Development of the RMIT external beam facility for PIXE

Abstract

An external Proton Induced X-Ray Emission (PIXE) facility for the 1 MV Tandetron accelerator based at Royal Melbourne Institute of Technology has been developed. The facility uses a 0.35 mm diameter focused beam of 1.6 MeV protons which are extracted from the vacuum through an 8 μm Kapton foil coated with a 20 nm thick layer of gold on both sides. The proton beam reaches the target traversing 13.5 mm in air. For quantitative analysis, the number of protons hitting the target was determined by the number of backscattered protons from the inner layer of gold on the window foil detected using an annular detector sitting behind the window. Calibration of the rate of protons backscattered from the gold layer was performed using the PIXE signal from a pure nickel standard. Radiation damage causes the Kapton vacuum window to exhibit increasing inward diffusion of air. This provides an excellent mechanism for determining the need to replace the window foil before it ruptures. The facility has been used to make non-destructive quantitative measurements of the composition of samples from the Museum of Victoria.