Distribution of fallout radionuclides through soil surface layer

The distribution of¹³⁷Cs through soil layers has been investigated by field sampling. The investigation deals with¹³⁷Cs concentration found after the Chernobyl accident. The relationship between important soil characteristics, total precipitation and cesium distribution are analyzed. Cesium is strongly sorbed in the top soil layer and its migration downward is limited. Measurements performed over a 3-year period revealed that approximately 20–38 per cent of total¹³⁷Cs is located in the upper soil layer.     

Separation of species of radionuclides from precipitation and fallout samples

The experience with determination of species of radionuclides using the method based on in-line separation of these species by filtration and retention on columns of cation and anion exchange resins and activated charcoal, respectively, is presented. For the combined precipitation and fallout samples from the point of view of their sampling passive and indicatively active arrangements of the method have been proved. During 1984–1986 some real samples from the locality of the Institute have been analyzed, obtained results are briefly discussed and evaluated.     

Comparison of radionuclides levels from the Chernobyl reactor accident and from global fallout

Studies on radioactive fallout from atmospheric nuclear weapons tests have been carried out at this laboratory since the mid-fifties. The data thus generated on the levels and composition of radioactive fallout in India has been published periodically. Consequent to the Chernobyl reactor accident in the USSR in April 1986, similar studies were carried out. A number of fairly active samples were collected from commercial aircraft which had flown over the USSR soon after the accident. Even though the levels of fallout from the Chernobyl reactor accident observed in India were not significant from a health hazard view point, the studies provided detailed information on differences in the composition of fallout from the accident and long term radiation exposures likely to accrue from the Chernobyl fallout as opposed to global fallout from atmospheric nuclear weapons tests. This paper presents the results and their interpretation on the above aspects.     

Distribution and mean residence time of natural radionuclides in the forest ecosystem

Activity concentrations of radionuclides,⁷Be,²¹⁰Pb and²¹⁰Po, in precipitation (rain, throughfall and stemflow), wood and soil were determined by using gamma-ray and alpha-ray spectrometry to estimate the migration behavior of these radionuclides in the forest canopy. The activity ratios between output and input precipitations for the forest canopy were 0.53 of⁷Be, 0.79 of²¹⁰Pb and 1.5 of²¹⁰Po for Pasania edulis forest. A dynamic model of the transport and fate of radionuclides in the forest ecosystem was constructed. Mean residence times of radionuclides were 56 days for⁷Be, 765 days for²¹⁰Pb and 653 days for²¹⁰Po for Pasania edulis forest.     

Distribution of natural radionuclides

The distribution of natural nuclides and of the effective specific radioactivity in processing of the sphene concentrate was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 8, 2004, pp. 1237–1240.Original Russian Text Copyright © 2004 by Melnik, Lokshin, Sedneva.     

Changes of sedimentation environment inferred from fallout radionuclides and physical properties of sediment in Sun Moon Lake,Taiwan

Journal of Radioanalytical and Nuclear Chemistry - This study describes the impact of dam construction at Sun Moon Lake, Taiwan, on lacustrine sedimentation. Analyses of the physical properties of...     

The reactor accident at Chernobyl': identification of radionuclides in fallout in Niigata City

The fallout caused by the accident of Chernobyl' nuclear reactor has been monitored in Niigata City (April 30-June 3, 1986). Twelve nuclides (131I, 132I, 129Te, 129mTe, 132Te, 134Cs, 136Cs, 137Cs, 103Ru, 99mTc, 140La, 140Ba) were identified in aerosol samples. The same nuclides plus 7Be were identified in rain-water. Gaseous and particle-bound 131I were separately trapped on a glass filter and a charcoal filter, respectively. Results indicate 50-60% of atmospheric 131I is gaseous and the rest is particle-bound. Chloroform extraction of rain-water revealed that 40-60% of 131I in the rain-water sample exists in the form of IO3- and 131IO3- (131IO4-)/131I- seemed to increase with the lapse of time after the accident.     

