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BRUKER ADVANCED X-RAY SOLUTIONS
TO N O I T C U D O R T E N I C N E C S E R O U L F Y X-RA ) F R X ( S I S ANALY
USER’S MANUAL TRAINING
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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
Introduction to X-ray Fluorescence Analysis (XRF) Table of Contents
Fundamental Principles ............................................................................................1 Electromagnetic Radiation, Quants ..............................................................................................1 The Origin of X-rays...................................................................................................................2 Bohr's Atomic Model ..................................................................................................................2 Characteristic Radiation.............................................................................................................4 Nomenclature ..................................................................................................................................4 Generating the Characteristic Radiation ......................................................................................5 X-ray Tubes, Bremsspektrum ....................................................................................................6 Tube Types, the Generator........................................................................................................7 Side-window Tubes ............................................................................................................8 End-window Tubes .............................................................................................................9 Generator..........................................................................................................................10 Excitation of Characteristic Radiation in Sample Material .......................................................10 Layer Thickness, Saturation Thickness ...................................................................................14 Secondary Enhancement.........................................................................................................14 Tube-spectrum Scattering at the Sample Material ....................................................................15 Measuring X-rays ..........................................................................................................................16 Detectors, Pulse Height Spectrum...........................................................................................16 Gas Proportional Counter .................................................................................................17 Scintillation Counters ........................................................................................................18 Pulse Height Analysis (PHA), Pulse Height Distribution..........................................................19 The Counter Plateau................................................................................................................22 Diffraction in crystals ...................................................................................................................23 Interference ..............................................................................................................................23 Diffraction .................................................................................................................................24 DOC-M84-E06001 July 2004
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X-ray Diffraction From a Crystal Lattice, Bragg's Equation..................................................... 25 Reflections of Higher Orders................................................................................................... 29 Crystal types............................................................................................................................ 30 Dispersion, Line Separation .................................................................................................... 32 Standard Types, Multilayers.................................................................................................... 33 Special Crystals....................................................................................................................... 36 Curved Crystals....................................................................................................................... 43
Instrumentation....................................................................................................... 45 The Multichannel Spectrometer MRS......................................................................................... 45 Scanners for MRS 400, MRS 404 and MRS 4000.................................................................. 47 The Sequential Spectrometers SRS 3X00 and S4..................................................................... 48 The End-window Tube and Generator .................................................................................... 51 The Primary Beam Filter ......................................................................................................... 51 Sample Cups, the Cup Aperture ............................................................................................. 54 The Vacuum Seal.................................................................................................................... 54 Collimator Masks..................................................................................................................... 55 Collimators, the Soller Slit ....................................................................................................... 55 The Crystal Changer ............................................................................................................... 56 The Flow Counter.................................................................................................................... 56 The Sealed Proportional Counter............................................................................................ 57 The Scintillation Counter ......................................................................................................... 58 Electronic Pulse Processing ....................................................................................................... 59 The Discriminator .................................................................................................................... 59 Main Amplifier, Sine Amplifier ................................................................................................. 59 Dead Time Correction ............................................................................................................. 60 Line-shift Correction ................................................................................................................ 62
Appendix A.............................................................................................................. 63 Supplementary Literature ............................................................................................................ 63 Books....................................................................................................................................... 63 Tables...................................................................................................................................... 65 Journals................................................................................................................................... 65
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Table of Contents
Appendix B ..............................................................................................................67 Sources of Standard Samples .....................................................................................................67
Appendix C ..............................................................................................................69 Sample Preparation Catalog for XRF Analysis ..........................................................................69 Introduction ..............................................................................................................................69 Preparation of solid samples....................................................................................................74 Metals ...............................................................................................................................74 Pressed pellets .................................................................................................................75 Fused beads .....................................................................................................................76 Preparation of liquid samples...................................................................................................77 Preparation of filter samples .............................................................................................78 Sample preparation equipment for XRF Analysis .....................................................................78 Crushing...................................................................................................................................78 Grinding....................................................................................................................................79 Pelletizing.................................................................................................................................92 Accessories for pressing...................................................................................................99 Desiccator and accessories............................................................................................101 Milling .....................................................................................................................................102 Fusing ....................................................................................................................................103 Accessories for fusing.....................................................................................................115 Fluxes .............................................................................................................................115 Liquid sample measurement accessories..............................................................................115 Liquid cups......................................................................................................................115 Foils for liquid cups .........................................................................................................116 Foils for liquid cells..........................................................................................................116 Paper filters.....................................................................................................................117 Pipettes and accessories................................................................................................117
Index....................................................................................................................... 119
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Fundamental Principles
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 described 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, O (= 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
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The following relationship (conversion formula) exists between the units E (keV) and O (nm): E ( keV )
1 . 24 O ( nm )
or O (nm)
1.24 E (keV )
The X-ray fluorescence analysis records the following range of energy or wavelengths: E = 0,11 - 60 keV O= 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 intensity is the number of X-ray quants that are emitted or measured per unit of time. We use the number of X-ray quants measured per second, cps (= counts per second) or KCps (= kilocounts per second) 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:
Fundamental Principles
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 innermost 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 (negative 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 another atomic shell electron (Auger effect). The probability of an X-ray resulting from this process is called the fluorescence yield Z. This depends on the element’s atomic number and the shell in which the “hole” occurred. Z 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 analysis.
