Abstract : Radiation chemical primary yields g(H2) have been determined for irradiations performed with 60Co γ-rays source of LCP (Orsay, France) and with helium ion beams (Eα=5.0 MeV-64.7 MeV) using protective agent bromide anions in solution. The α (4He2+) irradiation experiments were performed either at CEMHTI or at the new ARRONAX cyclotron facility (2010). Both sources (γ and cyclotrons) allow working with a large LET value range between 0.23 and 151.5 keV/μm. On one hand, the obtained results have been compared with those available in the literature and plotted as a function of the LET parameter in order to discuss the effects of track structure on the production of molecular hydrogen. On the other hand, the primary radiation chemistry yield g(H2) values are compared with global radiation chemical yields G(H2) obtained during irradiations of pure water irradiated under air or argon without scavenging. For each system, it appears that radiation chemical yields increase with the LET value. Our results suggest that using bromide anions, at low concentration, as a protective agent becomes ineffective when the LET value used is higher than 120±20 keV/μm.