Timo Jaakkola

Sedimentation and distribution of gamma-emitting radionuclides in bottom sediments of southern Lake Päijänne, Finland, after the Chernobyl accident

The rates of sedimentation of fallout nuclides were determined by means of sediment traps during 28 months after the Chernobyl accident in southern Lake Päijänne, Finland. The spatial distribution of the radionuclide content of the lake bottom was studied on 35 sediment cores in winters 1987/88 and 1988/89. The results were compared with simultaneous observations of the radionuclide content of the water and seston. The role of different transfer mechanisms in the elimination of radionuclides from the water column is discussed.The values recorded for the flux to the lake sediments were on average of the same order of magnitude as the initial deposition on the lake surface (Cs-137 65 kBqm−2). The radionuclide flux to the sediments was rapid during the first months after the accident. After that the elimination of dissolved nuclides from the water mass became significantly slower. The highest flux rate was that of Ce-144 and the lowest that of Rh-106 (Ru-106). Of the radiocesium, about half of the initial inventory was transferred to the sediments after the first observation year.The content of radionuclides showed considerable spatial variation on the lake bottom (Cs-137 7–280 kBqm−2). Direct adsorption of radiocesium explains unexpectedly high concentrations on shallow erosion bottoms. There was a clear tendency for the concentrations to increase with depth, as a result of the focusing effect. Sediment resuspension had a significant impact on the total flux of radionuclides to deepwater sediments. Estimates were made of the resuspended flux of radionuclides.

The use of fallout 137Cs and 239,240Pu for dating of lake sediments

The distribution of 137Cs and 239,240Pu in sediment core samples of the Finnish lakes Laukunlampi, Lovojärvi and Pääjärvi were determined. The sediment samples were collected using dry ice and liquid nitrogen freezing methods. The sediments of these lakes are annually laminated. A clear maximum concentration of 137Cs and 239,240Pu was found in sediment layers formed during 1962–1964, the years of maximum fallout, and the middle of the 1950s can be estimated from the 137Cs and 239,240Pu profiles. The highest concentrations, 11 500 and 820 pCi kg−1 dry wt for 137Cs and 239,240Pu, respectively, were found in the sediment of Laukunlampi. The vertical distribution was similar for 137Cs and 239,240Pu in the lakes investigated. A slight migration of 239,240Pu and 137Cs was found and the migration of 137Cs seems to be higher than that of 239,240Pu. The advantages of 137Cs dating method are rapidity and simplicity. 239,240Pu is preferable when the sample size is small. The agreement found between 137Cs and 239,240Pu dates and the annual laminae show that these fallout radio isotopes can be used for dating sediments formed during the past 25 years.

Plutonium fallout in Southern Finland after the chernobyl accident

Abstract The plutonium concentrations of fuel peat samples from southern and central Finland were analyzed. The same samples had previously gone through gamma-spectrometric analysis, in which the detected nuclides could be divided into two groups by calculating correlations between activities: the volatile Cs-I group and the non-volatile Ce-Zr group. The plutonium of Chernobyl origin correlates rather well with the non-volatile group and not at all with the volatile group. The volatile group comprises the nuclides 137 Cs, 134 Cs, 131 I and 132 Te, and the non-volatile group 95 Zr, 141 Ce and Chernobyl-Pu.

Simultaneous determination of 241Pu, 238Pu and 239,240Pu in low activity environmental samples

Abstract Studies on plutonium in the environment are mostly directed to the alpha emitting isotopes 238Pu and 239,240Pu. However, the largest contribution to the radioactivity of plutonium is due to the beta emitting isotope 241Pu. Plutonium was separated using anion exchange after leaching the 242Pu spiked sample with concentrated HNO3 and HCl. One aliquot of the eluate was spiked with an additional plutonium tracer, 236Pu, and electrodeposited for alpha spectrometric determination of 238Pu and 239,240Pu in the sample and for the determination of chemical recovery in the solution before electrodeposition. The activity of 241Pu was measured in the second aliquot using a calibrated liquid scintillation counter. For quench correction, the external standard channels ratio method was applied. The counting efficiency of 241Pu was about 35% and the lower limit of detection with a counting time of 120 min was 1 pCi (37 mBq). The concentration of 241Pu in lichen was about 3000 and 800 pCi/kg in 1964 and 1970, respectively and 2.5 pCi/kg in reindeer liver in 1977. The maximum activity ratio of 241Pu to 239,240Pu, about 16, in 1965 is in good agreement with that given for fresh fallout.

