Conceptual challenges and computational progress in X-ray simulation

Recent developments and validation tests related to the simulation of X-ray fluorescence and PIXE with Geant4 are reviewed. They concern new models for PIXE, which has enabled the first Geant4-based simulation of PIXE in a concrete experimental application, and the experimental validation of the content of the EADL data library relevant to the simulation of X-ray fluorescence. Achievements and open issues in this domain are discussed.