample type (for XRF/XRD analy-sis), three drops of Moviol will be used for 5 to 7 g samples, for example to be used with Polysius rings, aluminum rings or “freely” pressed 30 mm samples. For “freely” presses 40 mm samples (9 to 10 g) one should start with 4 drops.


DOC-M84-E06001 July 2004 76

We gently grind the sample containing Moviol by using a mortar and pestle, so that no more clumps are visible. Afterwards, the sample is transferred to a press. If the sample doesn’t bind firmly, then the amount of Moviol needs to be raised (quartzite or very quartz rich samples may need up to 50 drops / 10 g). Due to the volume of 150 ml = 1 drop, the concentration of C, H and O can be neglected.

User Tips Depending on the sample type (e.g. TiO2 or other “pasty” substances), it is helpful to cover the surface of the sample with a thick Mylar foil before pressing. A standard 12- m foil has proven to be success-ful for this purpose. The use of the foil keeps the sample from sticking to the plunger of the press and ensures an even smoother surface.

In the case of smaller amounts of a sample substance, one can prepare the sample by using the sandwich method:

Sample material

Boric acid

The afore mentioned sample will be pressed onto approx. 2 spatulas full of boric acid. The use of non-backscattering may is hereby be recommended. In all areas of application (XRD/XRF) it is necessary to make the sample layer on the boric acid so thick, that the sample appears to be infinitely thick. As a general rule, the thickness should be at least 1,5 mm.

For samples containing higher amounts of Moviol, the sample should be dried before measurement with the SRS or MRS; otherwise the evacuation time lasts too long.

Fused beads

The best way of completely removing these effects is to use the fusion technique. The dissolution or decomposition of a portion of the sample by a flux and the production of an homogeneous glass elimi-nates particle size and mineralogical effects entirely. The fusion technique also has additional advan-tages:

Possibility of high or low specimen dilution for the purpose of decreasing matrix effects

Possibility of adding compounds such as heavy absorbers or internal standards to decrease or compensate for matrix effects


DOC-M84-E06001 July 2004 77

Possibility of preparing standards of desired composition

Essentially the fusion procedure consists of heating a mixture of sample and flux at high temperatures (800 to 1200 °C) so that the flux melts and the sample dissolves. The overall composition and cooling conditions must be such that the end product after cooling is a one-phase glass.

Heating of the sample-flux mixture is usually done in platinum alloy crucibles, but graphite may also be used when the conditions permit.

The more frequently used fluxes are borates, namely sodium tetraborate, lithium tetraborate and lith-ium metaborate. Mixture of these fluxes are more effective in certain cases.

Preparation of liquid samples

Provided that the liquid sample to be analysed is single phase and relatively involatile, it represents an ideal form for presentation to the X-ray spectrometer. A special sample cup (liquid sample holder) and helium path instrument must be used for measurement. The liquid phase is particularly convenient since it offers a very simple means for the preparation of standards and most matrix interferences can be successfully overcome by introducing the sample into a liquid solution. Although the majority of matrix interferences can be removed by the solution technique, the process of dealing with a liquid rather than a solid can itself present special problems, which, in certain instances, can limit the useful-ness of the technique.

For example, the introduction of a substance into a solution inevitably means dilution and this, com-bined with the need for a support window in the sample cell, plus the extra background arising from scatter by the low atomic number matrix, invariably leads to a loss of sensitivity, particularly for longer wavelengths (greater than 2.5 Å). Problems can also arise from variations in the thickness and/or composition of the sample support film. The most commonly used type of films are 4 to 6 m Spec-trolene and 2.5 to 6.5 m Mylar.

The process of introducing a sample into a solution can be rather tedious and difficulties sometimes arise where a substance tends to precipitate during analysis. This itself may be due to the limited solubility of the compound or to the photochemical action of the X-rays causing decomposition. In addition, systematic variations in intensity can frequently be traced to the formation of air bubbles on the cell windows following the local heating of the sample. Despite these problems, the liquid solution technique represents a very versatile method of sample handling in that it can remove nearly all matrix effects to the extent that accuracies obtainable with solution methods approach very closely the ulti-mate precision of any particular X-ray spectrometer.


DOC-M84-E06001 July 2004 78

Preparation of filter samples

Where the concentration of an element in a sample is too low to allow analysis by one of the methods already described, work-up techniques have to be used in order to bring the concentration within the detection range of the spectrometer. Concentration methods can be employed where sufficiently large quantities of sample are available. For example, gases, air or water which are contaminated with solid particles can be treated very simply by drawing the gases, air or water through a filter disk followed by direct analysis of the disk in a vacuum environment. Concentration can sometimes be effected simply by evaporating the solution straight onto confined spot filter paper.

