Long-term radiocarbon variation studies in the air and tree rings of Slovakia

Fifty-five years of radiocarbon variation studies are reviewed with an emphasis on a better understanding of the impacts of the Bohunice nuclear power plant and fossil fuel CO2 on the atmosphere and biosphere of Slovakia. The maximum Δ14C levels in the air up to about 1200‰ were observed during the 1970s at the Žlkovce monitoring station, which after 2005 decreased to <30‰. A relative decrease in the atmospheric Δ14C levels due to increasing levels of fossil CO2 in the atmosphere has also been significant, for example, in Bratislava down to about -330‰, but after 2005 they were only <50‰ below the Jungfraujoch European clean-air level. The tree-ring data, averaging the annual Δ14C levels for several stations in Slovakia, have been in agreement with the atmospheric data, as well as with the newly established clean-air station at Jasná in central Slovakia. Future 14C levels will depend strongly on fossil CO2 levels in the atmosphere, which will change the bomb 14C era to the fossil CO2 era. New investigations of 14C variations in the atmosphere-biosphere-hydrosphere compartments represent a great challenge for radiocarbon science, important for better understanding of environmental processes, climate change, and impacts of human activities on the total environment. This new era of radiocarbon research will also need new developments in radiocarbon analytical technologies, as further progress in accuracy and precision of results (<1‰) will be needed to meet the new radiocarbon challenges.

Temporal changes of 137Cs concentrations in the Far Eastern Seas: partitioning of 137Cs between overlying waters and sediments

Deep-ocean sediments, similarly to seawater, are important reservoirs of 137Cs, an anthropogenic radionuclide with a relatively long half-live found in the Earth system. To better understand the geochemical behaviour of 137Cs in the ocean, we examined the temporal changes of 137Cs activity concentrations in the overlying waters and in sediments from the Far Eastern Seas (Sea of Japan, SOJ, and Okhotsk Sea, OS) during the period of 1998-2021. The 137Cs activity levels showed exponential changes during the observed period. The decay-corrected change rates of 137Cs in deep waters of SOJ exhibited a slow increase, while 137Cs levels in seawater and sediment in OS decreased gradually. This reflects a topographical difference, as SOJ is a semi-closed sea, whereas OS receives continuously inflow of subarctic waters. It was confirmed that 137Cs released after the Fukushima Dai-ichi Nuclear Power Plant accident was rapidly transported into the deep waters of the SOJ. To elucidate the transfer processes of 137Cs from seawater to sediment, we discussed the temporal changes of the partition coefficients (Kd) of 137Cs between the overlying water and the surface sediment. In shallow areas (< 1500 m water depth), Kd values were almost constant within the sampling periods, although the temporal changes in the Kd values occurred in deeper waters (> 2500 m depth). The Kd values increased with increasing depth, which may reflect a pressure effect as a possible mechanism. These findings suggest that chemical processes may be important factors controlling the transport of 137Cs between seawater and sediment, although more complicated phenomena occurred in deep waters and sediments of the SOJ (> 3000 m depth).

Impact of the Fukushima Accident on 3H and 14C Environmental Levels: A Review of Ten Years of Investigation

The investigation of the impact of the Fukushima accident is still going on although more than ten years have passed since the disaster. The main goal of this paper was to summarize the results of tritium and radiocarbon determinations in different environmental samples, possibly connected with the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A document containing compiled data may serve as a solid basis for further research in the selected fields. To accomplish such effort, we went through dozens of relevant published papers, reporting 3H and 14C activity concentrations in precipitations, groundwater, seawater, river systems, tree rings, and, in some more extraordinary samples, such as herbaceous plants or debris from the damaged reactor buildings. As the referenced results would not be obtainable without adequate analytical techniques, the most common methods for routine measurement of tritium and radiocarbon concentrations are discussed as well. We believe that the correct identification of the affected environmental compartments could help quantify the released 3H and 14C activities and track their following fate, which could be especially important for plans to discharge contaminated water from the FDNPP in the upcoming years.

