X-ray spectroscopy uses X-ray absorption, emission, and fluorescence spectra to determine elements in samples. X-rays are generated when high-speed electrons collide with objects or during electronic transitions in atoms. Atoms have electron shells corresponding to principal quantum numbers, with inner shells having higher energy. When X-rays or electrons collide with an atom, an inner shell electron may be ejected, causing an electron from an outer shell to fill the vacancy while emitting an X-ray. Moseley's law relates the wavelength of characteristic X-rays to the atomic number. X-ray methods include absorption, diffraction, fluorescence, and emission spectroscopy.
Here are some key points about the effects of multiple chromophores on absorption:
- Additional chromophores in the same molecule cause a bathochromic (red) shift, moving the absorption maximum to longer wavelengths. This is due to increased conjugation and delocalization of the π electrons.
- Absorption intensity (ε value) also increases with more chromophores, known as the hyperchromic effect. More π electrons means more efficient absorption.
- Conjugated chromophores, where the π systems are connected, exhibit significant bathochromic and hyperchromic effects. The π* orbitals are delocalized over the whole conjugated system, lowering the energy gap for π-π*
This document provides an introduction to mass spectrometry, including definitions, principles, instrumentation, ionization techniques, applications, advantages, and disadvantages. It describes how mass spectrometry works to ionize chemical compounds and measure their mass-to-charge ratios to determine molecular structures. The key components of a mass spectrometer and various ionization methods are defined. Applications including qualitative analysis, quantitative analysis, proteomics, and combination with chromatography are summarized.
Polarography is an electrochemical technique used to analyze reducible or oxidizable substances in solution. It involves varying the electric potential between a dropping mercury electrode and a reference electrode while monitoring the current. A polarogram is generated by plotting the current readings against the applied voltage. Key features of polarography include applied voltages between 0-2.5V and current values between 0.12-100 microamperes. Polarography finds applications in pharmaceutical analysis such as determining dissolved oxygen, trace metals in drugs, vitamins, hormones, antibiotics, and diagnosing cancer from blood serum.
Raman spectroscopy is a technique that uses lasers to study vibrational, rotational, and other low-frequency modes in a system. When light interacts with molecules, the light may be scattered at different wavelengths than the incident laser. This shift in wavelength provides information about molecular structure and symmetry. Raman spectroscopy can be used to examine inorganic, organic, and polymeric materials, determine molecular structure and interactions, and study chemical reactions and physical transformations.
Atomic emission spectroscopy is a technique used to identify elements in a sample based on the wavelengths of light emitted by atoms excited by a heat source like a flame, furnace, or plasma. It works by exciting the sample atoms, which then relax and emit light of characteristic wavelengths. The light is separated by wavelength and the intensities are used for qualitative and quantitative analysis. Common excitation sources include flames, arcs, sparks, and inductively coupled plasma, with the plasma being the most widely used currently due to its ability to analyze a wide range of elements simultaneously.
Mass spectrometry deals with the study of charged molecules and fragment ions produced from a sample exposed to ionizing conditions. It works by bombarding samples with electron beams or chemical ions, which causes the samples to form positively charged molecular or fragment ions. These ions are then separated based on their mass-to-charge ratio, producing a spectrum that can be used to determine molecular weights, identify unknown compounds, and detect impurities. Mass spectrometry is a versatile analytical technique with applications in pharmaceutical analysis, proteomics, and other areas.
The Wonderful World of Scanning Electrochemical Microscopy (SECM)InsideScientific
This document summarizes a presentation given by Dr. Janine Mauzeroll on scanning electrochemical microscopy (SECM). SECM is introduced, including operating modes and principles. Applications of SECM in studying multdrug resistance in cancer cells, electrochemical properties of battery materials, and corrosion of alloys are discussed. SECM allows visualization of heterogeneous electron transfer kinetics and mass transport at micro and nanoscale.
Here are some key points about the effects of multiple chromophores on absorption:
- Additional chromophores in the same molecule cause a bathochromic (red) shift, moving the absorption maximum to longer wavelengths. This is due to increased conjugation and delocalization of the π electrons.
- Absorption intensity (ε value) also increases with more chromophores, known as the hyperchromic effect. More π electrons means more efficient absorption.
- Conjugated chromophores, where the π systems are connected, exhibit significant bathochromic and hyperchromic effects. The π* orbitals are delocalized over the whole conjugated system, lowering the energy gap for π-π*
This document provides an introduction to mass spectrometry, including definitions, principles, instrumentation, ionization techniques, applications, advantages, and disadvantages. It describes how mass spectrometry works to ionize chemical compounds and measure their mass-to-charge ratios to determine molecular structures. The key components of a mass spectrometer and various ionization methods are defined. Applications including qualitative analysis, quantitative analysis, proteomics, and combination with chromatography are summarized.
Polarography is an electrochemical technique used to analyze reducible or oxidizable substances in solution. It involves varying the electric potential between a dropping mercury electrode and a reference electrode while monitoring the current. A polarogram is generated by plotting the current readings against the applied voltage. Key features of polarography include applied voltages between 0-2.5V and current values between 0.12-100 microamperes. Polarography finds applications in pharmaceutical analysis such as determining dissolved oxygen, trace metals in drugs, vitamins, hormones, antibiotics, and diagnosing cancer from blood serum.
Raman spectroscopy is a technique that uses lasers to study vibrational, rotational, and other low-frequency modes in a system. When light interacts with molecules, the light may be scattered at different wavelengths than the incident laser. This shift in wavelength provides information about molecular structure and symmetry. Raman spectroscopy can be used to examine inorganic, organic, and polymeric materials, determine molecular structure and interactions, and study chemical reactions and physical transformations.
Atomic emission spectroscopy is a technique used to identify elements in a sample based on the wavelengths of light emitted by atoms excited by a heat source like a flame, furnace, or plasma. It works by exciting the sample atoms, which then relax and emit light of characteristic wavelengths. The light is separated by wavelength and the intensities are used for qualitative and quantitative analysis. Common excitation sources include flames, arcs, sparks, and inductively coupled plasma, with the plasma being the most widely used currently due to its ability to analyze a wide range of elements simultaneously.
Mass spectrometry deals with the study of charged molecules and fragment ions produced from a sample exposed to ionizing conditions. It works by bombarding samples with electron beams or chemical ions, which causes the samples to form positively charged molecular or fragment ions. These ions are then separated based on their mass-to-charge ratio, producing a spectrum that can be used to determine molecular weights, identify unknown compounds, and detect impurities. Mass spectrometry is a versatile analytical technique with applications in pharmaceutical analysis, proteomics, and other areas.
The Wonderful World of Scanning Electrochemical Microscopy (SECM)InsideScientific
This document summarizes a presentation given by Dr. Janine Mauzeroll on scanning electrochemical microscopy (SECM). SECM is introduced, including operating modes and principles. Applications of SECM in studying multdrug resistance in cancer cells, electrochemical properties of battery materials, and corrosion of alloys are discussed. SECM allows visualization of heterogeneous electron transfer kinetics and mass transport at micro and nanoscale.
This document provides an overview of electron spectroscopy techniques, including X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and ultraviolet photoelectron spectroscopy (UPS). It discusses the basic principles, instrumentation, applications, and advantages/limitations of each technique. XPS is described as using X-rays to eject core electrons and measure their kinetic energy to determine elemental composition. AES uses electrons to eject core electrons which cause additional electrons to fall into the vacancy, emitting energy measured to identify elements. UPS uses UV light to eject valence electrons and measure their kinetic energy to determine molecular orbital energies.
Potentiometry is an electrochemical method of Analysis deals with the measurement of electric potential or emf of an electrolyte solution under the condition of constant current.
Potentiometry is the measurement of electrical potential of an electrolyte solution to determine its concentration.
The principle is based on the fact that the potential of the given sample is directly proportional to the concentration of its electro active ions or its activity (pH)
When the pair of electrodes is placed in the sample solution it shows the potential difference by the addition of the titrant or by the change in the concentration of the ions.
The theory of potentiometry is based on the nernst equation.It gives the basic relationship between the potential generated by an electrochemical cell and the concentration of the ions.
The potential E ( Half cell potential) of any electrode is given by nernst equation
Auger electron spectroscopy is a technique used to analyze the composition of solid surfaces. It works by bombarding a sample with electrons, which ejects inner shell electrons from atoms. The vacancy is then filled by an electron from a higher energy level, emitting an Auger electron. The kinetic energy of the Auger electron is characteristic of the emitting element and can be used to identify the elements present on the surface. AES provides information about surface composition and chemistry with high sensitivity to light elements. It has various applications in materials science and surface analysis.
Secondary ion mass spectrometry (SIMS) is an analytical technique that bombards a sample surface with a primary ion beam, causing charged secondary ions to emit. These secondary ions are then analyzed using mass spectrometry to determine their mass-to-charge ratios. SIMS has high sensitivity and can detect elements down to parts-per-million or parts-per-billion levels. It provides both elemental and molecular composition of solid surfaces with good depth resolution and lateral resolution in the 2-5 nm and 20 nm to 1 μm range, respectively. SIMS finds applications in composition analysis, depth profiling, trace detection in semiconductors, and imaging of surfaces.
This document provides an overview of X-ray spectroscopy techniques, including X-ray absorption and fluorescence. It discusses the production of X-rays, the principles of X-ray absorption spectroscopy and X-ray fluorescence spectroscopy, and their applications. Key topics covered include X-ray sources like X-ray tubes and synchrotrons, Beer's law and how it relates to X-ray absorption, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), and the use of these techniques in fields like chemistry, physics and materials science.
1. Infrared spectroscopy involves using infrared radiation to stimulate molecular vibrations in a sample. The infrared absorption spectrum produced can be used to identify functional groups and molecular structure.
2. Infrared radiation lies between the visible and microwave regions of the electromagnetic spectrum. When infrared light interacts with a molecule, it can cause the bonds to vibrate in different ways such as stretching and bending.
3. An infrared spectrum plots percent transmittance versus wavenumber and produces characteristic absorption bands corresponding to different vibrational modes. This "fingerprint" can be used to identify unknown molecules.
UV-VIS spectroscopy involves using ultraviolet or visible light to illuminate a sample and analyzing the light that is absorbed. Electronic transitions in molecules can be detected by observing which wavelengths of light are absorbed. This provides information about functional groups and conjugated systems present in the sample. A UV-VIS spectrophotometer directs light from a source through the sample solution and a monochromator selects wavelengths, which are then measured by a detector. The amount of light absorbed at each wavelength follows Beer's Law, allowing for determination of concentrations from a calibration curve.
