Abstract Radiation damage due to synchrotron radiation has been studied at the boundary of cooling metals; aluminum alloys, A2219 and A6063; stainless steel 316L and SO 2 film about 10 micro thick on the inside of an aluminum alloy pipe. The damage was evaluated utilizing dissolved ion density of the irradiated sample water from the pure water circulating system. At 1000 h operating time (∼ a time integrated beam current of 6 Ah, ∼ 3.5 × 10 22 photons) for Al and Si, and at 1700 h (10 Ah, 4.8 × 10 22 photons) for stainless steel), the dissolved ion densities are: Ni of the order of 1 mg l −1; Fe of the order of 0.1 mg l −1 and Cr of the order of 0.01 mg l −1 from the stainless steel: Si from SiO 2 film and Alfrom aluminum alloys of the order of 0.1 mg l −1. The data showed that these materials are suitable for vacuum chambers and components exposed to synchrotron radiation and cooling water. The order of magnitude of the dissolved ion density approximately coincides with that of the free energy of the formation of the oxides. SiO 2 coating film functions as a protecting film from the dissolving Al ions. The oxides or hydroxides on the aluminum alloys and stainless steel also function as protecting films from the dissolving ions of the base materials. The stability of the oxide film is higher than that of hydroxide. Therefore oxide film coating, not hydroxide film, is necessary to obtain the stability of the base material against irradiation.