I had already set the SYSTEM right. At proceeding, I used the 5.7 MeV alpha as the GunParticle,and we can see the elecronics ionizing from the Target. But I can't find any Fluorescence X-rays.
The problem is not related to Xray_Fluorescence example, but is related to Geant4 Low energy hadrons ionization process. In fact, at the moment, Fluorescence emission is not available for alpha particles but only for protons. Alf