Sources and vertical distribution of 137Cs, 238Pu, 239+240Pu and 241Am in peat profiles from southwest Spitsbergen

This paper presents a detailed survey of the activities of selected man-made radionuclides in peat deposits located in SW Spitsbergen. Peat cores from the High Arctic (SW Spitsbergen) were analyzed by gamma spectrometry (Cs-137), alpha spectrometry (Pu-238, Pu-239,Pu-240, Am-241 activities) and by ICPMS (Pu-240/Pu-239 atom ratios). Maximum activities evident in the peats correspond to the 1963/1964 global maximum fallout from atmospheric testing of nuclear weapons; some of the activity profiles have been altered post-deposition by water infiltration. Activity ratios of Pu-238/Pu239+240, Am-241/Pu239+240, Pu239+240/Cs-137 and Pu-240/Pu-239 atom ratios indicate mixing between global (stratospheric) and regional (tropospheric) sources of these radionuclides in the Svalbard area. The Pu-238/Pu239+240 activity ratios varied from 0.02 +/- 0.01 to 0.09 +/- 0.03, suggesting global fallout as the dominant source of Pu. The Pu239+240/Cs-137 activity ratios varied from 0.01 +/- 0.01 to 0.42 +/- 0.11, which apparently arises from the post-depositional mobility of Cs-137. The Am-241/Pu239+240 activity ratios ranged between 0.10 +/- 0.02 and 1.5 +/- 0.3 and exceed the published global fallout ratio for Svalbard of 0.37 due to the relatively higher geochemical mobility of Pu vs. Am and/or ingrowth of Am from the decay of Pu-241. The atom ratio Pu-240/Pu-239 ranged from 0.142 +/- 0.006 to 0.241 +/- 0.027; however, the vast majority of peat samples exhibited Pu-240/Pu-239 atom ratios similar to the stratospheric fallout (similar to 0.18). (C) 2012 Elsevier Ltd. All rights reserved.