Radioactive contamination from the JCO criticality accident

Radioactivity in environmental samples, soil, mugwort, dry leaves and pine needles, collected in the JCO facilities and the surrounding area was measured by γ-spectrometry. 131I and 133I were detected in environmental samples within an area of 1 km of the accident site. 133I concentrations in mugwort leaves were estimated to be more than 1000 Bq/kg at the time of the accident. The 131I/133I ratio in mugwort leaves was 20 at the time of the release. 24Na, 46Sc, 59Fe, 60Co and other neutron-induced radionuclides, as well as the fission products 140La and 137Cs, were detected in soils collected near the JCO facilities.