Occurrence of natural radionuclides and fallout cesium-137 in dry-season agricultural land of South Western Nigeria

The radioactivity of the Opa river — irrigated farmlands in the south western Nigeria was determined using an HpGe based, low-level passive gamma-counting system. With the exception of two isotopes, the main radionuclides analysed in the sample were the progenies of²³⁸U and²³²Th. The other two isotopes were the naturally occurring⁴⁰K and the anthropogenic¹³⁷Cs. The result obtained showed elevated levels of radioactivity from all detected radionuclides compared to the published data for this area. Enhanced levels of naturally occurring radionuclides is attributed to the use of phosphatic fertilizers for dry season vegetable cultivation along this river banks. The presence of the fission product¹³⁷Cs could be traced to the fallouts occasioned by the various French nuclear tests in the Sahara desert, and probably, some effect of the more recent nuclear reactor accident at Chernobyl in 1986.     

Relationships between deposition of Chernobyl originating caesium and ruthenium radionuclides and rainfall in Ireland.

Deposition data for caesium and ruthenium radionuclides in Ireland as a result of the Chernobyl accident were obtained by high-resolution gamma-ray spectrometry of soil samples taken at 111 locations throughout the country. Investigation of the relationships between deposition and recorded rainfall in relevant periods enabled an assessment to be made of the activity concentration within the plume during the wash-out phase. Detailed surveys in two regions of the country enabled a comparison to be made of the relative deposition of ruthenium and caesium isotopes. No evidence was found to suggest any difference in wash-out ratios for the two ruthenium isotopes.     

Local distribution of radioactivity in tree leaves contaminated by fallout of the radionuclides emitted from the Fukushima Daiichi Nuclear Power Plant

We analyzed fresh and dead leaves collected in forests in Fukushima after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, using autoradiography. Both fresh and dead leaves of Cryptomeria japonica were contaminated by radionuclides (¹³⁴Cs and ¹³⁷Cs). Contamination of the fresh leaves was possibly attributed to interception of radionuclides by tree canopies, whereas the dead leaves indicated the direct deposition of radionuclides by fallout and/or washout of radionuclides intercepted by tree canopies. Translocation of radiocesium from a contaminated branch to new leaves growing after the FDNPP accident was not clearly observed, although transfer of radiocesium from leaf parts to male flowers occurred. Fallen leaves of Quercus serrata, which started growing after the FDNPP accident, did not show radioactivity, indicating that significant amounts of translocation from other parts to new leaves did not occur. Fallen leaves of Q. serrata collected from a litter showed hot spots originating from direct fallout. Needles of Pinus densiflora were also contaminated by fallout. Leaching with pure water removed soluble fractions of radiocesium and hot particles from the surface of the contaminated leaves, but significant amounts of radioactivity remained. This means that foliar absorption occurred in both fresh and dead leaves. Further leaching experiments using surfactant and acetone could not remove the remaining radiocesium from the leaves. The leaching experiments indicate that radiocesium in the contaminated leaves is strongly fixed in leaf tissues and is not readily released unless leaf tissues are decomposed.     

Recent trends of plutonium fallout observed in Japan: Comparison with natural lithogenic radionuclides, thorium isotopes

PM_2.5 and PM₁₀ samples were simultaneously collected monthly at a downtown site in Beijing from May 2002 to April 2003 and analyzed by instrumental neutron activation analysis (INAA) combined with organic solvent extraction method for the concentrations and distributions of extractable organohalogens (EOX), including extractable organochlorinated (EOCl), organobrominated (EOBr) and organoiodinated compounds (EOI). The concentrations of EOCl, EOBr and EOI were 10.5–79.2 ng/m³, ND-8.2 ng/m³ and 1.6–8.2 ng/m³ in PM_2.5, respectively, and 37.0–73.3 ng/m³, 1.6–12.8 ng/m³ and 1.6–8.5 ng/m³ in PM₁₀, respectively, which were increasing in the order of EOCl≫EOBr∼EOI. EOCl accounted for 73–88% and 69–91% of EOX in PM_2.5 and PM₁₀, respectively, which showed that EOCl was the major component of the organohalogens. There was a significant difference of EOCl concentrations in PM_2.5 and PM₁₀ in different seasons, which suggested that the concentrations of EOCl in the atmosphere were significantly affected by the meteorologic conditions and anthropogenic activities.     

