Plutonium isotopes and 241Am in the atmosphere of Lithuania: A comparison of different source terms (original) (raw)
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Global distribution of Pu isotopes and 237Np
Science of The Total Environment, 1999
Inventories and compositions of Pu isotopes and 237Np in archived soil samples collected in the 1970s from 54 locations around the world were determined to provide regional baselines for recognizing possible future environmental inputs of non-fallout Pu and Np. As sample sizes used in this work were small (typically 1 g), inhomogeneities in Pu and Np concentrations were easily recognizable
Plutonium in the atmosphere: A global perspective
Journal of Environmental Radioactivity, 2017
A number of potential source terms have contributed plutonium isotopes to the atmosphere. The atmospheric nuclear weapon tests conducted between 1945 and 1980 and the re-entry of the burned SNAP-9A satellite in 1964, respectively. It is generally believed that current levels of plutonium in the stratosphere are negligible and compared with the levels generally found at surface-level air. In this study, the time trend analysis and long-term behavior of plutonium isotopes (239þ240 Pu and 238 Pu) in the atmosphere were assessed using historical data collected by various national and international monitoring networks since 1960s. An analysis of historical data indicates that 239þ240 Pu concentration post-1984 is still frequently detectable, whereas 238 Pu is detected infrequently. Furthermore, the seasonal and time-trend variation of plutonium concentration in surface air followed the stratospheric trends until the early 1980s. After the last Chinese test of 1980, the plutonium concentrations in surface air dropped to the current levels, suggesting that the observed concentrations post-1984 have not been under stratospheric control, but rather reflect the environmental processes such as resuspension. Recent plutonium atmospheric air concentrations data show that besides resuspension, other environmental processes such as global dust storms and biomass burning/wildfire also play an important role in redistributing plutonium in the atmosphere.
Sources of plutonium in the atmosphere and stratosphere-troposphere mixing
Scientific reports, 2015
Plutonium isotopes have primarily been injected to the stratosphere by the atmospheric nuclear weapon tests and the burn-up of the SNAP-9A satellite. Here we show by using published data that the stratospheric plutonium exponentially decreased with apparent residence time of 1.5 ± 0.5 years, and that the temporal variations of plutonium in surface air followed the stratospheric trends until the early 1980s. In the 2000s, plutonium and its isotope ratios in the atmosphere varied dynamically, and sporadic high concentrations of (239,240)Pu reported for the lower stratospheric and upper tropospheric aerosols may be due to environmental events such as the global dust outbreaks and biomass burning.
Determination of alpha-emitting Pu isotopes in environmental samples
The Analyst, 2002
This paper presents an improved radiochemical procedure for the determination of alpha-emitting Pu isotopes in environmental samples (soils, sediments, vegetation) by alpha-particle spectrometry. Quantitative Pu recovery yields were obtained (average 60%), 0.1 mBq being the average minimum detectable activity by the complete technique. Special efforts were made to ensure the removal of traces of different natural alpha-emitting radionuclides, which can interfere with the correct determination of 239+240 Pu and 238 Pu concentrations. The radiochemical procedure was validated by application to reference material and by participation in intercomparison exercises. This radiochemical procedure was applied to the different layers of a high-resolution sediment core taken from a lake in Sweden. The 239+240 Pu and 238 Pu/ 239+240 Pu profiles obtained in the high-resolution sediment core correctly reproduced the expected evolution of these quantities as observed historically in the atmosphere, validating the procedure for this purpose and showing the power of these radionuclides for dating purposes.