Sample preparation equipment for XRF Analysis

Crushing

Fine jaw crusher 7KP9000-8AH

Jaw crusher for unique 25 times size reduction in one pass, for example crushing up to 50 mm pieces to 2 mm or less in one operation

Jaws hold up to 5 kg (10 lbs) of sample as one load

Hinged one piece cover opens easily for cleaning and lubricating

Quick jaw adjustment

Air ducting, built into cabinet

Air vents for dust removal during sample loading

Safety switch, stops motor as soon as cover is opened

Flat 300 mm (12 inch) wide jaws for ease of cleaning

Sample collector can be altered to customer’s specification


DOC-M84-E06001 July 2004 79

Overall length:

Weight:

Width:

Height:

1160 mm

560 kg

720 mm

1030 mm

Grinding

Planetary mono mill 7KP9000-8BU

The planetary mono mill is used for sample pulverizing (down to 1 mm) starting from cuttings (diame-ter below 10 mm).

This planetary mill requires one grinding vessel with grinding bowls.


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Standard power supply 400 V, 50-60 Hz, 3 phases

Power consumption 500 W

Dimensions (hxwxd) 500x830x530mm

Weight Approx. 83 kg

Grinding vessel, for planetary mono mill, agate, 500 ml 7KP9000-8BX

This grinding vessel is used for sample pulverizing (down to 1 m) starting from cuttings (diameter below 10 mm, input volume: 80-225 ml).

The grinding vessel requires 10 agate grinding balls of 30 mm diameter (one ball: 7KP9000-8BV) or 25 of 20 mm diameter (one ball: 7KP9000-8CA).

Grinding vessel, for planetary mono mill, agate, 250 ml 7KP9000-8BW


This grinding vessels requires 6 agate grinding balls of 30 mm diameter (one ball: 7KP9000-8BV) or 15 of 20 mm diameter (one ball: 7KP9000-8CA).


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Agate grinding ball, for agate grinding vessel, 30 mm diameter 7KP9000-8BV

Agate grinding ball, for agate grinding vessel, 20 mm diameter 7KP9000-8CA

Grinding vessel, for planetary mono mill, zirconia 250 ml 7KP9000-8BY


The grinding vessel requires 6 zirconia grinding balls of 30 mm diameter (one ball: 7KP9000-8BZ) or 15 of 20 mm diameter (one ball: 7KP9000-8CB).

Zirconia grinding ball, for zirconia grinding vessel, 30 mm diameter 7KP9000-8BZ

Zirconia grinding ball, for zirconia grinding vessel, 20 mm diameter 7KP9000-8CB


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Vibrating disk mill HSM 100H, max. 100 cm KP9000-8AD

Automatic timer 8 to 16 s, 0 to 100 s, 0 to 16 min

Standard power supply 400 V, 50 Hz, 3 phases

Power consumption 1.2 kVA



Spare parts kit for HSM 100H 7KP9001-8AM

Vibrating disk mill HSM 50, max. 50 cm 7KP9000-8CH

Spare parts kit for HSM 50 7KP9000-8CJ

The vibrating disk mill HSM 100H is used to crush rocks, soils, minerals, sintered products, etc. Fi-brous materials can be ground by adding spectrally pure grinding aids such as wax etc.

Grinding vessel, chrome steel, 50 cm3, for HSM 100H 7KP9001-8AF

Grinding vessel, chrome steel, 50 cm3, for HSM 50 7KP9001-8CK

Grinding vessel, chrome steel, 100 cm3, for HSM 100H 7KP9001-8AG

Grinding vessel, tungsten carbide, 50 cm3, for HSM 100H 7KP9001-8AH


DOC-M84-E06001 July 2004 83

Grinding vessel, tungsten carbide, 100 cm3, for HSM 100H 7KP9001-8AJ

Grinding vessel, titanium carbide, 100 cm3, for HSM 100H 7KP9001-8AK

Grinding vessel, agate, 100 cm3, for HSM 100H 7KP9001-8AL


DOC-M84-E06001 July 2004 84

Automatic mill HP-MA 7KP9000-8AS

The automatic mill HP-MA is used to grind cuttings etc.

Grain size (input) Max. 5 mm

Milling time 0 to 999 s

Number of programs 8

Pressed air 5 to 10 bar

Pressed air Approx. 600 liter per sampleconsumption



Dimensions (h x w x d) 1558 x 850 x 900 mm

Weight 610 kg

30-position magazine, for automatic mill HP-MA, with 100-ml cups 7KP9000-8AP

Grinding vessel, chrome steel, for automatic Herzog grinding devices 7KP9001-8AD

Grinding vessel, tungsten carbide, for automatic Herzog grinding devices 7KP9001-8AE

Grinding aid dosage device, for automatic Herzog grinding devices 7KP9001-8BY

Dosage cleaning device, for automatic Herzog grinding devices 7KP9001-8BX

Swinging mill type PAL-M100M 7KP9000-8BL

The swinging mill type PAL-M100M is used for fine grinding of minerals and organic materials.

