X-Ray Generators - Experimental Control

As stated on the previous page, a user typically has no control over the target material used in the generator, although generators with different materials are available. However, the tube current and voltage are important variables in an XRF experiment.

The current controls the intensity of X-Rays emitted from the generator, and is primarily adjusted to optimize the signal level at the detector.

The voltage has an important effect on the spectral profile of the generator output. With low voltages (eg, 15kV or lower), the bremsstrahlung will be centered at relatively low energies, and the characteristic fluorescence will be restricted to the low energy L (and M) lines. At high voltages (eg, 40kV or above), the bremsstrahlung will be more intense and centered at higher energies, and the characteristic fluorescence will include the high energy K lines of the target material.

The most efficient XRF is stimulated when the incident X-Ray beam lies close in energy to the absorption edge in the element(s) in the sample. Thus, by adjusting the generator voltage it is possible to tune, to some degree, the efficiency of fluorescence in the sample.

The energy of the X-Ray beam also has an strong effect on the penetration of the X-Rays into the sample. The lower the energy, the less penetration. Once again, by adjusting the generator voltage some control is possible over the incident X-Ray beam penetration and hence the sampling depth.