Nomenclature The energy of an X-ray corresponds to the difference in energy of the energy levels concerned. Kradiation 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 D, E, F, ... 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:
Fundamental Principles
X-ray line labelling
Examples: Electron from sub-level LIII to the K-shell (KD) KD KD
Electron from sublevel LII to the K-shell (KD)
KD
if neither line is resolved by the spectrometer: KD Electron from sublevel M to the K-shell (KE1) Electron from sublevel M to the L-shell (LD)
KE1 LD
Generating the Characteristic Radiation The purpose of X-ray fluorescence is to determine chemical elements both qualitatively and quantitatively 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 electrons from the innermost shell of an atom. This involves adding to the inner electrons amounts of energy that are higher than the energy bonding them to the atom. This can be done in a number ways: x
Irradiation using elementary particles of sufficient energy (electrons, protons, D-particles, ...) that transfer the energy necessary for release to the atomic shell electrons during collision processes
x
Irradiation using x- or gamma rays from radionuclides
x
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 intensity of this type of X-ray is applied depending on the energy, the result is the Bremsspektrum (= continuum) of the tube.
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Fig. 3:
Fundamental Principles
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 decelerating them in a suitable anode material. The region of the electron beam in which this takes place must be evacuated in order to prevent collisions with gas molecules. Hence there is a vacuum within the
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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 arrangement of the exit window. The two most significant types are the end-window tubes and the sidewindow 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 voltage and thus has no difference in potential to the surrounding housing material and the laterally mounted 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 consequence, 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 electrons emanate from the heated cathode and are accelerated towards the electrical field lines on the anode. Due to the fact that there is a difference in potential between the positively charged anode and the surrounding material, including the beryllium window, the back-scattering electrons are guided back to the anode and thus do not contribute to the rise in the exit window’s temperature. The beryllium 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. Instruments with end-window tubes are therefore equipped with a closed, internal circulation system containing 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 produced 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 voltage 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 electrons. 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 excited 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: x
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.
x
The elements as far as molybdenum are excited by the Rh K radiation. The Rh-KE1 radiation can even excite the element ruthenium but is of lower intensity than the K-alpha radiation.
x
The light elements up to sulphur are excited very effectively by the Rh L radiation.
x
The Rh-LE1 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. Tungsten (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 cadmium) 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 higherenergy 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: I
I 0 e Px
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 ȡ (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 U of the material that was passed through P/U
= 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 energy or wavelength. 12
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Fig. 6:
Fundamental Principles
Schematic progression of the mass attenuation coefficient of energy or wavelength
Fig. 6 supplies the following: x
The overall progression of the coefficient decreases as energy increases, i.e. the higher the energy of the X-ray quants, the less they are absorbed.
x
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 KD1,2 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 KD1, 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 KD1,2, 0,282 keV). As a consequence, a specific layer thickness is analysed for each element which depends on the specific energy 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 practically infinitely thick for Fe KD1,2 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 plastics (hydrocarbons). Here, for the high-energy radiation of heavier elements, high saturation thicknesses 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 effects 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 KD1 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 14
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quant itself. The silicon radiation thus contributes to the X-ray emission of the aluminium. This is referred to as secondary enhancement (Fig. 7). In quantitative analyses, the effects of absorption and secondary enhancement may have to be corrected. Modern software packages offer a selection of correction models (matrix correction or interelement 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 radiation 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 samples 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 energy and can thus enter the detector and be measured. The peaks of the anode material (e.g. rhodium) 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 primary 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 Xrays. 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, 16
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KCps = kilocounts per second), is called their intensity and contains in a first approximation the information 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 counter and 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 material 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 electrons 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 electrons created in this way “see” an increasing electrical field on route to the wire. The high voltage in
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Introduction to X-Ray Fluorescence Analysis (XRF)
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 proportional 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 proportional 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 scintillation 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.
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Fig. 9:
Fundamental Principles
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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Fundamental Principles
Fig. 10a:
Pulse height distribution (S) Gas proportional counter
Introduction to X-Ray Fluorescence Analysis (XRF)
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.
20
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Fig. 11
Fundamental Principles
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 KD1,2 X-ray quant with an energy of 3 keV. If this Ar-fluorescence escapes from the counter then only the incident energy minus 3 keV remains for the measured 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 KD1,2) 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
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Fundamental Principles
Introduction to X-Ray Fluorescence Analysis (XRF)
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 application (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 changing 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 KD1 as the radiation source (Fig. 11a). The number of pulses has been applied 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 measurement of all pulses over the discriminator threshold. If the pulses are pushed over a discriminator window with a lower and upper threshold, the intensity drops once more as the peaks are pushed out of the window again.
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Fig. 11b:
Fundamental Principles
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 minima meets minima and maxima meets maxima. This is precisely the case when the phase difference 'O is zero or a multiple of the wavelength O, i.e.: 'O
nO
n = 0, 1, 2, ....
