The radiation decomposition of pure CO2 in the absence of added scavengers has been studied at high dose rates using protons from a Van de Graaff accelerator. Primary decomposition yields G(CO)= 4.25±0.25 and G(O2)= 2.24±0.1 have been measured in a fast flow system. Irradiations under static conditions have shown that these yields are obtained when the concentrations of products in the irradiated gas are < 4% of the relevant steady-state concentrations. Supporting work on the 14CO/CO2 radiation-induced exchange reaction confirms these primary yields and demonstrates the importance of a species derived from molecular O2 in initiating the radiation-induced back reaction involving the oxidation of CO.