were associated with or adhering to particles and pieces of inert debris of all kinds of material (glass, metal, plastic, rubber, etc.). The subsequent cleaning of the crash site was very effective and it was estimated that only 350 g of plutonium of the 3150 g released were trapped in the ice. Sedimentation studies of melted ice cores showed that 85 to 95% of the debris and associated plutonium oxide sank immediately (12) when contaminated ice was transferred into the sea and broke up in June-July 1968. . It is obvious that such delivery of plutonium and americium to the sea floor is quite different to other sources such as global fallout, releases from nuclear fuel reprocessing plants, etc. In the Thule case the elements have not undergone any interaction in the atmosphere and a very limited one, if any, in the water column. The interactions and resulting chemical partitioning have taken place in the sediments. Consequently the observed activity ratio sediment/water for plutonium at the point of impacts is in the order of 10 10 (4), while at areas in a similar marine environment where fallout plutonium has been transferred to the seafloor by particle interaction in the water column this ratio is in the order of 104 - 105 (13). The isotopic ratios 238p n/239+240pn and 2411311/239+240pn are different depending on source, being much higher in the releases from nuclear fuel reprocessing facilities and in fallout from the Chernobyl accident than in global fallout from nuclear detonation tests and these, in turn, are higher than those for weapon grade plutonium. The 238pn/239+240 Pu activity ratio was 0.016+0.01 (n=39, 1 SE) and the 241pn/239+240 Pu had earlier been determined to 3.3+0.4 (n=6, 1 SE) at the time of the accident (January 1968) (4). The 2445/239+240pu activity ratio was determined in this study to 0.098+0.005 (n=29, 1SE) in 1984. From the available data we can now calculate the decay of 238 Pu and 241Pu relative to 239+ 240Pu and also the build up of 241 Am as shown in Fig. 1. We then estimate that the 241239+240 Pu activity ratio was about 0.037 at the time of the accident. Supposing that there was no 241Am present after the initial plutonium separation we observe that the plutonium was fabricated in 1962 + 1 year. Furthermore, we find that when the sample collection took place in August 1968 and August 1984, about 8% and 62% respectively of the americium had been formed in situ. The integrated activity area per unit (Bq m -2 ) was studied in the three sediment cores collected in 1984 and given in Table 1 as a function of dry mass depth (kg m -2 ). These cores represent different distances from the point of impact and accordingly different activity levels. The results are given in Fig. 2. We cannot observe any difference in the distribution pattern between the three cores or between americium and plutonium in these total activity analysis. The vertical distribution of americium in 1979 was also similar to that of plutonium, consequently showing unchanged americium/plutonium ratio with depth. A downward displacement of activity as well as a horizontal translocation of activity with time have been observed (4). It was suggested that the presence of plutonium and americium in the deeper layers of sediment is due to bioturbation and that physico-chemical mechanisms are less important (3). The integrated activity area per unit for the different chemical fractions of sediment core No. 84.01377 is shown in Fig. 3 as a function

DOI link for were associated with or adhering to particles and pieces of inert debris of all kinds of material (glass, metal, plastic, rubber, etc.). The subsequent cleaning of the crash site was very effective and it was estimated that only 350 g of plutonium of the 3150 g released were trapped in the ice. Sedimentation studies of melted ice cores showed that 85 to 95% of the debris and associated plutonium oxide sank immediately (12) when contaminated ice was transferred into the sea and broke up in June-July 1968. . It is obvious that such delivery of plutonium and americium to the sea floor is quite different to other sources such as global fallout, releases from nuclear fuel reprocessing plants, etc. In the Thule case the elements have not undergone any interaction in the atmosphere and a very limited one, if any, in the water column. The interactions and resulting chemical partitioning have taken place in the sediments. Consequently the observed activity ratio sediment/water for plutonium at the point of impacts is in the order of 10 10 (4), while at areas in a similar marine environment where fallout plutonium has been transferred to the seafloor by particle interaction in the water column this ratio is in the order of 104 - 105 (13). The isotopic ratios 238p n/239+240pn and 2411311/239+240pn are different depending on source, being much higher in the releases from nuclear fuel reprocessing facilities and in fallout from the Chernobyl accident than in global fallout from nuclear detonation tests and these, in turn, are higher than those for weapon grade plutonium. The 238pn/239+240 Pu activity ratio was 0.016+0.01 (n=39, 1 SE) and the 241pn/239+240 Pu had earlier been determined to 3.3+0.4 (n=6, 1 SE) at the time of