“n” is referred to as the “order” (Fig. 12):
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Fundamental Principles
Fig. 12
Introduction to X-Ray Fluorescence Analysis (XRF)
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 coincide 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 corresponds with the image of light as a beam of particles (photons, quants). We know from waves that 24
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Fundamental Principles
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 (O = 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 (O = 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 elements in the sample (by X-rays), a blend of element-characteristic wavelengths (fluorescence radiation) leaves the sample. There are now two methods ( or procedures) in XRF of identifying these various wavelengths. The energy dispersive XRF calls on the assistance of an energy dispersive detector 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 subsequently 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" ('O= nO) is not precisely met, the reflected wave will interfere such that cancellation occurs. All that remains is the wavelength for which the amplification 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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Fundamental Principles
Fig. 14
Introduction to X-Ray Fluorescence Analysis (XRF)
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 T (theta) (1', 2'). The proportion of the beam that is scattered on the second plane has a phase difference of 'ACB' to the proportion of the beam that was scattered at the first plane. Following the definition of the sine: ' AC ' d
sin T or ' AC ' d sin T
The phase difference 'ACB' is twice that, so: ' ACB' 2d sin T
The amplification condition is fulfilled when the phase difference is a whole multiple of the wavelength O , so: ' ACB ' nO
This results in Bragg's Law: nO=2d sinT n = 1, 2, 3 ...
26
Bragg's equation Reflection order
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Fig. 15a:
1st order reflection: O = 2d sin T1
Fig. 15b:
2nd order reflection: 2O = 2d sin T2
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27
Fundamental Principles
Fig. 15c:
Introduction to X-Ray Fluorescence Analysis (XRF)
3rd order reflection: 3O = 2d sin T3
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 Tyou can determine either the wavelength O, and thus chemical elements, if the lattice plane distance 'd' is known or, if the wavelength O 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 O or the 2d-value is identified by measuring the angle T (Table 3).: Table 3: Known d O
28
Wavelength dispersive X-ray techniques Sought O d
Measured T T
Method Instrument type X-ray fluorescence Spectrometer X-ray diffraction Diffractometer
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In X-ray diffraction (XRD) the sample is excited with monochromatic radiation of a known wavelength (O) 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 element-characteristic wavelength (O).
Reflections of Higher Orders Fig. 15a-c illustrate the reflections of the 1st, 2nd, and 3rd order of one wavelength below the different angles T T THere, 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 'O' for greater orders, and shorter wavelengths 'O* < O' that satisfy the condition 'O* = O/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 'T': 1O = 2(O/2) = 3(O/3) = 4(O/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 hafnium (Hf) in a sample with a high proportion of zircon. The Zr KD1 – peak has twice the energy of the Hf LD1 – peak and appears, when the Hf LD1 – peak is set, at the same angle in the pulse height spectrum.
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Fundamental Principles
Fig. 16:
Introduction to X-Ray Fluorescence Analysis (XRF)
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 T can theoretically only be between 0° and 90° (in practice 2° to 75°), 'sin T' only accepts values between 0 and +1. When Bragg's equation is applied: 0%
30
nO 2d
sin T % 1
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Fundamental Principles
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: x
resolution
x
reflectivity (--! intensity)
Further criteria can be: x
temperature stability
x
suppression of higher orders
x
crystal fluorescence
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Introduction to X-Ray Fluorescence Analysis (XRF)
Table 4:
Crystal types
Crystal
Name
Element range
2d-value (nm)
LiF(420)
Lithiumfluoride
> Co KE1
0.1801
LiF(220)
Lithiumfluoride
> V KD1
0.2848
LiF(200)
Lithiumfluoride
> K KD1
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 'Tupon changing the wavelength by the amount 'O (thus: 'T'O is called “dispersion”. The greater the dispersion, the better is the separation of two adjacent or overlapping 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: dT dO
n 2d cos T
It can be seen from this equation that the dispersion (or peak separation) increases as the lattice plane distance 'd' declines.
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Examples: (cf. Table 5) The 2T-values of the KD1-peaks of vanadium (V) and chromium (Cr) are further apart when measuring with LiF(220) than when measuring with LiF(200). The 2Tvalues of the KD1-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)
2T (El1) (degrees)
2T (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 crystals”, “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).
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Fundamental Principles
Fig. 17:
Introduction to X-Ray Fluorescence Analysis (XRF)
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
KD1,2
-
V
KE1
Mn
KD1,2
-
Cr
KE1
U
LD1
-
Rb
KD1,2
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LiF(420): One of the special crystals; can be used for the element range atomic number 28 (Ni or Co KE1) onwards; 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 distances '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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Fundamental Principles
Fig. 18:
Introduction to X-Ray Fluorescence Analysis (XRF)
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).
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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 resolution 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
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Fundamental Principles
Introduction to X-Ray Fluorescence Analysis (XRF)
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 corresponding 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).