This presentation is about the monochromators and specifically their use in spectroscopy. It includes definition, principle, origin of term, principle, types, prism monochromator, diffraction grating monochromator, difference in both of them, their uses and working as well, optical filters and their uses and application.
A Monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light chosen from a wider range of wavelengths available at the input. And the unwanted radiations are blocked by the slit allowing only the desired ray to pass (monochromatic).
A dispersive element disperse the polychromatic light into several bands of single wavelength and then a slit is used which stops the unwanted bands of light, allowing only the desired monochromatic light to pass through its exit point.
By fixing the slit and rotating the dispersive element, the direction of the dispersed light is turned so that the colour of the resulting monochromatic light changes.
When electromagnetic radiation passes through a prism, it is refracted because the index of refraction of the prism material is different from that of air.
Shorter wavelengths are refracted more than longer wavelengths.
By rotation of the prism, different wavelengths of the spectrum can be made to pass through an exit slit and through the sample.
A prism works satisfactorily in the ultraviolet and visible regions and can also be used in the infrared region.
Because of its nonlinear dispersion, it works more effectively for the shorter wavelengths.
Glass prisms and lenses can be used in the visible region.
Quartz or fused silica must be used in the ultraviolet region.
The entire monochromatic compartment must be kept dry.
Infrared spectroscopy is a technique that uses infrared light to analyze chemical bonding and molecular structure. It works by detecting the frequencies at which molecules vibrate or rotate when exposed to infrared radiation. The document discusses the principles of infrared spectroscopy, including how molecular vibrations can be excited when their frequency matches the frequency of infrared radiation. It also covers factors that determine infrared absorption frequencies and the types of molecular vibrations that are infrared active.
The document describes the capabilities of an X-ray photoelectron spectroscopy (XPS) instrument called the K-Alpha XPS from Thermo Scientific. The K-Alpha provides high throughput analysis with micrometer-scale spatial resolution. It features an aluminum anode X-ray source for high chemical state resolution and a focused ion beam for sample cleaning and depth profiling. The document outlines how XPS can be used to identify elements, quantify elemental composition, and determine chemical bonding states at surfaces.
Electron microscopes use a beam of electrons to examine objects on a very fine scale. There are two main types: transmission electron microscopes (TEM) allow study of inner structures by passing electrons through thin samples, while scanning electron microscopes (SEM) are used to visualize surfaces by scanning a focused electron beam over the sample. SEMs detect signals from electron interactions to construct digital images, and require vacuum and conductive samples mounted on stubs. They provide three-dimensional topographical and compositional information at high magnifications.
The document provides an overview of mass spectrometry, including its basic principles, components, working principle, and various applications. Mass spectrometry involves ionizing chemical compounds and separating the resulting ions based on their mass-to-charge ratio, producing a mass spectrum that can be used to determine the elemental or isotopic composition of a sample. Key components include an ion source, mass analyzer, and detector. Common ionization methods are also described, such as electron impact, chemical ionization, electrospray ionization, and matrix-assisted laser desorption/ionization.
5. Wavelength dispersive (WDXRF) and energy dispersive (EDXRF) X- ray fluores...SyedMuhammadAli505652
This document summarizes and compares two methods of X-ray fluorescence (XRF) analysis: wavelength dispersive XRF (WDXRF) and energy dispersive XRF (EDXRF). WDXRF uses crystals to physically separate and detect X-rays by their wavelength, providing high resolution but slower analysis. EDXRF detects the energy of X-rays to identify elements, offering faster results but lower resolution. Both methods can perform non-destructive chemical analysis of solids from major to trace concentrations, with WDXRF typically having better detection limits. The document also discusses related techniques like micro-XRF and the differences between WDXRF, EDXRF, SEM-WDX, and WD-
The document discusses optical rotatory dispersion (ORD) and circular dichroism. It begins by introducing Sujit R. Patel from the Department of Pharmaceutics and provides an overview of topics to be covered including ORD, the ORD curve, circular dichroism, and the octant rule. It then discusses the fundamentals of ORD, how specific rotation changes with wavelength, and the different types of ORD curves including plain and anomalous curves. It also addresses the cotton effect seen in anomalous dispersion curves. Finally, it covers applications of circular dichroism spectroscopy such as determining protein and nucleic acid conformation.
Quadrupole and Time of Flight Mass analysers.Gagangowda58
Description about important mass analysers Quadrupole and TOF: Principle, Construction and Working, Advantages and Disadvantages and their Applications.
Case Study: Cyclic Voltametric MeasurementHasnain Ali
The design of an ac Cyclic Voltammetric Measurement System for the in –situ measurement of dissolved oxygen in sediment on the seabed. The measurement strategy should be based on linear ramp cyclic voltammetry
This presentation provides an overview of electrophoresis techniques. It defines electrophoresis as a separation technique where solutes migrate through a conductive medium under an applied electric field. It describes how charges migrate based on their size and charge. It then discusses the different forms of electrophoresis, focusing on capillary zone electrophoresis and gel electrophoresis. For capillary electrophoresis, it explains the concepts of electrophoretic mobility, electroosmotic mobility, and their roles in solute migration. It also outlines the basic instrumentation and processes involved like injection, separation, and detection. For gel electrophoresis, it discusses how it separates biomolecules like DNA and proteins based on size and provides examples of its applications.
This document discusses NMR spectroscopy of inorganic compounds. It begins by introducing NMR spectroscopy and its use in determining molecular structure and purity of samples. It then covers the principles of NMR, including how nuclei align in magnetic fields and absorb and emit radiofrequency energy. It discusses nuclear relaxation processes and how they influence NMR experiments. It provides examples of tin and platinum NMR, describing their NMR-active nuclei, typical chemical shift ranges, and coupling behaviors. References for further reading are also included.
Electrogravimetry is a method used to separate and quantify ions of a substance, usually a metal, through electrolysis. The analyte solution is electrolyzed, causing the analyte to deposit on the cathode. The cathode is weighed before and after the experiment, and the mass difference is used to calculate the amount of analyte originally present. There are two types of electrogravimetry - constant current electrolysis, where the current is kept constant, and constant potential electrolysis, where the potential is kept constant. In both cases, the deposited analyte on the cathode is measured through changes in mass to determine the concentration in the original solution.
Production and Emission of X-Rays - Sultan LeMarcslemarc
This document describes an experiment to investigate the production and emission of x-rays. It will measure the count rate of x-rays reflected off a lithium fluoride crystal at varying angles to determine the characteristic peaks and wavelength of copper using Bragg's law. It will also examine the absorption of homogeneous x-rays by measuring the relationship between intensity and count rate. The document provides background on x-ray production, emission spectra, Bragg diffraction, and absorption. It describes using a Tel-X-Ometer device to measure count rates at different scattering angles in order to analyze the diffraction patterns.
Diploma sem 2 applied science physics-unit 5-chap-1 x-raysRai University
X-rays are produced when electrons accelerated to speeds of 1 kV to 1 MV strike a metal target. Less than 1% of the kinetic energy is converted to X-radiation, with the rest becoming heat in the target. Moseley's law states that the wavelength of characteristic X-rays is related to the atomic number by the formula 1/λ = c(Z - s)2, where c and s are constants and Z is the atomic number. This helped establish atomic number as more fundamental than atomic weight in determining an element's position in the periodic table. X-rays have various applications including medical imaging and material characterization.
This document provides an overview of electron spectroscopy techniques, including X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and ultraviolet photoelectron spectroscopy (UPS). It discusses the basic principles, instrumentation, applications, and advantages/limitations of each technique. XPS is described as using X-rays to eject core electrons and measure their kinetic energy to determine elemental composition. AES uses electrons to eject core electrons which cause additional electrons to fall into the vacancy, emitting energy measured to identify elements. UPS uses UV light to eject valence electrons and measure their kinetic energy to determine molecular orbital energies.
Potentiometry is an electrochemical method of Analysis deals with the measurement of electric potential or emf of an electrolyte solution under the condition of constant current.
Potentiometry is the measurement of electrical potential of an electrolyte solution to determine its concentration.
The principle is based on the fact that the potential of the given sample is directly proportional to the concentration of its electro active ions or its activity (pH)
When the pair of electrodes is placed in the sample solution it shows the potential difference by the addition of the titrant or by the change in the concentration of the ions.
The theory of potentiometry is based on the nernst equation.It gives the basic relationship between the potential generated by an electrochemical cell and the concentration of the ions.
The potential E ( Half cell potential) of any electrode is given by nernst equation
Auger electron spectroscopy is a technique used to analyze the composition of solid surfaces. It works by bombarding a sample with electrons, which ejects inner shell electrons from atoms. The vacancy is then filled by an electron from a higher energy level, emitting an Auger electron. The kinetic energy of the Auger electron is characteristic of the emitting element and can be used to identify the elements present on the surface. AES provides information about surface composition and chemistry with high sensitivity to light elements. It has various applications in materials science and surface analysis.
Secondary ion mass spectrometry (SIMS) is an analytical technique that bombards a sample surface with a primary ion beam, causing charged secondary ions to emit. These secondary ions are then analyzed using mass spectrometry to determine their mass-to-charge ratios. SIMS has high sensitivity and can detect elements down to parts-per-million or parts-per-billion levels. It provides both elemental and molecular composition of solid surfaces with good depth resolution and lateral resolution in the 2-5 nm and 20 nm to 1 μm range, respectively. SIMS finds applications in composition analysis, depth profiling, trace detection in semiconductors, and imaging of surfaces.
This document provides an overview of X-ray spectroscopy techniques, including X-ray absorption and fluorescence. It discusses the production of X-rays, the principles of X-ray absorption spectroscopy and X-ray fluorescence spectroscopy, and their applications. Key topics covered include X-ray sources like X-ray tubes and synchrotrons, Beer's law and how it relates to X-ray absorption, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), and the use of these techniques in fields like chemistry, physics and materials science.
1. Infrared spectroscopy involves using infrared radiation to stimulate molecular vibrations in a sample. The infrared absorption spectrum produced can be used to identify functional groups and molecular structure.
2. Infrared radiation lies between the visible and microwave regions of the electromagnetic spectrum. When infrared light interacts with a molecule, it can cause the bonds to vibrate in different ways such as stretching and bending.
3. An infrared spectrum plots percent transmittance versus wavenumber and produces characteristic absorption bands corresponding to different vibrational modes. This "fingerprint" can be used to identify unknown molecules.
