Radionuclide Ratios Research Articles

Cosmogenic nuclide-derived downcutting rates of canyons within large limestone plateaus of southern Massif Central (France) reveal a different regional speleogenesis of karst networks

Abstract. We present 35 new burial ages (27 sites) based on 26Al / 10Be ratios of terrestrial cosmogenic radionuclides measured in clasts and sediments deep within 12 caves in the southern Massif Central, France. Our results, together with previously published burial ages, verify that cave morphogenesis has been continuously active in this region for at least the past ∼ 6 Myr. Combining sample burial ages with their associated cave elevation above the modern stream bed gives a mean regional incision rate of 88 ± 5 m Ma−1 for the Grands Causses area. South of the Cevennes Fault Zone bordering the Grands Causses, the incision rate is 43 ± 5 m Ma−1, suggesting that this difference might be accommodated by the fault zone. Sediment burial ages from caves which are not located on river valley flanks or cliff walls are surprisingly too young compared to their expected ages when calculated using this regional average river incision rate. This suggests that the classical epigenic speleogenesis model that presumes a direct correlation between cave level development and regional base level lowering does not apply for the study area. Therefore, we propose that regional speleogenesis is mainly controlled by the removal of ghost rocks by headward erosion from river canyons to central parts of the plateaus, emptying incipient primokarst passages to create cave systems. Our results suggest a continuum process from hypogene primokarst composed of passages filled with ghost rock to one of epigene karst dynamics emptying these passages and creating cave networks. We propose that these processes are the major mechanism in the southern Massif Central that initiates speleogenesis and controls the geometry of the networks. In this region, tiered karst cannot be associated with the pace of incision of the major rivers but must be explained by former ghost rock (or hypogene) processes.

Activity Concentrations of Cs-137, Sr-90, Am-241, Pu-238, and Pu-239+240 and an Assessment of Pollution Sources Based on Isotopic Ratio Calculations and the HYSPLIT Model in Tundra Landscapes (Subarctic Zone of Russia)

The paper is devoted to the assessment of the content of anthropogenic radionuclides in tundra landscapes of the subarctic zone of Russia. The authors of the article studied the features of accumulation and migration of anthropogenic radionuclides and identified probable sources of their entry into environmental objects. Peat samples were collected on the territory of the Kaninskaya Tundra of the Nenets Autonomous Okrug (Northwest Russia). A total of 46 samples were taken. The following parameters were determined in each peat sample: (1) activity and pollution density of anthropogenic radionuclides; (2) isotopic ratios of anthropogenic radionuclides; (3) activity ratios of each radionuclide for layers 10–20 cm and 0–10 cm. The results of the studies showed that the pollution density of the Nes River basin with the radionuclides Cs-137 and Sr-90 is up to 4.85 × 103 Bq×m−2 and 1.88 × 103 Bq×m−2, respectively, which is 2–5 times higher than the available data for the Kanin tundra, as well as for Russia and the world as a whole. The data obtained for Am-241, Pu-238, and Pu-239+240 showed insignificant activity of these radionuclides and generally correspond to the values for other tundra areas in Russia and the world. It was found that some tundra areas (“peat lowlands”) are characterized by increased radionuclide content due to the process of accumulation and migration along the vertical profile. Calculations of isotope ratios Sr-90/Cs-137, Pu-238/Pu-239+240, Pu-239+240/Cs-137, Am-241/Pu-239+240 and air mass trajectories based on the HYSPLIT model showed that the main sources of anthropogenic radionuclide contamination are global atmospheric fallout and the Chernobyl accident.

