unknown at first, these photons from innershell transitions have played a vital role in materials...

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