Continuous X-ray spectrum

Last revised by Lachlan McKay on 14 Mar 2024

The continuous X-ray spectrum refers the range of photon energies produced in an X-ray tube due to the properties of Bremsstrahlung radiation.

The energy of X-ray photons can take a value from zero to the maximum kinetic energy of the incident electrons.

Both the continuous X-ray spectrum and the characteristic peaks specific to the absorber will contribute to the total X-ray spectrum.

Factors

  • kilovoltage peak (kVp): increases kVp not only causes an increase in maximum photon energy, but it also increases the number of photons produced 3,4

  • voltage waveform: reducing voltage ripple increases the yield of high-energy photons where maximum photon energy remains unchanged 2,4

  • anode angle: increasing anode angle reduces absorption length of the X-ray spectrum (see anode heel effect), thus increasing the yield of high energy photons where maximum photon energy remains unchanged 2

  • filtration: results in X-ray spectrum hardening and reduction in tube output 2,4.

  • tube current does not affect the distribution of photon energies but photon intensities increases proportionally with mAs 2,5.

  • anode materials: different anode materials such as tungsten, molybdenum, and rhodium produces different x-ray spectra 3

  • anode roughness: over an operational lifetime of an X-ray tube, anode surface will become rougher. This causes a slight increase in X-ray filtration, causing X-ray spectrum hardening

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