You manually pour the sample material into the grinding vessel and manually introduce the vessel into the machine. With the complete closed and sound proofed housing including interlocked cover the


DOC-M84-E06001 July 2004 85

machine is designed according to the highest safety standards. The operator uses a menu at the input terminal. A manual vessel clamping mechanism and grinding vessel made by chrome steel is part of the basic configuration. As an option the mill could be tuned for all sample materials by selectable grinding speed and grinding vessel made out of a different material.

Power supply 380 to 460 V, 3 phases, 16 A, 50 to 60 Hz, PE, 1.5 kW

Insulation class B

Grinding speed 50 Hz: 1500 rpm

60 Hz: 1800 rpm

Grinding vessel mate-rial

Chrome steel

Volume 100 cm³

Dimensions 1230 x 680 x 700 mm

Weight 425 kg

Grinding vessel type 100WC, for PAL-M100M 7KP9000-8BM

Vessel including cover, ring and stone made of tungsten carbide, volume 100 cm3


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Swinging mill type PAL-M100M with pelletizing press type PAL-P40M 7KP9000-8BN


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Vibrating disk mill HK 40 incl. grinding vessel (100 ml, Corundum) 7KP9000-8AV

Powerful swing mill for desktop operation

Standard grinding vessel of sintered corundum, 100 cm³

Reproducible setting of milling time by electronic timer

Wellbalanced construction for stable desktop positioning

Dimensions: 34.5 x 29.5 x 54.0 mm Weight: ca. 40 kg Mains: 230 V, 50 Hz, 200 W


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3 K ring mill, Rotoclamp, 3 kg 7KP9000-8AJ

Ring mill designed for samples up to 3 kg. This mill comes with an adaptor plate for smaller heads to be used and will pulverize up to 800 g in a smaller head much faster than in a normal ring mill.


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Ring mill, Rotoclamp, 100 g 7KP9000-8AK

Used for pulverizing rocks, soil, coal, cement, glass, bricks, wood, plant material, slags, concrete etc. for subsequent analysis by instrumental methods or wet chemistry.

A wide range of sample containers are available for samples from 1 to 1000 g. These are made from agate, alumina, carbon steel, chrome steel, tungsten carbide, tungsten carbide, and zirconia.

Manual clamp 220 to 240 V, 3 phases, 50 Hz, 500 rpm

or 210 to 240 V, 3 phases, 60 Hz, 500 rpm


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Grinding vessel, zirconia, 100 g, for ring mill 7KP9001-8AP

Grinding vessel, tungsten carbide, 100 g, for ring mill 7KP9001-8AS

Grinding vessel, chrome steel, 100 g, for ring mill 7KP9001-8AR

Grinding vessel, agate, 50 g, for ring mill 7KP9001-8AU

Grinding vessel, agate, 100 g, for ring mill 7KP9001-8AV








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Minimill, 40 g 7KP9000-8AL

The bench-top ring mill is designed for laboratories pulverizing samples from 2 to 40 g.


Weight 58 kg

Grinding vessel, zirconia, 40 g, for minimill 7KP9001-8AN

Grinding vessel, tungsten carbide, 40 g, for minimill 7KP9001-8AT

Grinding vessel, chrome steel, 40 g, for minimill 7KP9001-8AQ

Grinding vessel, chrome steel, 20 g, for minimill

Grinding vessel, zirconia, 20 g, for minimill

Grinding vessel, tungsten carbide, 20 g, for minimill

Grinding vessel, alumina, 20 g, for minimill


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Pelletizing

Manual lab press TP 40 7KP9000-8AM

Manually operated oleo-hydraulic pelletizing press for the easy production of tablets with different di-ameters (depending on the spectrometer).

For this purpose a special press tool with the corresponding diameter is inserted into the press and can be filled upon moving back the upper cross beam. The press tool is delivered as special accesso-ries.

The hydraulic pump is operated by the handle. The direction of motion of the piston press can be re-versed by changing over the valve. The threaded spindle is intended as a counter piece for pressure absorption.

Max. pressure 400 kN

Max. piston stroke Approx. 40 mm

Netweight 170 kg

Pressing tool for free pressing, for TP 40 7KP9001-8BM

Pressing tool for Al cups, for TP 40 7KP9001-8BN

Manual lab press TP/2d 40

The TP/2d is more robust and easier to use than the TP version, but is also more expensive. It would be more suitable for larger sample throughput.

SIETRONICS manual sample press incl. 40 mm pressing tool 7KP9000-8AN

Manual press for preparation of pressed powder pellets (boric acid backed pellets, powder only with wax binder, aluminium cups etc.)


DOC-M84-E06001 July 2004 93

Simple rugged construction

Hand operated pump with pressure gauge

30 t maximum ram rating

Dimensions: height 450 mm; base 340 mm x 142 mm

Specac manual lab press 15011 – 15 tonnes

Specac manual lab press 25011 – 25 tonnes

Manual lab press PY 10

Manual lab press PY 30

Semi-automatic pelletizing press HTP 40 7KP9000-8AE

Spare parts kit for HTP 40 7KP9001-8BF

The HTP 40 semi-automatic sample press is used to press powdered materials into tablets with or without addition of a binder (wax). It is also possible to press in aluminium dishes or rings.


