Deposition of90Sr and plutonium isotopes derived from the Chernobyl accident in Japan

To clarify environmental effects of the Chemobyl radionuclides, long-lived Chernobyl radioactivity (^239,240Pu,²³⁸Pu,²⁴¹Pu and⁹⁰Sr) in deposition samples in May 1986 was measured at 11 stations in Japan. Temporal variation of weekly deposition of⁹⁰Sr differed from that of volatile radionuclides such as¹³¹I and¹³⁷Cs, which may reflect the released process at Chernobyl. On the other hand, the geographical distributions of the monthly deposition of long-lived radionuclides were similar to those of volatile radionuclides, in which maximum deposits of⁹⁰Sr and plutonium were observed in Akita, a northwestern Japan Sea coast site of Honshu Island. Higher²⁴¹Pu deposition in most of the stations, as well as high²³⁸Pu/^239,240Pu activity ratios were observed. The²⁴¹Pu/²³⁸Pu activity ratios in deposition samples were nearly equal to that in the total release, which is clear evidence that Chernobyl-derived plutonium was transported to Japan in May 1986 together with volatile radionuclides although the contribution of Chernobyl Pu was about three orders of magnitude lower than¹³⁷Cs.     

Plutonium isotopes in the surface air in Japan: Effect of Chernobyl accident

Plutonium isotope concentrations in the surface air at Tsukuba, Japan are reported during the period from 1981 to the end of 1986. The^239,240Pu concentration in the surface air, which showed a marked seasonal variation with a spring maximum and fall minimum, decreased until the end of 1985 according to the stratospheric residence time of 1.15 years. In May 1986, elevated^239,240Pu concentrations with high²³⁸Pu/^239,240Pu activity ratios were observed. The serial trend of plutonium concentration in the surface air is similar to the concentrations of the Chernobyl-released radionuclides. These findings suggest that a significant part of the plutonium in the surface air in May 1986 was due to the Chernobyl fallout. The size distribution of plutonium bearing particles indicates that plutonium isotopes were mechanically released in the Chernobyl accident. The surface air concentration of plutonium from the Chernobyl accident was much lower than the concentrations of the volatile fission products, and increased the monthly mean^239,240Pu concentration by only 0.03 Bqm^–3.     

Plutonium isotopes in the surface air at Vinča-Belgrade site in May 1986

Surface air concentrations of plutonium isotopes at the Vinca-Belgrade site for the period May 1–15, 1986, are reported. The increase in²³⁸Pu/^239,240Pu ratios confirms that the source of plutonium in surface air was the Chernobyl accident.     

Measurement of 241Pu in Environmental Samples

Concentrations of ²⁴¹Pu in the air and deposition samples in Finland after the 1986 Chernobyl accident were estimated with the aid of ingrowth of ²⁴¹Am. Plutonium-241 was clearly shown to be present in the Chernobyl fallout in Finland. Pu was unevenly distributed and the mean radioactivity ratio of ²⁴¹/^239,240Pu was 70 for air and 71 for deposition samples. Here, a radiochemical method for determination of ²⁴¹Pu in the environmental samples was also developed. The method was based on the liquid scintillation measurement of ²⁴¹Pu with a pulse shape analyser after Pu separation. Efficiency calibration was performed with the aid of ³H standard instead of the ²⁴¹Pu standard. The method was tested by comparing the results with the method of ²⁴¹Am ingrowth and some reference samples. The detection limit for ²⁴¹Pu was 0.007 Bq per sample. The ²⁴¹Pu concentrations in the sediment samples taken from the Baltic Sea varied between <0.5 and 27 Bq·kg^-1. The effect of the Chernobyl accident could be seen both from the ²⁴¹Pu concentrations and from the Pu isotope ratios in vertical distributions of sliced samples.     

