Production of X-rays (1)

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Production of X-rays (1)

• X-rays are produced when rapidly moving electrons
  that have been accelerated through a potential
  difference of order 1 kV to 1 MV strikes a metal
  target.

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Production of X-rays (2)

• Electrons from a hot element are accelerated onto
  a target anode.
• When the electrons are suddenly decelerated on
  impact, some of the kinetic energy is converted
  into EM energy, as X-rays.
• Less than 1 of the energy supplied is converted
  into X-radiation during this process. The rest is
  converted into the internal energy of the target.

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Properties of X-rays

• X-rays travel in straight lines.
• X-rays cannot be deflected by electric field or
  magnetic field.
• X-rays have a high penetrating power.
• Photographic film is blackened by X-rays.
• Fluorescent materials glow when X-rays are
  directed at them.
• Photoelectric emission can be produced by X-rays.
• Ionization of a gas results when an X-ray beam is
  passed through it.

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X-ray Spectra (1)

• Using crystal as a wavelength selector, the
  intensity of different wavelengths of X-rays can
  be measured.

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X-ray Spectra (2)

• The graph shows the following features.
• A continuous background of X-radiation in which
  the intensity varies smoothly with wavelength.
  The background intensity reaches a maximum value
  as the wavelength increases, then the intensity
  falls at greater wavelengths.
• Minimum wavelength which depends on the tube
  voltage. The higher the voltage the smaller the
  value of the minimum wavelength.
• Sharp peaks of intensity occur at wavelengths
  unaffected by change of tube voltage.

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Minimum wavelength in the X-ray Spectra

• When an electron hits the target its entire
  kinetic energy is converted into a photon.
• The work done on each electron when it is
  accelerated onto the anode is eV.
• Hence hf eV and the maximum frequency

Therefore,
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Characteristic X-ray Spectra

• Different target materials give different
  wavelengths for the peaks in the X-ray spectra.
• The peaks are due to electrons knock out
  inner-shell electrons from target atoms.
• When these inner-shell vacancies are refilled by
  free electrons, X-ray photons are emitted.
• The peaks for any target element define its
  characteristic X-ray spectrum.

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Uses of X-rays

• In medicine
• To diagnose illness and for treatment.
• In industry
• To locate cracks in metals.
• X-ray crystallography
• To explore the structure of materials.