Typical X-ray Spectra by Anode Material

Summary

Oxford Instruments offers X-ray tubes with different anode materials designed to suit a wide variety of applications. The anode material defines an X-ray tube’s characteristic spectrum. This application note shows the typical spectra of several different anode materials. The spectra provided are for reference only; your spectrum may differ from these according to the particular model of detector you are using, the geometry of your measurement setup, and the voltage and current on your X-ray tube.

X-ray Spectrum Theory

X-ray production involves bombarding a metal target in an X-ray tube with high-speed electrons that have been accelerated by tens to hundreds of kilovolts of electric potential. The electrons can eject other electrons from the inner shells of the atoms of the metal anode. Those vacancies will be filled when electrons drop down from higher energy levels and emit X-rays. These are known as characteristic X-rays and they have sharply defined energies associated with the difference between the atomic energy levels of the anode atoms. The Bohr atomic model predicts the energies of the characteristic X-rays. An X-ray spectrum is partially defined by the “peaks” or “lines” that result from bombarding different anode materials with highly accelerated electrons.

In addition to the characteristic peaks, an X-ray spectrum also has a background radiation pattern called the “Bremsstrahlung.” Bremsstrahlung means “braking radiation” and describes the radiation that is emitted when electrons are decelerated through a metal anode. The deceleration leaves behind excess energy, some of which is emitted in the form of radiation. Decelerated charges give off electromagnetic radiation, and when the energy of the electrons is high enough, that radiation is in the X-ray region of the electromagnetic spectrum.

Thus, the X-ray spectrum that is emitted from your X-ray tube is a combination of the characteristic peaks of the specific anode material and the Bremsstrahlung radiation that is present in all X-ray tubes.

Experimental Setup

The following spectra were gathered by pointing Oxford Instruments X-Ray Technology’s tubes directly at an Amptek model XR-100CR Si-PIN photodiode detector system. There are a total of approximately one million counts in each spectrum.