The basic premise of XRF is that high energy x-rays are aimed at a sample and then the atoms in the sample may absorb an x-ray. This ionizes the atom by displacing an electron from one of the shells close to the atom. The next step is for an electron from an outer shell to fall into the shell vacancy, emitting the excess energy in the form of characteristic x-ray radiation. The energy of the x-ray is dependent on the energy levels of the shells participating in the process and therefore is “characteristic” to the material of the sample. A critical detail for the x-ray source used for XRF is that x-ray source needs to produce x-rays at energies higher than absorption edge of the element in order to ionize the atom. Every element has different absorption edges, just as they have different characteristic x-ray lines. The x-ray source needs to be tuned in various ways for effective detection of different elements. There are three basic methods for tuning the spectrum-shape from the x-ray source: • Setting the high voltage on the x-ray tube. • Putting an x-ray filter between the x-ray source and the sample. • Selection of the anode material on the x-ray tube. This report will focus on the selection of the anode material on the x-ray tube. For additional information about setting the high voltage or selecting a filter please go to www.moxtek.com and select the “Consult our Experts” option in the bottom right of the page.