All XRF spectrometers require a source of X-Rays, and these are usually provided by an in situ X-Ray generator, or, less frequently, by a radioisotope material.

A typical X-Ray generator passes an electric current through a filament, which causes electrons to be emitted. These electrons are then accelerated by high voltage (usually somewhere between 20 and 100kV) towards an anode (target). The deceleration of the electrons when they hit the anode causes a broad X-Ray continuum to be emitted. This radiation is known as bremsstrahlung (German: braking radiation). In addition, a fraction of the electrons will cause characteristic X-Ray fluorescence from the anode material.

Thus, the X-Ray emission from a generator will comprise both the broad, relatively weak bremsstrahlung, overlaid with very intense and sharp characteristic fluorescence lines from the target material.

A thin beryllium window is used to allow the X-Rays out of the generator, and onto the sample.