Vertical random variability of the distribution coefficient in the soil and its effect on the migration of fallout radionuclides

In the field, the distribution coefficient, K _d, for the sorption of a radionuclide by the soil cannot be expected to be constant. Even in a well defined soil horizon, K _d will vary stochastically in horizontal as well as in vertical direction around a mean value. The horizontal random variability of K _d produce a pronounced tailing effect in the concentration depth profile of a fallout radionuclide, much less is known on the corresponding effect of the vertical random variability. To analyze this effect theoretically, the classical convection-dispersion model in combination with the random-walk particle method was applied. The concentration depth profile of a radionuclide was calculated one year after deposition assuming (1) constant values of the pore water velocity, the diffusion/dispersion coefficient, and the distribution coefficient (K _d = 100 cm^3.g^-1), and (2) exhibiting a vertical variability for K _d according to a log-normal distribution with a geometric mean of 100 cm^3.g^-1 and a coefficient of variation of CV = 0.53. The results show that these two concentration depth profiles are only slightly different, the location of the peak is shifted somewhat upwards, and the dispersion of the concentration depth profile is slightly larger. A substantial tailing effect of the concentration depth profile is not perceivable. Especially with respect to the location of the peak, a very good approximation of the concentration depth profile is obtained if the arithmetic mean of the K _d-values (K _d = 113 cm^3.g^-1) and a slightly increased dispersion coefficient are used in the analytical solution of the classical convection-dispersion equation with constant K _d. The evaluation of the observed concentration depth profile with the analytical solution of the classical convection-dispersion equation with constant parameters will, within the usual experimental limits, hardly reveal the presence of a log-normal random distribution of K _d in the vertical direction in contrast to the horizontal direction.     

Distribution of some natural and anthropogenic radionuclides in Sudanese harbour sediments

The distribution of some natural and anthropogenic radionuclides (²²⁶Ra,²²⁸Ra,²¹⁰Po,⁴⁰K,¹³⁷Cs) in surface marine sediments from the harbours at Port Sudan and Sawakin on the Sudanese coast of the Red Sea has been investigated using α-spectrometry and direct high-resolution γ-spectrometry. The prime ams were to assess the levels of radioactivity and the influence of factors such as dredging and the organic matter content of the sediments on the distribution pattern of the radionuclides. The results have been evaluated and the leves indicate the absence of any possible enhancement by anthropogenic influx from the hinterland. The spatial distribution pattern is more heterogeneous in Sawakin harbour where some parts have recently been dredged and the sludge is removed to maintain the required depth. The data also show an insignificant relationship between the activity concentrations of all the radionuclides and the content of organic matter in the sediments.     

Distribution of radionuclides and elements in Cubatão River sediments

Summary Cubat?o River is located in Santos Basin, S?o Paulo State, Brazil. This region is characterized by the occurrence of estuaries and mangrove. Due to its location, near the coastal line, it is also an important industrial area, where phosphate fertilizer plants, petrol refineries, and chemical and steel industries are present. Such human activities contribute to the enhancement of elemental composition in sediments and, in some cases, also increase the radionuclide concentrations, the so called Technologically Enhanced Natural Occurring Radioactive Materials (TENORM). The contamination of land and sediments by TENORM is of major concern. The activity concentration of U and Th series radionuclides was determined in five sediment samples from Cubat?o River. The activity concentration ratio was also determined. Equilibrium was observed for the ratio ²³⁴U/²³⁸U. The activity ratios of Th/²³⁸U, ²²⁸Ra/²²⁶Ra and ²¹⁰Pb/²²⁶Ra were higher than the unity. In the first two cases, the observed values are due to the higher activity of Th in the sediment and in the last case are probably due to the atmospheric deposition of ²¹⁰Pb.     

Resuspension of radionuclides into the atmosphere due to forest fires

Two major wild fire episodes occurred in north-western Russia in April/May and August 2008. The burning biomass and heating of the surface soil released several hazardous components into the atmosphere. During the spring smoke episode the ¹³⁷Cs activity concentration in the air in southern Finland increased by a factor of 10 compared to values just before the episode. Simultaneously there was an increase of a same order of magnitude in the concentrations of PM₁₀, trace metals (e.g. lead), polycyclic aromatic hydrocarbons (e.g. benzo[a]pyrene) and potassium. The ²¹⁰Po/²¹⁰Pb activity ratio increased from the usual 3–5% to even as high as 35% because Po is more volatile than Pb. The summer episode was less severe but still the mercury concentration in the air increased by a factor of two while ¹³⁷Cs activity concentration rose by a factor of eight. From the radiological point of view the exposure to the increased radionuclide concentration was insignificant compared to health hazards due to the increased concentration of aerosol particles and their chemical components.     

