Small X-Ray Tubes for Energy Dispersive Analysis Using Semiconductor Spectrometers

Abstract

Fast X-ray fluorescence analysis with radioisotope excitation requires intense sources to produce reasonable counting rates. The inconvenience of handling such sources and the small number of suitable radioisotopes places severe limitations on their use.

We have explored the possibility of using low-power X-ray tubes as exciting sources for energy-dispersive fluorescence analysis. The principal advantage to X-ray tubes is the ability to produce X-ray fluxes to three orders of magnitude higher than those obtained with convenient radioisotope sources while dissipating only a few watts in the tube. Furthermore, the variety of possible anode materials and range of currents in the tube make possible optimum choice of exciting energy and intensity for particular applications.

We have designed and tested such tubes in a variety of anode configurations suitable for fluorescence excitation. Using either X-ray filtering techniques or multiple fluorescence geometries it is possible to significantly reduce the Brems Strahlung background relative to characteristic radiation.

As compared with noimal radioisotope-target assemblies, excitation of a sample by the X-ray tube results in comparable sensitivity in only a tenth to one hundredth of the time.