Modeling Radionuclide Transfer from Pasture to Milk in Kisoro, South-western Uganda

Determination of radionuclide transfer from animal feeds to animal products and ingestion transfer rates is important in assessing internal radiation risk to humans who consume the animal products. Seventy-nine (79) pasture samples and milk samples were collected from cattle farms in seven sub-counties. Activity concentrations of radionuclides in the samples were determined using gamma spectroscopy. Transfer ratios of radionuclides to from pasture to milk were calculated. Ingestion transfer rates of radionuclide from pasture to cow were also determined. Radionuclide accumulation to the body of the cow was modeled. Contributions to radiological effects due to accumulation of radionuclides in the body were estimated. Transfer ratios of uranium and thorium from pasture to milk varied from 0.07 to 0.17, and 0.05 to 0.17, respectively. The ingestion transfer rates of uranium varied from 3.110-6 to 7.6 10-6 y l-1 while for thorium, the ingestion transfer rates varied from 2.2 10-6 to 7.5 10-6 y l-1. The contribution to radium equivalent (Bq l-1), annual effective dose equivalent (mSv y l-1), and excess lifetime cancer Risk due to the radionuclide transfer were 0.074, 0.002, and 0.0061 10-3, respectively. Comparing with the safe values of annual effective dose equivalent in foodstuffs of 0.14 mSv y l-1 which translates to excess cancer risk of 0.42 10-3, these contributions to radiological effects only account for about 1.5% of the total safe value of excess lifetime cancer risk, therefore, radionuclide transfer from pasture to milk causes a minimal radiation hazard to the milk consumers in Kisoro District.

Insights on the Sun Birth Environment in the Context of Star Cluster Formation in Hub–Filament Systems

Cylindrical molecular filaments are observed to be the main sites of Sunlike star formation, while massive stars form in dense hubs at the junction of multiple filaments. The role of hub–filament configurations has not been discussed yet in relation to the birth environment of the solar system and to infer the origin of isotopic ratios of short-lived radionuclides (SLR, such as 26Al) of calcium–aluminum-rich inclusions (CAIs) observed in meteorites. In this work, we present simple analytical estimates of the impact of stellar feedback on the young solar system forming along a filament of a hub–filament system. We find that the host filament can shield the young solar system from stellar feedback, both during the formation and evolution of stars (stellar outflow, wind, and radiation) and at the end of their lives (supernovae). We show that a young solar system formed along a dense filament can be enriched with supernova ejecta (e.g., 26Al) during the formation timescale of CAIs. We also propose that the streamers recently observed around protostars may be channeling the SLR-rich material onto the young solar system. We conclude that considering hub–filament configurations as the birth environment of the Sun is important when deriving theoretical models explaining the observed properties of the solar system.

Investigation of natural radionuclide variations and the possible uranium migration by testing with gamma-ray spectrometer: An example from Tuğlu Tepe and Deliler Sites in Şefaatli/Yozgat, Central Anatolia Region, Turkey

The in-situ gamma-ray spectrometry measurements are performed to define and map natural radionuclide variations and the possible uranium migration on the sandstone in the Central Anatolia Region and Deliler sites in Yozgat, Turkey. The concentrations of radionuclide (eU, eTh, K%) and dose rate values were measured totally on 384 points in both areas with a duration of 5 min at each measurement point. The radionuclide ratios (eTh/K, eU/K, and eU/eTh), geochemical indicators (Ume, F parameter and eU-(eTh/3,5) rate) of uranium remobilization in the rocks, and the hazard parameters were calculated and evaluated by using measured data. The separation of uranium-rich or poor areas was made easily and associated with lithological formations by evaluating all the maps produced together. While the highest concentrations of radionuclide, and dose rate values were recorded in the sandstone units under the cover layer that are Eocene neritic limestones, the lowest concentration values and dose rate were measured on siltstone and claystone in the northern part of the Tuğlu Tepe area. At the Deliler study area, the lower anomaly zones are coincide with the soils used for the cultivation of chickpeas consists of loosely cemented sandy clay siltstone, claystone, gravel, sand, silt, and clay whereas the highest concentrations observed in the outcropped sandstone and limestones. It can be seen that the study areas have variable radioactivity levels as a result of both the weathering from the surrounding granitic rocks and the transport and accumulation of sediments through different factors. On sandstones serving as reservoir rock for uranium mineralization in both Tuğlu Tepe and Deliler sites, there is a uranium migration from the granitic rocks towards these masses and sandstones have been enriched by uranium. As a result of the evaluations, it has been seen that the areas showing uranium enrichment originated from migration can be determined very easily by radioactivity measurements, which is a fast, economical and effective method.

