The external scanning proton microprobe in Florence: set-up and examples of applications

Abstract

During 2003, at the LABEC laboratory (labec@fi.infn.it), Firenze, Italy, a new 3MV tandem accelerator was installed, mainly for Accelerator Mass Spectrometry (AMS) and Ion Beam Analysis (IBA) measurements. Our system is equipped with a cesium sputtering ion source for AMS and two sources for IBA applications, i. e. a duoplasmatron and a second cesium sputtering; duoplasmatron is usually preferred for micro beam applications, because, working with this source, it is possible to deliver more intense beam on target. The ion beam is focussed by two electrostatic lenses EL1 and EL2 and mass/energy analyzed by a ∼ 90° dipole magnet; beam waist is some 0.4m after the exit port of this magnet. Here a remotely controlled aperture is installed, to allow beam intensity regulation, and a beam profile monitor BPM1, to control shape, dimensions and intensity of the beam as it is transmitted through the slits; it is also possible to measure the beam current after the slits with a Faraday cup (FC1). The beam is then focussed by the electrostatic lenses EL3 and EL4 just at the entrance of the accelerator, where BPM2 allows monitoring proper beam shaping and FC2 is used to measure the current. The beam is then focalized in the high voltage terminal, inside the stripping canal; as the accelerating column has a strong focussing action, at the entrance of the column, a pre-acceleration electrode is installed, so that, increasing the speed of the ions, the particles are less sensitive to the column focussing.