15:30 〜 15:45
[MAG33-05] Characteristics of radioactive particles from 1950s nuclear testing legacy sites in Australia
★Invited Papers
キーワード：radioactive particles from fission events, radiological and stable element composition, nuclear tests vs nuclear power accidents, fallout characteristics
The legacy sites in Australia from the 1950s former British nuclear testing program contain radioactive particles that present ongoing environmental monitoring and management challenges. Meeting these challenges with success requires knowledge of particle characteristics. We gathered particle samples originating from fission and non-fission tests of varying energies (<< 1kt to ~100 kt) and that were configured as tower, ground-surface, air bursts and ship detonations. The particles had interacted with soils and waters for decades in varying arid desert and marine environments. We interrogated whole particles, as well as polished interior surfaces using multiple microscopy methods, accelerator mass spectrometry and conventional radiochemistry.
Our findings confirm that large numbers of radioactive particles are persistent in soils near their sources and that their characteristics relate to both source (detonation type) and environment. Particle sizes varied significantly, spanning orders of magnitude in diameter. Surface coatings were present on some, but not all particles. Fissures were present inside all particles and many of these connected pathways from the interior to the exterior surfaces, suggesting a strong role in the potential for leaching of radionuclides into the environment. The size, number and nature of the fissures varied and related mainly to the composition of the dominant formation materials (e.g., island soils, tower and ship metals). Composition was distinguished by Ca/Fe and Si/Fe elemental ratios with greater fracturing in high-Ca content particles and less in particles from Si-dominated settings. In all study particles, the actinide activity concentrations were dominant, which contrasts with the particles from the nuclear power accident at Fukushima, which were 137Cs-dominated and had only minute amounts of Pu isotopes. However, some similarity exists between the isotopic “fingerprints” of the early Australian tests and that from the 1945 Nagasaki detonation.
Our findings confirm that large numbers of radioactive particles are persistent in soils near their sources and that their characteristics relate to both source (detonation type) and environment. Particle sizes varied significantly, spanning orders of magnitude in diameter. Surface coatings were present on some, but not all particles. Fissures were present inside all particles and many of these connected pathways from the interior to the exterior surfaces, suggesting a strong role in the potential for leaching of radionuclides into the environment. The size, number and nature of the fissures varied and related mainly to the composition of the dominant formation materials (e.g., island soils, tower and ship metals). Composition was distinguished by Ca/Fe and Si/Fe elemental ratios with greater fracturing in high-Ca content particles and less in particles from Si-dominated settings. In all study particles, the actinide activity concentrations were dominant, which contrasts with the particles from the nuclear power accident at Fukushima, which were 137Cs-dominated and had only minute amounts of Pu isotopes. However, some similarity exists between the isotopic “fingerprints” of the early Australian tests and that from the 1945 Nagasaki detonation.