Methodology and Applications of the Determination of Cosmogenic Radionuclides ¹⁰Be and ²⁶Al by Accelerator Mass Spectrometry

The measurement of cosmogenic radionuclides 10Be and 26Al by accelerator mass spectrometry (AMS) has become an invaluable tool for dating events and processes in Quaternary geochronology, and in archaeology and paleoanthropology. Here we present an overview of the current state of research by providing the theoretical and methodological background and describe processes of sample preparation and measurement by AMS. We also summarize the main geochronology calculation models for exposure and burial dating for the above applications and analysis of extra-terrestrial materials.

Tritium and radiocarbon in the water column of the Red Sea

Despite being the busiest transient sea in the world due to the Suez Canal, radionuclide distribution studies in seawater and sediment of the Red Sea remain rare. A sampling expedition in the Red Sea was conducted from June 9 to July 6, 2021, visiting a transect of several deep sampling stations located along the central axis of the basin from the Gulf of Aqaba to the southern Red Sea (near Farasan Island, Saudi Arabia). The collected seawater profile samples were analyzed for tritium, radiocarbon and oxygen-18. The observed tritium levels in surface waters of the Red Sea peaked at 0.3-0.4 TU, similar to the values observed in the western Arabian Sea (decay corrected). The values observed at waters below 150 m were around 0.2 TU, however, at depths of 450 and 750 m, tritium minima (<0.2 TU) were observed, which could be associated with a partial return flow of bottom waters from the southern to the northern Red Sea. At two stations at the depth of about 550 m, deep Δ14C minima were observed as well (-4‰ and -10‰), documenting ongoing transport of carbon in the water column, important for sink of anthropogenic carbon.

Ten years of investigations of Fukushima radionuclides in the environment: A review on process studies in environmental compartments

In March 2011, severe nuclear accident happened at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the gigantic earthquake and following huge tsunami wave. A lot of investigations to assess environmental and radiological impacts of released radionuclides have been conducted by domestic and international organizations. Environmental radioactivity research related to the FDNPP accident has spread widely over different scientific fields due to specific features of the accident, and specifically its impact on the marine environment. The present paper summarizes major lessons learned from the environmental investigations of the FDNPP accident. Environmental radioactivity studies have typical interdisciplinary character; especially physics and chemistry are fundamental as a base of process studies in the environment. In this sight, we review chemical aspects regarding FDNPP-derived radiocesium transfer within and between compartments (atmosphere, ocean and land). We also discuss future trends in investigations of behavior of anthropogenic radionuclides in the environment, important not only for a better understanding of impacts of the FDNPP accident on the environment, but also for improving our general knowledge of the total environment in the Anthropocene era and its protection for the future.

Sequential scavenging and measurement of seawater radiocesium concentrations and plutonium isotopic ratios offshore Fukushima

The scientific interest in radiocesium and plutonium found in the oceans and seas has increased enormously in the past years as a consequence of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident and is expected to be ongoing due to many unresolved questions. Hence, continuous development of new and verification of old analytical methods should be at the top of the list of the community, working on the topic. In this study, we processed and analyzed several seawater samples, collected in different time frames (2011-2015) from the North Pacific Ocean offshore Fukushima, to determine their radiocesium activities, ¹³⁴Cs/¹³⁷Cs activity ratios and ²⁴⁰Pu/²³⁹Pu isotopic ratios using the sequential scavenging method, gamma spectrometry and accelerator mass spectrometry (AMS). The observed radiocesium levels in seawater (0.07-0.042 Bq L^-1) clearly indicated that the investigated region remained impacted by releases from the damaged power plant even after four years after the accident. Regarding plutonium, its successful separation from large volume seawater samples was confirmed by detection of ²⁴⁰Pu by AMS. However, several problems emerged during the analyzes, which we tried to address with the use of additional methods (e.g., measurements of uranium by ICPMS). The efficiencies of the applied methods and other issues are also discussed.