UV-VIS spectroscopy involves using ultraviolet or visible light to illuminate a sample and analyzing the light that is absorbed. Electronic transitions in molecules can be detected by observing which wavelengths of light are absorbed. This provides information about functional groups and conjugated systems present in the sample. A UV-VIS spectrophotometer directs light from a source through the sample solution and a monochromator selects wavelengths, which are then measured by a detector. The amount of light absorbed at each wavelength follows Beer's Law, allowing for determination of concentrations from a calibration curve.
This presentation is about the monochromators and specifically their use in spectroscopy. It includes definition, principle, origin of term, principle, types, prism monochromator, diffraction grating monochromator, difference in both of them, their uses and working as well, optical filters and their uses and application.
A Monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light chosen from a wider range of wavelengths available at the input. And the unwanted radiations are blocked by the slit allowing only the desired ray to pass (monochromatic).
A dispersive element disperse the polychromatic light into several bands of single wavelength and then a slit is used which stops the unwanted bands of light, allowing only the desired monochromatic light to pass through its exit point.
By fixing the slit and rotating the dispersive element, the direction of the dispersed light is turned so that the colour of the resulting monochromatic light changes.
When electromagnetic radiation passes through a prism, it is refracted because the index of refraction of the prism material is different from that of air.
Shorter wavelengths are refracted more than longer wavelengths.
By rotation of the prism, different wavelengths of the spectrum can be made to pass through an exit slit and through the sample.
A prism works satisfactorily in the ultraviolet and visible regions and can also be used in the infrared region.
Because of its nonlinear dispersion, it works more effectively for the shorter wavelengths.
Glass prisms and lenses can be used in the visible region.
Quartz or fused silica must be used in the ultraviolet region.
The entire monochromatic compartment must be kept dry.
Infrared spectroscopy is a technique that uses infrared light to analyze chemical bonding and molecular structure. It works by detecting the frequencies at which molecules vibrate or rotate when exposed to infrared radiation. The document discusses the principles of infrared spectroscopy, including how molecular vibrations can be excited when their frequency matches the frequency of infrared radiation. It also covers factors that determine infrared absorption frequencies and the types of molecular vibrations that are infrared active.
The document describes the capabilities of an X-ray photoelectron spectroscopy (XPS) instrument called the K-Alpha XPS from Thermo Scientific. The K-Alpha provides high throughput analysis with micrometer-scale spatial resolution. It features an aluminum anode X-ray source for high chemical state resolution and a focused ion beam for sample cleaning and depth profiling. The document outlines how XPS can be used to identify elements, quantify elemental composition, and determine chemical bonding states at surfaces.
Electron microscopes use a beam of electrons to examine objects on a very fine scale. There are two main types: transmission electron microscopes (TEM) allow study of inner structures by passing electrons through thin samples, while scanning electron microscopes (SEM) are used to visualize surfaces by scanning a focused electron beam over the sample. SEMs detect signals from electron interactions to construct digital images, and require vacuum and conductive samples mounted on stubs. They provide three-dimensional topographical and compositional information at high magnifications.
The document provides an overview of mass spectrometry, including its basic principles, components, working principle, and various applications. Mass spectrometry involves ionizing chemical compounds and separating the resulting ions based on their mass-to-charge ratio, producing a mass spectrum that can be used to determine the elemental or isotopic composition of a sample. Key components include an ion source, mass analyzer, and detector. Common ionization methods are also described, such as electron impact, chemical ionization, electrospray ionization, and matrix-assisted laser desorption/ionization.
5. Wavelength dispersive (WDXRF) and energy dispersive (EDXRF) X- ray fluores...SyedMuhammadAli505652
This document summarizes and compares two methods of X-ray fluorescence (XRF) analysis: wavelength dispersive XRF (WDXRF) and energy dispersive XRF (EDXRF). WDXRF uses crystals to physically separate and detect X-rays by their wavelength, providing high resolution but slower analysis. EDXRF detects the energy of X-rays to identify elements, offering faster results but lower resolution. Both methods can perform non-destructive chemical analysis of solids from major to trace concentrations, with WDXRF typically having better detection limits. The document also discusses related techniques like micro-XRF and the differences between WDXRF, EDXRF, SEM-WDX, and WD-
The document discusses optical rotatory dispersion (ORD) and circular dichroism. It begins by introducing Sujit R. Patel from the Department of Pharmaceutics and provides an overview of topics to be covered including ORD, the ORD curve, circular dichroism, and the octant rule. It then discusses the fundamentals of ORD, how specific rotation changes with wavelength, and the different types of ORD curves including plain and anomalous curves. It also addresses the cotton effect seen in anomalous dispersion curves. Finally, it covers applications of circular dichroism spectroscopy such as determining protein and nucleic acid conformation.
Quadrupole and Time of Flight Mass analysers.Gagangowda58
Description about important mass analysers Quadrupole and TOF: Principle, Construction and Working, Advantages and Disadvantages and their Applications.
Case Study: Cyclic Voltametric MeasurementHasnain Ali
The design of an ac Cyclic Voltammetric Measurement System for the in –situ measurement of dissolved oxygen in sediment on the seabed. The measurement strategy should be based on linear ramp cyclic voltammetry
This presentation provides an overview of electrophoresis techniques. It defines electrophoresis as a separation technique where solutes migrate through a conductive medium under an applied electric field. It describes how charges migrate based on their size and charge. It then discusses the different forms of electrophoresis, focusing on capillary zone electrophoresis and gel electrophoresis. For capillary electrophoresis, it explains the concepts of electrophoretic mobility, electroosmotic mobility, and their roles in solute migration. It also outlines the basic instrumentation and processes involved like injection, separation, and detection. For gel electrophoresis, it discusses how it separates biomolecules like DNA and proteins based on size and provides examples of its applications.
This document discusses NMR spectroscopy of inorganic compounds. It begins by introducing NMR spectroscopy and its use in determining molecular structure and purity of samples. It then covers the principles of NMR, including how nuclei align in magnetic fields and absorb and emit radiofrequency energy. It discusses nuclear relaxation processes and how they influence NMR experiments. It provides examples of tin and platinum NMR, describing their NMR-active nuclei, typical chemical shift ranges, and coupling behaviors. References for further reading are also included.
Electrogravimetry is a method used to separate and quantify ions of a substance, usually a metal, through electrolysis. The analyte solution is electrolyzed, causing the analyte to deposit on the cathode. The cathode is weighed before and after the experiment, and the mass difference is used to calculate the amount of analyte originally present. There are two types of electrogravimetry - constant current electrolysis, where the current is kept constant, and constant potential electrolysis, where the potential is kept constant. In both cases, the deposited analyte on the cathode is measured through changes in mass to determine the concentration in the original solution.
Production and Emission of X-Rays - Sultan LeMarcslemarc
This document describes an experiment to investigate the production and emission of x-rays. It will measure the count rate of x-rays reflected off a lithium fluoride crystal at varying angles to determine the characteristic peaks and wavelength of copper using Bragg's law. It will also examine the absorption of homogeneous x-rays by measuring the relationship between intensity and count rate. The document provides background on x-ray production, emission spectra, Bragg diffraction, and absorption. It describes using a Tel-X-Ometer device to measure count rates at different scattering angles in order to analyze the diffraction patterns.
Diploma sem 2 applied science physics-unit 5-chap-1 x-raysRai University
X-rays are produced when electrons accelerated to speeds of 1 kV to 1 MV strike a metal target. Less than 1% of the kinetic energy is converted to X-radiation, with the rest becoming heat in the target. Moseley's law states that the wavelength of characteristic X-rays is related to the atomic number by the formula 1/λ = c(Z - s)2, where c and s are constants and Z is the atomic number. This helped establish atomic number as more fundamental than atomic weight in determining an element's position in the periodic table. X-rays have various applications including medical imaging and material characterization.
B.Tech sem I Engineering Physics U-IV Chapter 2-X-RaysAbhi Hirpara
This document discusses X-rays, including their discovery, production, properties, diffraction, absorption, and applications. X-rays were discovered in 1895 by Röntgen during experiments with cathode ray tubes. They are generated when high-speed electrons strike a metal target in an X-ray tube. X-rays have various wavelengths and are used in fields like medicine, science research, and industry for applications such as medical imaging, defect detection, and crystal structure analysis.
X-rays are electromagnetic radiation of wavelengths shorter than visible light. They have typical wavelengths ranging from 0.01 to 10 nanometers. X-rays are produced when high-speed electrons collide with a metal target in an X-ray tube. There are two main production methods - bremsstrahlung and characteristic line emission. Bremsstrahlung produces a continuous X-ray spectrum, while characteristic lines produce peaks at specific wavelengths. X-ray diffraction is used to determine crystal structures by analyzing the diffraction pattern produced when X-rays interact with a crystalline material. Bragg's law describes the angles at which diffraction occurs based on the wavelength and crystal plane spacing.
Light travels at 300,000 km/s. It has properties of both waves and particles. Spectral lines identify elements in stars - each element produces a unique set of lines. Astronomers use spectral lines and Wien's and Stefan-Boltzmann laws to determine surface temperatures of stars and planets from their emitted light.
B.tech sem i engineering physics u iv chapter 2-x-raysRai University
This document provides an overview of X-rays, including their discovery, production, properties, diffraction, absorption, and applications. It discusses how X-rays are generated via the bombardment of a metal target by electrons in an X-ray tube. Key points covered include Bragg's law of diffraction, Moseley's law relating atomic number to X-ray wavelength, the continuous and characteristic spectra produced, and common medical and scientific uses of X-rays.
This document discusses the structure of the atom and various atomic models throughout history. It describes J.J. Thomson's "plum pudding" model, and how Rutherford's alpha scattering experiments showed that the atom's mass and positive charge must be concentrated in a small nucleus. Later, Planck's quantum theory and the photoelectric effect provided evidence that electromagnetic radiation behaves as quantized packets of energy called photons. This led to developments like the dual wave-particle nature of matter and Heisenberg's uncertainty principle.
This document discusses the electromagnetic spectrum and properties of light. It describes how light exhibits both wave-like and particle-like properties. The wave properties of light include frequency, wavelength, speed and amplitude. The particle properties include photons and the photoelectric effect. The document also covers the Bohr model of the hydrogen atom and how it led to the development of quantum theory, which explained atomic spectra and the dual wave-particle nature of matter and energy.
The document provides an overview of radiation physics, beginning with the composition of matter and basic atomic structure. It describes the Bohr-Rutherford model of the atom and the development of the quantum mechanical model. Key concepts covered include atomic number, mass number, ionization, electrostatic and centrifugal forces, electron binding energy, and the nature of radiation.
