Global transport of plutonium from Nagasaki to the Arctic: Review of the Nagasaki Pu investigation and the future

Abstract

Abstract A historic event, the release of man-made global pollutants, was observed at Nagasaki, Japan on August 9, 1945 with the detonation of a plutonium (10-15 kg) atomic bomb. A portion, 1.2 kg of 239 Pu , was fissioned releasing 21 kt TNT energy along with various fission products. The rest of the unexpended fissile material, 13.8 kg (3.49 × 10 13 Bq) of 239+240 Pu , was discharged into the atmosphere along with the fission product, 137 Cs, 23.4 g (7.44 x 10 13 Bq). The fate of the 239+240 Pu and 137 Cs was investigated by analysing both local and global fallout. The highest concentration of 239+240 Pu was 64.5 mBq/g (181 mBq/cm 2 ) while it was 188 mBq/g (526 mBq/cm 2 ) for 137 Cs, both at 2.8 km east of the hypocentre. The total amount of deposition in the local fallout region of 264 km 2 was 37.5 g (9.48 × 10 10 Bq) for 239+240 Pu and 3.14 mg (5.88 × 10 10 Bq) for 137 Cs. The ratio of the local fallout against the total amount of the radionuclides released was 0.27% for 239+240 Pu and 0.134% for 137 Cs. Recent advances in analytical technology have made it possible for artificial radionuclides released from the Nagasaki explosion to be detected in the Arctic ice core layer of 1945. The unexpended fissile material, 239+240 Pu , and the fission product, 137 Cs, originating from the Nagasaki A-bomb, were measured by collecting 10 ice cores on the Agassiz ice cap, Ellesmere Island, Canada. The deposition was 0.16/zBq/cm 2 for 239+240 Pu and 20 tBq/cm 2 for 137 Cs originating from Nagasaki. During atmospheric testing, the deposition of 239+240 Pu and 137 Cs varied by more than 100 times with the highest peaks of over 50 g, Bq/cm 2 for 239+240 Pu and over 8 mBq/cm 2 for 137 Cs both occurring ill 1962. Deposition from the first French nuclear test in 1960 was also clearly shown in the ice cores. Assuming there is consistency in climate for the next 10 000 years, the chronological anthropogenic deposits, mainly of 239+240 Pu , should be detectable in the ice layer between 97-98 m from the snow surface on the Agassiz ice cap in 11 999 AD. Even if there were no improvements in the radioanalytical method used, the ice layers for the 1945-1980 periods could still be easily identified with the present analytical technology. Hopefully this study may establish a way to use our generation's artifacts for the benefit of our future descendants.