Determining burnup, cooling time and operational history of VVER-440 spent fuel assemblies based on in-situ gamma spectrometry at Paks Nuclear Power Plant

Non-destructive assay of spent nuclear fuel assemblies using high-resolution gamma spectrometry has been developed to improve the in-situ measuring technique and the complete analytical procedure to support nuclear safeguards verification and nuclear forensics investigations. A total of 119 VVER-440 type spent fuel assemblies having individual operating histories were measured by gamma spectrometry and the activity ratios of various radionuclides were determined. The energy dependence of the detection efficiency of gamma radiation and the activities of fission products were determined by an internal calibration method. Empirical relationship between activity ratios of radionuclides, 137Cs, 134Cs, 154Eu, 144Ce, 106Ru, and 110mAg and some main fuel parameters, such as burnup, cooling time and operational history, were calculated by regression and cluster analysis. Good empirical correlation was found between the burnup and the 134Cs2/(106Ru137Cs) activity ratio, yielding burnup predictions with average deviation of 5.3% and 5.8% if the cooling time is known and unknown, respectively. The cooling time could be determined within 13.3% average deviation by using the 110mAg/134Cs activity ratio. Results of the cluster analysis of the measured data indicate a deterministic relationship between the linear combinations of the 134Cs/137Cs, 154Eu/137Cs, 144Ce/137Cs, and 106Ru/137Cs activity ratios and the operational history of the fuel assemblies.

Measurement and calculation of radionuclide concentration ratios from soil to grass in semi-natural terrestrial habitats in Greece

The results of the measurements of radionuclide transfer from soil to vegetation (Poaceae spp.) that conducted during 2010–2014, in free-ranged grazing regions in Greece, are presented in this work. The specific activities of 137Cs, 226Ra, 228Ra and 228Th radionuclides were measured and the activity concentrations were calculated in samples of soil and grass obtained from several studied regions in Greece. The respective soil-to-plant radionuclide transfer parameters (as Concentration Ratio) were calculated and the results were analyzed in terms of spatial deviation caused by the different climate type among the studied regions, provided that the same plant and soil types are studied. The Concentration Ratios ranged from 0.02 to 2.5 for 137Cs, 0.01 to 0.7 for 226Ra, from 0.07 to 1.1 for 228Ra, and, from 0.08 to 0.17 for 228Th. Although, the concentration ratios of the primordial radionuclides show some consistency among the different regions, significant differences are observed for 137Cs, which may be particularly attributed to the different climatic types (according to the Koppen-Geiger climate classification) that govern these regions.

Grass/Soil Concentration Ratios (CRs) of Natural 226Ra, 232Th, and 40K in Vetiveria zizanioides (Vetiver Grass) in Thailand

This work investigated the grass/soil concentration ratios (CRs) of natural radionuclides (226Ra, 232Th, and 40K) in vetiver grass collected from three different regions of Thailand using an HPGe (high-purity germanium) gamma spectrometer. The sampled grass blades were divided into three equal parts to investigate the dependence of grass/soil CRs on the positions of grass blades. The results showed that 40K had the highest grass/soil CRs due to being an essential nutrient for most plants, with ranges of 1.12–7.92, in comparison with 226Ra and 232Th that had ranges of 0.32–1.48 and 0.20–1.31, respectively. In addition, the results indicated that the natural radionuclides investigated were uniformly transferred and accumulated throughout grass blades (p < 0.05), which implied the independence of CRs on the section of the leaf. Furthermore, it was found that the soil samples collected from the central region of Thailand had the highest activity concentrations in all radionuclides, mainly due to a primary composition of dark clay, leading to the highest contents of potassium and calcium (Total K and Total Ca, respectively), and the highest cation exchange capacity (CEC) that led to high concentrations of nutrients and radionuclides. Based on the results from this work, the vetiver grass presented potentials to be utilized as radionuclide absorbers in polluted soil and water due to its high CRs in comparison with other reported plants.

