Duane–Hunt law

The Duane–Hunt law, named after the American physicists William Duane and Franklin L. Hunt, gives the maximum frequency of X-rays that can be emitted by Bremsstrahlung in an X-ray tube by accelerating electrons through an excitation voltage V into a metal target.

The maximum frequency ν_max is given by

${\displaystyle \nu _{\rm {max}}={\frac {eV}{h}},}$

which corresponds to a minimum wavelength

${\displaystyle \lambda _{\rm {min}}={\frac {hc}{eV}},}$

where h is the Planck constant, e is the charge of the electron, and c is the speed of light. This can also be written as:

${\displaystyle \lambda _{\rm {min}}\approx {\frac {1239.8\,\mathrm {kV{\cdot }pm} }{V{\text{ in kV}}}}.}$

The process of X-ray emission by incoming electrons is also known as the inverse photoelectric effect.