Trace americium contamination sources in the environment can be detected using 243Am/241Am

Abstract Despite the widespread presence of americium in the environment since the 1950s from nuclear activities, the use of americium isotopic composition to trace contamination sources has not been investigated. Here we report the detection of 243 Am in environmental samples and demonstrate that the ratio of 243 Am to 241 Am can serve as a distinctive fingerprint of radioactive emissions, with characteristic values of 0.05 for thermonuclear explosions, 0.023 for global fallout, below 0.0015 for low-yield nuclear tests, and 0.0013 for releases from a nuclear reprocessing facility. In nuclear detonations, 243 Am is produced as the decay product of 243 Pu. The ratio of 243 Am to 239 Pu in global fallout is about 3.2 × 10⁻⁴, supporting the predicted formation of neutron-rich heavy plutonium isotopes during nuclear detonations.