177Lu-DOTATATE Peptide Receptor Radionuclide Therapy: Indigenously Developed Freeze Dried Cold Kit and Biological Response in In-Vitro and In-Vivo Models.

Somatostatin receptors (SStR) based 177Lu-DOTATATE therapy is known as one of the highly effective neuroendocrine tumors (NETs) treatment strategy. Development of DOTATATE freeze-dried kit for imaging and therapy of SStR positive NETs is a prime goal in neuroendocrine cancer research. The present work describes the development of 177Lu-DOTATATE freeze dried cold kit for indigenous needs, through technology development fund (TDF) program offered by Higher Education Commission (HEC) Pakistan. The parameters for freeze dried kit production was optimized and tested the stored lyophilized cold kits for different time intervals after labeling with 177Lu radioisotope. The effect of ligand to radionuclide ratio, pH and reaction time at 90°C was recorded. Five times greater molar concentration of ligand, pH 5 and 30 min reaction time were the effective reaction conditions for maximum radiochemical yield. The radiolabeling yield at 1 day, 1-week and 4-week post storing period showed ∼100% radiochemical yield. The biodistribution study using rat model depicted the absence of non-targeted accumulation while glomerular filtration rate also explains the rapid renal washout. Cytotoxicity study showed quite favorable results for subjecting the radiopharmaceutical to clinical practice in Pakistan.

The study of Canadian Arctic freshwater system toward radioactive contamination - status in 1999

This work provides a novel data set on accumulations of both anthropogenic (137Cs, 238Pu, 239+240Pu, 241Am) and natural (210Pb, 226Ra, 232Th) radionuclides and an element (K). Sampling of soils and lake sediments was accomplished in 1999 during Tundra Northwest (TNW-99) international expedition to a remote region of the Canadian Arctic. The sediment ages and sedimentation rates were determined. The obtained results overall indicated a high geographical diversity of contamination levels and trends. Accumulation rates were also differential, and a sediment focusing contribution was distinctly visible. Radioactive pollution was found to be lower relative to temperate counterparts. The activity ratios of anthropogenic radionuclides corresponded to global fallout as a prevailing source in the entire examined area. The post-Chernobyl radiocaesium was observed for the westernmost lake only. The elevated level of 137Cs and 239+240Pu in the topmost sediment at the northern and eastern Arctic Archipelago was attributed to recent resuspension and subsequent redistribution of radionuclides.

Radiological safety of groundwater around a uranium mine in Namibia

Uranium mining activities produce the main element used in nuclear energy production. However, it can also negatively affect the environment including groundwater by release of residues or effluent containing radioactive elements. The study investigated the concentration and radiological hazard of uranium in groundwater and seepage water from the tailings of a uranium mine in Namibia. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to assess the concentration of uranium in the groundwater and seepage water and the radiological hazards were determined. The radiological hazard indices Radium equivalent activity (Raeq), Absorbed dose (D), Annual Effective Dose equivalent (AEDE), External hazard index (Hex) and Internal hazard index (Hin) were determined and compared to limits recommended by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). The calculated average value of D and Hin of groundwater is 108.11nGyh−1 and 1.26, respectively and are above the UNSCEAR values (55 nGyh−1 and 1). Further, the average values of Raeq, AEDE and Hex were below the recommended values. The isotopic ratio of uranium radionuclides in groundwater indicates that the uranium in the sampled groundwater is below 1 suggesting it is not natural uranium present but a possible contamination from the mine seepage. The radiological hazard parameters of the seepage water were above the recommended values and thus pose a radiation risk to human and environment.