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B KA1,2 in BN (OVOs; 2,0°; 20kV/50mA) SqE - Scale 7,025
7,03
7,04
7,05
7,06
7,07
7,08
7,09
7,10
4,0
4,0
3,9
3,9
3,8
3,8
OVO-B
3,7
3,7
3,6
3,6
3,5
3,5
3,4
3,4
3,3
3,3
3,2
3,2
3,1
3,1
3,0
3,0
2,9
2,9
2,8
2,8
2,7
2,7
2,6
2,6
2,5
2,5
2,4
2,4
2,3
2,3 2,2
2,1
2,1
OVO-160
2,0
2,0
1,9
1,9
1,8
1,8
1,7
1,7
1,6
1,6
1,5
1,5
1,4
1,4
1,3
1,3
1,2
Lin (KCps)
Lin (KCps)
2,2
1,2
OVO-C
1,1
1,1
1,0
1,0
0,9
0,9
0,8
0,8
0,7
0,7
0,6
0,6
OVO-N
0,5
0,5
0,4
0,4
0,3
0,3
0,2
0,2
0,1
0,1
0
0 7,025
7,03
7,04
7,05
7,06
7,07
7,08
7,09
7,10
SqE - Scale Immediate Measurement Operations: Import [001] Immediate Measurement Operations: Import [002] Immediate Measurement Operations: Import [003] Immediate Measurement Operations: Import [004]
Fig. 19a:
- Crystal: OVO-B - 2T h.0: 1
05 (#) - B - - - - - -
- Crystal: OVO-160 - 2T h.0 - Crystal: OVO-C - 2T h.0: 4 - Crystal: OVO-N - 2T h.0: 5
OVO-B is the best multilayer crystal for analysing Boron (B).
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Introduction to X-Ray Fluorescence Analysis (XRF)
C KA1,2 in Graphite (OVOs; 1,0°; 20kv/50mA) 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
40
40
39
39
38
38
37
37
OVO-160
36
36
35
35
34
34
33
33
32
32
31
31
30
30
29
29
28
28
27
27
26
26
25
25
24
24
23
23 22
OVO-C
21
21
20
20
19
19
18
18
17
17
16
16
15
15
14
14
13
13
12
12
11
Lin (KCps)
Lin (KCps)
22
11
OVO-N
10
10
9
9
8
8
7
7
6
6
OVO-B
5
5
4
4
OVO-55
3
3
2
2
1
1
0
0 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
SqE - Scale Immediate Measurement Operations: Import [001] Immediate Measurement Operations: Import [002] Immediate Measurement Operations: Import [003] Immediate Measurement Operations: Import [004]
Fig. 19b:
40
- Crystal: OVO-C - 2T h.0: 3 - Crystal: OVO-N - 2T h.0: 3
Immediate Measurement - Crystal: OVO-55 - 2T h.0: Operations: Import [005] 06 (#) - C - - - - - -
- Crystal: OVO-160 - 2T h.0 - Crystal: OVO-B - 2T h.0: 1
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) SqE - Scale 6,837
6,84
6,85
6,86
6,87
6,88
6,89
6,90
6,91
OVO-N 3
3
2
2
OVO-160 1
1
0,6
Sqr (KCps)
Sqr (KCps)
OVO-B
0,6
OVO-55
0,5
0,5
OVO-C
0,4
0,4
0,3
0,3
0,2
0,2
0,1
0,1
0,01
0,01
0,001
0,001
0
0 6,837
6,84
6,85
6,86
6,87
6,88
6,89
6,90
6,91
SqE - Scale Immediate Measurement Operations: Import [001] Immediate Measurement Operations: Import [002] Immediate Measurement Operations: Import [003] Immediate Measurement Operations: Import [004]
Fig. 19c:
- Crystal: OVO-N - 2T h.0: 2 - Crystal: OVO-160 - 2T h.0
Immediate Measurement - Crystal: OVO-55 - 2T h.0: Operations: Import [005] 07 (#) - N - - - - - -
- Crystal: OVO-C - 2T h.0: 2 - Crystal: OVO-B - 2T h.0: 1
Nitrogen (N) is best analysed using the OVO-N.
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Fundamental Principles
Introduction to X-Ray Fluorescence Analysis (XRF)
O KA1,2 in NOPS (OVOs; 0,46°; 20kV/50mA) SqE - Scale 6,72
6,73
6,74
6,75
6,76
6,77
6,78
6,79
6,80
6,81
6,82
4,0
4,0
3,9
3,9
3,8
3,8
3,7
3,7
3,6
3,6
3,5
3,5
3,4
3,4
3,3
3,3
3,2
3,2
3,1
3,1
3,0
3,0
2,9
2,9
2,8
2,8
2,7
2,7
2,6
2,6
2,5
2,5
2,4
2,4
2,3
2,3
2,2
2,2
2,1
2,1
2,0
2,0
1,9
1,9
1,8
1,8
1,7
1,7
1,6
1,6
1,5
1,5
1,4
1,4
1,3
Lin (KCps)
Lin (KCps)
6,712
1,3
OVO-C
1,2
1,2
1,1
1,1
1,0
1,0
0,9
0,9
0,8
0,8
OVO-160
0,7
0,7
0,6
0,6
0,5
0,5
0,4
0,4
OVO-N
0,3
0,3
OVO-55
0,2
0,2
0,1
0,1
0
0 6,712
6,72
6,73
6,74
6,75
6,76
6,77
6,78
6,79
6,80
6,81
6,82
SqE - Scale Immediate Measurement Operations: Import [001] Immediate Measurement Operations: Import [002] Immediate Measurement Operations: Import [003] Immediate Measurement Operations: Import [004]
Fig. 19d:
42
- Crystal: OVO-55 - 2T h.0:
08 (#) - O - - - - - -
- Crystal: OVO-160 - 2T h.0 - Crystal: OVO-N - 2T h.0: 1 - Crystal: OVO-C - 2T h.0: 1
Oxigen (O) and all further „heavier“ light elements have to be analysed with the OVO-55.
