Radhabai Kale Mahila Mahavidhyalaya Ahmednagar PPT NAME Pawar

Radhabai Kale Mahila Mahavidhyalaya, Ahmednagar PPT. NAME Pawar. K. S.

X-RAY TECHNIQUES 2016 - 2017 Electron Beam

X-rays Discovered by Roentgen, 1895 λ = 0. 1 – 10 nm

The smaller wavelengths of X-Rays (0. 1 – 10 nm) are similar to the size of atoms (0. 1 – 0. 2 nm), and have energies that correspond to the energy differences between the inner atomic orbitals. Fundamental Equivalency Energy versus Wavelength of Photons E = h. ergs per single photon E = h. c/ ergs per single photon h = Planck's constant = 1. 38 10 -16 erg sec

emission

1)XRD Characterization CHARACTERIZATION TECHIQUES

In 1912 Van Laue postulated that if X-rays are waves & the distance between atoms in solids is comparable to wavelength of x-rays then they should be diffracted by atoms in solid. X-rays have wavelength in the range of(3900 -7800 A 0) & therefore are diffracted by crystals. Therefore x-ray diffractin are widely used for the study of crystal structures. X-ray diffraction technique is used to study the following aspects, 1]For phase analysis. 2]Determination of crystals size. 3]Determination of crystal lattice.

X-rays are electromagnetic radiation of wavelength ~1 A 0(10^-10 m). X-rays are produced when high energy charged particles collide with matter. In this process, electrons are ejected from the core shell around the nucleus and another electron of higher energy from the outer shells fill the resulting hole these electrons give up there excess energies in the form of x-rays. If the electron jumps from L-shell then it gives K λ radiation or if it jumps from the next higher shell it will give to K λ radiation. X-rays for diffraction are usually generated in an evacuated & selected tube by applying a high voltage(30 -60) Kv between a cathode (usually tungsten) and a selected anode such as copper. X-rays leaves the tube through windows made of beryllium. This must be adequate cooling of the tube to remove the heat generated. For analytical purpose monochromatic beam of x-rays are used.

X-Ray Tubes

Braggs Law (1912) X-Ray diffraction by atomic lattice planes of crystals n × λ = 2 × d × sin(θ)

Principle: X-rays are electromagnetic radiation of wavelength ~1 A 0(10^-10 m). X-rays are produced when high energy charged particles collide with matter. In this process, electrons are ejected from the core shell around the nucleus and another elaectron of higher energy from the outer shells fill the resulting hole. These elecrons give up there excess energies in the form of x-rays. If the electron jumps from L-shell then it gives K λ radiation or if it jumps from the next higher shell it will give to K λ radiation. Xrays for diffraction are usually generated in an evacuated & selected tube by applying a high voltage(30 -60)Kv between a cathode (usually tungsten) and a selected anode such as copper. X-rays leaves the tube through windows made of beryllium. This must be adequate cooling of the tube to remove the heat generated. For analytical purpose monochromatic beam of x-rays are used.

n × λ = 2 × d × sin(θ) Antigorite Counts 2 θ degrees X-ray Diffractogram

n × λ = 2 × d × sin(θ) X-ray Diffractogram

Electron Microprobe Electrons can be focused with magnetic fields to spot sizes on the order of 1 micron or less. By using an electron beam as the excitation source, one can analyze very small spots on mineral grains, and thus investigate phenomena such as compositional zoning in crystals, partitioning of elements between coexisting phases, etc. The disadvantage of electron beam excitation is that a relatively high background radiation is created by the electrons, which makes the detection limits for most elements ~0. 01 wt. %.

Interaction between the Electron Beam and Sample Surface Back-scattered electrons are those which interact with atomic nucleii electrostatically and are flung back out of the sample, in much the same way that a comet interacts gravitationally with the sun. Secondary electrons are produced by inelastic collisions of electrons from beam with valence electrons. These secondary electrons typically have lower energies than backscattered electrons. Auger electrons are produced by the interaction between the characteristic X-rays produced by an element with electrons in higher energy orbitals. Auger electrons typically have energies that are the difference between the energy of the initial electronic transition that produced the characteristic radiation and the ionization energy of the element. Bremsstrahlung X-rays are the radiation that is emitted when electrons are decelerated by a target. Accelerated charges give off electromagnetic radiation, and when the energy of the bombarding electrons is high enough, that radiation is in the X-ray region and is characterized by a continuous distribution of radiation which becomes more intense and shifts toward higher frequencies as the energy of the bombarding electrons is increased. This background radiation is the principle limitation in analyzing elements at very low concentrations with the electron microprobe.

Interaction between the Electron Beam and Sample Surface ~ 1 micron spot

WDS: Wavelength Dispersive Analysis Electron Microprobe Analysis

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