I am studying x-ray production by accelerating electrons produced through thermionic emission at a cathode towards an anode.

My textbook says when the anode is at a few thousand volts, the x rays are emitted from the anode surface.

Why does this process produce x-rays? Also, why do we need the anode to be at a few thousand volts?

  • $\begingroup$ What is your x-ray energy? $\endgroup$
    – Jon Custer
    Commented Jun 1, 2017 at 17:23
  • $\begingroup$ @JonCuster The textbook doesn't say. It says the wavelengths of emitted x-rays is between $10^{-9}$ and $10^{-12}$... $\endgroup$ Commented Jun 1, 2017 at 17:24
  • $\begingroup$ And that corresponds to an energy of? $\endgroup$
    – Jon Custer
    Commented Jun 1, 2017 at 17:34
  • $\begingroup$ @JonCuster The textbook does not say. My question is solely about x rays are produced when they hit the anode. $\endgroup$ Commented Jun 1, 2017 at 17:35
  • $\begingroup$ The anode needs to be at several kV to accelerate the electrons to energies of several keV. $\endgroup$
    – user137289
    Commented Jun 1, 2017 at 20:31

1 Answer 1


The electrons undergo deceleration when they hit the anode and emit bremsstrahlung(braking) radiation in the form of X-rays. In addition, you get large peaks for certain energies as the electrons in the anode are excited to the $\ n=\infty$ energy level, and another electron will de-excite to the gap left behind by the electron, emitting an X-ray in the process. The peaks arise as the electrons can only occupy discrete energy levels, unlike the bremsstrahlung which is a continuous spectrum. I believe high voltages are used in order to provide the incident electrons with sufficient energy to produce high intensity X-rays, as the X-rays themselves are also very energetic (from $\ E=\frac{hc}{\lambda}$).


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