DOC-M84-E06001 July 2004 94

Pressure Max. 40 t

Pressure holding time 0 to 1000 s, continu-ously adjustable




Floor load 800 kg/m2


Pressing tool for free pressing, for HTP 40/60 7KP9001-8BA

Pressing tool for aluminium cups, for HTP 40/60 7KP9001-8BB

Pressing tool for steel rings, for HTP 40/60 7KP9001-8BC


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Automatic sample press HP-PA 7KP9000-8AQ

30-position magazine for automatic sample press HP-PA, with 100-ml cups 7KP9000-8AR

Grain size (input) Max. 0.1 mm

Time per sample Typ. 60 s

Number of programs 8

Pressure 5 to 40 t

Pressure holding time 1 to 99 s

Pressed air 5 to 10 bar

Pressed air Approx. 1000 liter per sampleconsumption

Standard dimensions of the steel rings

35/40 mm dia, 14 mm height or 35/51.5 mm dia, 8.5 mm eight



Dimensions (hxwxd) 1558x1050x900 mm

Weight 750 kg


DOC-M84-E06001 July 2004 96

Pelletizing press type PAL-P40M 7KP9000-8BK

Semi-automatic pelletizing press, type PAL-P40M with manual sample feeding for the production of pellets of fine ground mineral material for X-ray analysis in aluminium cups or steel rings. The machine meets the highest security requirements with closed and sound proofed housing and control of the input hood. The press is equipped with hydraulic unit, press stand and press tool holder. The operator uses a menu at the input terminal, where pressure force increase time, pressure force maintenance time, pressure force decrease time and pressure force can be selected. A press tool for steel rings with outside diameter of 51.5 mm is part of the basic configuration.

As an option different press tools could be selected.


Weight 425 kg

Power supply 380 to 460 V, 3 phases, 50 to 60 Hz, PE, 1.5 kW

Pressure force 1 to 40 bar

Pressing tool for steel rings, for PAL-P40M 7KP9000-8BQ

Steel ring size:


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Outside diameter 40 mm

Inside diameter 32 mm

Height 14 mm

Pressing tool for aluminium cups, for PAL-P40M 7KP9000-8BR


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Manual press PE-MAN 7KP9000-8AW

Manual Press PE-MAN:

- compact laboratory benchtop machines for X-ray sample pelletizing

safety valve allowing to set maximum final pressure up to 20 tons

easy handling - wide space for die set positioning and removal

maintainance free mechanism, covered in solid steel housing

manual press with adjustable lever - recommended for non-routine work

Available pressure 200 kN (20 t)

Hight between spindle and piston max. 175 mm

Width between supporting columns 130 mm

Spindle adjusting range 120 mm

Available piston stroke 20 mm

Dimensions (width, depth, height) 375 x 500 x 190 mm

Mass approx. 36 kg

Volume of hydraulic oil approx. 2 l

Power supply --

Pressing tool for PE-MAN 7KP9000-8AX

for 32 mm diameter pellets


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Accessories for pressing

Aluminium cups, 40 mm diameter, 1000 off 7KP9001-8BD

Aluminium cups, 32 mm diameter, 1000 off 7KP9000-8AY

Evacuable pellet dies, 20 mm diameter, for Specac presses

Evacuable pellet dies, 40 mm diameter, for Specac presses

Steel ring, 35/51.5 mm diameter, 8.6 mm height, 1 off 7KP9001-8BS

Steel ring, 35/40 mm diameter, 14 mm height, 10 off 7KP9001-8BE

To prepare pressed powder pellets for process sample handling

Hoechst wax C powder, 20 kg M34055-A1901

Hoechst wax C powder is an organic binder to be added to milled powder samples to achieve compact pressed powder pellets for XRF analysis. When Carbon will be analysed by XRF analysis, boric acid is an alternative Carbon-free binder.

EMO Grinding aid pellets, 1 kg 7KP9001-8DF

These EMO wax grionding aid pellets improve grinding of powders and serve as organic binder during pressing to get very complex powder pellets.

Boric acid, 5 kg 7KP9001-8BL


DOC-M84-E06001 July 2004 100

Boric acid is a binder material to be added to milled powder samples to achieve compact pressed powder pellets for XRF analysis. Boric acid can also be used as a base for free pressed powder pel-lets.

Sample cassette for fused bead process samples (40 mm x 14 mm) C79298-A3173-B23

Sample cassette for fused bead process samples (51.5 mm x 8.5 mm) C79298-A3173-B22

Moviol liquid binding agent, 10 g 7KP9001-8BP

Liquid organic binder for pressing of very solid powder pellets.


