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Basic Radiation Physics
Energy Conversion and Generation of X-rays

Course Author(s): Hassem Geha, DDS, MDS, Diplomate of the ABOMR

Energy Conversion and Generation of X-rays

When an electron traveling at high speed strikes a target atom, it will be slowed or completely stopped by the gravitational forces of that atom (Figure 1). Based on the law of conservation of energy, the kinetic energy of the incoming electron cannot be lost and must be absorbed by the atom or converted to another form of energy. About 99% of this kinetic energy will be converted into heat and the remaining will be converted to a radiating energy that is known as x-ray.2,3,4,5,6

Figure 1. An electron traveling at high speed and abruptly slowed down or stopped. The kinetic energy will be converted to heat and radiation.
An electron traveling at high speed and abruptly slowed down or stopped. The kinetic energy will be converted to heat and radiation.

If the electron is completely stopped by the gravitational forces of an atom, the x-ray energy will be equal to the total kinetic energy of the electron. The electrons that are not completely stopped will interact with new atoms in a similar fashion to produce more radiation but at lower energy levels. This will result in a continuous spectrum of x-rays varying from very low energies to very high energies (Figure 2).7

Figure 2. Theoretical x-ray spectrum before filtration. There are more low energy photons than high energy photons.
Theoretical x-ray spectrum before filtration. There are more low energy photons than high energy photons.
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