[en] A mixture of hydrogen (H₂) and carbon dioxide (CO₂) was irradiated with γ-rays from a cobalt-60 source. The molar ratio of H₂ to CO₂ was 4.0, the pressure of the mixture 9.0 kg/cm² gauge at 30⁰C, the temperature 50⁰ - 450⁰C, the dose rate 8.34 x 10⁵ rad/hr, and the total dose 20 Mrad. Carbon monoxide (CO), methane (CH₄), and ethane (C₂H₆) were observable as the main products. The G-values for formations of CO, CH₄, and C₂H₆ were 0.24, 0.25, and 0.03 at 100⁰C, and increased to 27.7, 2.1, and 1.9 at 450⁰C, respectively. The G-values were calculated from the yields after subtracting the yields due to the pure thermal reactions from the ones of the reactions under γ-irradiation. The activation energies of the G-values were 4.8, 0.0, and 0.0 kcal/mol below 200⁰C, and 11.3, 6.7, and 15.7 kcal/mol above 250⁰C for formations of CO, CH₄, and C₂H₆, respectively. The boundary temperatures at which the activation energies changed were estimated to be 240, 221, and 239⁰C for the respective products. On the basis of these results, the temperature dependence of the radiation effect in the reaction of H₂ with CO₂ is discussed. (author)