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Desiccator and accessories

Desiccator for safe storage of reference samples 7KP9001-8BT

40 liter volume

Magnetic lock

With 4 shelves

Integrated hygrometer

Outer dimensions 300x395x510 mm

White frame with transparent walls

Remark: Pressed powder pellets and fused beads change with atmospheric humidity and should therefore always be stored in a desiccator.

Shelf for desiccator, additional one 7KP9001-8BU

Drying agent (granulate) for desiccator, 1 kg 7KP9001-8BW


DOC-M84-E06001 July 2004 102

Milling

Automatic sample miller HN-FF 7KP9000-8AF

Spare part kits for HN-FF 7KP9001-8BG

Power supply 400 V, 50 Hz, 3 phases




Air pressure 5 to 10 bar

Air consumption Approx. 0,3 m3 per sample


DOC-M84-E06001 July 2004 103

Fusing

ISP mini fusion manual furnace 7KP9000-8BS

High performance and reliability

Simple maintenance requirements

2 crucible and 2 mold unit

Completely electronic

Top loading with cantilever lid

Auto agitation of mix during fusion

Dimensions (hxwxd)

450 x 1000 x 850 mm

Mains voltage 220 to 260 V single phase

Power dissipation Max. 3 kW

Weight 65 kg (net); 100 kg (shipping)

Standard bead size

40 mm fused beads, with 32 mm option

Temperature range

1050 to 1100 °C

ISP 4x4 manual furnace 7KP9000-8BT

High performance and reliability

Simple maintenance requirements

4 crucible & 4 mould unit

All electric


DOC-M84-E06001 July 2004 104

Top loading with cantilever lid

Auto agitation of mix during fusion

Dimensions (hxwxd) 450 x 1000 x 850 mm

Mains voltage 220 to 260 V single phase

Power dissipation Max. 3 kW

Weight 85 kg (net); 120 kg (shipping)

Standard bead size 40 mm fused beads, with 32 mm option

Temperature range 1050 to 1100 °C

Crucible, Pt/Au (approx. 30 g), for ISP manual furnaces 7KP9001-8BV

Casting mould, Pt/Au (for 40 mm beads, aprox. 80 g), for ISP manual furnaces 7KP9001-8DP

Casting mold, 40 mm upper diameter, 4,5 mm height, approx. 45 g 7KP9001-8CX for ISP and Linflux fusing devices

ISP Manual Furnace F-M4 for mouldible crucibles 7KP9000-8EE

Automatice Iodine gas injection system for ISP F-M4 7KP9001-8DM

Automatice Oxygen admit control system for ISP F-M4 7KP9001-8DN

Furnace refractories, complete, for ISP manual furnace (-8BT) 7KP9001-8DQ

Matched resistance for ISP manual furnace (8BT), 4 off 7KP9001-8DR

VAA2 automatic fusing device, with 2 burners, incl. 2 crucibles and molds 7KP9000-8CE

VAA4 automatic fusing device, with 4 burners, incl. 4 crucibles and molds 7KP9000-8CF


DOC-M84-E06001 July 2004 105

Fully automatic sample preparation for any mineral, ore, ferro-ally etc.

Highest flexibility in melting and colling parameter setting for each station

Accurately reproducible melting conditions in low and high temperature mode

independent temperature setting for each crucible and mold burner

Temperature range up to 1600°C by use of standard propane / Oxygen burners

Effective oscillationg agitation of crucible with setting of oscillation rate and time

Air cooling of hot mold via pre-warmed nozzle with air volume and time control

Gas leakage control with automatic gas and oxygen smut off and LED-indicator

Pilot burner control and air pressure control with water trap

Solid state mechanics, one printed circuit card only, easily accessible components

Reliable, safe and proven machine, code programming not required, simple operation


DOC-M84-E06001 July 2004 106

Type VAA 2 and VAA 4

Number of burner stations VAA 2 - 2 stations

VAA 4 - 4 stations

Voltage 230 Volt/50 Hertz

Wattage VAA 2 - 170 Watt

VAA 4 - 210 Watt

Permiss. air pressure max. 6 bar

Permiss. natural gas pressure VAA 2 = 22 - 60 mbar

Permiss. natural gas pressure VAA 4 = 55 - 80 mbar

Permiss. propane gas pressure 50 mbar

Permiss. oxygen pressure max. 6 bar

Air consumption VAA 2 max. 2 m³/hr

VAA 4 max. 4 m³/hr

Oxygen consumption VAA 2 max, 1 m³/hr at 3 bar

VAA 4 max. 2 m³/hr at 3 bar

Natural gas consumption VAA 2 max. 0,66 m³/hr

VAA 4 max. 1,2 m³/hr

or liquid propane gas VAA 2 max. 0,5 m³/hr

VAA 4 max. 0,9 m³/hr

Lenght 250 mm

Width 530 mm

Height 530 mm

Weight VAA 2 approx. 40 kg

VAA 4 approx. 45 kg

The above data for consumption of air, gas and oxygen is maximum volume for burners at highest temperature.


