Unknown at first, these photons from innershell transitions have played a vital role in materials analysis

X-Ray Generation Where do X-Rays come from?

Source of X-rays as vacancy filled by cascade of electrons from lower energy levels

X-Ray Generation X-ray tube  Filament (Tungsten)  Target metal (Cu, Cr)  Electrons are accelerated by a potential of about 55,000 Volts

Continuous X-Ray Spectrum 35 keV electrons strike the metal target They collide with the electrons in the metal Rapid deceleration results in emissions of proton Photons with a wide range of energies are emitted because the degree of deceleration is different

Characteristic X-Ray The incident e - collides with an e - from a cores level (K shell) An e - in the core level escapes The vacant K shell can be filled by a core electron from a higher energy level A photon is emitted during this transition Specific energies are emitted since the core e - energy levels are well-defined

X-Ray Diffraction Waves interact with crystalline structures whose repeat distance is about the same the wavelength. X-rays scattered from a crystalline structure constructively interferes and produces a diffracted beam.

Bragg’s Law n = 2d sin  n = integer = wavelength (Å) d = interatomic spacing (Å)  = diffraction angle (  )

Diffractometer A: Chiller B: Regulator C: Computer D: Strip chart recorder

E: X-ray source F:  compensating slit G: Sample chamber H: Scintillation counter J: Goniometer

Diffraction Pattern Diffraction patterns are a plot of intensity vs 

Sample Type Single Crystal Sample is placed in a beam and the reflections are observed for specific orientations Time consuming and difficult to orient the crystal Powder Sample Many small crystallites with random orientations Much easier to prepare and one can see reflections in all directions

Analyzing a powder sample

X-Ray Fluorescence Spectrometry What is it? How does it work? Properties Advantages Disadvantages

X-Ray Fluorescence Spectrometry  What is it? Instrumental method of qualitative and quantitative analysis for chemical elements Based on the measurement of the wavelength and intensities of element’s spectral lines emitted by secondary excitation

X-Ray Fluorescence Spectrometry How does it work? A beam of sufficiently short-wavelength X radiation irradiates the sample Excites each chemical element to emit secondary spectral lines Spectral lines have wavelengths characteristics This process is known as the secondary excitation

X-Ray Fluorescence Spectrometry  How does it work? (continued) Sample can have practically any form Sample size and shape can be largely varied The material to be analyzed can be almost anything

X-Ray Fluorescence Spectrometry  Properties The intensities of the resulting fluorescent X-rays are smaller The method is feasible only when high- intensity X-ray tubes, very sensitive detectors and suitable X-ray optics are available A certain number of quanta can reduce the statistical error of the measurement

X-Ray Fluorescence Spectrometry  Properties (continued) Intensity influence the time that will be necessary to measure a spectrum The sensitivity of the analysis depend on the peak-to-background ratio of the spectral lines Few cases of spectral interference occur

X-Ray Fluorescence Spectrometry  Advantages X-ray spectra is simple and regular Matrix effect in X-ray emission are systematic, predictable and readily evaluated X-ray fluorescence spectroscopy is non- destructive.

X-Ray Fluorescence Spectrometry  Disadvantages Small surface layer contributes to the observed X-ray line intensity Not all of the elements in a sample can be measured using the same X-ray tube, crystals, and detector

X-ray Applications Electron Microprobe Scattering Absorptiometry Radiography Fluoroscopy

Electron Microprobe Nondestructive determines composition of tiny amounts of solids. Virtually all elements can be analyzed except hydrogen helium and lithium. An Electron Microprobe

Scattering A fluorescence spectrometer is used on a gas, liquid, colloidal suspension or solid. Coherent and Incoherent scattering rays. Ratio of these rays are analyzed. Measures radius of gyrations. Widely used in proteins, viruses, catalysts, hardening and precipitation in alloys and lattice deformation.

Absorptiometry Chemical analysis is possible for gases, lipids or solids to measure densities porosities as well as coating, plating and insulation thickness. Most often applied to living patients in measurements of bone densities, iodine in the thyroid gland, liver diseases and other medical uses. Two types Single and Dual X-ray Absorptiometry.

Single X-ray Absorptiometry Single X-ray absorptiometry is used to measure the bone mineral content. Used for diagnosis of osteoporosis, providing reasonable accuracy and precision and low radiation exposure.

Dual X-ray Absorptiometry Used when single X- ray absorptiometry is not feasible. Used in areas with variable soft tissue and composition such as the spine, hip or the whole body. A Dual X-ray Absorptiometry

Radiography Involves use of registration on film of the differential absorption of a beam passing through a specimen. Medical uses. Industrial uses. Nondestructive method.

Fluoroscopy Similar to radiography except the image is registered on a fluorescent screen. Instantaneous and permits observation of internal motions and other changes.

Auger electron spectrometer