Equis ISSN 2398-2977

Radiography: processing

Contributor(s): Tim Donovan, Patricia Rose, Jeffrey Watkins, Jonie Watkins

Formation of the latent Image

  • When film is exposed to x-rays and light from intensifying screens, the silver halide crystals are affected forming theLatent image.
  • The latent image is not visible since, although the reduction of silver halide to metallic silver has begun there is not enough of this to appear black.
  • The silver halide in the emulsion is in the form of a crystal lattice containing (negative) bromide ions and (positive) silver ions.
  • Some of these ions are free to move within the crystal lattice.
  • Around the crystal lattice is a "barrier" of electrons.
  • During manufacture a defect is introduced into the crystal   →  sensitivity speck  Radiation physics: sensitivity speck  .
  • When the film is exposed to ionizing radiation:
  • Some of the bromide ions in the lattice emit electrons.
  • These electrons travel rapidly to the sensitivity speck which acts as anelectron trap.
  • The electron trap builds up a negative charge.
  • Silver ions are attracted to the negative charge.
  • The positive charge of the silver ions is neutralised by the electrons in the trap (reduction) and silver atoms are produced.
  • The presence of metallic silver in the crystal lattice makes a break in the electron barrier which surrounded it and it is therefore susceptible to the action of developer.

Development

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Rinsing

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Fixing

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Washing

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Drying

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