Matrix effects in PIXE analysis of aerosols and ashes

A comparison of instrumental neutron activation analysis (INAA) and proton- induced X-ray emission (PIXE) results for size-fractionated atmospheric aer osols ("coarse" and "fine" fractions with an equivalent aerodynamic diamete r of 2-10 mu m and < 2 mu m, respectively, or the PM10 fraction) showed tha t PIXE yielded significantly lower results for the PM10 and coarse fraction s, especially for elements with a low Z resulting from a particle size effe ct. Somewhat lower PIXE results were also obtained for the fine fraction of atmospheric aerosols. A correction is also needed for irregularly shaped d eposits of combustion aerosols collected by a cascade impactor in 11 size f ractions ranging from 0.016 to 14.3 mu m, as well as for thick samples of f ly and bottom ashes. An equivalent layer thickness (ELT) model is proposed to correct the matrix effects in PIXE. The approaches for the calculation o f ELT using a comparison of PIXE and INAA results or by comparing PIXE resu lts obtained using two different incident proton beam energies (1.31 and 2. 35 MeV) are described. The correction for the ash pellets and irregular dep osits are also discussed.