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SummaryTo study the distribution of free radicals produced by ionizing radiations in bone, the influence of different parameters (Ca/P ratio, crystalline structure, influence of impurities, molecular weight) on the production and stabilization of free radicals in synthetic apatitic crystals and collagens is investigated at room temperature and − 180°K.Whole bone and fractions of different densities were irradiated in air and in vacuum. The yields of the different types of radicals have been studied. We have shown that(1) the nature of the free radicals in the organic phase depends on the density;(2) the yield in apatite-like radicals increases with the density;(3) bone presents an increase of the radiosensitivity of the collagen and of the radioresistance of the mineral phase as compared with its isolated components;(4) toluene produces radicals in unirradiated bone; the nature and the concentration of these radicals depend on the density.Annealing after irradiation in liquid nitrogen has also been studie...