Résumé
In this communication devoted to the prompt emission of GRBs, we claim thatsome important parameters associated to the magnetic field, such as its indexprofile, the index of its turbulence spectrum and its level of irregularities,will be measurable with GLAST. In particular the law relating the peak energyEpeak with the total energy E (like Amati's law) constrains the turbulencespectrum index and, among all existing theories of MHD turbulence, iscompatible with the Kolmogorov scaling only. Thus, these data will allow a muchbetter determination of the performances of GRBs as particle accelerators. Thisopens the possibility to characterize both electron and proton accelerationmore seriously. We discuss the possible generation of UHECRs and of itssignature through GeV-TeV synchrotron emission.