The document then focuses on the history and properties of x-rays, the components and functioning of an x-ray machine, including the x-ray tube, cathode, anode, target, transformers, and power supply. Factors that control the x-ray beam such as exposure time, current and voltage are also summarized.
This document discusses the discovery and production of X-rays. It begins by introducing Wilhelm Roentgen, the German physicist who discovered X-rays in 1895. It then describes how Roentgen made his accidental discovery while experimenting with cathode rays. The rest of the document details the physics behind X-ray production, including the interaction of electrons with targets, the emission of characteristic and bremsstrahlung radiation, and the attenuation and scattering of X-rays as they pass through matter. Examples are provided to illustrate key concepts.
Structure of atom plus one focus area notessaranyaHC1
The document discusses the structure of the atom, including:
1) Rutherford's nuclear model of the atom based on alpha particle scattering experiments. This established the atom's small, dense nucleus at the center with electrons in orbits around it.
2) Planck's quantum theory and the photoelectric effect, which demonstrated light behaving as discrete packets of energy called quanta and supported the nuclear model.
3) Bohr's model of the hydrogen atom incorporating Planck's quanta and explaining atomic spectra through electron transitions between discrete energy levels.
4) Later developments including de Broglie's matter waves, Heisenberg's uncertainty principle, and Schrodinger's wave mechanical model describing electrons as
X-raydiffraction has a very significant role in crystal determination.. specially in the field of Pharmaceutical analysis.
It contains the requirement for M.pharm 1st year according to RGUHS syllabus.
X-ray crystallography uses X-ray diffraction to determine the atomic and molecular structure of crystals. Monochromatic X-rays are generated by a cathode ray tube and directed at a crystalline sample. The regular arrangement of atoms in the crystal causes the X-rays to diffract into specific patterns determined by Bragg's law, providing information about the crystal structure. X-ray diffraction is widely used in fields like biochemistry, materials science, and engineering to study the structure of molecules, crystals, and solid materials.
This document provides a summary of key concepts about electrons in atoms, including:
1) It discusses the evolution of atomic models from Rutherford to Bohr, focusing on explaining the arrangement of electrons. The quantum mechanical model describes electron probability clouds rather than fixed orbits.
2) It covers atomic orbitals and how electrons fill different orbitals based on their principal and angular momentum quantum numbers. Higher principal quantum numbers correspond to higher energy levels further from the nucleus.
3) The document emphasizes that electrons fill orbitals based on the Aufbau principle to achieve the lowest possible energy configuration. Understanding electron configurations is essential to describing elements and their properties.
This chapter discusses the evolution of atomic models and the arrangement of electrons in atoms. It covers difficult concepts such as electrons occupying specific energy levels and orbitals. Students are advised to do all assigned homework and bring their textbook to class to fully understand these abstract ideas. Key models discussed include the Rutherford model, the planetary model, Bohr's model linking electrons and photon emission, and the modern quantum mechanical model based on probability.
In your previous class you have already studies about the structure of an atom but some of the exception you can learn here in this chapter how the structure of an atom is fully defined
1. The document discusses the discovery of the electron through cathode ray experiments and the determination of the charge to mass ratio of electrons.
2. Rutherford's alpha particle scattering experiments showed that the atom has a small, dense nucleus containing positive charge and mass, surrounded by electrons. This led to the development of the Rutherford model of the atom.
3. The document also discusses the discovery of protons and neutrons, atomic number and mass number, isotopes, drawbacks of the Rutherford model, wave-particle duality of light, and Planck's quantum theory.
1) Experiments with cathode ray tubes led to the discovery of the electron as a negatively charged fundamental particle.
2) Further experiments showed that atoms are mostly empty space and contain a small, dense nucleus made up of protons and neutrons, around which electrons orbit.
3) The photoelectric effect showed that light behaves as a particle (photon) rather than just a wave, transferring its energy in discrete quantized amounts to electrons and ejecting them from metal surfaces.
Radiation physics in Dental Radiology...navyadasi1992
This document discusses the physics of radiation and x-rays. It defines radiation and describes the electromagnetic spectrum. X-rays are a type of electromagnetic radiation that were discovered in 1895 by Wilhelm Roentgen. The document outlines the production of x-rays using an x-ray tube, and describes how factors like tube voltage, current, and filtration control the x-ray beam. It also explains how x-rays interact with and are attenuated by matter, including effects like the photoelectric effect and Compton scattering.
Raman spectroscopy involves scattering of monochromatic light, usually from a laser. When light interacts with molecules, the light may be scattered at different wavelengths due to molecular vibrations. This allows measurement of vibrational modes of a compound. Raman spectroscopy has advantages over infrared spectroscopy as it can be used to study aqueous solutions and water does not interfere. It has applications in studying inorganic compounds, organic compounds, and biological systems like proteins and nucleic acids.
Fermented rice bran has several health benefits. Rice bran was fermented using Lactobacillus Plantarum to produce compounds that lower cholesterol and improve sensory properties. Optimal fermentation conditions like 20% rice bran concentration with added nutrients at pH 6.0 and 30°C produced high L. Plantarum growth. The fermented rice bran reduced cholesterol in vitro by 45-68% and had antimicrobial activity. It also reduced the antinutrient phytic acid level. The fermented product had an improved flavor and texture over unfermented rice bran.
Field capacity refers to the amount of water in soil after excess water has drained away by gravity. It typically occurs 2-3 days after rainfall or irrigation. There are three types of water in soil: gravitational, capillary, and hygroscopic. Factors like soil texture, structure, organic matter, temperature and depth of wetting influence field capacity. Field capacity is important for plant growth as it provides soluble nutrients and regulates soil temperature and microbial activity. It can be measured using pressure-based methods that determine water content at -33 kPa tension or flux-based methods using hydraulic conductivity functions.
Effect of Precipatation on Distribution of Plants.pptxCHZaryabAli
Useful for the students who wants to study this topic & enhances the knowledge for a specific topic.
PRECIPITATION:
is any product of the condensation of atmospheric water that falls under gravity from clouds.
The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor (reaching 100% relative humidity), so that the water condenses and "precipitates". Thus, fog and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate.
Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air.
REASON FOR CHANGE IN PRECIPITATION:There are many reasons for changes in precipitation. The leading cause is a change in temperature. Many scientists believe an increase in temperature could lead to a more intense water cycle. The rates of evaporation from soils and water, as well as transpiration from plants, could increase. The amount of precipitation could also increase. Predicted changes in the water cycle differ according to the region of the planet being examined. Many scientists believe rates of evaporation will be greater than precipitation in the middle latitudes such as the United States. This could result in drier summers in these regions. Of course, predicted changes in the water cycle also differ according to the climate.EFFECT OF PRECIPITATION ON PLANTS:Precipitation, especially rain, has a dramatic effect on plants distribution. All plants need at least some water to survive, therefore rain (being the most effective means of watering) is important to agriculture. While a regular rain pattern is usually vital to healthy plants, too much or too little rainfall can be harmful, even devastating to crops. Drought can kill crops and increase erosion, while overly wet weather can cause harmful fungus growth. Plants need varying amounts of rainfall to survive. For example, certain cacti require small amounts of water, while tropical plants may need up to hundreds of inches of rain per year to survive.In areas with wet and dry seasons, soil nutrients diminish and erosion increases during the wet season.
DISTRIBUTION OF PLANTS IN DIFFERENT BIOMES:The geographical distribution (and productivity) of the plants in the various biomes is controlled primarily by the climatic variables precipitation and temperature. There are 8 major terrestrial biomes >Tropical Rain Forest >Tropical Savanna > Deserts >Grass Lands > Chaparral > Temperate Deciduous Forests > Temperate Boreal Forests > Artic And Alpine TundraEach biome plants have different adaptation to survive in that environment.
Tundra means marshy plain. The geographical distribution of the tundra biome is largely poleward of 60° North latitude.
The tundra biome is characterized by an absence of trees, the presence of dwarf plants
Ecological Characteristics of Plant Community.pptxCHZaryabAli
A plant community is a group of plants that grow together in a specific habitat. Ecological characteristics of plant communities can be analyzed or synthetic. Analytic characteristics include physiognomy, periodicity, life form, and sociability, and can be measured qualitatively or quantitatively. Synthetic characteristics like presence, constancy, and fidelity describe how species are distributed and restricted within a community. Dominant species are most important in determining the type of community.
- An ecosystem is comprised of biotic and abiotic components that interact with each other within a specific environment. Biotic components include producers, consumers, decomposers and transformers. Producers harness energy from the sun via photosynthesis. Consumers feed on producers or other consumers. Decomposers and transformers break down dead organic matter.
- Key abiotic components are climate/physical factors, inorganic substances and organic substances. Sunlight, water, oxygen, temperature and soil are particularly important abiotic factors for organisms. Biotic and abiotic components interact through nutrient and water cycles, providing resources and affecting one another.
- Energy and matter flow through food chains and webs. Producers are the
Carotenoids are fat-soluble plant pigments that range in color from yellow to purple. There are two main types: carotenes and xanthophylls. Carotenes are pure hydrocarbons found in plants and some animals. They are responsible for colors like orange. Xanthophylls contain oxygen and are found in plant leaves and tissues to modulate light absorption during photosynthesis. Both types serve protective and energy transfer functions in plants and determine colors in fruits, vegetables, and some animals.
The light-harvesting antenna complex is composed of protein and chlorophyll molecules. It transfers light energy absorbed from the sun to the reaction centers of photosystem I and photosystem II. The antenna complex broadens the absorption spectrum and protects plants from high intensity sunlight by absorbing excess energy. It contains pigments like chlorophyll a, chlorophyll b, carotenoids, and xanthophylls that absorb different wavelengths of light and transfer energy resonantly to the reaction centers through Forster transfer.
This document discusses soil as a source of minerals for plant nutrition. It describes the formation of soil through weathering processes like physical, chemical, and biological weathering. Soil composition includes minerals, humus, living organisms, and water and air. Key minerals in soil that plants extract as nutrients are nitrogen, phosphorus, and potassium. These are considered primary nutrients. Secondary nutrients include calcium, magnesium and sulfur. Trace nutrients that plants need smaller amounts of include iron, manganese, copper, zinc, boron and molybdenum. The document focuses on the roles of nitrogen, phosphorus and potassium in plant growth and the deficiency symptoms plants exhibit when lacking these primary nutrients.
How to Setup Warehouse & Location in Odoo 17 InventoryCeline George
In this slide, we'll explore how to set up warehouses and locations in Odoo 17 Inventory. This will help us manage our stock effectively, track inventory levels, and streamline warehouse operations.
LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
Main Java[All of the Base Concepts}.docxadhitya5119
This is part 1 of my Java Learning Journey. This Contains Custom methods, classes, constructors, packages, multithreading , try- catch block, finally block and more.
How to Manage Your Lost Opportunities in Odoo 17 CRMCeline George
Odoo 17 CRM allows us to track why we lose sales opportunities with "Lost Reasons." This helps analyze our sales process and identify areas for improvement. Here's how to configure lost reasons in Odoo 17 CRM
How to Fix the Import Error in the Odoo 17Celine George
An import error occurs when a program fails to import a module or library, disrupting its execution. In languages like Python, this issue arises when the specified module cannot be found or accessed, hindering the program's functionality. Resolving import errors is crucial for maintaining smooth software operation and uninterrupted development processes.
How to Make a Field Mandatory in Odoo 17Celine George
In Odoo, making a field required can be done through both Python code and XML views. When you set the required attribute to True in Python code, it makes the field required across all views where it's used. Conversely, when you set the required attribute in XML views, it makes the field required only in the context of that particular view.
Exploiting Artificial Intelligence for Empowering Researchers and Faculty, In...Dr. Vinod Kumar Kanvaria
Exploiting Artificial Intelligence for Empowering Researchers and Faculty,
International FDP on Fundamentals of Research in Social Sciences
at Integral University, Lucknow, 06.06.2024
By Dr. Vinod Kumar Kanvaria
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
How to Build a Module in Odoo 17 Using the Scaffold MethodCeline George
Odoo provides an option for creating a module by using a single line command. By using this command the user can make a whole structure of a module. It is very easy for a beginner to make a module. There is no need to make each file manually. This slide will show how to create a module using the scaffold method.
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1. X-ray Spectroscopy
X-rays were discovered in 1895 by Wilhelm Conrad who received the
first Nobel Prize in Physics, awarded in 1901, for his discovery. X-ray
absorption, emission, and fluorescence spectra are used in the qualitative and
quantitative determination of elements in solid and liquid samples. X-ray
absorption is used in the nondestructive evaluation of flaws in objects,
including voids or internal cracks in metals, cavities in teeth, and broken bones
in humans, a technique called radiography or X-ray fluoroscopy. This same
technique is used to perform security screening of baggage at airports. X-rays
consist of electromagnetic radiation with a wavelength range from 0.005 to 10
nm (0.05 – 100 A˚ ). X-rays have shorter wavelengths and higher energy than
UV radiation. X-rays are generated in several ways, such as when a high-speed
electron is stopped by a solid object or by electronic transitions of inner core
electrons.
2. Energy Levels in Atoms
An atom is composed of a nucleus and electrons. The electrons
are arranged in shells around the nucleus with the valence
electrons in the outer shell. The different shells correspond to the
different principal quantum numbers of the possible quantum
states. The principal quantum number, n, can have integral values
beginning with 1. The shells are named starting with the shell
closest to the nucleus, which is called the K shell. The K shell is
the lowest in energy and corresponds to the quantum level with
n= 1. The shells moving out from the nucleus are named the L
shell, M shell, and so on alphabetically. The letters used for the
two lowest shells are historical; K is from the German word kurz,
meaning short, L is from the German word lang, meaning long.
When an X-ray or a fast-moving electron collides with an atom,
its energy may be absorbed by the atom. If the X-ray or electron
has sufficient energy, it knocks an electron out of one of the
atom’s inner shells (e.g., the K shell) and the atom becomes
ionized
3. An electron from a higher-energy shell (e.g., the L-shell) then falls
into the position vacated by the dislodged inner electron and an X-
ray photon is emitted as the electron drops from one energy level to
the other . The wavelength of this emitted X-ray is characteristic of
the element being bombarded. A fourth process can also occur,
Instead of emitting an X-ray photon, the energy released knocks an
electron out of the M shell. This electron is called an Auger
electron. This Auger process is the basis for a sensitive surface
analysis technique.
X-ray emission lines from electron transitions terminating in the K
shell are called K lines, lines from transitions terminating in the L
shell are called L lines, and so on. There are three L levels differing
by a small amount of energy and five M levels. These sublevels are
different quantum states. An electron that drops from an L shell
sublevel to the K shell emits a photon with the energy difference
between these quantum states.
4.
5. Moseley’s Law
Henry Moseley, a young graduate student working at
Cambridge, UK, in 1913, discovered the relationship
between wavelength for characteristic X-ray lines
and atomic number. After recording the X-ray spectra
from numerous elements in the periodic table, he
deduced the mathematical relationship between the
atomic number of the element and the wavelength of
the Ka line. A similar relationship was found between
the atomic number and the Kb line, the La line, and so
on. The relationships were formulated in Moseley’s
Law, which states that
n ¼ c=l ¼ a(Z - s)2
6. where c is the speed of light; l, the wavelength of the
X-ray; a, a constant for a particular series of lines
(e.g., Ka or La lines); Z, the atomic number of the
element; and s, a screening constant that accounts for
the repulsion of other electrons in the atom.
Shortly after this monumental discovery, Moseley
was killed in action in World War I. The impact of
Moseley’s Law on chemistry was substantial, in that
it provided a method of unequivocally assigning an
atomic number to newly discovered elements, of
which there were several at that time. In addition, it
clarified disputes concerning the positions of all
known elements in the periodic table, some of which
were still in doubt in the early part of the 20th
century.
7. X-Ray Methods
There are several distinct fields of X-ray
analysis used in analytical chemistry
and materials characterization; namely,
X-ray absorption, X-ray diffraction, X-
ray fluorescence, and X-ray emission.
X-ray emission is generally used for
microanalysis, with either an electron
microprobeor a scanning electron
microscope.
8. The X-ray Absorption Process
The absorption spectrum obtained when a beam of X-rays is passed
through a thin sample of a pure metal. As is the case with other
forms of radiation, some of the intensity of the incident beam may be
absorbed by the sample while the remainder is transmitted. We can
write a Beer’s Law expression for the absorption of X-rays by a
thin sample:
where I(λ) is the transmitted intensity at wavelength λ; I0(λ), the
incident intensity at the same wavelength; µm, the mass absorption
coefficient (in cm2/g); ρ, the density of the sample (in g/cm3); and x,
the sample thickness (in cm). The mass absorption coefficient is a
constant for a given element at a given wavelength and is
independent of both the chemical and physical state of the element.
9. Of course, most samples do not consist of a single pure
element. The total mass absorption coefficient for a
sample can be calculated by adding the product of the
individual mass absorption coefficients for each element
times the weight fraction of the element present in the
sample. That is, for a metal alloy like steel,
mtotal = wFeµFe + wCrµCr + wNiµNi +···
where wFe is the weight fraction of iron and µFe is the
mass absorption coefficient for pure iron, wCr is the
weight fraction of chromium, and so on for all the
elements in the alloy. For accurate quantitative work,
the mass attenuation coefficient is used in place of the
mass absorption coefficient. The mass attenuation
coefficient takes into account both absorption and
scattering of X-rays by the sample.
10. The amount of light absorbed increases as the
wavelength increases. This is reasonable since
longer wavelengths have less energy and a less
energetic photon has less “penetrating power”
and is more likely to be absorbed. Only a few
absorption peaks are seen in an X-ray
absorption spectrum, but there is a very distinct
feature in these spectra. An abrupt change in
absorptivity (or the mass absorption coefficient)
occurs at the wavelength of the X-ray necessary
to eject an electron from an atom. These abrupt
changes in X-ray absorptivity are termed
absorption edges.
11. As the wavelength of the X-ray decreases, its energy increases,
its penetrating power increases, and the percent absorption
decreases. As the wavelength decreases further, the X-ray
eventually has sufficient energy to displace electrons from the K
shell. This results in an abrupt increase in absorption. This is
manifested by the K absorption edge. After the absorption edge,
the penetrating power continues to increase as the wavelength
decreases further until finally the degree of absorption is
extremely small at very small wavelengths. At wavelengths less
than 0.2 A˚ , penetrating power is extremely great and we are
approaching the properties of interstellar radiation such as
cosmic rays, which have extremely high penetrating power.
Wavelengths shorter than the K absorption edge have sufficient
energy to eject K electrons; the bombarded sample will exhibit
both continuum radiation and the characteristic K lines for the
sample. This process is called XRF. Wavelengths just slightly
longer than the K absorption edge do not have enough energy to
displace K electrons.
12. The wavelengths of the absorption edges and of the
corresponding emission lines do not quite coincide. This
is because the energy required to dislodge an electron
from an atom (the absorption edge energy) is not quite
the same as the energy released when the dislodged
electron is replaced by an electron from an outer shell
(emitted X-ray energy). The amount of energy required
to displace the electron must dislodge it from its orbital
and remove it completely from the atom. This is more
than the energy released by an electron in an atom falling
from one energy level to another. As opposed to emission
spectra, only one K absorption edge is seen per element,
since there is only one energy level in the K shell. Three
absorption edges of different energies are observed for
the L levels, five for the M levels, and so on.
13. The X-ray Fluorescence (XRF) Process
X-rays can be emitted from a sample by bombarding it with
electrons or with other X-rays. When electrons are used as
the excitation source, the process is called X-ray emission.
This is the basis of X-ray microanalysis using an electron
microprobe or a scanning electron microscope. When the
excitation source is a beam of X-rays, the process of X-ray
emission is called fluorescence. This is analogous to
molecular fluorescence and atomic fluorescence because the
wavelength of excitation is shorter than the emitted
wavelengths. The beam of exciting X-rays is called the
primary beam; the X-rays emitted from the sample are
called secondary X-rays. The use of an X-ray source to
produce secondary X-rays from a sample is the basis of
XRF spectroscopy. The primary X-ray beam must have a
λmin that is shorter than the absorption edge of the element to
be excited.
14. The X-ray Diffraction (XRD) Process
Crystals consist of atoms, ions or molecules arranged in a
regular, repeating 3D pattern, called a crystal lattice. This
knowledge came from the pioneering work of German physi-
cist Max von Laue and the British physicists, W.H. Bragg and
W.L. Bragg. Max von Laue demonstrated in 1912 that a
crystal would diffract X-rays, just as a ruled grating will dif-
fract light of a wavelength close to the distance between the
ruled lines on the grating. The fact that diffraction occurs
indicates that the atoms are arranged in an ordered pattern,
with the spacing between the planes of atoms on the order of
short wavelength electromagnetic radiation in the X-ray
region. The diffraction pattern could be used to measure the
atomic spacing in crystals, allowing the determination of the
exact arrangement in the crystal, the crystal structure. The
Braggs used von Laue’s discovery to determine the
arrangement of atoms in several crystals and to develop a
simple 2D model to explain XRD.
