How the sensitivity in PIXE elemental analysis is affected by the type of particle, cross-sections, background radiation and other factors?

The purpose of this paper is to review the relevant factors to be taken into account to obtain a more sensitive PIXE (Particle induced X-ray emission) elemental analysis. In quantitative PIXE analysis, matrix effects become a fundamental factor. Depending on the analyzed element, the projectile particle type and its energy, material composition can have a major effect on the X-ray yields. Background in the X-ray spectrum, detection limits, particle stopping powers and X-ray photons attenuation, should be considered. Also the ionization cross-sections could be affected by the previous state of the projectile, conditioned by the passage in the material producing multiple ionizations and changes in its state of charge. A variety of experimental results and theoretical models, are analyzed here for protons, deuterons and heavier incident ions.