Abstract
Dolon village, located about 110 km ENE from the ground-zero point in the Semipalatinsk Nuclear Test Site, was heavily contaminated by the radioactive fallouts from the first USSR atomic bomb testing in 1949. The current level of Cs-137 soil contamination in Dolon was measured to be 2 – 10 kBq/m2, showing a log-normal distribution with an average of 4.2 kBq/m2. A 90 percentile of this log-normal distribution was chosen as a referential contamination in Dolon, which corresponded to 32 kBq/m2 in 1949. A VB Excel program, FPCOMP.xls was developed to follow temporal change of FP composition after nuclear explosions, using JNDC FP Data Library containing 1,227 nuclides. From the results of the FPCOMP calculation for Pu-239 fission by fast neutrons, 29 gamma-emitting nuclides were selected as possible FPs that could contribute external radiation in Dolon village. Conversion coefficients from the unit deposition of each of 29 FPs to air-dose at 1 m above the ground were calculated using infinite plane model. Cumulative air-dose per unit Cs-137 deposition was calculated at arbitrary time after the fallout deposition. Air-dose of about 0.016 ± 0.004 Gy per 1 kBq/m2 of Cs-137 deposition was obtained for the time period from 3 hr (assumed arrival time of radioactive clouds to Dolon village) to 1 yr after the explosion. Thus, combining this value with the Cs-137 deposition of 32 kBq/m2, external radiation of 0.51 ± 0.13 Gy was evaluated as the referential air-dose in Dolon village.
