Radioactive Particles from a Range of Past Nuclear Events: Challenges Posed by Highly Varied Structure and Composition

Abstract

While they have appeared only recently in geologic time scales, radioactive particles from anthropogenic sources are widespread in global environments and present radiological harm potentials to living organisms. Exposure potentials vary greatly, however few studies examine a wide range of source and particle types. Here we compare a varied set of particles from past nuclear fission and non-fission sources in Australia of highly diverse magnitudes, release modes, and environments. The radiochemistry and microscopy methods revealed that numerous radioactive particles persist in soils 60+ years after their release events. The particles formed with Si- and Ca-dominant protective coatings persist in corrosive environments (e.g., marine), where those with exposed Fe matrices have dissipated and released their radionuclides. Particles can be distinguished by their Ca/Fe and Si/Fe elemental ratios, which in this study range over orders of magnitude and reflect the materials available during individual formation events. The particles from nuclear testing have dominant 239+240Pu activity concentrations, relative to 90Sr and 137Cs, which increases radiological hazard if inhaled or ingested and contrasts with particles from nuclear power accidents (e.g., Fukushima). Internal fracturing is more prevalent than previously reported, and fracturing is greater in Ca-rich vs. Si-dominated matrices. The fractures often form connective pathways from the interior to exterior surfaces, increasing the potential to leach radionuclides into a host organism or the environment. Additional physical/chemical/radiological measurements are needed to fully understand long-term fate and hazard potentials.

Keywords: radiological hazards, nuclear weapons tests vs nuclear power accidents, plutonium, strontium, ceasium: fallout debris, hot particles