Variation of uranium isotopic composition in soil within the JCO grounds from the 30 September 1999 criticality accident at JCO, Tokai-mura, Japan.

Following the 30 September 1999 criticality accident at JCO, 29 surface and 3 core soil samples were collected inside and outside the JCO grounds to evaluate possible contamination by 235U-enriched uranium (18.8%) being handled at the time of the accident. Uranium (234U, 235U, and 238U) and thorium (228Th, 230Th, and 232Th) isotopes were determined by alpha-spectrometry and ICP-MS after radiochemical separation.