Preliminary estimates of cumulative caesium and plutonium deposition in the Irish terrestrial environment

A number of soil and peat cores, sampled throughout Ireland from November 1987 to March 1988, have been analyzed for fallout caesium and plutonium. Specifically,¹³⁴Cs and¹³⁷Cs levels were measured by high resolution gamma spectrometry while²³⁸Pu and^239,240Pu were determined after chemical extraction by alpha spectrometry. The inventories of these nuclides at the locations sampled have been calculated from the resulting profiles and, by extrapolation, preliminary estimates made of the cumulative deposition throughout Ireland. The relative contribution from weapons testing in the atmosphere and the Chernobyl accident to the total caesium inventory have been determined by the¹³⁴Cs/¹³⁷Cs isotopic ratio. As expected, no plutonium of Chernobyl origin was detected in surface layers. The cumulative²³⁸Pu/^239,240Pu ratio measured in Irish soils was found to be consistant with mid-latitude ratios reported by others.     

Soil factor influence on the plutonium isotope distribution among soil profile layers and mobile forms in the 30 km Chernobyl zone

The results of observation of plutonium isotopes (²³⁸Pu and^239,240Pu) vertical distribution dynamics (including mobile forms) in the profile of peaty-podzol-gley soil within 30 km limits from the Chernobyl Nuclear Power Station (ChNPS) are considered. Correlation of the plutonium distribution with some characteristics of the soil layers are discussed.     

Plutonium and americium in the sediments off the Thule air base, Greenland

In 1968 a U.S. B-52 bomber from USA with four nuclear weapons crashed on the sea ice near the Thule air base and contaminated the surroundings. Most of contamination was recovered during the cleanup program. However, some of the plutonium still remains in the bottom sediments of the area. In 1997 an international expedition with a comprehensive sampling program was performed. A lot of sediment samples were taken with a Finnish Gemini corer. Sediment samples from 5 sampling stations, 80 samples altogether, were pretreated in Ris, Denmark, and analysed for transuranic elements at STUK, Finland. The samples were analysed primarily for Pu, but gamma-spectrometric measurements of ²⁴¹Am were also made. Generally, the Pu concentrations in the area studied were from 1 to 3 magnitudes higher than the fallout level in the Arctic sea area. None of the vertical profiles of Pu at the various stations showed a typical Pu peak originating from the accident in 1968, but the sediments were mixed down and contaminated to the depths studied (20 cm). The presence of large quantities of hot particles distorted the estimations of mean concentrations and inventories. Samples with plutonium from the accident show significant variations of nuclide ratios, ²³⁸Pu/^239,240Pu, ²⁴¹Pu/^239,240Pu and ²⁴¹Pu/²⁴¹Am. This indicates that Pu at Thule may be from more than one source of different quality.     

Geochemical studies on the Chernobyl radioactivity in environmental samples

Artificial radionuclides in deposition and airborne dust samples in 1986 were measured at Tsukuba and 11 stations in Japan. In May 1986, the Chernobyl radioactivity was observed in rain and air samples in Japan. The Chernobyl-derived Pu isotopes, which are characterized by higher²³⁸Pu/^239,240Pu (85) and²⁴¹Pu/²³⁸Pu (0.5) activity ratios than those of the nuclear test-derived Pu and⁹⁰Sr, were detected in deposition and airborne dust samples in Japan, as well as volatile radionuclides such as¹³¹I and¹³⁷Cs. However, the activities of Pu isotopes and⁹⁰Sr observed in Japan were about two and three orders of magnitude lower than those expected from the activity ratios in the total release at Chernobyl, which means that the residence time of Pu in the air was shorter than that of¹³⁷Cs. In order to understand the fractionation between the Chernobyl radionuclides we studied about individual wet and dry deposition. The results suggest that this cause is due to the difference of the particle size of radionuclide-bearing particles, which may be related to the release process of Chernobyl radionuclides.     

<Superscript>237</Superscript>Np in peat and lichen in Finland

Activity concentrations of ²³⁷Np in peat and lichen samples in Finland were determined and contributions from nuclear weapons testing in 1950–1960s and the Chernobyl accident were estimated. ²³⁷Np was determined with ICP-MS using ²³⁵Np as a tracer. Activity concentrations of ²³⁷Np in peat samples varied between 1.98 ± 0.05 and 14.1 ± 0.3 mBq/m². The contribution from the Chernobyl accident to the total ²³⁷Np deposition in peat was 0.1–13%, the Chernobyl-derived fraction of total ²³⁷Np in peat being much lower than the previously determined corresponding Chernobyl-derived fractions of ^239+240Pu, ²⁴¹Pu, ²⁴¹Am and ²⁴⁴Cm.     

