For three heavily exposed workers in the Tokai-mura criticality accident, the levels of 24Na, 42K and 82Br were measured in blood, urine, vomit and hair. 24Na showed the highest activity and was found to have a specific activity of 8.24·104, 4.34·104 and 1.23·104 Bq 24Na per g Na in blood of the three exposed workers. Based on these data the individual neutron fluences were calculated. Radionuclides
were also measured in environmental samples from the JCO campus. The fission products 131I, 133I, 140Ba-140La and 137Cs were determined in plant samples and the activation products 59Fe, 46Sc, 60Co and 152Eu were identified in soil samples. 235U/238U ratios in soil and plant samples were measured by ICP-MS.