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X-ray microtomography

X-ray microtomography, like tomography and x-ray computed tomography, uses x-rays to create cross-sections of a physical object that can be used to recreate a virtual model (3D model) without destroying the original object. The prefix micro- (symbol: µ) is used to indicate that the pixel sizes of the cross-sections are in the micrometre range. These pixel sizes have also resulted in the terms high-resolution x-ray tomographymicro–computed tomography (micro-CT or µCT), and similar terms. Sometimes the terms high-resolution CT (HRCT) and micro-CT are differentiated, but in other cases the term high-resolution micro-CT is used. Virtually all tomography today is computed tomography.

X-ray microtomography

Micro-CT has applications both in medical imaging and in industrial computed tomography. In general, there are two types of scanner setups. In one setup, the X-ray source and detector are typically stationary during the scan while the sample/animal rotates. The second setup, much more like a clinical CT scanner, is gantry based where the animal/specimen is stationary in space while the X-ray tube and detector rotate around. These scanners are typically used for small animals (in vivo scanners), biomedical samples, foods, microfossils, and other studies for which minute detail is desired.

The first X-ray microtomography system was conceived and built by Jim Elliott in the early 1980s. The first published X-ray microtomographic images were reconstructed slices of a small tropical snail, with pixel size about 50 micrometers.

WAS – X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter. The experiment is usually performed at synchrotron radiation facilities, which provide intense and tunable X-ray beams. Samples can be in the gas-phase, solution, or as solids.

XAS data is obtained by tuning the photon energy, using a crystalline monochromator, to a range where core electrons can be excited (0.1–100 keV, 16–16,022 aJ). The edges are, in part, named by which core electron is excited: the principal quantum numbers n = 1, 2, and 3, correspond to the K-, L-, and M-edges, respectively. For instance, excitation of a 1s electron occurs at the K-edge, while excitation of a 2s or 2p electron occurs at an L-edge.

X-ray absorption spectroscopy

XAS is a type of absorption spectroscopy from a core initial state with a well defined symmetry therefore the quantum mechanical selection rules select the symmetry of the final states in the continuum which usually are mixture of multiple components. The most intense features are due to electric-dipole allowed transitions (i.e. Δℓ = ± 1) to unoccupied final states. For example, the most intense features of a K-edge are due to core transitions from 1s → p-like final states, while the most intense features of the L3-edge are due to 2p → d-like final states.

XAS methodology can be broadly divided into four experimental categories that can give complementary results to each other: metal K-edge, metal L-edge, ligand K-edge, and EXAFS.

ABOUT

S.A.V.E.D. was founded by Sophie BOUAT, Ph.D in Physics & Engineer in Material Physics.

R&D manager at ENERBEE (2016-2018)

AVSIS (2014-2015)

Polygon Physics (2012-2013)

SAVED Expertise

  • Scientific data analysis and experiment plans,
  • Non-destructive testing, 2D/3D imaging and X-ray and neutron analysis and Co,
  • Material physics : ceramics, semi-conductors, superconductors, metals,
  • Microelectronics, MEMS, metallurgy, mechanics and fluid mechanics and Co,
  • Instrumentation, modelling and medical applications of physics,

SEM – Scanning Electron Microscope

scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the detected signal to produce an image. SEM can achieve resolution better than 1 nanometer. Specimens are observed in high vacuum in conventional SEM, or in low vacuum or wet conditions in variable pressure or environmental SEM, and at a wide range of cryogenic or elevated temperatures with specialized instruments.

The most common SEM mode is the detection of secondary electrons emitted by atoms excited by the electron beam. The number of secondary electrons that can be detected depends, among other things, on specimen topography. By scanning the sample and collecting the secondary electrons that are emitted using a special detector, an image displaying the topography of the surface is created.