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Continuous X-ray spectrum
Intermediate
Bremsstrahlung with a cut-off wavelength.
λ_min = hc/eVElectrons slowing in the target emit bremsstrahlung with a continuous spectrum and a sharp minimum wavelength λ_min = hc/(eV), independent of the target.
30 kV tube: λ_min = 0.041 nm.
Depends on tube voltage, not current.
In more detail
The continuous X-ray spectrum is produced when fast electrons decelerate in a target, emitting a range of wavelengths. It has a sharp short-wavelength cut-off set by the electron energy.
Real-world uses
- X-ray tubes use this continuous spectrum for imaging.
- The cut-off gives the maximum photon energy.
- Hospitals and X-ray tube designers use the cut-off wavelength to set the maximum energy of the emitted X-rays.
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Frequently asked questions
What sets the cut-off?
The maximum electron kinetic energy, equal to eV divided by the photon energy.
Why is it continuous?
Because electrons lose energy in many different ways during deceleration.
What sets the minimum wavelength?
The accelerating voltage: the most energetic photon can carry at most the energy of an electron through that voltage.
Related topics in Atomic & Nuclear Physics
Ionisation energy · Franck–Hertz experiment · Characteristic X-rays · Moseley's law · X-ray diffraction · Electron configuration