15. The X-ray Diffraction (XRD) Process
If the spacing between the planes of atoms is about the same as the
wavelength of the radiation, an impinging beam of X-rays is reflected at
each layer in the crystal, as shown in Fig. Assume that the X-rays falling
on the crystal are parallel waves that strike the crystal surface at angle ɵ
. That is, the waves O and O/ are in phase with each other and reinforce
each other. In order for the waves to emerge as a reflected beam after
scattering from atoms at points D and B, they must still be in phase with
each other, that is, waves Y and X must still be parallel and coherent. If
the waves are completely out of phase, their amplitudes cancel each
other, they are said to interfere destructively, and no beam emerges. In
order to get reinforcement, it is necessary that the two waves stay in
phase with each other after diffraction at the crystal planes.
16. The X-ray Diffraction (XRD) Process
It can be seen in Fig. that the lower wave travels an extra
distance AB+ BC compared with the upper wave. If AB+ BC is a
whole number of wavelengths, the emerging beams Y and X will
remain in phase and reinforcement will take place. From this
deduction, we can calculate the relationship between the
wavelengths of X-radiation, the distance d between the lattice
planes, and the angle at which a diffracted beam can emerge.
18. INSTRUMENTATION
Instrumentation for X-ray spectrometry requires a
source, a wavelength (or energy) selector, a detector,
collimators, and filters. The component parts of the
instrument are similar for XRF, XRD, and the other
fields, but the optical system varies for each one. For
example, in XRF spectrometry, either the energies or
wavelengths of emitted X-rays are measured to
characterize the elements emitting them. In the
wavelength-dispersive mode of analysis (WDXRF), a
dispersing device separates X-rays of differing
wavelength by deflecting them at different angles
proportional to their wavelength. In the energy-
dispersive mode (EDXRF), there is no dispersing
device, and a detector measures and records the
energies of each individual detected X-ray photon.
19. INSTRUMENTATION
The low energy X-rays emitted by elements with atomic
numbers less than sodium (Z ˂11) are easily absorbed by air.
Therefore most X-ray systems operate either under vacuum or
purged with helium. The entire spectrometer, including the
source, sample, optics, and most detectors are within the
vacuum/purge chamber. Liquid samples cannot be analyzed
under vacuum, so most systems permit the analyst to switch
from a vacuum to a helium purge as needed, usually in less than
2 min.
Commercial X-ray spectrometers may be equipped with
automatic sample changers for unattended analysis of multiple
samples. Computer-controlled spectrometers permit the
identification of the position of liquid samples in the sample
changer, and automatically switch to a helium purge to avoid
exposing the liquid samples to vacuum.
20. X-Ray Source
Three common methods of generating X-rays for analytical use in
the laboratory are:
1. Use of a beam of high-energy electrons to produce a broad band
continuum of X-radiation resulting from their deceleration upon
impact with a metal target as well as element-specific X-ray line
radiation by ejecting inner core electrons from the target metal
atoms. This is the basis of the X-ray tube, the most common
source used in XRD and XRF.
2. Use of an X-ray beam of sufficient energy (the primary beam) to
eject inner core electrons from a sample to produce a secondary X-
ray beam (XRF).
3. Use of a radioactive isotope which emits very high energy X-
rays (also called gamma radiation) in its decay process.
21. X-Ray Source
A fourth method of producing X-rays employs a massive,
high-energy particle accelerator called a synchrotron. These
are available at only a few locations around the world, such
as the Brookhaven National Laboratory or the Stanford
Accelerator Center in the US, and are shared facilities
servicing a large number of clients. X-rays may be generated
when alpha particles or other heavy particles bombard a
sample; this technique is called particle-induced X-ray
emission (PIXE) and requires a suitable accelerator facility.
The use of an electron beam to generate X-rays from a
microscopic sample as well as an image of the sample
surface is the basis of X-ray microanalysis using an electron
microprobe or scanning electron microscopy. These different
X-ray sources may produce either broad band (continuum)
emission or narrow line emission, or both simultaneously,
depending on how the source is operated.
22. The X-ray Tube
A schematic X-ray tube is depicted in Fig.. The X-ray tube
consists of an evacuated glass envelope containing a wire
filament cathode and a pure metal anode. A thin beryllium
window sealed in the glass envelope allows X-rays to exit the
tube. The glass envelope is encased in lead shielding and a
heavy steel jacket with an opening over the window, to protect
the tube. When a cathode (a negatively charged electrode) in
the form of a metal wire is electrically heated by the passage
of current, it gives off electrons, a process called thermionic
emission.
23. If a positively charged metallic electrode (called an anode) is
placed near the cathode in a vacuum, the negatively charged
electrons will be accelerated toward the anode. Upon striking
it, the electrons give up their energy at the metallic surface of
the anode. If the electrons have been accelerated to a high
enough velocity by a sufficiently high voltage between the
cathode and anode, energy is released as radiation of very short
wavelength (0.1 – 100 A˚ ), called X-radiation or X-rays. X-
ray tubes are generally operated at voltage differentials of 4 –
50 kV between the wire filament cathode and the anode.
The cathode is normally a tungsten wire filament. The anode is
called the target. The X-ray tube is named for the anode; a
copper X-ray tube has a copper anode and a tungsten wire
cathode, a rhodium tube has a rhodium anode and a tungsten
wire cathode, a tungsten tube has a tungsten anode and a
tungsten wire cathode.
24. Numerous metals have been used as target materials, but common target
elements are copper, chromium, molybdenum, rhodium, gold, silver,
palladium, and tungsten. The wavelengths of the X-ray line radiation
emitted by the target depend on the metal used. The voltage between the
anode and cathode determines how much energy the electrons in the
beam acquire, and this in turn determines the overall intensity of the
wide range of X-ray intensities in the continuum distribution and the
maximum X-ray energy (shortest wavelength). In choosing the element
to be used for the target, it should be remembered that it is necessary for
the energy of the X-rays emitted by the source to be greater than that
required to excite the element being irradiated in an XRF analysis. As a
simple rule of thumb, the target element of the source should have a
greater atomic number than the elements being examined in the sample.
This ensures that the energy of radiation is more than sufficient to cause
the sample element to fluoresce. This is not a requirement in X-ray
absorption or XRD, where excitation of the analyte atoms is not
necessary. In many X-ray tube designs, the anode, or target, gets very hot
in use, because it is exposed to a constant stream of high-energy
electrons, with most of the energy being dissipated as heat on collision.
This problem is overcome by water-cooling the anode. Modern X-ray
tubes have been designed to operate at lower voltages and do not require
water-cooling of the anode.
25. The exit window of the X-ray tube is usually made of beryllium,
which is essentially transparent to X-rays. The Be window is thin,
generally 0.3 – 0.5 mm thick, and is very fragile. The window may
be on the side of the tube, as shown in Fig. 8.9, or in the end of the
tube. Side window tubes are common, but end-window tubes permit
the use of a thinner beryllium window. This makes end-window
tubes good for low energy X-ray excitation by improving the low-
energy output of the tube. X-ray tubes must provide adequate
intensity over a relatively wide spectral range for XRF in order to
excite a reasonable number of elements. In some applications,
monochromatic or nearly monochromatic X-rays are desired; that is
accomplished by using filters or a monochromator as described
below or by using a secondary fluorescent source, described
subsequently. The tube output must be stable over short time periods
for the highest precision and over long time periods for accuracy
without frequent recalibration. The X-ray emission lines from the
anode element must not interfere with the sample spectrum. Tube
lines can be scattered into the detector and be mistaken for an
element present in the sample.
26. Secondary XRF Sources
If it is necessary to prevent the continuum emission from an X-ray
tube from falling on a sample, a standard tube can be used to excite
another pure metal target. The resulting XRF from the secondary
target is used as the source of X-ray excitation for the sample. A
standard tungsten X-ray tube is used to produce the emission
spectrum, with the tungsten characteristic lines superimposed on the
continuum radiation. The radiation from this tube is used to strike a
secondary pure copper target. The resulting emission from the copper
is the copper XRF spectrum.
This source emits very little or no continuum radiation but does emit
quite strongly at the copper K and L lines. Of course, the metal used
in the target of the first source must have a higher atomic number than
copper to generate fluorescence. The Cu lines then can be used as an
excitation source, although the intensity of the secondary source is
much less than that of a Cu X-ray tube. However, when
monochromatic or nearly monochromatic radiation is required, the
loss of intensity is more than offset by the low background from the
secondary source.
27. Radioisotope sources
X-radiation is a product of radioactive decay of certain
isotopes. The term gamma ray is often used for an X-ray
resulting from such a decay process. Alpha and beta decay and
electron capture processes can result in the release of gamma
rays. The advantages of radioisotope sources are that they are
small, rugged, portable, and do not require a power supply.
They are ideal for obtaining XRF spectra from bulky samples
that do not fit into conventional spectrometers (and cannot have
pieces cut from them), such as aircraft engines, ship hulls, art
objects, and the like. The disadvantage is that the intensity of
these sources is weak compared with that of an X-ray tube,
the source cannot be optimized by changing voltage as can be
done with an X-ray tube, and the intensity of the source drops
off with time, depending on the half-life of the isotope. In
addition, the source cannot be turned off. This requires care on
the part of the analyst to avoid exposure to the ever-present
ionizing radiation.
28. Collimators
The X-rays emitted by the anode are radially directed.
As a result, they form a hemisphere with the target at
the center. In WDXRF spectroscopy or XRD structural
determination, the monochromator’s analyzing crystal
or the crystalline substance undergoing structure
determination requires a nearly parallel beam of
radiation to function properly. A narrow, nearly
parallel beam of X-rays can be made by using two sets
of closely packed metal plates separated by a small
gap. This arrangement absorbs all the radiation except
the narrow beam that passes between the gap.
Decreasing the distance between the plates or
increasing the total length of the gap decreases the
divergence of the beam of X-rays (i.e., it collimates, or
renders them parallel).
29. Collimators
The use of a collimator increases the wavelength
resolution of a monochromator’s analyzing crystal, cuts
down on stray X-ray emission, and reduces
background. Commercial instruments use multiple tube
or multiple slit collimator arrangements, often both
before the analyzing crystal (the primary collimator)
and before the detector (the secondary collimator). The
collimator positions in a sequential WDXRF
spectrometer are shown schematically in Figure below.
