The external beam microprobe facility in Florence: Set-up and performance

An external beam microprobe facility, based on a quadrupole doublet supplied by Oxford Microbeam Ltd, has been installed on a new beamline at the 3 MV single-ended Van de Graaff accelerator in Florence. The goal was to obtain a beam with a spot size on target of 10–20 μm and a current in the order of at least 1 nA, in order to allow PIXE, PIGE and RBS elemental analysis in air or in a helium atmosphere. The beam was extracted from the vacuum lines through a 0.1 μm thick Si₃N₄ window to minimise lateral straggling. The design goals have been successfully achieved; the measurements of the beam spot characteristics in vacuum as well as in air and in helium atmosphere, are here reported.