Real-time Raman scattering measurements are performed during and after 3keV-He+ irradiation at sample temperature from room temperature to 573 K. The time dependence of relative intensity of the disorder-induced peak with respect to the original Raman active E2g2 mode peak shows that thermal relaxation of defects created by irradiation. Fast and slow processes exist in the thermal relaxation, the corresponding activation energies being 0.89±0.10 eV and 1.8±0.3 eV respectively.