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Fundamental Principles
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 curvatures that follow a logarithmic spiral (Fig. 20a) and the Johansson curvature (including grinding) (Fig. 20b).
Fig. 20a:
Logarithmic spiral curvature
DOC-M84-E06001 July 2004
Fig. 20b:
Johansson curvature
43
Introduction to X-Ray Fluorescence Analysis (XRF)
Instrumentation
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 installed 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) window. 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 qualitative analysis.
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As all elements are measured simultaneously, a generator setting (kV/mA) must be selected that provides the best compromise in each case for the components to be measured. The measurement period depends on statistical accuracy requirements of the element with the lowest intensity and is typically 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 elements 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:
46
Beam entry in the MRS
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Introduction to X-Ray Fluorescence Analysis (XRF)
Fig. 22:
Instrumentation
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 coverage of a large element range. As only a single curved crystal (LiF(200) or PET) is fitted, several elements in the periodic table must be measured in the 2nd reflection order as the scanner's 24-angular range is limited (30 - 120 degrees). A flow counter or a sealed proportional counter serves as a detector. 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.
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Instrumentation
Fig. 23:
Introduction to X-Ray Fluorescence Analysis (XRF)
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 TT 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 remotediagnosed by the Bruker AXS-Service-Centers via Teleservice, without being able to access securityrelevant 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 provides the user with great flexibility.
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Instrumentation
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 analysis computer. The separate TTgoniometer drive with two independent stepper motors allows a precise TTangle alignmentvia 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 scintillation 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 instrument. 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 components. A flexible, modifiable sample changer with a robot arm that moves in the directions X and Y allows fully automatic transport of: x
sample cups with a grab
x
'bare samples' with a suction unit
x
combinations of both
x
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
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Introduction to X-Ray Fluorescence Analysis (XRF)
stack operation without time-loss through transporting samples, i.e. while one sample is being measured, the next is being inserted into the pre-vacuum chamber.
Sample
Vacuum Seal
Primary Beam Filters
Collimators
Analyzer Crystals
X-ray Tube
Proportional Counter
Fig. 24
Scintillation Counter
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.
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Instrumentation
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.: x
27 kV / 150 mA
= 4,05 kW
x
30 kV / 134 mA
= 4,02 kW
x
40 kV / 100 mA
= 4,00 kW
x
50 kV / 80 mA
= 4,00 kW
x
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 onwards 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
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Introduction to X-Ray Fluorescence Analysis (XRF)
of thickness as absorbers. The one fitted can be selected to suit individual requirements when purchasing 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 highvoltage 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:
52
Cd- and Rh-peak without a copper primary beam filter
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Instrumentation
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
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Introduction to X-Ray Fluorescence Analysis (XRF)
When analysing a sample of very pure graphite, peaks of the elements Cr, Fe, Ni und Cu can occur and in the 2T-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 components.
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 chamber 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 diameters and materials are available on request. Depending on type of sample magazine, the samples have to be placed in the cups manually (magazine 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 fixing plate radiation.
The Vacuum Seal When measuring (liquid) samples in a helium atmosphere, the vacuum can be maintained in the spectrometer 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.
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Instrumentation
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° collimator 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 significantly. This enables intensity to be increased without a loss in angle resolution when analysing the light elements (Fig. 28).
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Instrumentation
Fig. 28:
Introduction to X-Ray Fluorescence Analysis (XRF)
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 customequipped 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.
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Instrumentation
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% permeability. 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 measuring 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 installed 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 window).
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Instrumentation
Fig. 29:
Introduction to X-Ray Fluorescence Analysis (XRF)
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 radiation measured inside it must pass through the flow counter, a 0.1 mm thick vacuum-chamber sealing 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 KD1) 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°).
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In the S4 EXPLORER the scintillation counter is directly beside the proportional counter in the spectrometer 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 photomultiplier, 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 interference 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 amplification 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 a sin T
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Introduction to X-Ray Fluorescence Analysis (XRF)
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 formation 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 intensity 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.
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Fig. 30:
The dead time effect
Fig. 31:
Dead time corrected readings
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Introduction to X-Ray Fluorescence Analysis (XRF)
Line-shift Correction Line-shift correction is only important for the flow counter and the proportional counter at high intensities. 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).
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Appendix A: Literature
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, Ron Jenkins, Deane K. Smith (Eds.)
A practical guide for the preparation of specimens for X-ray fluorescence and X-ray diffraction analysis Wiley-VCH, 1998, 333 pp. ISBN 0-471-19458-1
Harry Bennet, Graham J. Oliver
XRF Analysis of Ceramics, Minerals and allied materials John Wiley & Sons, 1992 ISBN 0-471-93457-7
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Appendix A: Literature
Introduction to X-ray Fluorescence (XRF) Analysis
Dekker
Handbook of X-ray Spectrometry, 1993, 704 pp. ISBN 0-8247-8483-9
P. Hahn-Weinheimer A. Hirner K. Weber-Diefenbach
Röntgenfluoreszenzanalytische Methoden, Grundlagen und praktische Anwendung in den Geo-, 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 (Hrsg.)