DOC-M84-E06001 July 2004 107

Crucible (approx. 42 g) for VAA2 or VAA4 HER-87043878

Casting mold, (for 40 mm beads, aprox. 45 g) 7KP9001-8CC

Cover for crucibles with 39 mm upper diameter 7KP9001-8CD


DOC-M84-E06001 July 2004 108

HERZOG HAG 12/1500 semi-automatic fusing unit 7KP9000-8BA

Spare parts kit for HAG 12/1500 7KP9001-8BJ

The fusing unit can be used to produce borate melts. The sample mixture is pressed by means of an HAP press and then filled into crucibles. The magazine of the fusing unit accommodates 12 crucibles. The samples are automatically inserted in succession into the muffle furnace of the fusion unit and then transported to the cooling device.

Fusion temperature 600 to 1500 °C

Fusion time 0 to 30 min

Air pressure 6 bar

Air consumption 74 l/min

Power supply 220 V, 50 Hz

Power consumption Approx. 4 kVA



Sample preparation press HAP, for HAG 12/1500 7KP9001-8BH

Spare parts kit for HAP 7KP9001-8BK

Crucible (aprox. 94 g), for HAG 12/1500 7KP9001-8CE


DOC-M84-E06001 July 2004 109

CLAISSE semi-automatic fluxer BIS (6 burners) 7KP9000-8BB

The CLAISSE fluxer BIS is an automated fusion fluxing device capable of simultaneously preparing 6 samples as glass disks for XRF.

Propane, butane or liquified petroleum gas (LPG) is required for the burners, approx. 6 l/min per burner at 200 mbar. These burners require no compressed air.

Mains voltage 100/115/230 V

Mains frequency 50/60 Hz


Dimensions (hxwxd)

Fluxer

Controller

330x610x330mm

90 x 400 x 300 mm

Total weight 30 kg


DOC-M84-E06001 July 2004 110

CLAISSE semi-automatic Fluxy (3 burners) 7KP9000-8BE

The CLAISSE Fluxy is an automated fusion fluxing device capable of simultaneously preparing 3 samples as glass disks for XRF.

Propane, butane or liquid petroleum gases only. No oxygen, no compressed air. Only one regulator is needed to set the max. gas pressure, which should be less than 500 mbar; recommended when the three burners are used is 200 to 300 mbar for a gas hose 1 m long and with 6 mm inside diameter. The fusion of one sample requires approx. 3 g of gas.

Mains voltage 100/115/230 V



Dimensions (hxwxd)

Shipping weight

Fluxer

Remote

30 kg

430x280x420mm

20 x 80 x 170 mm

Crucible, for CLAISSE fluxer (approx. 31 g) 7KP9001-8CF

Casting mould, for CLAISSE fluxer (for 40 mm beads, approx. 34 g) HER-87043221

Casting mold, for CLAISSE fluxer (for 32 mm beads, approx. 28 g) HER-87021258

Claisse semi-automatic M4 fluxer HRT-M4


DOC-M84-E06001 July 2004 111

fully automatic, efficient, 3-position fluxer with individual burner selection

automatic, pilotless ignition with flame monitoring for increased safety

standard DB-9 connector for linking to a PC (advanced interface software included)

user can manually operate the instrument and record its actions in realtime in an automatic pro-gram for future use

several preset programs (for most sample types)

ten independent and user-customizable fusion programs

programs can be saved to a floppy or hard disk when fluxer is connected to a computer

seven to fifteen functions per program for increased versatility

all parameters can be modified: gas flow, mixing speed, function duration, crucible angle, cooling air flow, solution stirring speed...

independent mold holder allowing low-temperature fusions - useful for fluor-bearing samples

three burners that only use propane gas: no compressed air or oxygen is required

superior homogenization and heating uniformity

very compact design (17.5x20.5x16 in = 45x52x41 cm ; weighs only 50 lb= 23 kg)


DOC-M84-E06001 July 2004 112

LINN Lifumat-2,0-Ox semi-automatic induction fusing unit 7KP9000-8BG

By high-frequncy induction heatingbeads fused in Pt/au or graphite crucibles with temperatures up to 1500 °C can be achieved within 3 min.

The eddycurrents guarantee that the melt is mixed up optionally by the bath movement. So that a con-stant and homogeneous quality of the melt is achieved.

All components are well-arranged within the machine housing. All electrically functional groups are made in PC board technique and are easy to replace by plugs. The RF section with water-cooled tube and water-cooled tank capacitor is designed for high production rates. Particular attention has been payed to easy servicing of all components.

The radio interference suppression of the HF unit is FTZ tested so that Lifumat-2.0-Ox can also be installed beside sensitive analysers and computerized equipment in the laboratory. The wiring cor-responds to VDE regulation.

