Synthesis of radioactive, bimetallic nanoparticles was successfully accomplished using the Missouri S&T research nuclear reactor (MSTR). Aqueous solutions of 2 mM gold chloride and 2 mM silver nitrate were prepared and mixed with a solution of 1 mM polyvinylpyrrolidone and 60 mM of 2‐propanol. Four different samples with volume ratios of 70/30, 50/50, 30/70, and 0/100 of Au/Ag were irradiated at a reactor thermal power of 10 kW for 3 min. The morphology, crystal structure, and chemical composition of the resulting nanoparticles were characterized with Transmission Electron Microscopy (TEM), Gatan Microscopy Suite Software and the Java‐based image‐processing program ImageJ. It was found that the structure obtained depended on the composition of the irradiated sample, with production of core‐shell and alloyed nanoparticles obtained at different conditions.