The Duane -Hunt law (including Duane - Hunt 's displacement law and inverse photoelectric effect ), named after the American physicists William Duane and Franklin Hunt, describes the relationship between the acceleration voltage of an X-ray tube and the maximum frequency or the minimum wavelength of their bremsspectrum. Since X-ray electron radiation (photons) emit, instead receive as in the photoelectric effect, the law is referred to as "inverse photoelectric effect."
The maximum energy that can donate an electron in an X-ray tube, is its kinetic energy it has received in acceleration. There the energy conservation is now recognized.
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After frequency converted this gives: For maximum frequency heard the minimum wavelength of the Planck's quantum of action, speed of light, the acceleration voltage and the elementary charge.
Substituting the constants of nature into the equation, the following relationship for the minimum wavelength:
For a given voltage of the X-ray tube so the minimum possible wavelength of the brake spectrum can be determined.
The picture to the Bragg angle, which depends directly on the wavelength is plotted against the intensity of the radiation. Where the intensity is 0 ( at about 10 ° ), the wavelength of X-rays is minimal. By increasing the voltage, then the zero crossing of the name moves further to the left, so displacement law.