Röntgenfluoreszenzanalyse Anwendung in Betriebslaboratorien Springer Verlag ISBN 3-540-18641-7, ISBN 0-387-18641-7
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Appendix A: Literature
Tables J. Leroux T. Ph. Thinh
Revised Tables of X-Ray Mass Attenuation Coefficients Corporation Scientifique Claisse Inc. Quebec 1977
R. Theisen D. Vollath
Tables of X-Ray Mass Attenuation Coefficients 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
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Introduction to X-ray Fluorescence Analysis (XRF)
Appendix B: Sources of standard samples
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
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Appendix B: Sources of standard samples
Introduction to X-ray Fluorescence Analysis (XRF)
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
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Appendix C: Sample Preparation Catalog
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 reproducibilities 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 fluorescence 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: x
representative of the material
x
homogeneous
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x
thick enough to meet the requirements of an infinitely thick sample
x
without surface irregularities
x
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 reproducible 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 depends on the sample material (Tab. 1). Therefore especially for analysis of light elements, sample preparation has to be carried out extremely carefully.
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Layer thickness (in Pm), where 90 % of the fluorescence radiation originate from
Tab. 1:
Sample matrix Line
Graphite
Glass
Iron
Lead
h_(90%,Pm)
h_(90%,Pm)
h_(90%,Pm)
h_(90%,Pm)
U
LD1
28000
1735
154
22.4
Pb
LE1
22200
1398
125
63.9
Hg
LD1
10750
709
65.6
34.9
W
LD1
6289
429
40.9
22.4
Ce
LE1
1484
113
96.1
6.72
Ba
LD1
893
71.3
61.3
4.4
Sn
LD1
399
44.8
30.2
3.34
Cd
KD1
144600
8197
701
77.3
Mo
KD1
60580
3600
314
36.7
Zr
KD1
44130
2668
235
28.9
Sr
KD1
31620
1947
173
24.6
Br
KD1,2
18580
1183
106
55.1
As
KE1
17773
1132
102
53
6861
466
44.1
24
Zn
KD1,2
5512
380
36.4
20
Cu
KD1,2
4394
307
29.8
16.6
Ni
KD1,2
2720
196
164
11.1
Fe
KD1,2
2110
155
131
9.01
Mn
KD1,2
1619
122
104
7.23
Cr
KD1,2
920
73.3
63
4.52
Ti
KD1,2
495
54.3
36.5
3.41
Ca
KD1,2
355
40.2
27.2
3.04
K
KD1,2
172
20.9
14.3
2.19
Cl
KD1,2
116
14.8
10.1
4.83
S
KD1,2
48.9
16.1
4.69
2.47
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Sample matrix
Introduction to X-ray Fluorescence Analysis (XRF)
Graphite
Glass
Iron
Lead
KD1,2
31.8
10.5
3.05
1.7
Al
KD1,2
20
7.08
1.92
1.13
Mg
KD1,2
12
5.56
1.15
0.728
Na
KD1,2
3.7
1.71
0.356
0.262
F
KD1,2
1.85
2.50
0.178
0.143
O
KD1,2
0.831
1.11
0.08018
0.07133
N
KD1,2
13.6
0.424
0.03108
0.03124
C
KD1,2
4.19
0.134
0.01002
0.01166
B
KD1,2
Si
Massive materials, such as rocks, soils, slags and similar samples have to be crushed, e.g. in a crushing 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 Pm. 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 Pm. 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 spectrometer (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 containing 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 calibration curve should show the same grain size distribution as the standard samples used for calibration. 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-
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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 coefficients (“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 contaminants in a diluent.
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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 necessary 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 shielding effect which results in a decrease in fluorescence intensities. As expected, the decrease in intensity 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 intensities 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 striation be of the same size and that the sample composition be similar (same effective wavelength). In practice, striation depths of 100 Pm are acceptable for elements with characteristic lines of short wavelengths, but striations deeper than few Pm 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 necessary to remove contamination as well as grease stains and handling residue.
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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 Pm in diameter, the sample 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 necessary 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 elements 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. Although 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 specific 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 compacted 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 analysis), 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
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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-Pm foil has proven to be successful 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 nonbackscattering 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 eliminates particle size and mineralogical effects entirely. The fusion technique also has additional advantages: x Possibility of high or low specimen dilution for the purpose of decreasing matrix effects x Possibility of adding compounds such as heavy absorbers or internal standards to decrease or compensate for matrix effects
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x 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 lithium 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 usefulness of the technique. For example, the introduction of a substance into a solution inevitably means dilution and this, combined 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 Pm Spectrolene and 2.5 to 6.5 Pm 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 ultimate precision of any particular X-ray spectrometer.