RADIOCARBON DATING OF CHARCOALS FROM HISTORICAL MORTARS FROM TÝŘOV AND PYŠOLEC CASTLES

Organic inclusions in lime binders provide useful samples for radiocarbon dating of historical objects. Two Czech castles Týřov and Pyšolec from Late Middle Ages were explored, and tens of charcoals were found in their walls. The radiocarbon content of the charcoals was measured with accelerator mass spectrometry. The dating results showed that none of the charcoals were younger than the known historical ages (Týřov: 1260 - 1270, Pyšolec: 1300 - 1340), but some were considerably older. Two charcoals from Pyšolec castle dated to Palaeolithic, likely originating from fluvial sediments added as an aggregate to the mortar. When excluding these two charcoals, the others indicated most likely dates being 50-100 y older than the building dates of the castles. This systemic effect corresponds to the age of wood used for lime burning and shall be accounted for when dating mortars using charcoals.

Distribution of 241Am and Pu isotopes in the Curonian Lagoon and the south-eastern Baltic Sea seawater, suspended particles, sediments and biota

Distribution trends and temporal variations of 241Am and Pu isotopes in the south-eastern Baltic Sea during the study period of 1999-2001 and 2011-2015 were investigated with the aim to study temporal changes of radionuclide levels in seawater, suspended particles and sediment, to estimate 241Am and 239,240Pu levels in marine biota and to assess the radiation doses received by the biota. The activities of 241Am and 239,240Pu were measured by alpha spectrometry after radiochemical purification. 241Pu was determined radiometrically via the ingrown daughter 241Am after 10-12 years of storage, while the 240Pu/239Pu atom ratio of was measured by accelerator mass spectrometry. The 239,240Pu activities in suspended particles collected in the coastal waters of the Baltic Sea decreased by a factor of ∼3 during the study period, while they decreased about fourfold in the Curonian Lagoon. This could indicate a decrease in the influx of particles containing Pu isotopes into the Baltic Sea. While in the Curonian Lagoon, the 239,240Pu activities in the sediment samples varied insignificantly during the study periods, in the Baltic Sea, the maximum activity decreased by a factor of 6, and the mean/median values decreased by ∼4 times. The assessment tool ERICA was used to calculate the dose rates for biota. The total dose rate from all analysed radionuclides was <0.1 μGy/h, therefore no risk to organisms was identified.

Temporal variability of plutonium in surface waters of the Sea of Japan

Long-term temporal variations of plutonium in Sea of Japan (SOJ) surface waters have been examined with the aim to better understand its behavior during several decades. The first observation is that ^239,240Pu activity concentrations in surface waters of the SOJ during 1977-2019 were 6.5 ± 4.7 mBq m^-3 in average, and 5.1 mBq m^-3 as the median, whereas ¹³⁷Cs and ⁹⁰Sr activity concentrations decreased with time, except of the perturbation due to the 2011 Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Another observation is that sporadic high ^239,240Pu activity concentrations occurred in the east Japan Basin, ranging from 1 to 39 mBq m^-3. The spatial distribution of ^239,240Pu activity concentrations in surface waters revealed that high ^239,240Pu levels (>20 mBq m^-3) occurred in 1994 in the northern SOJ, which was considered to be due to winter convection. To elucidate factors controlling the temporal variability of surface ^239,240Pu levels in the SOJ, a relationship between surface ^239,240Pu activity concentrations and vertical diffusion coefficients was examined. The results revealed that this relationship could be classified into two groups: one group did not show a change with increasing diffusion coefficient, while the other group showed a positive correlation. The vertical ^239,240Pu distribution in SOJ waters suggests that the high surface ^239,240Pu levels occurred due to the upwelling of cyclonic eddy. The rapid recycling of deeper plutonium occurred in the SOJ due to deep winter convection and upwelling associated with cyclonic eddy. The plutonium levels in the SOJ have been found to be sensitive to climate changes. Warming of the SOJ may cause a reduction of winter convection and eddy activity as a result of increasing sea surface temperature. This leads to a decline of recirculation of plutonium and other bioavailable elements from Japan Sea Proper Water (JSPW) to surface water layers. Plutonium would be, therefore, an important indicator of biogeochemical processes in the marine environment, helping to assess climate change impacts on marine ecological systems.