Solid/liquid ratios of trace elements and radionuclides during a Nuclear Power Plant liquid discharge in the Seine River: Field measurements vs geochemical modeling

This study focuses on the determination of field solid/liquid ratios (Rd) values of trace element (TE) and radionuclide (RN) in the Seine River (France) during a concerted low radioactivity level liquid regulatory discharge performed by a Nuclear Power Plant (NPP) and their confrontation with Kd values calculated from geochemical modeling. This research focuses on how field Rd measurements of TE and RN can be representative of Kd values and how Kd models should be improved.For this purpose 5 sampling points of the Seine River during a NPP's liquid discharge were investigated: upstream from the discharge in order to assess the natural background values in the area of effluent discharge, the total river water mixing distance (with transect sampling), and 2 points downstream from this last area. The main parameters required determining field Rd of TE and RN and their geochemical modeling (Kd) were acquired. Filtered waters were analyzed for alkalinity, anions, cations, dissolved organic carbon (DOC), TE, and RN concentrations. Suspended particulate matter (SPM) was analyzed for particulate organic carbon (POC), TE and RN concentrations and mineralogical composition. Field Rd and Kd values are in good agreement for stable Cd, Cu, Ni, Pb and Zn and for 7Be. Conversely, measured field Rd for stable Ag, Ba, Sr, Co and Cs are systematically higher than modeled Kd values. Even if only the lowest possible values were obtained for 137Cs and 60Co Rd measurements, these estimated limits are higher than calculated Kd for 137Cs and in good agreement for 60Co. Finally, only two RN exhibit field Rd lower than calculated Kd: 234Th and 210Pb.Comparison of field Rd vs. modeled Kd values for TE and RN allows the identification, for each element, of the main involved adsorption phases and geochemical mechanisms controlling their fate and partitioning in river systems.

Cryoconite: an efficient accumulator of radioactive fallout in glacial environments

Abstract. Cryoconite is rich in natural and artificial radioactivity, but a discussion about its ability to accumulate radionuclides is lacking. A characterization of cryoconite from two Alpine glaciers is presented here. Results confirm that cryoconite is significantly more radioactive than the matrices usually adopted for the environmental monitoring of radioactivity, such as lichens and mosses, with activity concentrations exceeding 10 000 Bq kg−1 for single radionuclides. This makes cryoconite an ideal matrix to investigate the deposition and occurrence of radioactive species in glacial environments. In addition, cryoconite can be used to track environmental radioactivity sources. We have exploited atomic and activity ratios of artificial radionuclides to identify the sources of the anthropogenic radioactivity accumulated in our samples. The signature of cryoconite from different Alpine glaciers is compatible with the stratospheric global fallout and Chernobyl accident products. Differences are found when considering other geographic contexts. A comparison with data from literature shows that Alpine cryoconite is strongly influenced by the Chernobyl fallout, while cryoconite from other regions is more impacted by events such as nuclear test explosions and satellite reentries. To explain the accumulation of radionuclides in cryoconite, the glacial environment as a whole must be considered, and particularly the interaction between ice, meltwater, cryoconite and atmospheric deposition. We hypothesize that the impurities originally preserved into ice and mobilized with meltwater during summer, including radionuclides, are accumulated in cryoconite because of their affinity for organic matter, which is abundant in cryoconite. In relation to these processes, we have explored the possibility of exploiting radioactivity to date cryoconite.

Sources and variation of isotopic ratio of airborne radionuclides in Western Arctic lichens and mosses

This research concerned radioactivity of lichens and mosses from coastal zones of the Canadian Arctic and Alaska. Over 50 samples were collected from 7 positions during two scientific expeditions in 2012 and 2013. The tundra contamination caused by anthropogenic radionuclides was relatively low, reaching mean values with SD's of: 17.4 ± 3.5 Bq/kg for 90Sr, 14.0 ± 2.9 Bq/kg for 134Cs, 38.4 ± 7.5 Bq/kg for 137Cs, 0.86 ± 0.24 Bq/kg for 239+240Pu, 0.065 ± 0.017 Bq/kg for 238Pu and 0.50 ± 0.13 Bq/kg for 241Am. The increase of activity concentration with increasing latitudes was noticed mostly in regard to 90Sr, Pu isotopes and 241Am. The analysis of isotopic ratios exhibited dominant contribution of the global fallout (+SNAP 9A satellite re-entry fallout) for the presence of plutonium isotopes and 241Am. The Fukushima fallout signature was identified in a few lichens from Alaska. However, the influence of additional unknown factor on the occurrence of 90Sr and 137Cs has been detected in western part of Canadian Arctic. Natural radioisotopes of thorium and uranium were found throughout the entire investigated region and the average values of activity concentration with SD's were as follows: 2.92 ± 0.47 Bq/kg for 230Th, 2.61 ± 0.48 Bq/kg for 232Th, 4.32 ± 0.80 Bq/kg for 234U and 3.97 ± 0.71 Bq/kg for 238U. Examined Western Arctic tundra was not affected with any technically enhanced natural radioactivity.

