Grazing-exit particle-induced X-ray emission analysis with extremely low background

The grazing-exit technique is applied to particle-induced X-ray emission (PIXE) analysis of thin-films and aerosols deposited on fiat silicon wafers. PIXE is known as a trace-analytical method; however, Bremsstrahlung background is still important in the low-energy region. A 2.5 MeV proton beam bombarded the sample at an incident angle of 90°, and the emitted X-rays were detected at grazing exit angles by using an energy-dispersive detector. When the characteristic X-rays were measured at grazing exit angles, this background almost disappeared. The characteristic X-rays of Ca Kα and Zn Kα emitted from atmospheric particles could hardly be observed by PIXE in the normal arrangement; however, they were clearly observed with low background under grazing-exit conditions. The detection limit for Ca was improved by a factor of 7. It is also demonstrated that analysis of the topmost layer and depth analysis for double-layered samples are both possible by adjusting the exit angle. Consequently, grazing-exit PIXE is a promising method for surface-, micro-, and trace analysis.