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Production of X-Rays

Production of X-Rays. The X-ray tube Basic X-ray circuit Voltage rectification Physics of X-ray production X-ray energy spectra. The X-ray tube. The anode-- target material:high atomic number and high melting point, Tungsten Copper anode : conduction of heat

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Production of X-Rays

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  1. Production of X-Rays • The X-ray tube • Basic X-ray circuit • Voltage rectification • Physics of X-ray production • X-ray energy spectra

  2. The X-ray tube • The anode--target material:high atomic number and high melting point, Tungsten • Copper anode: conduction of heat • Anode hood: prevent stray electrons from striking the walls or other non-target components;absorbs the secondary electrons (copper shield); absorbs the unwanted X-ray (tungsten shield)

  3. The X-ray tube • The cathode:wire filament, circuit to provide filament current and a negatively charged focusing cup • Cathode cup: direct the electrons toward the anode

  4. Copper shield Tungsten shield Fig. Therapy X-ray tube

  5. Basic X-ray circuit • High-voltage circuit: provide the accelerating potential for the electrons • Low-voltage circuit: supply heating current to the filament

  6. Fig. Self-rectified X-ray unit

  7. Voltage rectification

  8. Fig. The variation with time of the line voltage, the tube kilovoltage, the tube current

  9. Fig. Full-wave rectification

  10. Physics of X-ray production • Bremsstrahlung • Characteristic X-rays

  11. Bremsstrahlung • A part or all of its energy is dissociated from it • An electron may have one or more bremsstrahlung interactions • The bremsstrahlung photon may have any energy up to the initial energy of the electron

  12. Characteristic X-rays • Characteristic radiation are emitted at discrete energies • hv = Ek-El • Ek and Elare the electron binding energies of the K shell and the L shell

  13. X-ray energy spectra (1) • Heterogenous in energy: bremsstrahlung photons superimposed by characteristic radiation of discrete energies • The maximum possible energy that a bremsstrahlung photon can have is equal to the energy of the incident electron

  14. Fig. Spectral distribution of X-ray calculated for a thick tungsten target

  15. IE = KZ(Em-E) • IE : intensity of photons with energy E • Z : atomic number of the target • Em : maximum photon energy • K : constant • IE = 0 when E = Em

  16. X-ray energy spectra (2) • The filtration is to enrich the beam with higher energy photons by absorbing the lower energy components of the spectrum—hardens, higher average energy and greater penetrating power

  17. X-ray energy spectra (3) • Alternating voltage applied to the tube, multiple bremsstrahlung interactions within the target and filtration in the beam • The average X-ray energy is approximately 1/3 of the maximum energy

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