In many wavelength dispersive instruments, two
detectors are used in tandem, and a third auxiliary
collimator may be required. Such an arrangement is
also shown in Figure below. Collimators are not needed
for curved crystal spectrometers where slits or pinholes
are used instead nor are they needed for energy
dispersive spectrometers.
30. Schematic of the optical path in a wavelength-dispersive sequential
spectrometer, showing the positions of the collimators
31. A sequential spectrometer with two tandem detectors, showing the
placement of the collimators in the optical path.
32. Filters
One of the problems of using the X-ray tube is that both continuum
and characteristic line radiation is generated at certain operating
voltages. For many analytical uses, only one type of radiation is
desired. Filters of various materials can be used to absorb unwanted
radiation but permit radiation of the desired wavelength to pass by
placing the filter between the X-ray source and the sample. A
simple example of how a filter is used is shown in Fig. The solid
line spectrum is the output of a Rh tube operated at 20 kV with no
filter between the tube and the detector. The Rh La line at 2.69 keV
is seen, along with a broad continuum of X-rays from 4 to 19 keV.
If the Rh La line gets scattered into the detector, as it can from a
crystalline sample, it can be mistaken for an element in the sample
or may overlap another line, causing spectral interference. Placing
a cellulose filter over the tube window causes the low energy Rh
characteristic line to be absorbed; only the continuum radiation
reaches the detector, as shown by the dotted line spectrum.
33. The use of a filter to remove unwanted radiation from entering the
spectrometer is demonstrated. A cellulose filter placed between a Rh X-
ray tube and the sample removes the Rh La line at 2.69 keV and
allows only the continuum radiation to excite the sample.
34. Filters
Alternatively, when monochromatic radiation is desired, a
filter is chosen with its absorption edge between the Ka
and the Kb emission lines of the target element. The filter
then absorbs the Kb line and all shorter wavelengths,
including much of the continuum; the light reaching the
sample is essentially the Ka line of the target. Filters are
commonly thin metal foils, usually pure elements, but
some alloys such as brass and materials like cellulose are
used. Varying the foil thickness of a filter is used to
optimize peak-to- background ratios. Figure on next slide
shows a commercial sequential X-ray spectrometer with a
series of selectable beam filters located between the X-ray
tube and the sample. The filters are computer controlled
and are changed automatically according to the analytical
program set up in the instrument software.
35. The schematic layout of a commercial sequential X-ray spectrometer, the
MagiX, showing a series of selectable beam filters located between the X-
ray tube and the sample.
37. WDXRF Spectrometers
In the configurations shown, the source is placed under the sample; the sample
is presented surface-down to the X-ray beam. Some instruments have the tube
above the sample, with the sample surface facing up. There are advantages
and disadvantages to both designs, as we shall see. The sample fluoresces as a
result of excitation by the source. The sample fluorescence is directed through
the primary collimator to the analyzing crystal. Diffraction occurs at the
crystal planes according to Bragg’s Law and X-rays of different wavelengths
are diffracted at different angles. The diffracted X-rays are passed through
another collimator to one or more detectors. Figure 2 in previous slide depicts
two detectors in tandem, one behind the other. The analyzing crystal is
mounted on a turntable that can be rotated through ɵ degrees (see the arrow
marked ɵ on the lower left side of the diagram). The detector(s) are
connected to the crystal turntable so that when the analyzing crystal rotates by
ɵ degrees, the detector rotates through 2 ɵ degrees, as shown by the marked
arrow. Therefore the detector is always in the correct position (at the Bragg
angle) to detect the dispersed and diffracted fluorescence. This crystal
positioning system is called a goniometer.
38. Figure below shows the turntable and the concentric circles made by the
crystal and the detector. In most systems, the maximum diffraction angle
attainable is 75° ɵ (or 150 ° 2 ɵ). In some systems the rotation of the crystal
and the detector is mechanically coupled with gears. Other systems have no
mechanical coupling but use computer-controlled stepper motors for the
crystal and the detector. The newest systems use optical position control by
optical sensors or optical encoding devices. Optical position control permits
very high angular precision and accuracy and very fast scanning speeds
39. The Analyzing Crystal
A crystal is made up of layers of ions, atoms, or
molecules arranged in a well-ordered system, or lattice. If
the spacing between the layers of atoms is about the same
as the wavelength of the radiation, an impinging beam of
X-rays is reflected at each layer in the crystal. Bragg’s
Law indicates that at any particular angle of incidence ɵ,
only X-rays of a particular wavelength fulfill the
requirement of staying in phase and being reinforced, and
are therefore diffracted by the crystal. If an X-ray beam
consisting of a range of wavelengths falls on the crystal,
the diffracted beams of different wavelengths emerge at
different angles. The incident beam is thus split up by the
crystal into its component X-ray wavelengths, just as a
prism or grating splits up white light into a spectrum of
its component colors.
40. The principle is illustrated in Figure below. Figure shows schematically that
two detectors placed at the proper locations could detect the two wavelengths
simultaneously. Alternatively, the detector or analyzing crystal could move,
allowing each wavelength to be detected sequentially. Both types of
spectrometers are commercially available.
41. A serious limitation in XRF was the lack of natural crystals with d spacings
large enough to diffract the low energy X-rays from low atomic number
elements. That limitation has been overcome by the synthesis of multilayer
“pseudocrystals”. These are made from alternating layers of materials with
high and low optical densities deposited on a silicon or quartz flat. The PX3
multilayer is made from B4C alternating with Mo, for example. These
engineered multilayers are stable, commercially available, and permit the
routine determination o f elements as light as Be in samples.
Flat crystals are used in scanning (sequential) spectrometers. Curved
crystals, both natural and synthetic multilayers, are used in simultaneous
spectrometers, electron microprobes, and for synchrotron X-ray
spectrometry. The advantage to a curved crystal is that the X-rays are
focused and the collimators replaced by slits, resulting in much higher
intensities than with flat crystal geometry. This makes curved crystals
excellent for analysis of very small samples.
42. Detectors
X-ray detectors transform photon energy into electrical
pulses. The pulses (and therefore, the photons) are
counted over a period of time. The count rate, usually
expressed as counts per second, is a measure of the
intensity of the X-ray beam. Operating the detector as a
photon counter is particularly useful with low-intensity
sources, as is often the case with X-radiation.
There are three major classes of X-ray detectors in
commercial use: gas-filled detectors, scintillation
detectors, and semiconductor detectors. Semiconductor
detectors will be discussed with EDXRF equipment.
Both WDXRF and EDXRF detection makes use of a
signal processor called a pulse height analyzer or
selector in conjunction with the detector, and discussed
subsequently.
43. Gas-Filled Detectors
Suppose we take a metal cylinder, fit it with X-ray transparent
windows, place in its center a positively charged wire, fill it
with inert filler gas, such as helium, argon, or xenon, and seal
it. If an X-ray photon enters the cylinder, it will collide with
and ionize a molecule of the filler gas by ejecting an outer
shell electron, creating a primary ion pair. With helium as a
filler gas, the ion pair would be He+ and a photoelectron e-.
A sealed gas-filled detector of this type is shown on next
slide.
The following interaction takes place inside the tube.
hν + He → He+ +e- +h ν
44. Schematic diagram of a gas-filled X-ray detector tube. He filler gas is
ionized by X-ray photons to produce He+ ions and electrons, e-. The
electrons move to the positively charged center wire and are detected.
45. The electron is attracted to the center wire by the applied potential on the
wire. The positive charge causes the wire to act as the anode, while the
positive ion, He+ in this case, migrates to the metal body (the cathode). The
ejected photoelectron has a very high kinetic energy. It loses energy by
colliding with and ionizing many additional gas molecules as it moves to
the center wire, A plot of the number of electrons reaching the wire vs. the
applied potential is given in Fig. shown below.
Figure Gas-filled detector response vs. potential. A detector
operating at the plateau marked B is an ionization counter. A
proportional counter operates in the sloping region marked C where
the response is proportional to the energy of the incoming photon.
The plateau marked D represents the response of a Geiger counter.
46. With no voltage applied, the electron and the positive ion (He+)
recombine and no current flows. As the voltage is slowly
increased, an increasing number of electrons reach the anode, but
not all of them; recombination still occurs. This is the sloping
region marked A in Fig. At the plateau marked B in Fig., all the
electrons released by a single photon reach the anode and the
current is independent of small changes in the voltage. A
detector operating under these voltage conditions is known as an
ionization counter. Ionization counters are not used in X-ray
spectrometers because of their lack of sensitivity. As the
voltage increases further, the electrons moving toward the center
wire are increasingly accelerated. More and more electrons reach
the detector as a result of an avalanche of secondary ion pairs
being formed and the signal is greatly amplified. In the region
marked C in Fig. , the current pulse is proportional to the energy
of the incoming X-ray photon.
47. This is the basis of a proportional counter. In X-
ray spectrometry, gas-filled detectors are used
exclusively in this range, that is, as proportional
counters. The amplification factor is a complex
function that depends on the ionization
potential of the filler gas, the anode potential, the
mean free path of the photoelectrons, and other
factors. It is critical that the applied potential,
filler gas pressure, and other factors be kept
constant to produce accurate pulse amplitude
measurements. There are two main types of
proportional counter: flow proportional counters
and sealed proportional counters.
48. As shown in Fig., if the voltage is further increased, electrons formed in
primary and secondary ion pairs are accelerated sufficiently to cause the
formation of more ion pairs. This results in huge amplification in electrons
reaching the center wire from each X-ray photon falling on the detector. The
signal becomes independent of the energy of the photons and results in another
plateau, marked D. This is called the Geiger-Muller plateau; a detector operated
in this potential range is the basis of the Geiger counter or Geiger-Mu¨ller
tube. It should be noted that a Geiger counter gives the highest signal for
an X-ray beam without regard to the photon energy. However, it suffers from a
long dead time. The dead time is the amount of time the detector does not
respond to incoming X-rays. It occurs because the positive ions move more
slowly than the electrons in the ionized gas, creating a space charge; this stops
the flow of electrons until the positive ions have migrated to the tube walls.
The dead time in a Geiger counter is on the order of 100 ms, about 100 times
longer than the dead time in a proportional counter. Due to the long dead time
compared with other detectors, Geiger counters are not used much for
quantitative X-ray spectrometry. They are, however, very important portable
detectors for indicating the presence or absence of X-rays. Portable radiation
detectors equipped with Geiger counters are used to monitor the operation of
equipment that creates or uses ionizing radiation to check for leaks in the
shielding.
