DEVELOPMENT OF THE RMIT EXTERNAL-BEAM FACILITY FOR PIXE

An external Proton Induced X-Ray Emission (PIXE) facility for the 1 MV Tandetron accelerator based at Royal Melbourne Institute of Technolog y has been developed. The facility uses a 0.35 mm diameter focused bea m of 1.6 MeV protons which are extracted from the vacuum through an 8 mu m Kapton foil coated with a 20 nm thick layer of gold on both sides . The proton beam reaches the target after traversing 13.5 mm in air. For quantitative analysis, the number of protons hitting the target wa s determined by the number of backscattered protons from the inner lay er of gold on the window foil detected using an annular detector sitti ng behind the window. Calibration of the rate of protons backscattered from the gold layer was performed using the PIXE signal from a pure n ickel standard. Radiation damage causes the Kapton vacuum window to ex hibit increasing inward diffusion of air. This provides an excellent m echanism for determining the need to replace the window foil before it ruptures. The facility has been used to make non-destructive quantita tive measurements of the composition of samples from the Museum of Vic toria. (C) 1998 Elsevier Science B.V.