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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
x
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
x
Jaws hold up to 5 kg (10 lbs) of sample as one load
x
Hinged one piece cover opens easily for cleaning and lubricating
x
Quick jaw adjustment
x
Air ducting, built into cabinet
x
Air vents for dust removal during sample loading
x
Safety switch, stops motor as soon as cover is opened
x
Flat 300 mm (12 inch) wide jaws for ease of cleaning
x
Sample collector can be altered to customer’s specification
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Overall length:
1160 mm
Weight:
560 kg
Width:
720 mm
Height:
1030 mm
Grinding Planetary mono mill
7KP9000-8BU
The planetary mono mill is used for sample pulverizing (down to 1 mm) starting from cuttings (diameter 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 Pm) 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 vessel is used for sample pulverizing (down to 1 Pm) starting from cuttings (diameter below 10 mm, input volume: 30-125 ml). 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). 80
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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
This grinding vessel is used for sample pulverizing (down to 1 Pm) starting from cuttings (diameter below 10 mm, input volume: 30-125 ml). 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
Dimensions (hxwxd)
900x650x530mm
Weight
Approx. 200 kg
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. Fibrous 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
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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
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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
Standard power supply
400 V, 50 Hz, 3 phases
Power consumption
2.5 kVA
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 84
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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 material
Chrome steel
Volume
100 cm³
Dimensions
1230 x 680 x 700 mm
Weight
425 kg
Grinding vessel type 100WC, for PAL-M100M Vessel including cover, ring and stone made of tungsten carbide, volume 100 cm
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7KP9000-8BM 3
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Swinging mill type PAL-M100M with pelletizing press type PAL-P40M
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7KP9000-8BN
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Vibrating disk mill HK 40 incl. grinding vessel (100 ml, Corundum) x
Powerful swing mill for desktop operation
x
Standard grinding vessel of sintered corundum, 100 cm³
x
Reproducible setting of milling time by electronic timer
x
Wellbalanced construction for stable desktop positioning Dimensions: Weight: Mains:
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7KP9000-8AV
34.5 x 29.5 x 54.0 mm ca. 40 kg 230 V, 50 Hz, 200 W
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3 K ring mill, Rotoclamp, 3 kg
Introduction to X-ray Fluorescence Analysis (XRF)
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
Appendix C: Sample Preparation Catalog
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 x 220 to 240 V, 3 phases, 50 Hz, 500 rpm or x 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
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
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. Dimensions
420 x 420 x 500 mm
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 diameters (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 accessories. The hydraulic pump is operated by the handle. The direction of motion of the piston press can be reversed 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.) 92
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x
Simple rugged construction
x
Hand operated pump with pressure gauge
x
30 t maximum ram rating
Appendix C: Sample Preparation Catalog
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.
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Pressure
Max. 40 t
Pressure holding time
0 to 1000 s, continuously adjustable
Standard power supply
400 V, 50 Hz, 3 phases
Power consumption
1.2 kVA
Dimensions (hxwxd)
1250x670x690mm
Floor load
800 kg/m2
Weight
Approx. 400 kg
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 35/40 mm dia, 14 mm the steel rings height or 35/51.5 mm dia, 8.5 mm eight Standard power supply
DOC-M84-E06001 July 2004
400 V, 50 Hz, 3 phases
Power consumption
2.5 kVA
Dimensions (hxwxd)
1558x1050x900 mm
Weight
750 kg
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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.
Pressing tool for steel rings, for PAL-P40M
Dimensions
1230 x 680 x 700 mm
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
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
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7KP9000-8BR
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Manual press PE-MAN
7KP9000-8AW
Manual Press PE-MAN: x - compact laboratory benchtop machines for X-ray sample pelletizing x
safety valve allowing to set maximum final pressure up to 20 tons
x
easy handling - wide space for die set positioning and removal
x
maintainance free mechanism, covered in solid steel housing
x
manual press with adjustable lever - recommended for non-routine work
Pressing tool for PE-MAN
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
--
7KP9000-8AX
x 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
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7KP9001-8BL
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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 pellets.
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
x 40 liter volume x Magnetic lock x With 4 shelves x Integrated hygrometer x Outer dimensions 300x395x510 mm x 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
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Milling Automatic sample miller HN-FF
7KP9000-8AF
Spare part kits for HN-FF
7KP9001-8BG
102
Power supply
400 V, 50 Hz, 3 phases
Power consumption
6.0 kVA
Dimensions (hxwxd)
1500x1030x800mm
Weight
Approx. 750 kg
Air pressure
5 to 10 bar
Air consumption
Approx. 0,3 m3 per sample
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Fusing ISP mini fusion manual furnace
7KP9000-8BS
x High performance and reliability x Simple maintenance requirements x 2 crucible and 2 mold unit x Completely electronic x Top loading with cantilever lid x Auto agitation of mix during fusion
ISP 4x4 manual furnace x
High performance and reliability
x
Simple maintenance requirements
x
4 crucible & 4 mould unit
x
All electric
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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
7KP9000-8BT
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x
Top loading with cantilever lid
x
Auto agitation of mix during fusion
Introduction to X-ray Fluorescence Analysis (XRF)
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 for ISP and Linflux fusing devices
7KP9001-8CX
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
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x Fully automatic sample preparation for any mineral, ore, ferro-ally etc. x Highest flexibility in melting and colling parameter setting for each station x Accurately reproducible melting conditions in low and high temperature mode x independent temperature setting for each crucible and mold burner x Temperature range up to 1600°C by use of standard propane / Oxygen burners x Effective oscillationg agitation of crucible with setting of oscillation rate and time x Air cooling of hot mold via pre-warmed nozzle with air volume and time control x Gas leakage control with automatic gas and oxygen smut off and LED-indicator x Pilot burner control and air pressure control with water trap x Solid state mechanics, one printed circuit card only, easily accessible components x Reliable, safe and proven machine, code programming not required, simple operation
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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.
