The Solution
The scientists performed the first experiment of its kind to study a small radioactive particle (450 x 280 x 250 μm) from the Fukushima fallout site. Using a unique combination of tomography and micro‑fluorescence measurements from the I13‑1 and I18 beamlines at Diamond, the team analysed its internal structure and 3D elemental distribution.
The composition and structure of the particle indicates that it was likely to have been formed predominantly from materials from the reactor building, mainly silicon‑based fibrous insulation. Radiocaesium and other fission products were incorporated into the molten material, and fragments of the structural steel and concrete stuck to the surface after the hydrogen explosion.
The structures observed in the particle had a remarkable resemblance to a volcanic pumice, containing gas‑filled bubbles. The pumice‑like internal structure means that the particle is susceptible to weathering and fragmentation, which would increase the effective surface area and subsequent dispersal of iron‑associated radiocaesium into the environment. Within the particle, radioactive material was shown to be encased in a glass‑like silicon, analogous to the vitrification process used for nuclear waste disposal.