Power supply 220/240 V, 50/60 Hz


RF power Max. 2.0 kW

Frequency 1.5 MHz

Cooling-water supply 3 l/min


LIFUMAT - C2000 - 3.3 - VAC induction fusing device LIN-C2000-33VAC


DOC-M84-E06001 July 2004 113

LIFUMAT benchtop induction fusing unit 7KP9000-8EF

The LIFUMAT Benchtop offers rapid production of fused bead samples for XRF analysis by induction heating. This compact unit satisfy the fusion needs of small laboratories. The 10 step selectable melt-ing power is generated by a powerful solid state power generator. A crucible vibration facility can be operated as required.

This small table top unit is simple to install and safe to operate with low power consumption.

One graphite crucible and mold for testing is included. The platinware is not included.

mains voltage 230V, 50/60Hz (other voltages on request and surcharge)

current approx. 16A

power, short time 1.5kW

power, continuous op-eration

1.2kW

frequency approx. 200kHz

cooling water approx. 1 l/min at 3bar

weight approx. 57kg

dimensions (HxWxD) approx. 400mm x 465mm x 480mm

Infrared spectral pyrometer for LINN Lifumat LIN-IS5

Crucible SPT-1 for LINN Lifumat-2.0-OX (ca. 35g) HER-87001440

Casting mold AGS-40 for LINN Lifumat-2.0-OX (ca. 45g, for 40 mm beads) HER-87001439


DOC-M84-E06001 July 2004 114

AFT PHOENIX 4000 semi-automatic fusing machine 7KP9000-8BJ

The PHOENIX series of fusion machines is designed to prepare permanent and homogeneous fused beads under accurately reproducible conditions. The process for bead production is straightforward. Samples are mixed and dissolved into a lithium borate flux at temperatures ranging from 1000 to 1600 °C and then poured into heated moulds. The melting, swirling, pouring, and cooling operations are all carried out automatically to preset timers.

Temperature 1 600 °C

Supply pressures

Gas

Oxygen

Air

0,2 to 1 bar

6 bar

6 bar

Mains voltage 1 10 or 240 VAC




Weight 90 kg

No. of burners 8

Beads produced 4per cycle

Beads produced 384 per 24-h cycle (as-suming a cycle time of 15 min.)


DOC-M84-E06001 July 2004 115

Accessories for fusing

Platinum headed tongs 7KP9001-8CH for handling of platinum ware, 30 cm long, approx. 5 g

Fluxes

A100, Lithiumtetraborate flux, 1 kg 7KP9001-8CJ

A100, Lithiumtetraborate flux, 5 kg 7KP9001-8CK

Liquid sample measurement accessories

Liquid cups


DOC-M84-E06001 July 2004 116

Liquid cup, standard (35/40 mm diameter), 500 off 7KP1901-8FA

Liquid cup, large (43/51 mm diameter), 500 off 7KP1901-8BF

Liquid cups, (36/45mm diameter), 500 off 7KP1901-8BB-Z

Foils for liquid cups

Strength, transmission, purity and resistance against chemical attacks are the most important proper-ties determining the best choice for your application. The problem however is to weigh strength versus transmission.

StrengthMylar is a relatively very strong material. Polycarbonate is strong enough for most applications, how-ever not as strong and resistant to chemical attack.

Transmission Generalizing, transmission increases from Mylar to Polypropylene and from Polypropylene to Polycar-bonate. Polypropylene is often used for general purposes and shows good transmission.

Purity Mylar foils contain ppm levels of Ca, P, Fe, Cu, Zn or Sb. Polypropylene foils contain ppm levels of Ca, Zr, P, Fe, Zn, Cu, Ti and Al.

Resistance against chemical attacks For new samples, the proposed foil should be tested several times for the longest anticipated measur-ing time. Mylar is in general chemically more resistant than other materials.

Foils for liquid cells

Mylar, 15 m, roll of 150 m C71298-A18-C286

Mylar, 6 m, roll of 90 m 7KP1901-8BZ

Mylar, 2.5 m, roll of 90 m 7KP1901-8BR


DOC-M84-E06001 July 2004 117

Hostaphan, 15 m, roll of 150 m C71298-A18-C262

Hostaphan, 6 m, roll of 150 m C71298-A18-C264

Polypropylene, 5 m, roll of 90 m 7KP1901-8BS

Polypropylene, 6 m, roll of 90 m C71298-A18-C288

Polypropylene, 12 m, roll of 90 m 7KP1901-8BU

Ultrapolyester, 1.5 m, roll of 90 m 7KP1901-8BT

Prolene, 4 m, roll of 90 m 7KP1901-8BG

Prolene, 4µm, precut foils, 500 off 7KP7804-8CB

Polycarbonate, 5 m, roll of 90 m 7KP1901-8BX

Paper filters

Whatman paper filter, 50 mm diameter with 25 mm diameter ink ring, 100 off 7KP1901-8BH

Whatman paper filter, 50 mm diameter with 32 mm diameter ink ring, 100 off 7KP1901-8BJ

