Measuring Pu Isotope Ratios with Mass Spectrometry

INTRODUCTION Anthropogenic plutonium has been introduced into the environment over the past 50 years as the result of the detonation of nuclear weapons and operational releases from the nuclear industry. In the Arctic environment, the main source of plutonium is from atmospheric weapons testing, which have resulted in a relatively uniform, underlying global distribution of plutonium. Other releases can give rise to enhanced local or regional concentrations, such as from underwater weapons tests, reactor accidents, and dumped radioactive waste. Nuclear installations discharging waste to marine (e.g., Sellafield) and terrestrial waters (e.g., Mayak, Tomsk-7, Krashnoyarsk) represent an additional long-range source. Plutonium isotope ratios are known to vary with reactor type, nuclear fuel-burn up time, neutron flux, and energy, and for fallout from nuclear detonations, weapon type and yield. Weapons-grade plutonium is characterized by a low content of the Pu isotope, with Pu/Pu isotope ratio less than 0.05. In contrast, both global weapons fallout and spent nuclear fuel from civil reactors have higher Pu/Pu isotope ratios (civil nuclear power reactors have Pu/Pu atom ratios of between about 0.2-1). Thus, different sources often exhibit characteristic plutonium isotope ratios and these ratios can be used to identify the origin of contamination, calculate inventories, or follow the migration of contaminated sediments and waters (Oughton et al. 2000; Oughton et al. 2004; Skipperud et al. 2004).