Americium and curium deposition in Finland from the Chernobyl accident

Summary 241Am and 244Cm were analysed from peat samples collected in Finland immediately after the Chernobyl accident. The separation method included co-precipitation, anion exchange and extraction chromatography. Activities of 241Am and 244Cm were measured by alpha spectrometry. The activity of Chernobyl-derived 241Am varied between 0.0115 and 9.32 Bq/m2 and that of 244Cm from < 0.002 to 1.97 Bq/m2 (reference date 1.5.1986). The origin of 241Am in Finland is predominantly from atmospheric nuclear tests. However, the geographical distribution of Chernobyl-americium is uneven and depending on a location even 100% of 241Am in peat originated from the Chernobyl accident. The deposition pattern of Chernobyl-derived 241Am and 244Cm resembles that of other refractory nuclides, such as 95Zr, 141Ce and 239,240Pu.

137Cs, 239,240Pu and 241Am in bottom sediments and surface water of Lake Päijänne, Finland.

The concentrations and vertical distribution of (239,240)Pu, (241)Am and (137)Cs in the bottom sediments and water samples of Lake Päijänne were investigated. This lake is important, since the Päijänne area received a significant deposition from the Chernobyl fallout. Furthermore Lake Päijänne is the raw water source for the Helsinki metropolitan area. In addition no previous data on the distribution of plutonium and americium in the sediment profiles of Lake Päijänne exist. Only data covering the surface layer (0-1cm) of the sediments are previously available. In the sediments the average total activities were 45+/-15Bq/m(2) and 20+/-7Bq/m(2) for (239,240)Pu and (241)Am, respectively. The average (241)Am/(239,240)Pu ratio was 0.45+/-0.14. The (241)Am/(239,240)Pu ratio is lowest in the surface layer of the sediments and increases as a function of depth. The (238)Pu/(239,240)Pu ratio of the sediment samples varied between 0.012+/-0.025 and 0.162+/-0.079, decreasing as a function of depth. The average activity in water was 4.9+/-0.9mBq/m(3) and 4.1+/-0.2mBq/m(3) for (239,240)Pu and (241)Am, respectively. The (241)Am/(239,240)Pu ratio of water samples was 0.82+/-0.17. (239,240)Pu originating from the Chernobyl fallout calculated from the average total activities covers approximately 1.95+/-0.01% of the total (239,240)Pu activity in the bottom sediments. The average total (137)Cs activity of sediment profiles was 100+/-15kBq/m(2) and 19.3+/-1.4Bq/m(3) in water samples.

Regional distribution of Chernobyl-derived plutonium deposition in Finland

The Chernobyl nuclear power plant accident in April 1986 caused a widely spread plume of radionuclides containing, amongst other materials, plutonium isotopes. The regional deposition of these nuclides in Finland has been assessed, based on samples of lichen, peat, precipitation, surface soil and grass. Unlike the deposition of transuranium elements from the weapons tests in the 1950s and the 1960s, the deposition in Finland from the Chernobyl accident was very unevenly distributed. Even then, the Chernobyl-derived deposition of 239,240Pu in the most contaminated regions of Finland was only around 10% of the global fallout from weapons tests. The total amount of 239,240Pu deposited in Finland was 1.1011 Bq (»25 g), i.e., approximately half of a percent of the activity deposited in the 1950s and the 1960s. In addition to the alpha-emitting Pu isotopes, the Chernobyl plume also contained a significant amount of the beta-emitting 241Pu, which is the precursor of the long-lived alpha-emitter 241Am. The highest plutonium deposition values were found in a relatively narrow swath from the southwestern coast of Finland northeastwards across the country. This is related to the calculated route of the air parcel trajectory associated with the initial explosion of the Chernobyl reactor. The high deposition values found in the northeastern part of the plume route over Finland can be attributed to the simultaneous occurrence of precipitation. The relatively high plutonium deposition in the southwestern part of Finland occurred, however, without concurrent precipitation. This indicates that the plutonium was at least partly associated with relatively large particles having a substantial deposition velocity due to gravitational setting

