Comparative experiments on the formation and annealing of radiation defects in float-zonen-Si (ρ0≃200 ω cm) irradiated with 8600 MeV protons or 60Co γ-rays were carried out. From the analysis of the temperature dependences of the Hall coefficient the values of the activation energy δEof radiation defect ionization are determined. The annealing character and nature of radiation defects with close values of δEare found to be dependent on the kind of irradiation. The results obtained are discussed taking into account the radiation defect formation mechanism for the kinds of irradiation used and the influence of the potential barrier Ψ of proton-produced defect clusters on the value of δEfor defects localized in clusters (δE= δE— Ψ, where δEis the radiation defect ionization energy). Proton-irradiation-produced radiation defects with δE=Ec— 012 eV (annealing temperature range 200–300°C) are concluded to represent planar tetravacancies (Si-A3 centres) whose ionization energy is δE≃Ec— 0.23 eV, localized in the central region (the core) of the defect cluster.