PIXE analysis by means of an external proton beam

To optimize PIXE analysis by means of an external proton beam we determined the minimum detection limits for 14 different exit foils. Influences of geometrical parameters were investigated. One important result of our measurements is that the continuous background yields are nearly independent of the matrix thickness. On that account analysis of thick samples is indispensable for obtaining highest relative detection sensitivity. To evaluate actual concentrations from measured X-ray spectra of thick samples we imagine the samples to consist of thin layers so that the X-ray yields can be computed numerically. The ionization cross-section data used in these calculations are theoretically as well as experimentally determined values. Examples of the application of this technique to the analysis of metals and to the analysis of water, making use of appropriate preconcentration methods are shown. (orig.)