49. Proportional Counters
Proportional counters are of two types
1. Flow Proportional counter
2. Sealed Proportional Counter
Flow Proportional Counter. The flow proportional counter covers a wide
wavelength range and is generally used for wavelengths longer
than 2 A˚ (elements with Z , 27). This detector is illustrated in Fig.
on next slide. The windows are thin (,6 mm) polymer film, coated on
the inside surface with aluminum to permit a homogeneous electric field
to be established within the detector. The thin windows allow the filler
gas to leak out; therefore a supply of filler gas is constantly provided to
the detector through the inlet as shown in Fig. The filler gas for a flow
proportional counter is often 10% CH4 , 90% Ar, a mixture called P10
gas. The pressure, flow, and temperature of the gas must be precisely
controlled for accurate detector response. The operating voltage range
for a flow proportional counter is 1 – 3 kV. The amplification factor,
which is the number of ion pairs discharged at the electrodes divided by
the number of primary ion pairs formed, is 102– 106. The current pulse is
converted to a voltage pulse, is processed through a pulse height selector
or discriminator and counted.
50. Schematics of (a) a flow proportional counter and (b) a
sealed proportional counter.
51. Sealed Proportional Counter. A sealed proportional counter is
shown schematically in Fig. above. The windows are thicker, so
they do not leak. Window materials include polymers, mica,
aluminum, and beryllium. The filler gas used in a sealed proportional
counter may be Ne, Kr, or Xe. Window and gas combinations are
optimized for the wavelength of radiation to be detected; Al and Ne
would be best for light elements, for example.
Multiple proportional counters are used in simultaneous X-ray
spectrometers, while one proportional counter is often used in
tandem with a scintillation counter in a sequential system. It is for
this reason that the detector has two windows as shown in Fig.
X-ray photons pass through the proportional counter to the
scintillation counter located behind it, and signals are obtained
from both detectors. It should be noted that this tandem
arrangement does not permit independent optimization of both
detectors. There are sequential spectrometer systems available
with independent proportional and scintillation detectors.
52. Scintillation Counter
Photomultiplier detectors, are very sensitive to visible and UV
light, but not to X-rays, to which they are transparent. In a
scintillation detector the X-radiation falls on a compound that
absorbs X-rays and emits visible light as a result. This
phenomenon is called scintillation. A PMT can detect the
visible light scintillations. The scintillating compound or
phosphor can be an inorganic crystal, an organic crystal or an
organic compound dissolved in solvent.
The most commonly used commercial scintillation detector
has a thallium-doped sodium iodide crystal, NaI(Tl), as the
scintillating material. A single crystal of NaI containing a
small amount of Tl in the crystal lattice is coupled to a PMT,
shown in Fig. on next slide. When an X-ray photon enters
the crystal, it causes the interaction and the ejection of
photoelectrons, as in the gas-filled detector.
53. Figure The NaI(Tl) scintillation detector. (a) The assembled detector; (b)
a schematic representation of the photomultiplier and its circuitry.
54. The ejected photoelectrons cause excited electronic
states to form in the crystal by promotion of valence
band electrons. When these excited electrons drop
back to the ground state, flashes of visible light
(scintillations) are emitted. The excited state lies
about 3 eV above the ground state, so the emitted
light has a wavelength of 410 nm. The intensity of
the emitted light pulse from the crystal is
proportional to the number of electrons excited by
the X-ray photon. The number of electrons excited is
proportional to the energy of the X-ray photon;
therefore the scintillation intensity is proportional to
the energy of the X-ray.
55. The scintillations (visible light photons) from the crystal fall
on the cathode of the PMT, which is made of a photo-emissive
material such as indium antimonide. Photo-emissive materials
release electrons when struck by photons. Electrons ejected
from the cathode are accelerated to the first dynode,
generating a larger number of electrons. The electron
multiplication process occurs at each successive dynode,
resulting in approximately 106 electrons reaching the anode
for every electron that strikes the cathode. The amplitude of
the current pulse from the photomultiplier is proportional to
the energy of the X-ray photon causing the ionization in the
crystal.
To summarize, the scintillation detector works by (1)
formation of a photoelectron in the NaI(Tl) crystal after an X-
ray photon hits the crystal, (2) emission of visible light
photons from an excited state in the crystal, (3) production of
photoelectrons from the cathode in the photomultiplier, and
(4) electron multiplication.
56. Sample Holders
XRF is used for the analysis of solid and liquid samples. For
quantitative analysis the surface of the sample must be as flat as
possible, as will be discussed in the applications section. There are
two classes of sample holders, cassettes for bulk solid samples and
cells for loose powders, small drillings, and liquids. The cassette is a
metal cylinder, with a screw top and a circular opening or aperture,
where the sample will be exposed to the X-ray beam. The maximum
size for a bulk sample is shown. The sample is placed in the cassette.
For a system where the sample is analyzed face down, the cassette
is placed with the opening down and the bulk sample sits in the
holder held in position by gravity. If the system requires the sample
face up, the body of the cassette must be filled with an inert support
(often a block of wood) to press the sample surface against the
opening. These cassettes are available with a variety of apertures,
usually from 8 to 38 mm in diameter, to accommodate samples of
different diameters. Other types of solid samples, such coatings on a
solid substrate can be placed directly in this type of cassette.
57. The analysis of liquids, loose powders, or small pieces
requires a different holder. The cells for these types of samples
are multipart plastic holders and require squares or circles of
thin polymer film to hold the sample in the cell. The body of
the cell is a cylinder open on both ends. One end of the
cylinder is covered with the plastic film (or even clear
plastic adhesive tape) and the film or tape is clamped into
place by a plastic ring. The cell is placed with the film down
and the sample of liquid, powder, or filings is added. The film
surface should be completely covered, as uniformly as
possible. A plastic disk that just fits into the cell is inserted and
pressed against the sample to obtain as flat a surface as
possible and a top cap is screwed or pressed on. For liquid
samples, a vented top is used to avoid pressure build-up from
heating of the sample by the X-ray beam. This assembled cell
may be used “as is” or may be inserted into a standard
cassette, in a face-down configuration.
58. As you can imagine, if the thin polymer film breaks,
samples of loose powder, chips, or liquid will spill into
the interior of the spectrometer, contaminating the
analyzing crystal and the rest of the system and possibly
breaking the Be window of the X-ray tube, if the tube is
below the sample. It is for this reason that liquid
samples cells are vented and that a vacuum is not used.
This is the main disadvantage of the face-down
configuration; for any- thing other than bulk samples,
there is a risk of contaminating the instrument if the
film covering the sample ruptures. In the face-down
configuration, a liquid naturally assumes a flat surface.
Imagine what the liquid sample would look like face-
up. An air bubble will form at the film surface if a
sealed cell is used and not filled completely. A bubble
may form at the surface by heating of the sample in the
X-ray beam if the cell is filled completely.
59. If this occurs, the intensity of X-ray fluorescence from
the sample will drop dramatically and the possibility of
film rupture as the pressure in the cell builds increases
dramatically. So, if liquid samples must be analyzed, the
face-down configuration gives better quantitative results,
even at the risk of contaminating the spectrometer.
The sample cassette is moved into position, either
manually or with the automatic sample changer. In
position, the sample is spun, generally at about 30 rpm,
to homogenize the surface presented to the X-ray beam.
Polymer films used to cover the cell opening must be
low in trace element impurities, strong enough to hold
the sample without breaking, thermally stable, and
chemically inert. They certainly must not be soluble in
any liquid samples to be analyzed.
60. Simultaneous WDXRF Spectrometers
A simultaneous WDXRF system uses multiple channels, with each
channel having its own crystal/detector combination optimized for a
specific element or background measurement. Instruments with as many
as 40 fixed crystal/detector channels or as few as two are available.
These systems are designed for specific applications, such as the analysis
of steel in a production facility where hundreds of samples must be
analyzed for the same suite of elements every day. They have the
advantage of being very fast compared with a sequential system, but are
not flexible.
Most simultaneous systems have the X-ray tube above the sample, with
the sample facing up. As discussed earlier, this makes the analysis of
liquids difficult or impossible. Several instrument manufacturers offer
combination systems with a simultaneous set of channels as well as a
sequential monochromator. These systems offer the speed needed for
routine analysis and the flexibility needed for non-routine analysis, but
are expensive.
61. EDXRF Spectrometers
In EDXRF spectrometry, there is no physical
separation of the fluorescence radiation from the
sample. There is no dispersing device prior to the
detector. All of the photons of all energies arrive at the
detector simultaneously. The semiconductor detector
used in EDXRF is a proportional detector with very
high intrinsic energy resolution. In this system, the
detector resolves the spectrum. The signal pulses are
collected, integrated and displayed by a multichannel
analyzer (MCA). A primary beam filter is often used to
improve the signal-to-noise ratio for given energy
regions. As with WDXRF systems, most EDXRF
systems have a series of selectable filters.
62. A schematic energy dispersive XRF system with an X-ray
tube source. There is no dispersion device between the
sample and the detector. Photons of all energies are collected
simultaneously.
63. Semiconductor Detectors
When an X-ray falls on a semiconductor, it generates an
electron (-e) and a hole (+ e) in a fashion analogous to the
formation of a primary ion pair in a proportional counter.
Based on this phenomenon, semiconductor detectors have
been developed and are now of prime importance in EDXRF
and scanning electron microscopy. The principle is similar
to that of the gas ionization detector as used in a
proportional counter, except that the materials used are in
the solid-state. The total ionization caused by an X-ray
photon striking the detector is proportional to the energy of
the incident photon.
The most common semiconductor detector for laboratory
EDXRF systems is the lithium-drifted silicon diode,
represented as Si(Li). (It is called a “silly” detector for
short).
64. The Si(Li) semiconductor detector. (a) Schematic shows the
n-type Si region on one end of the Si crystal, a central charge
depleted intrinsic region and p-type Si on the other end. (b)
65. A cylindrical piece of pure, single crystal silicon is used.
The size of this piece is 4 – 19 mm in diameter and 3
– 5 mm thick. The density of free electrons in the silicon is
very low, constituting a p-type semiconductor. If the density
of free electrons is high in a semiconductor, then we have
an n-type semiconductor. Semiconductor diode detectors
always operate with a combination of these two types. The
diode is made by plating lithium onto one end of the
silicon. The lithium is drifted into, that is diffused into, the
silicon crystal by an applied voltage. The high con-
centration of Li at the one end creates an n-type region. In
the diffusion process, all electron acceptors are neutralized
in the bulk of the crystal, which becomes highly
nonconducting. This is the “intrinsic” material. The lithium
drifting is stopped before reaching the other end of the
silicon crystal, leaving a region of pure Si (p-type),