Physics Glossary – X

Xerography (Photocopy or Electrophotography)

A machine is forming permanent images from a brightly lit original, but is using the transfer of static electrical charges rather than photographic film, hence the term electrophotography.

X-Rays

Are a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm – 10 nanometers (corresponding to frequencies in the range 30 PHz – 60 EHz). X-rays were first observed and documented in 1895 by Wilhelm Conrad Röntgen. X-rays are highly penetrating of many materials, and are used in medicine to take pictures of bones and teeth. This is because bones absorb the radiation more than the less-dense soft tissue. X-rays from a source are passed through the body and onto a photographic plate; areas where radiation is absorbed show up as white and can be used to show broken or fractured bones.

X-Rays Crystallography

A technique in crystallography in which the pattern produced by the diffraction of x-rays through the closely spaced lattice of atoms in a crystal are recorded and then analyzed to reveal the nature of that lattice. The material and molecular structure of a substance can often be inferred from the quantitative study of this pattern. It is widely used in chemistry and biochemistry to determine the structure of molecules.

X-Rays Astronomy

Energetic X-rays (E > 30 keV) can penetrate the air at least for distances of a few meters (they would never have been detected and medical X-ray machines would not work if this was not the case) the Earth’s atmosphere is thick enough that virtually none are able to penetrate from outer space all the way to the Earth’s surface. X-rays in the 0.5 – 5 keV range, where most celestial sources give off the bulk of their energy, can be stopped by a few sheets of paper; ninety percent of the photons in a beam of 3 keV X-rays are absorbed by traveling through just 10 cm of air!

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