Airborne radionuclides and heavy metals in high Arctic terrestrial environment as the indicators of sources and transfers of contamination

Abstract. A survey of airborne radioactive isotopes (137Cs, 238Pu, 239+240Pu, 241Am, and 210Pb) and trace metals (Pb, Cu, Zn, Cd, Fe, Al) in tundra soils and cryoconite hole material sampled from several locations in the Kaffiøyra region of Spitsbergen revealed significant variability in spatial concentration. Lithogenic radionuclides (230Th, 232Th, 234U, 238U) show less variability than the airborne radionuclides because their activity concentrations are controlled by mixing of local material derived from different types of bedrock. Activity ratios of the artificial radionuclides in most cryoconite samples differ from global fallout signatures. The contribution of radionuclides from additional and more specific sources might be enhanced by non-continuous exposure of cryoconite to atmospheric deposition. We assumed that the main source of Pu, which was detected only in cryoconite samples, is derived from nuclear tests and non-exploded weapons-grade material. Approximately one-third of the total observed Pu activity concentration is 238Pu, most likely originating from the SNAP9A satellite re-entry, which was powered by a 238Pu thermoelectric generator. In samples from Waldemarbreen the influence of glacial local morphology on the capability of cryoconite for trapping and accumulating airborne radionuclides is apparent. Local glacial morphology plays an important role in determining the accumulation of airborne pollutants. Trace metal concentrations in soils were typical or slightly higher than concentrations characteristic for the natural background; the 206Pb∕207Pb signature was also close to the natural ratio of the parent rocks. Conversely, trace metal concentrations in cryoconite samples (Pb and Cd) were higher than in soil samples and exceeded natural values. Cryoconite is an effective monitor of the spread of artificial radionuclides and heavy metals in their surrounding environment.

Whole organism concentration ratios of radionuclides and metals in terrestrial vertebrates of an Australian tropical savanna environment

Preliminary values of whole organism concentration ratio (CRwo-soil) were derived for terrestrial vertebrates of an Australian tropical savanna environment. Wildlife groups included bird, bat, ground-dwelling mammal and reptile. Sample data for some of the wildlife groups (bird and bat in particular) were limited. The bird and bat CRwo-soil values were generally lower than the ground-dwelling mammal and reptile CRwo-soil values based on the available data. Arithmetic mean CRwo-soil values for two species of native marsupial and two species of non-native placental were not significantly different (p < 0.05) when tested using a one-way analysis of variance. The results hinted at possible sampling efficiencies for terrestrial vertebrates. However, verification with additional data was recommended. Used cautiously, the CRwo-soil values may assist in environmental assessments of Australian uranium mining sites. They also enhance the available data on radionuclide transfer to wildlife for use internationally.

Nonhuman biota dose rate estimation from liquid effluent releases during normal operations of light water reactors using the LADTAP II computer code

The LADTAP II computer code was used to estimate the dose rates to seven nonhuman biota (fish, algae, invertebrate, muskrat, raccoon, heron, and duck) from liquid effluent releases during the normal operations of new light water reactor facilities in the United States. The estimated dose rates to nonhuman biota depended on the nuclear power plant design but were orders of magnitude less than the ‘derived consideration reference levels’ (DCRL) in International Commission on Radiological Protection (ICRP) Publication 108. The estimated dose rates were at least three orders of magnitude lower than the guideline values identified by the International Atomic Energy Agency (IAEA) and the National Council on Radiation Protection and Measurements to cause observable changes in populations of biota. Radionuclides that contributed most of the dose rates for seven nonhuman biota depended on the nuclear power plant design. The differences in the estimated dose rates to seven nonhuman biota calculated from the default bioaccumulation factors used in the LADTAP II computer code and the dose rates calculated from the concentration ratios of radionuclides in the IAEA Technical Report Series (TRS) wildlife handbook were less than one order of magnitude for most default biota in LADTAP. The concentration ratios for some radionuclides in liquid effluent releases from nuclear power plant designs that contributed more than 5% of the internal dose rates for invertebrates (P, and Ru) and algae (La and Pr) were not available in the IAEA TRS wildlife handbook.