Calculation of artificial radionuclides in the ocean by an ocean general circulation model

The concentrations of three artificial radionuclides (⁹⁰Sr, ¹³⁷Cs and ^239+240Pu) introduced into seawaters from global fallout were simulated from 1957 to 1994 by using an ocean general circulation model. The distributions of the calculated ¹³⁷Cs and ⁹⁰Sr concentrations were in good agreement with the observed concentrations. The vertical distribution of the calculated ^239+240Pu concentration in the South Pacific also agreed with the observed data. However, the calculated ^239+240Pu concentrations in the North Pacific water columns were significantly underestimated in comparison with the observed data, which strongly suggests the presence of additional sources of plutonium input to the North Pacific.     

Distribution of environmental radionuclides in sediment cores of the Jinheung catchment

Sediment core samples taken from the Jinheung catchment located in the middle of the Korean Peninsula were used to know environmental radionuclide distribution. The grain sizes of the sediment cores were found at depth of about 17 cm suggesting that it might have occurred during a dry period of 1969. The radionuclides, ¹³⁷Cs, ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, ²³⁴U, ²³⁸U, ²²⁸Th, ²³⁰Th, ²³²Th, were analyzed by sector type ICP-MS and gamma-spectrometry. The Cs and Pu distribution changed with the depth, in which the maximum ranged from 14 to 22 cm. This was due to the high activity of the results of nuclear bomb tests in the air from 1960s and showed different distribution pattern on the soil surface. The average activity ratio of ²⁴⁰Pu/²³⁹Pu and ²³⁷Np/²³⁹Pu was 0.173 and 0.45, respectively. These values were similar to the north hemisphere global fallout ratio of ²⁴⁰Pu/²³⁹Pu (0.18) and ²³⁷Np/²³⁹Pu (0.45). The ²³⁷Np/²³⁹Pu ratio showed a higher value than the global fallout ratio above 14 cm depth. The U, Th and their daughter radionuclides kept secular equilibrium in the sediment core because the average activity ratios were nearly 1.     

Distribution of radionuclides in potato tubers: Implications for dose assessments

A study of the distribution of¹³⁷Cs,⁹⁰Sr, Pu and Am in potato tubers has been carried out. Cesium-137 was essentially uniformly distributed throughout the tuber, whereas up to about 50% of the⁹⁰Sr activity was found in the peel. Results for actinides indicated that most of the activity would be found in the peel and of this more than half would be located in the thin outemost skin. When account is taken of the form in which potatoes are consumed in the UK, the values of soil-plant transfer factors currently assumed in the NRPB model FARMLAND are reasonable for general assessment purposes.     

Distribution and environmental impact of radionuclides in marine sediments along the Venezuelan coast

The activity concentrations of ¹³⁷Cs, ⁴⁰K, ²²⁶Ra and ²³²Th in Bq/kg from 42 marine sediment samples collected at nine sampling sites were determined in order to establish a radiological baseline along the Venezuelan coast. The radioactivity levels were determined by means of a gamma-ray spectroscopy system using a hyper-pure germanium detector in a low-background configuration. Particle size distribution and total organic matter content were also determined. Activity concentrations of ¹³⁷Cs were lower than the detection limit of the analytical technique (0.9 Bq/kg) in all studied sites. The results suggest that the variation of grain-size distribution is one of the most important factors influencing the spatial variations of ⁴⁰K, ²²⁶Ra and ²³²Th in sediments along the Venezuelan coasts. In all sampling sites, average concentrations of ⁴⁰K, ²²⁶Ra and ²³²Th were lower than the world average values. Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in coastal marine sediments along the Venezuelan coast could be considered to be low when compared with global average values, indicating that they are not apparently above of the range that might be considered normal or background. These results suggest that the studied sites do not pose any significant radiological threat to the population. The results attained in this study should be of considerable value as baseline data and background reference levels for Venezuelan coastlines.