X-Ray Generators - Target, Current and Voltage

The target material, filament current and accelerating voltage all have significant effect on the final output of an X-Ray generator.

Target (anode)

The target material is a fixed component of the generator – generators with different target materials are available (eg, Mo, Rh, W), but these are not switchable within a single generator unit. A key part of the generator’s output is formed from the characteristic X-Ray Fluorescence of the target material. Since the fluorescence yield increases with atomic mass, increased output at a set voltage/current will be seen by using higher atomic mass target materials. In addition, the energies of the fluorescence lines will vary depending on the material used, and as a result different target materials can result in more or less efficient excitation of particular elements in the sample.

Current

The filament current controls the number of electrons bombarding the target material. As a result, the current directly impacts on the X-Ray output intensity for both the bremsstrahlung and characteristic radiation.

Voltage

The bremsstrahlung radiation displays a high energy cut off, since the energy of the radiation cannot exceed the applied voltage. By changing this voltage, the bremsstrahlung cut off (and overall continuum profile) can be modified. The characteristic radiation from the anode material can only be generated when the accelerating voltage (and hence, the energy of the impinging electrons) lies above the absorption edge for that material. Thus, if the voltage is reduced to below the absorption edge, the characteristic line(s) will no longer be present.