[en] The effects of ⁶⁰Co gamma radiation on the mirror surfaces of nickel deposited glass plates, which were planned to be used as the neutron guide tubes in the upgraded JRR-3, were examined by visual tests, surface flatness measurements and X-ray diffraction. After irradiation at a dose of 10⁸ rad in air atmosphere, a good number of small spots were seen on the mirror surface. In the case of 10⁹ rad irradiation in air atmosphere the spots were enlarged and a few new peaks were observed in the X-ray diffraction patterns. On the other hand, in vacuum and helium atmosphere, the nickel deposited mirror surfaces were not changed appreciably, even after irradiating to 10⁹ rad. (author)