IMPACT ON ABSORBED DOSE RATE IN AIR IN THE IZU ISLANDS FROM LONG HALF-LIFE RADIONUCLIDES RELEASED BY THE FUKUSHIMA DAIICHI NUCLEAR POWER PLANT ACCIDENT.

Car-borne surveys were carried out on eight islands of the Izu Islands located 339-570 km southwest of the Fukushima Daiichi Nuclear Power Plant. The mean dose rates measured in 2015, 2016 or 2017 on each island were from 12 to 47 nGy h-1, meaning that the contribution ratios of artificial radionuclides were 5-31%. Based on the environmental half-life for long half-life radionuclides (134Cs + 137Cs) measured on Izu-Oshima (3.1 y), the mean dose rates in March 2011 were estimated to be 15-53 nGy h-1 and the contribution ratios of artificial radionuclides were 11-55%. The estimated annual external effective doses were 0.06-0.21 mSv which were 13-44% of the worldwide average (0.48 mSv).

Natural and artificial radionuclides in a marine core. First results of 236U in North Atlantic Ocean sediments

There are very few data available of 236U in marine sediment cores. In this study we present the results from the first oceanic depth profile of 236U in a sediment core sampled in the North Atlantic Ocean, at the PAP site (4500 m depth, Porcupine Abyssal Plain (PAP) site, 49°0′ N, 16°30′ W). Additionally, the sediment core was radiologically characterized through the measurement of anthropogenic 137Cs, 239Pu, 240Pu, 129I and 14C and natural 210Pb, 40K and 226Ra.The measured 236U concentrations decrease from about 90·106 at g−1 at the seafloor down to 0.5·106 at g−1 at 6 cm depth. They are several orders of magnitude lower than the reported values for soils from the Northern Hemisphere solely influenced by global fallout (i.e. from 2700·106 to 7500·106 at g−1). 236U/238U atom ratios measured are at least three orders of magnitude above the estimated level for the naturally occurring dissolved uranium. The obtained inventories are 1·1012 at m−2 for 236U, 80 Bq m−2 for 137Cs, 45 Bq m−2 for 239+240Pu and 2.6·1012 at m−2 for 129I. Atomic ratios for 236U/239Pu, 137Cs/236U and 129I/236U, obtained from the inventories are 0.036, 0.11 and 2.5 respectively. Concentration profiles show mobilization probably due to bioturbation from the abundant detritivore holothurian species living at the PAP site sea-floor. The range of 236U, 137Cs, 239+240Pu and 129I values, inventories and ratios of these anthropogenic radionuclides are more similar to the values due to fall-out than values from a contribution from the Nuclear Fuel Reprocessing Plants dispersed to the south-west of the North Atlantic Ocean. However, signs of an additional source are detected and might be associated to the nuclear wastes dumped on the Eastern North Atlantic Ocean.

Uncertainty of determination of 158Tb in the RBMK nuclear reactor waste

The activity of 158Tb was measured in waste samples from the Ignalina NPP Unit I RBMK-1500 reactor using gamma-ray spectrometry. The origin of 158Tb and the other observed gamma-ray emitters has been studied by using SCALE 6.1 modeling and comparing radionuclide ratios in the RBMK-1500 radioactive waste. The results of the calculation of the massic activity of gamma-ray emitters were used for interpretation of the total gamma-ray spectrum and the determination of 158Tb massic activity uncertainty in the waste of RBMK-1500.