Scientific Reports, 2019
Global fallout plutonium isotopic ratios from the 1960s are important for the use of Pu as environmental tracers. We measured the 240 pu/ 239 pu and 242 pu/ 239 pu atomic ratios of monthly atmospheric deposition samples collected in Tokyo and Akita, Japan during March 1963 to May 1966. To our knowledge, our results represent the first data measured for actual atmospheric deposition samples collected continuously during the 1960s. Both atomic ratios increased rapidly from March 1963 to June 1963, followed by a gradual increase until September 1963. Then, both ratios declined with a half-life of approximately 5.6 months. The observed temporal changes of the ratios were likely caused by the upper-stratospheric input of nuclear debris from high-yield atmospheric nuclear weapon testing during 1961-62, followed by its downward transport to the troposphere. Most plutonium isotopes in the environment today are derived from artificial sources, primarily atmospheric nuclear weapon tests during 1945-1980, though an extremely small amount of 239 Pu occurs naturally 1 . Atmospheric detonations of 502 nuclear devices with a total yield of 440 Mt (TNT equivalent) have occurred at the proving sites shown in Fig. , including the two combat uses in Hiroshima and Nagasaki. The former USSR performed nuclear testing mainly at high latitudes in the Northern Hemisphere, whereas the USA performed testing at low latitudes. Additional detonation tests were carried out by People's Republic of China at middle latitude of Northern hemisphere and by France and the UK in the Southern Hemisphere. Plutonium introduced into the troposphere and stratosphere by these detonations was advected and diffused in the atmosphere before final deposition throughout the world 2 . Various industrial and military accidents have dispersed a much smaller amount of Pu compared to nuclear weapon testing. Nuclear accidents at the Chernobyl nuclear power plant (NPP) in the former USSR in 1986 3 and the Fukushima Dai-ichi NPP in Japan in 2011 dispersed artificial radionuclides including Pu 4 . A waste storage tank at the Mayak nuclear material production complex in the Chelyabinsk region in the former USSR had major leaks in 1957, and the leakage, containing Pu, flowed into the Techa River 5 . Furthermore, bomber aircrafts carrying atomic bombs crashed in Palomares, Spain in 1966 6 and Thule, Greenland in 1968 7 , resulting in local Pu contamination. Plutonium isotopic compositions differ depending on their origin. For example, the mean 240 Pu/ 239 Pu atomic ratio (±a standard deviation) of cumulative global fallout Pu is 0.18 ± 0.01 in surface soils collected from 24 sites in 31-70°N region 8 . 240 Pu/ 239 Pu atomic ratios above 0.18 were observed in soils around the Chernobyl 3,9 and Fukushima Dai-ichi NPPs 4 , whereas the 240 Pu/ 239 Pu atomic ratios of spent nuclear fuels from civilian nuclear reactors vary based on the type of reactor and burn-up . Ratios below 0.18 have been measured in soils around
Journal of Environmental Radioactivity, 2013
Stratospheric fallout-derived 236 U has been detected by sector field ICPMS at two field locations for which our laboratory possessed available archived samples: A) four soil cores from Washington state (northwestern USA) and B) sediment cores from three small lakes in the Pechora region (Russian Arctic). Four Washington state soil cores exhibit 236 U inventories of 8.1 AE 1.3, 11.1 AE 0.9, 18 AE 2, and 30.2 AE 3.9 Tatoms/m 2 ; the respective 239 Pu contents are 52.9 AE 3.5, 67 AE 3, 71 AE 2, and 151 AE 2 Tatoms/ m 2. A 236 U/ 239 Pu atom ratio of 0.19 AE 0.04 (1 SD) has been determined from the Washington state soil cores. The three Pechora region lake cores each exhibit coincident maxima in their 236 U and 239 Pu atom concentration profiles. The 236 U/ 238 U atom ratios are controlled by two independent factors; 236 U is from fallout deposition and 238 U concentrations are a property of the geochemical distribution of naturally occurring U. A 236 U/ 238 U atom ratio as high as 8.9 Â 10 À6 has been observed for acid-leached soils containing Pu solely derived from bomb-test fallout. Accordingly, a non-zero 236 U background from stratospheric fallout must be recognized and taken into account when detectable 236 U is used to infer specific local or regional influences of reactor-irradiated U.
Environment International, 2013
A combination of state-of-the-art isotopic fingerprinting techniques and atmospheric transport modelling using real-time historical meteorological data has been used to demonstrate direct tropospheric transport of radioactive debris from specific nuclear detonations at the Semipalatinsk test site in Kazakhstan to Norway via large areas of Europe. A selection of archived air filters collected at ground level at 9 stations in Norway during the most intensive atmospheric nuclear weapon testing periods (1957-1958 and 1961-1962) has been screened for radioactive particles and analysed with respect to the concentrations and atom ratios of plutonium (Pu) and uranium (U) using accelerator mass spectrometry (AMS). Digital autoradiography screening demonstrated the presence of radioactive particles in the filters. Concentrations of 236 U (0.17-23 nBq m −3 ) and 239 + 240 Pu (1.3-782 μBq m −3 ) as well as the atom ratios 240 Pu/ 239 Pu (0.0517-0.237) and 236 U/ 239 Pu (0.0188-0.7) varied widely indicating several different sources. Filter samples from autumn and winter tended to have lower atom ratios than those sampled in spring and summer, and this likely reflects a tropospheric influence in months with little stratospheric fallout. Very high 236 U, 239 + 240 Pu and gross beta activity concentrations as well as low 240 Pu/ 239 Pu (0.0517-0.077), 241 Pu/ 239 Pu (0.00025-0.00062) and 236 U/ 239 Pu (0.0188-0.046) atom ratios, characteristic of close-in and tropospheric fallout, were observed in filters collected at all stations in Nov 1962, 7-12 days after three low-yield detonations at Semipalatinsk (Kazakhstan). Atmospheric transport modelling (NOAA HYSPLIT_4) using real-time meteorological data confirmed that long range transport of radionuclides, and possibly radioactive particles, from Semipalatinsk to Norway during this period was plausible. The present work shows that direct tropospheric transport of fallout from atmospheric nuclear detonations periodically may have had much larger influence on radionuclide air concentrations and deposition than previously anticipated.