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Crucible (approx. 42 g) for VAA2 or VAA4
Appendix C: Sample Preparation Catalog
HER-87043878
Casting mold, (for 40 mm beads, aprox. 45 g)
7KP9001-8CC
Cover for crucibles with 39 mm upper diameter
7KP9001-8CD
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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
Dimensions (hxwxd)
1300x700x800mm
Weight
Approx. 300 kg
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
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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
Power consumption
200 W
Dimensions (hxwxd) Fluxer
330x610x330mm
Controller
90 x 400 x 300 mm
Total weight
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30 kg
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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
Mains frequency
50/60 Hz
Power consumption
100 W
Dimensions (hxwxd) Shipping weight
30 kg
Fluxer
430x280x420mm
Remote
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 110
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x
fully automatic, efficient, 3-position fluxer with individual burner selection
x
automatic, pilotless ignition with flame monitoring for increased safety
x
standard DB-9 connector for linking to a PC (advanced interface software included)
x
user can manually operate the instrument and record its actions in realtime in an automatic program for future use
x
several preset programs (for most sample types)
x
ten independent and user-customizable fusion programs
x
programs can be saved to a floppy or hard disk when fluxer is connected to a computer
x
seven to fifteen functions per program for increased versatility
x
all parameters can be modified: gas flow, mixing speed, function duration, crucible angle, cooling air flow, solution stirring speed...
x
independent mold holder allowing low-temperature fusions - useful for fluor-bearing samples
x
three burners that only use propane gas: no compressed air or oxygen is required
x
superior homogenization and heating uniformity
x
very compact design (17.5x20.5x16 in = 45x52x41 cm ; weighs only 50 lb= 23 kg)
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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 constant 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 corresponds to VDE regulation. Power supply
220/240 V, 50/60 Hz
Power consumption
3.5 kVA
RF power
Max. 2.0 kW
Frequency
1.5 MHz
Cooling-water supply
3 l/min
Dimensions (hxwxd)
1530 x 680 x 680 mm
LIFUMAT - C2000 - 3.3 - VAC induction fusing device
112
LIN-C2000-33VAC
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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 melting 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 operation
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
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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
114
Gas
0,2 to 1 bar
Oxygen
6 bar
Air
6 bar
Mains voltage
1 10 or 240 VAC
Mains frequency
50/60 Hz
Power consumption
75 W
Dimensions (hxwxd)
330 x 880 x 630 mm
Weight
90 kg
No. of burners
8
Beads produced
4per cycle
Beads produced
384 per 24-h cycle (assuming a cycle time of 15 min.)
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Accessories for fusing Platinum headed tongs for handling of platinum ware, 30 cm long, approx. 5 g
7KP9001-8CH
Fluxes A100, Lithiumtetraborate flux, 1 kg
7KP9001-8CJ
A100, Lithiumtetraborate flux, 5 kg
7KP9001-8CK
Liquid sample measurement accessories Liquid cups
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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 properties determining the best choice for your application. The problem however is to weigh strength versus transmission. Strength Mylar is a relatively very strong material. Polycarbonate is strong enough for most applications, however not as strong and resistant to chemical attack. Transmission Generalizing, transmission increases from Mylar to Polypropylene and from Polypropylene to Polycarbonate. 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 measuring time. Mylar is in general chemically more resistant than other materials. Foils for liquid cells Mylar, 15 Pm, roll of 150 m
C71298-A18-C286
Mylar, 6 Pm, roll of 90 m
7KP1901-8BZ
Mylar, 2.5 Pm, roll of 90 m
7KP1901-8BR
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Hostaphan, 15 Pm, roll of 150 m
C71298-A18-C262
Hostaphan, 6 Pm, roll of 150 m
C71298-A18-C264
Polypropylene, 5 Pm, roll of 90 m
7KP1901-8BS
Polypropylene, 6 Pm, roll of 90 m
C71298-A18-C288
Polypropylene, 12 Pm, roll of 90 m
7KP1901-8BU
Ultrapolyester, 1.5 Pm, roll of 90 m
7KP1901-8BT
Prolene, 4 Pm, roll of 90 m
7KP1901-8BG
Prolene, 4µm, precut foils, 500 off
7KP7804-8CB
Polycarbonate, 5 Pm, 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
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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
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Index
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
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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
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F
M
flow counter .................................................. 56 fluorescence yield ............................................4
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
G gamma radiation ..............................................1 generator ................................................ 10, 51
H high voltage .................................................. 10
N Nomenclature.................................................. 4
I intensity............................................................2 interference................................................... 23
O output ............................................................ 10
K
P
KCps ................................................................2 kiloelectronvolts keV ...............................................................1
photon ............................................................. 2 primary beam filter ........................................ 51 proportional counter sealed ........................................................ 57 pulse height analysis (PHA).......................... 19 pulse height distribution ................................ 19 pulse height spectrum................................... 16
L layer thickness .............................................. 14 LiF(200), LiF(220), LiF(420) ......................... 33 line separation .............................................. 32 line-shift correction........................................ 62
Q quants ............................................................. 1
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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
DOC-M84-E06001 July 2004
Index
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
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