Comparison Between XRF and PIXE Techniques

The penetration depths and irradiation areas are totally different in PIXE and XRFS. In XRFS penetration depths are relatively large, of the order of a few millimeters while in PIXE analysis, the analytical depths are ss 10-50 pm because of the limited penetration of particles into the sample. Therefore PIXE analysis is essentially a surface technique even when applied to thick samples. 

In PIXE analysis, using proton beam of 1-3 MeV for most favored elements in low-Z matrices and think targets, the best sensitivities down to 0.1 ppm have been obtained. These levels are achieved for elements near Z = 40 using K lines and Z = 80 using L lines. For elements with Z valves different from 40 and 80 the LLDs increase rapidly to 100 ppm and are 100 ppm for Z 20. For thick targets and Z 20 most matrices yield LLDs that are generally lower than 100 ppm and can be as low as 1 ppm under favorable conditions (absolute detection limits down to 10 g and relative detection limit down to 0.1 p.gg ). Compared to XRF, the detection limit offered by PIXE is better by one order of magnitude. 

Similar LLDs are found in XRFs although LLDs for Z 20 are very much lower than those attainable by PIXE. Using WDXRF it is now possible to obtain LLDs in the range of 50-200 ppm for elements F through B. 

Since the equipment used in XRF technique including radioisotope source is portable, the energy dispersive XRF spectrometers are used in various divergent fields like that in the metal industry, in gold mines, in oilfields for oil analysis (to determine sulfur in petroleum products and residual catalysts, monitor additives in lubricating oils, analyze regular wear metal in lubricants 

Some specific problems undertaken include location of heavy metals in soil specimens due to application of sewage sludge, trace element profiling in electrical insulators, analysis of air particulate collected at urban locations, multilayer thin film analysis of solar cells. 

---