Ge 1−x Si x solid solutions are one of promissing materials for semiconductor technique. However, their electrical and optical properties, especially with silicon content more than 5 at. % have been little studied. In particular, in the number of works [1-3] there have been presented the experimental results of study in the region 0.52 eV in germanium irradiated by fast electrons, gamma-rays and protons at the temperature of liquid nitrogen. In the literature, however, there are no data on studying the absorption band in the range 0.52 eV in Ge 1−x Si x solid solution irradiated by fast electrons.