the accident (January 1968) (4). The 2445/239+240pu activity ratio was determined in this study to 0.098+0.005 (n=29, 1SE) in 1984. From the available data we can now calculate the decay of 238 Pu and 241Pu relative to 239+ 240Pu and also the build up of 241 Am as shown in Fig. 1. We then estimate that the 241239+240 Pu activity ratio was about 0.037 at the time of the accident. Supposing that there was no 241Am present after the initial plutonium separation we observe that the plutonium was fabricated in 1962 + 1 year. Furthermore, we find that when the sample collection took place in August 1968 and August 1984, about 8% and 62% respectively of the americium had been formed in situ. The integrated activity area per unit (Bq m -2 ) was studied in the three sediment cores collected in 1984 and given in Table 1 as a function of dry mass depth (kg m -2 ). These cores represent different distances from the point of impact and accordingly different activity levels. The results are given in Fig. 2. We cannot observe any difference in the distribution pattern between the three cores or between americium and plutonium in these total activity analysis. The vertical distribution of americium in 1979 was also similar to that of plutonium, consequently showing unchanged americium/plutonium ratio with depth. A downward displacement of activity as well as a horizontal translocation of activity with time have been observed (4). It was suggested that the presence of plutonium and americium in the deeper layers of sediment is due to bioturbation and that physico-chemical mechanisms are less important (3). The integrated activity area per unit for the different chemical fractions of sediment core No. 84.01377 is shown in Fig. 3 as a function

were associated with or adhering to particles and pieces of inert debris of all kinds of material (glass, metal, plastic, rubber, etc.). The subsequent cleaning of the crash site was very effective and it was estimated that only 350 g of plutonium of the 3150 g released were trapped in the ice. Sedimentation studies of melted ice cores showed that 85 to 95% of the debris and associated plutonium oxide sank immediately (12) when contaminated ice was transferred into the sea and broke up in June-July 1968. . It is obvious that such delivery of plutonium and americium to the sea floor is quite different to other sources such as global fallout, releases from nuclear fuel reprocessing plants, etc. In the Thule case the elements have not undergone any interaction in the atmosphere and a very limited one, if any, in the water column. The interactions and resulting chemical partitioning have taken place in the sediments. Consequently the observed activity ratio sediment/water for plutonium at the point of impacts is in the order of 10 10 (4), while at areas in a similar marine environment where fallout plutonium has been transferred to the seafloor by particle interaction in the water column this ratio is in the order of 104 - 105 (13). The isotopic ratios 238p n/239+240pn and 2411311/239+240pn are different depending on source, being much higher in the releases from nuclear fuel reprocessing facilities and in fallout from the Chernobyl accident than in global fallout from nuclear detonation tests and these, in turn, are higher than those for weapon grade plutonium. The 238pn/239+240 Pu activity ratio was 0.016+0.01 (n=39, 1 SE) and the 241pn/239+240 Pu had earlier been determined to 3.3+0.4 (n=6, 1 SE) at the time of the accident (January 1968) (4). The 2445/239+240pu activity ratio was determined in this study to 0.098+0.005 (n=29, 1SE) in 1984. From the available data we can now calculate the decay of 238 Pu and 241Pu relative to 239+ 240Pu and also the build up of 241 Am as shown in Fig. 1. We then estimate that the 241239+240 Pu activity ratio was about 0.037 at the time of the accident. Supposing that there was no 241Am present after the initial plutonium separation we observe that the plutonium was fabricated in 1962 + 1 year. Furthermore, we find that when the sample collection took place in August 1968 and August 1984, about 8% and 62% respectively of the americium had been formed in situ. The integrated activity area per unit (Bq m -2 ) was studied in the three sediment cores collected in 1984 and given in Table 1 as a function of dry mass depth (kg m -2 ). These cores represent different distances from the point of impact and accordingly different activity levels. The results are given in Fig. 2. We cannot observe any difference in the distribution pattern between the three cores or between americium and plutonium in these total activity analysis. The vertical distribution of americium in 1979 was also similar to that of plutonium, consequently showing unchanged americium/plutonium ratio with depth. A downward displacement of activity as well as a horizontal translocation of activity with time have been observed (4). It was suggested that the presence of plutonium and americium in the deeper layers of sediment is due to bioturbation and that physico-chemical mechanisms are less important (3). The integrated activity area per unit for the different chemical fractions of sediment core No. 84.01377 is shown in Fig. 3 as a function