Migration of plutonium isotopes in forest soil profiles in Lublin region (Eastern Poland)

The distribution of Pu isotopes in three profiles of forest soil in Lublin region was determined. The retention half-time and migration velocity of^239,240Pu originated from global and Chernobyl fallouts was calculated. The average rate of migration of the global fallout plutonium was 0.4 cm/year and that of the Chernobyl one 0.7 cm/year. Good correlation between Pu concentration and organic matter contents was found only in the case of podzolic soil profile. In two profiles a good negative correlation between Pu activity and exchangeable pH of the soil layer was determined.     

Plutonium Activity Ratios in Plankton: New Evidence of Hold-Up Time in Irish Sea Sediments

The determination of activity ratios for radioisotopes of different half-lives can be used to estimate transit times from a point source to locations further away. For conservative elements, this time is approximately equivalent to the net hydrological transport. However, for non-conservative elements such as plutonium, the additional influence of biogeochemical processes decreases the net transport time. In this study, ²⁴¹Pu and ^239,240Pu concentrations in Irish Sea plankton samples, collected in May 1994, were determined and the ²⁴¹Pu/^239,240Pu ratios calculated. Plutonium-239,240 was measured using a standard method by ion exchange chromatography and alpha counting, and ²⁴¹Pu was determined by liquid scintillation counting using the disk-supported technique. The latter showed some methodological problems, which are briefly discussed. The ²⁴¹Pu/^239,240Pu ratios gave an estimate of the "transit time" from Sellafield to the different sampling points. In fact, this time represents the age of plutonium in plankton, i.e., the time lag between release from Sellafield and detection at the different sampling stations. The mean plutonium age was 17±2 years (n = 10) and 18.6±0.8 years (n = 13) in phytoplankton and zooplankton, respectively. The spatial distribution was reasonably homogeneous over the Irish Sea. The assimilation-elimination processes of plutonium in plankton are rather rapid. Therefore, it may be assumed that, in this time scale, the plutonium concentrations were in equilibrium with surrounding waters. Thus, it is concluded that plutonium was rather old because resuspension-sedimentation processes had occurred that delayed its transport within the Irish Sea. Therefore, the age of plutonium in plankton represented the hold-up time of plutonium in the sediments from the Irish Sea.     

Concentration and vertical distribution of plutonium and americium in Italian mosses and lichens

The plutonium and americium concentration and vertical distribution in some Italian mosses and lichens have been determined. The^239,240Pu,²³⁸Pu and²⁴¹Am concentration ranges in tree trunk lichens 0.83–1.87, 0.052–0.154 and 0.180–0.770 Bq/kg, respectively. The corresponding values in tree mosses are higher and more scattered ranging from 0.321 to 4.96, from 0.029 to 0.171 and from 0.200 to 1.93 Bq/kg. The mean²³⁸Pu/^239,240Pu and²⁴¹Am/^239,240Pu ratios are 0.088±0.037 and 0.38±0.13 in lichens and 0.091±0.072 and 0.54±0.16 in tree mosses. The Pu and Am concentrations are relatively low in terrestrial mosses. The^239,240Pu,²³⁸Pu and²⁴¹Am vertical distributions in a terrestrial moss core (Neckera Crispa) collected near Urbino (central Italy) show an exponential decrease with the height. On the contrary the²⁴¹Am vertical distribution in another terrestrial moss core (Sphagnum Compactum) collected in the Alps (northern Italy) shows an interesting peak at 16 cm which corresponds to the deposition of fallout from the nuclear weapon tests in 1960's. The²⁴¹Am movement upward and downward in the moss core is also studied. The results show once again that both mosses and lichens are very effective accumulators of Pu and Am and that they can be used as good biological indicators of the radionuclide airbome pollution from nuclear facilities and nuclear weapon tests. They can play a very impotant role in cycling naturally or artificially enhanced radionuclides in the atmosphere over long time scales.     

