The in-vacuum PIXE setup is shown in the figure below. The sample is bombarded with a proton beam with energy of 2.4 MeV and a few nA of current, which induces the emission of characteristic X-rays. For X-ray detection, two refrigerated Si(Li) detectors are used, both with X-ray absorbers to avoid the entrance of scattered protons into the detector and also to optimize the experimental conditions.