Recent developments in IBA analysis at CENTA, Bratislava

An experimental setup used at the CENTA (Centre for Nuclear and Accelerator Technologies) laboratory to carry out IBA (Ion Beam Analysis) techniques is described. PIXE (Particle Induced X-ray Emission) technique offers a unique way of non-destructive elemental analysis using accelerated ion beams. The calibration of instrumental constants (H-values) of SDD and BEGe detectors, used in the setup, is described in detail. The H-value was determined as a function of X-ray energy by using thin MicroMatter standards of chosen elements. The calibrated H-values were then used in GUPIXWIN for the determination of elemental concentrations in two IAEA reference materials, which were compared with reference values. A reasonable agreement was achieved between the measured and reference values, while the calibrated H-values will be used for further analyses.

Determination of ultra-trace levels of uranium and thorium in electrolytic copper using radiochemical neutron activation analysis

Uranium and thorium as natural radioactive elements are present everywhere in the environment. Their trace levels are also present in various materials, such as copper, used as a shielding material in gamma-ray spectrometry, usually located very close to the detector. Ultra-low levels of uranium and thorium in electrolytic copper were determined in this study using radiochemical neutron activation analysis (RNAA) via their induced nuclides U-239/Np-239 and Pa-233, respectively. After irradiation of copper together with uranium and thorium standards, various techniques were used for their separation from the matrix. To isolate of short-lived U-239, solvent extraction in a combination of tributyl phosphate (TBP) in toluene was used. To separate Np-239 and Pa-233, extraction chromatography using TEVA and TK-400 resins was applied. Special attention was paid to the estimation of radiochemical recovery, which was determined in each sample aliquot using U-235, Np-238 and Pa-231 tracers. For quantification of induced nuclides and tracers used in the experiment, gamma-ray spectrometry was used. Obtained results showed that electrolytic copper samples contained impurities of uranium and thorium in ultra-trace levels: up to 45 pg/g (550 nBq/g) for uranium and up to 80 pg/g (330 nBq/g) for thorium. The electrolytic copper also contained impurities of Ag, As, Au, Sb, Se and Zn as observed using the k₀-INAA technique.

The neutron component of background of an HPGe detector operating in a surface laboratory

Investigation of neutron-induced background was carried out by studying interactions of cosmic-ray neutrons with an HPGe detector inside its shield placed on a ground floor of a 3-storey building. The study was conducted experimentally and by Monte Carlo simulations using GEANT4 simulation tool. Detailed analysis of measured background γ-ray spectra showed that many γ-lines visible in the spectra were induced by neutrons. The majority of detected γ-rays originated in germanium, copper, lead and tin. Iron and aluminium components were less important background sources. Inelastic scattering and neutron capture were the most often occurring processes of neutron interactions with the detector and its shielding. The contamination by natural radionuclides, specifically of ⁴⁰K, ²¹⁴Pb, ²¹⁴Bi and ²⁰⁸Tl, was also present in the background spectra. Nevertheless, approximately 35% of ²⁰⁸Tl peak at the energy of 2614.51 keV was produced by inelastic scattering of neutrons on ²⁰⁸Pb nuclei. The experimental background was compared with GEANT4 simulations, which were carried out without and with the shielding layer of the building. The final integral counting rates for measured spectrum in the energy range from 50 keV to 2875 keV was 1.26 ± 0.07 s^-1 and for simulated one 1.25 ± 0.13 s^-1, indicating very good agreement with the experiment.