Plutonium and cesium isotopes in river waters in Japan

Concentrations of cesium isotopes and plutonium in river water samples in Japan, collected during the period from June 1985 to February 1987, have been measured. The total¹³⁷Cs concentrations in the Japanese river waters ranged from 0.063 to 1.89 mBq·l^–1. The portion of particulate¹³⁷Cs to total was observed to be less than 10 to 35%. The total^239,240Pu concentrations ranged from 0.56 to 1.93 Bq·l^–1. Particulate^239,240Pu occupied 13 to 95% of the total. After the Chernobyl fallout, elevated¹³⁷Cs concentrations were observed in the Japanese river waters as well as the detection of¹³⁴Cs, whereas there was no effect on the river plutonium from the Chernobyl fallout. The partition coefficients of¹³⁷Cs and plutonium between suspended particulate and dissolved phases in the Japanese rivers were determined: from 1.0·10⁴ to 3.2·10⁵ and from 4.1·10⁴ to 2.3·10⁶ for¹³⁷Cs and plutonium, respectively. The result suggests that these radionuclides, especially plutonium, are tightly associated with soil particles and/or suspended matter.     

Plutonium isotopes in the Sea of Japan

Plutonium isotopes in the Sea of Japan were determined to assess radioactive contamination. Concentrations of ^239,240Pu in surface water of the Sea of Japan were maintained at a constant level over the past two decades in contrast to ¹³⁷Cs. A median value of surface ^239,240Pu in the Sea of Japan in this period was 5.6 mBq/m³ with the range between 2.1 and 14.0 mBq/m³, which is slightly higher than that in the western North Pacific. The vertical distribution of ^239,240Pu showed a surface minimum, a subsurface maximum and gradual decrease with increasing depth. The ²⁴¹Pu/^239,240Pu activity ratios in water columns were almost constant except for surface water. In regard to ^239,240Pu in surface water of the Sea of Japan, these findings suggest that rapid recycling of deeper plutonium occurs in the Sea of Japan due to deep convection in winter and biogeochemical processes such as particle scavenging and remineralization.     

Behaviour of239,240Pu and241Am in the Baltic Sea; Measurements and interpretation in 1980–1984

Concentrations of^239,240Pu and²⁴¹Am in filtered seawater, particulate fraction and sediment were measured. Methods for determination of these nuclides were critically chequed and a new rapid method for²⁴¹Am in sediment was developed. Due to seasonal variation a significant decrease of plutonium and americium concentrations in surface water takes place in summer. Americium is more efficiently associated with particulate matter than plutonium. From May 1980 to September 1984 soluble plutonium in the water was reduced to about half. The residence half-time of^239,240Pu in the water of Baltic Sea is of the order of 5 years. About similar concentrations of^239,240Pu and²⁴¹Am were found in particulates in water as in the surface layer of the sediment. The average K_d-values for plutonium and americium were 10⁵ and 10⁵–10⁶ ml/g, respectively.     

Depth profiles of long lived radionuclides in Chernobyl soils sampled around 10 years after the accident

Depth profiles of the long-lived radionuclides, ¹³⁷Cs, ⁹⁰Sr, Pu isotopes and ²⁴¹Am were examined in undisturbed sandy, peaty and Podsol soils in the Chernobyl 30 km exclusion zone sampled around 10 years after the accident. Two Podsol soils, which have different radioactive deposition characteristics, have also been examined. Activity ratios of ^239,240Pu/¹³⁷Cs, ⁹⁰Sr/¹³⁷Cs, and ²⁴¹Am/¹³⁷Cs in the 0-1 cm layer of the two Podsol soils differed very much. Speciation of the radionuclides by sequential selective extraction was examined in the soils. Depth profiles of the soils have been analyzed according to the speciation results and soil characteristics.     

