The influence of low‐energy (E∼5 eV per proton) ionizing radiation on predamaged, amorphous SiO2has been studied through the electron spin resonance of oxygen vacancy centers (E’1). It is demonstrated that the observed line shapes can be explained in terms of dipolar broadening. By independent methods, line‐shape fitting, and numerical integration, we extract the defect density as a function of low‐energy irradiation dose and observe significant annealing for doses in excess of 10 J/cm2accumulated. For medium‐energy proton irradiations, contradictory results of line fitting and integration suggest the overall number of defects increases during proton irradiation but the mean defect density decreases (i.e., the defect‐defect spacing increases). The fractional increase in defect numbers is much smaller than that found by others using 1‐MeV electron irradiation.