A high energy (a few MeV) proton beam is directed at the sample. The protons cause electrons within the atoms of the target to be excited from core shells. The X-rays emitted when electrons fall back into the core hole can be used to identify each element within the sample. Scanning the proton beam across the surface enables maps of the concentration of each element to be acquired. X-ray detection is by Si(Li) detector (see EDX). An advantage of PIXE over other methods is its speed and sensitivity.