Abstract: A method to synthesize radioactive nanoparticles includes the production of metallic and multimetallic nanoparticles in a single step by providing an aqueous solution of the metal precursor, and irradiating the aqueous solution thereby producing nanoparticles. The obtained nanoparticles include one or more radioactive isotopes of gold, such as 198Au and 199Au as well as radioisotopes of silver when the obtained nanoparticles are bimetallic. The aqueous solution is irradiated in a radiation field that includes neutrons and gamma rays. The radiation field may be provided by a nuclear reactor. The aqueous solution may include silver, and bimetallic nanoparticles may be produced. Duration of the irradiation time is selected to control the particle size distribution of the produced nanoparticles. The bimetallic nanoparticles can include core-shell nanoparticles and alloyed nanoparticles.