HEIDELBERG PROTON MICROPROBE

A microprobe facility capable of focussing proton beams to a spot size of 2 ωm × 2 ωm has been constructed and installed at the 6 MV tandem Van de Graaff accelerator of the Max-Planck-Institut. The beam profile is rectangular with current densities from 5 to 20 pA/ωm2 for initial beam currents between 0.3 and 1 ωA. This facility has been used so far for chemical analyses of small grains (∼ 100 ωm diam.) of minerals via proton-induced X-ray emission (PIXE). The proton microprobe compares favourably to the electron microprobe, in particular for analysing trace elements whose concentrations are below the detection limit of the electron microprobe. Also, it is possible to analyse structurally complex objects with numerous trace elements spanning a wide range of atomic numbers. The application of the proton microprobe to mineralogical studies is demonstrated here, but the technique is now being extended to problems in molecular biology. © 1978.