X-Ray Generation

So far our discussion has been primarily centered around radioactive elements, the structure of the atom, and the phenomenon of radioactivity. As mentioned earlier, another type of radiation commonly utilized is X-radiation. Where as gamma radiation is one of the products of nuclear decay of radioactive elements, X-rays are produced in high voltage electron tubes. You will recall from the history section that W.C. Roentgen discovered X-rays in the late 1800's while working with a cathode tube in his lab. X-rays can be produced in parcels of energy called photons, just like light.

How do you generate an X-ray?

To generate X-rays, we must have three things. We need to have a source of electrons, a means of accelerating the electrons at high speeds, and a target material to receive the impact of the electrons and interact with them.

Why do we need electrons to produce x-rays?

X-rays are generated when free electrons give up some of their energy when they interact with the orbital electrons or nucleus of an atom. The energy given up by the electron during this interaction appears as electromagnetic energy known as X-radiation. There are two different atomic processes that can produce x-ray photons. One is called Bremsstrahlung and the other is called K-shell emission. X-rays produced by Bremsstrahlung are the most useful for medical and industrial applications.

What is bremsstrahlung?

Bremsstrahlung is a German term that means "braking rays." It is an important phenomenon in the generation of X-rays. In the Bremsstrahlung process, a high speed electron traveling in a material is slowed or completely stopped by the forces of any atom it encounters. As a high speed electron approaches an atom, it will interact with the negative force from the electrons of the atom, and it may be slowed or completely stopped. If the electron is slowed down, it will exit the material with less energy. The law of conservation of energy tells us that this energy cannot be lost and must be absorbed by the atom or converted to another form of energy. The energy used to slow the electron is excessive to the atom and the energy will be radiated as x-radiation of equal energy.

If the electron is completely stopped by the strong positive force of the nucleus, the radiated x-ray energy will have an energy equal to the total kinetic energy of the electron. This type of action occurs with very large and heavy nuclei materials. The new x-rays and liberated electrons will interact with matter in a similar fashion to produce more radiation at lower energy levels until finally all that is left is a mass of long wavelength electromagnetic wave forms that fall outside the x-ray spectrum.