Photons have a small magnetic field


Structure of an X-ray tube

The electrons emitted by a hot cathode are in the electric field between the cathode and anode by the Acceleration voltage UB. accelerated and strongly decelerated when hitting the anode. This creates X-rays (bremsstrahlung).

X-rays can be similar to radioactive radiation with one Counter tube be detected. The "cracking" of the counter tube can be seen:

X-rays give off their energy like (visible) light in quanta.

On the other hand, X-rays show interference phenomena on regular crystal structures (→ see Bragg reflection). Like visible light, X-rays have both wave and particle properties.

X-ray spectrum

If one examines the X-rays produced in the manner described above, one finds that the radiation is not monochromatic, but consists of many different wavelengths

If one plots the intensity of the resulting X-ray radiation as a function of the wavelength, the following diagram results:

So there is a continuous Spectrum that begins at a certain wavelength. Below this Cutoff wavelength no radiation is emitted.

The cut-off wavelength is smaller, the greater the anode voltage (i.e. the greater the kinetic energy of the electrons). She hangs Not from the anode material.

The following diagram shows the spectra for different anode materials with the same acceleration voltage:

X-ray spectra for various anode materials

The cutoff wavelength depends Not from the anode material.

The cutoff wavelength depends only on the Accelerating voltage from:

X-ray spectra for the anode material tungsten at different acceleration voltages

These relationships can hardly be explained plausibly with wave theory and support the quantum hypothesis.

The electrons get their energy from the electric field. The kinetic energy of the electrons thus corresponds to the energy of the electric field:


Each decelerated electron generates exactly a X-ray photon. The electrons give up different proportions of their kinetic energy.

The resulting X-ray photon can therefore have at most the same energy that an electron had before it was slowed down.


This results in the Cutoff wavelength

This consideration is confirmed by the measurement results.

In addition to the continuous bremsstrahlung, there is another one that depends on the anode material characteristic radiation.

However, this can only be understood with the internal structure of the atoms in the anode material. You can find more about this in the chapter about Atomic physics.