Origin and release date assessment of environmental plutonium by isotopic composition

The origin and release date of environmental plutonium have been assessed by the measurement of plutonium and americium isotopic composition. The applicability and sensitivity of different plutonium isotope ratios, ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu measured by inductively coupled plasma sector field mass spectrometry and ²³⁸Pu/²³⁹Pu analysed by alpha spectrometry, have been evaluated for origin determination in several types of environmental samples. With use of mixing models the contribution of different sources (e.g. global fallout or Chernobyl) can be calculated. By the measurement of the ²⁴¹Am/²⁴¹Pu isotope ratio, the release date (i.e. formation of ²⁴¹Pu by irradiation) can be estimated in environmental samples, which is an important parameter to distinguish recent plutonium release from previous (e.g. Chernobyl) emissions.     

Studies of the vertical distribution of134Cs,137Cs,238Pu,239, 240Pu,241Pu,241Am and210Pb in ombrogenous mires at mid-latitudes

Six peat cores taken from three unmodified blanket and raised bogs in Ireland were sectioned and analyzed for a range of radionuclides including¹³⁴Cs,¹³⁷Cs,²³⁸Pu,²³⁹Pu,²⁴¹Am, and²¹⁰Pb.¹³⁴Cs and¹³⁷Cs were measured by high resolution gamma-spectrometry, while the transuranium nuclides were determined after chemical separation by alpha-spectrometry.²⁴¹Pu, present on the electroplated discs together with Pu(), was measured directly by low-level liquid scintillation counting. Core chronologies were established by measuring the unsupported²¹⁰Pb component using low energy photon spectrometry (LEPS). From the resulting profiles, relaxation depths and migration rates for the above mentioned radionuclides have been determined and differences in the values of these parameters interpreted.²³⁸Pu/^239,240Pu and²⁴¹Pu/^239,240Pu ratios have been examined carefully and are discussed in some detail. Finally, the contribution from Chernobyl to the total radiocaesium inventory in each core has been established using the¹³⁴Cs/¹³⁷Cs ratio observed in the initial fallout from Chernobyl.     

Fallout of transuranium elements following the Chernobyl accident

The deposition of transuranium elements in Sweden following the Chernobyl accident was investigated through the analysis of carpets of lichen-and moss-samples and also air-filters and precipitation. The impact of transuranium elements was small compared to that of radiocesium. The deposition of^239+240Pu was, as for other actinides, inhomogeneously distributed and ranged from 0.1% to 100% of the inventory in 1986 from nuclear detonation tests. The activity ratio of^239+240Pu/¹³⁷Cs was between 10^–3 and 10^–6 in comparison to 10^–2 for nuclear test fallout. The activity ratios of²⁴¹Pu,²⁴²Cm,²³⁸Pu,^243+244Am and^239+240Pu were about 86, 14, 0.47, 0.14, and 0.13 respectively, but large variations were observed. The results from Sweden were compared with those found in South Finland, Denmark and Southern Europe. The deposition over Scandinavia originated from the initial explosion at Chernobyl, which contained relatively higher amounts of actinide elements than the second emission, which occurred a few days later and was a result of actions taken to bring the fire under control.     

Rapid determination of 239,240Pu, 238Pu, 241Am and 90Sr in radioactive waste using combined SPE sorbents AnaLig? Pu02, AnaLig? Sr01 and TRU? Resin

A rapid separation method has been developed which allows measurement of plutonium, americium and strontium isotopes in the radioactive sludge from Nuclear power plant A1 Jaslovske Bohunice (NPP A1) with high chemical recoveries and effective removal of matrix interferences. This method uses different commercial products stacked AnaLig^? Pu02, AnaLig^? Sr01 and TRU^? Resin cartridges from IBC Advanced Technologies and Eichrom Technologies. The method allows the rapid separation of plutonium, strontium and americium using a single multi-stage column in the vacuum box (cartridge technology) with rapid flow rates to minimize sample separation time. The ^239,240Pu, ²³⁸Pu and ²⁴¹Am were determined by alpha spectroscopy, ⁹⁰Sr was counted on TRICARB 2900 TR by Cerenkov counting of its progeny ⁹⁰Y.