X-ray Tube & X-Ray Films

 The mechanism of heat loss in the modern X-ray tube is radiation.














The atomic number of tungsten is 74.


X-ray film is coated with a photosensitive emulsion on both sides. The active is silver bromide and silver iodide.

In routine films, both sides are coated, whereas, in mammography, only one side of the film is coated.

X-ray films are most sensitive to blue light and least sensitive to red light. So, the safe light used in the darkroom is a red light.

X-rays are produced when the electron beam decelerates close to the nucleus of

the atom in the anode.

The production of X-rays is as follows:

Current is passed through a tungsten filament which acts as the cathode

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Electrons are emitted as a result of thermionic emission

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Electrons bombard the target anode, a tungsten disc

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Results in the conversion of energy into heat (99%) and X-ray photons(1%)

The target anode is made of a tungsten disc in ordinary diagnostic X-ray tubes and molybdenum in mammography X-ray tubes.

At the anode, fast-moving electrons interact with the atoms of the anode in one of the following ways:

  • Nucleus field interaction: aka continuous spectrum radiation or Bremsstrahlung reaction (80%)
  • Inner shell interaction: produces characteristic spectrum radiation(20%)

Important parameters with respect to X rays:

  • Kilovolt peak (kVP) - Potential difference between cathode and anode. When the voltage increases, energy increases, and penetration also increases. Hence more kVP is required for obese patients.
  • Milliampere second (mAS) - Determines the amount of film blackening. More mAS more is radiation exposure.
  • Contrast is influenced by both kVP and mAS.
  • kVP is inversely proportional whereas mAS is directly proportional to the contrast produced.

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