Removal of 234,238U, 226Ra, 210Po and 210Pb from drinking water by ion exchange

Six organic and five inorganic ion exchangers were studied for the removal of natural radionuclides from drinking water. In the first phase, distribution coefficients (KD) of uranium and radium were determined in three model solutions: a good quality water, an Fe-Mn-rich water and a saline water simulant. The exchangers showing highest KD´s for U and Ra were tested in column mode experiments for the removal of U, 226Ra, 210Po and 210Pb from a real ground water. Considering the total 1800 processed bed volumes, the best decontamination factors (DF) for U, 20-120, were obtained with the strong base anion exchange resin. The most efficient exchangers for the removal of 226Ra were the weak and strong cation resins and zeolite A. With use of long regeneration intervals, conventional organic resins are thus most suitable for the removal of radionuclides. When only a few hundred bed volumes were processed, with the corresponding regeneration interval about one week, the aminophosphonate resin was most effective for the removal of both uranium and radium. 210Po and 210Pb in ground water were mainly bound in particles and adsorbed on the surface of the anion resins. The use of the aminophosphonate resin to remove uranium and radium would therefore require an anion resin to take up polonium and lead.

Preparation of [ 18F]β-CFT-FP and [ 11C]β-CFT-FP, selective radioligands for visualisation of the dopamine transporter using Positron Emission Tomography (PET)

In this study the N-fluoropropyl analogue of the cocaine congener β-CFT (I), N-(3-fluoropropyl)-2β-carbomethoxy-3β-(4-fluorophenyl)nortropane (β-CFT-FP, III), was labelled with 18F or 11C. Syntheses of the precursors nor-β-CFT (II) and β-CFT-FP acid (IV) as well as III itself are described. [18F]β-CFT-FP was prepared starting from I using two different labelling reagents: [18F]fluoropropyl bromide (V) and [18F]fluoropropyl tosylate (VI). A reversed-phase HPLC system proved to be effective in separating the labelled product from precursor II. The radiochemical incorporation of V or VI to yield [18F]β-CFT-FP (18F-III) was in general 30–50% and the radiochemical purity was higher than 99%. [11C]β-CFT-FP (11C-III) was synthesised by esterification of IV using [11C]methyl triflate (VII). An HPLC-purification system using a reversed-phase column proved to be effective in separating the product from the acid precursor. The radiochemical yield starting from [11C]carbon dioxide was 30–40% and the radiochemical purity was better than 99%. 18F-III and 11C-III have potential as radioligands for visualisation of the dopamine transporter (DAT) using Positron Emission Tomography (PET). Copyright

Deposition of gamma emitters from Chernobyl accident and their transfer in lichen-soil columns.

Lichen-soil column samples were taken from several locations in the Southern Finland between 1986 and 2006. Columns were divided into three parts, upper lichen, lower lichen and underlying soil, and their gamma emitting radionuclides, 134Cs, 137Cs, 103Ru, 95Zr, 106Ru, 110mAg, 125Sb and 144Ce, were measured with gamma spectrometry. Deposition values were calculated as Bq/m2 for each sampling site. Distribution of various radionuclides in the three compartments as a function of time was determined. Both effective and ecological half-lives of all radionuclides were calculated for upper lichen, whole lichen and whole lichen-soil column. A linear relation was derived between the physical half-lives and effective half-lives for whole lichen and for whole lichen-soil column. Reindeer meat activity concentrations of various radionuclides and ensuing radiation doses to reindeer-herding people were also estimated for a hypothetical case where a similar high radioactive pollution, as was taken place in the Southern Finland, would have occurred in the reindeer-herding areas in the Finnish Lapland.