Pipettes and accessories

Disposable pipette, 500 off 7KP1901-8BY

Sputter target (Au plated) for Drip Filter method 7KP1901-8BY


DOC-M84-E06001 July 2004 118

Suction device for Drip Filter method 7KP1901-8CL

Micro pipette, digital, 50-200 ml, Roth 7KP9001-8CM

Pipette point for ml pipette, 1-200 ml, for Roth pipettes, 1000 off 7KP9001-8CN

Pipette point for ml pipette, 1-200 ml, for Eppendorf pipettes, 1000 off 7KP9001-8CP

ml pipette, fix volume, 50 ml, Roth 7KP9001-8CQ

ml pipette, fix volume, 100 ml, Roth 7KP9001-8CR

ml pipette, fix volume, 200 ml, Roth 7KP9001-8CS

ml pipette, variable volume, 20-200 ml, Eppendorf 7KP9001-8CT

ml pipette, fix volume, 50 ml, Eppendorf 7KP9001-8CU

ml pipette, fix volume, 100 ml, Eppendorf 7KP9001-8CV

ml pipette, fix volume, 200 ml, Eppendorf 7KP9001-8CW

Introduction to X-ray Fluorescence Analysis (XRF) Index

DOC-M84-E06001 July 2004 119

Index

A

absorption......................................................12 absorption edge...............................................3 Angström (Å) ...................................................1 anode...............................................................8 anode material.................................................6 atomic number.................................................4 atomic shell......................................................2 Auger effect .....................................................4

B

back-scattering electrons ................................8 binding energy.................................................3 Bohr's atomic model ........................................2 Bragg's equation............................................25 Bremsspektrum ...............................................6

C

cathode............................................................8 characteristic radiation ....................................4

of the elements in the sample material......10 collimator masks............................................55

Collimators.................................................... 55 Compton scattering....................................... 16 counter plateau ............................................. 22 crystal changer ............................................. 56 crystal types.................................................. 30 cup aperture.................................................. 54 curved crystals.............................................. 43

D

dead time correction ..................................... 60 detectors ....................................................... 16 diffraction ...................................................... 23 discriminator ................................................. 59 Dispersion..................................................... 32

E

electromagnetic radiation............................ 1, 2 electron shells................................................. 2 electronic pulse processing................................ 59 end-window tube....................................... 9, 51 energy levels................................................... 3 energy shells................................................... 3 exit window ..................................................... 8

Index Introduction to X-ray Fluorescence Analysis (XRF)

120 DOC-M84-E06001 July 2004

F

flow counter .................................................. 56 fluorescence yield ............................................4

G

gamma radiation ..............................................1 generator ................................................ 10, 51

H

high voltage .................................................. 10

I

intensity............................................................2 interference................................................... 23

K

KCps ................................................................2 kiloelectronvolts

keV ...............................................................1

L

layer thickness .............................................. 14 LiF(200), LiF(220), LiF(420) ......................... 33 line separation .............................................. 32 line-shift correction........................................ 62

M

main amplifier................................................ 59 mass attenuation coefficient ............................. 12 multichannel spectrometer

scanner...................................................... 47 multichannel spectrometer

MRS........................................................... 45 multilayer

OVO-55, OVO-N, OVO-C, OVO-B............ 35 multilayers ..................................................... 33

N

Nomenclature.................................................. 4

O

output ............................................................ 10

P

photon ............................................................. 2 primary beam filter ........................................ 51 proportional counter

sealed ........................................................ 57 pulse height analysis (PHA).......................... 19 pulse height distribution ................................ 19 pulse height spectrum................................... 16

Q

quants ............................................................. 1

Introduction to X-ray Fluorescence Analysis (XRF) Index

DOC-M84-E06001 July 2004 121

R

radiation intensity ............................................2 Rayleigh scattering........................................16 Reflexionen

höherer Ordnung .......................................29

S

Sample cups..................................................54 saturation thickness.......................................14 scintillation counter........................................58 Secondary enhancement ..............................14 sequential spectrometers

SRS 3X00 and S4......................................48 side-window tube.............................................8 sine amplifier .................................................60 Soller slit ........................................................55 Sources of standard samples........................67 special crystals

InSb............................................................37 special crystals ..............................................36

AdP ............................................................37 Ge ..............................................................37 LiF(420)......................................................36 TIAP ...........................................................37

special crystals OVO-C .......................................................37

special crystals OVO-N .......................................................37

special crystals OVO-B .......................................................37

standard samples sources...................................................... 67

standard types .............................................. 33 sub-levels........................................................ 4 Supplementary literature............................... 63

T

tube current................................................... 10 Tube types ...................................................... 7 Tube-spectrum scattering

at the sample material ................................. 15

V

vacuum seal.................................................. 54

W

wavelengths.................................................... 1

X

X-ray fluorescence spectrometer instrumentation.......................................... 45

X-ray generator............................................. 10 X-ray quants ................................................... 2 X-ray tube ....................................................... 6

Documents

Note - XRF - Introduction to X-Ray Fluorescence Analysis M84-E06001