Thermally stimulated transformation of the EPR spectra in γ-irradiated bone tissue

γ-irradiated bone tissue annealed at different temperatures is studied by EPR. In powder samples the annealing-induced changes of the EPR spectra are mainly determined by sharp growth of a signal caused by the products of thermal decay of an organic component in the tissue. This signal considerably complicates the analysis of the EPR spectrum shape for the annealed samples. On the other hand, in the spectra of the plates of bone tissue a change in the lineshape of the EPR signal from CO2- radicals after annealing is more pronounced than in powder, and it is attributed to the change in the contributions from axial and orthorhombic CO2- radicals. The analysis of different radicals concentrations vs. annealing temperature revealed above 210 deg. C the temperature-induced transformation of orthorhombic CO2- radicals into axial ones in bone tissue which (together with organic component) is responsible for the changes of EPR lineshape at annealing.