Applications Analysis of Air Pollution Samples

A matrix of light elements (e.g. plastic, or organic tissue) containing a large number of trace elements constitutes an ideal sample for PIXE analysis, and air pollution samples provide a good example of the technique. 

The sample environment was filled with He gas to prevent the argon X-ray emission from air. Beam scanning, data acquisition, evaluation and the generation of elemental maps were controlled by a computer. Micro-PIXE measurements were performed with a scanning 2.5MeVH+ microbeam accelerated by the 3 MV single-end accelerator. The beam diameter was 1-2 pm, so that individual particles could be analysed. The beam current was 100 pA and the irradiation time was about 3(M0 min. 

More than 20 Si-containing particles are seen to exist within the 25 pm2 area shown. Ca, Fe and Si were found to be the most abundant components in single particles. 

Faiz et al. (1996) have applied micro-PIXE analysis to study solute distributions in a single crystal sample of YiBa2Cu307 5 high temperature superconductor (YBCO) of dimensions 1.3 mm x 1.5 mm x 75 pm. It contained a small secondary crystal overgrowth of dimensions 340 x 340 x 100 pm3. The interface region between the smaller crystal and the base crystal was covered with a material which appeared to be residual flux. The instrument employed a 2.5 MeV focused proton beam of about 4 pm resolution, which could scan an area of 500 x 500 pm2 on the sample surface. The microbeam current was kept low (typically about 30 pA) to avoid any damage to the sample. 

An average compositional spectrum as well as two-dimensional element distribution maps were acquired simultaneously from each scanned area. Line spectra could also be obtained by allowing the microbeam to scan along a line across the crystal face. The authors examined the base crystal, the smaller crystal as well as the interface region. 

---