Temporal changes in tritium and radiocarbon concentrations in the western North Pacific Ocean (1993-2012)

The western North Pacific is one of the most studied oceanic basins due to its diverse structure and important role in connection with the adjacent reservoirs. Tritium (³H) and radiocarbon (¹⁴C) have been frequently exploited as oceanographic tracers due to their suitable properties; several extensive observation projects, such as GEOSECS, WOCE and WOMARS, used these two radionuclides to investigate different oceanographic processes, pathways, ocean currents and time scales of deep and bottom water formation. Here we evaluate temporal changes in ³H and ¹⁴C levels in seawater of the western North Pacific Ocean from 1993 to 2012. When compared to the background levels from 1993, the data from 2012 suggests significant impact of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on surface and vertical ³H seawater profiles, increasing its water column inventories in the southern part of the 149°E meridian by a factor of 2-7. On the other hand, ¹⁴C content in surface seawater has been steadily decreasing from 1993, with the accelerated rate from 2005, probably due to downwelling of bomb-produced radiocarbon and its transport along isopycnal layers. The influence of the Oyashio current on ¹⁴C levels in the northern part of the investigated transect and formation of its intrusion was also clearly visible in the collected datasets. Regarding bomb-produced radiocarbon, its water column inventories decreased or remained same from 2005 to 2012 at all stations, except the ones located in the coastal areas of the New Guinea island (3.5°S).

Radiocarbon analysis of carbonaceous aerosols in Bratislava, Slovakia

Aerosols dispersed in the atmosphere represent important factors influencing not only the environment, but also human health. Carbonaceous aerosols are one of the main components of total atmospheric aerosols, and their sources are of great interest. Radiocarbon analysis provides an excellent way to determine the fraction of fossil and non-fossil aerosols in the atmosphere. Over the period of one year (June 2017-June 2018), we sampled atmospheric aerosols with size greater than 0.3 μm in Bratislava, Slovakia and used the exposed quartz filters for radiocarbon analysis of the elemental carbon (EC) aerosol fraction. The results show that on average the fossil fuel combustion is the dominant source of EC aerosol particles in Bratislava. In summer months, they represent more than half (65-80%) of the total EC aerosols. The relative amount of EC particles derived from biomass burning was 20-35% in summer, which increased to 40-55% in winter months. The dominance of fossil fraction is caused by high degree of industrialization and urbanization of the city. The increase of biomass fraction in winter is probably caused by domestic wood burning in areas surrounding the Bratislava city.

Radiocarbon in tree rings from a clean air region in Slovakia

In order to study radiocarbon levels at a clean air location in Slovakia with no significant local anthropogenic effects, we took tree ring samples from a tree in the vicinity of Jasná recreational area in the Low Tatras region in the central part of Slovakia. There are no significant local fossil fuel emission sources, so these samples represent a regional clean air background important for ¹⁴C studies in Slovakia and Central Europe. The growth rings from the sampled tree (European spruce, Picea abies) cover the period from 1911 to 2016. The first part of the data (1911-1952) represents natural radiocarbon levels influenced by Suess effect. The following period exhibits an increase in radiocarbon levels due to atmospheric nuclear weapons tests (Δ¹⁴C maximum of 850‰ in 1964), and then a gradual decrease characterized by an exponential trend with time constant of 14.3 ± 0.5 years. The Δ¹⁴C data from Jasná was used as a reference for comparison with two previously reported modern tree ring data sets from Slovakia. This comparison showed that radiocarbon levels at both locations are lower than clean air reference values, indicating the influence of local fossil fuel emissions.

Radiocarbon and 137Cs dating of wines

Wine dating methods based on anthropogenic ¹⁴C and ¹³⁷Cs, as well as on the cosmogenic ¹⁴C were studied with the aim to improve the accuracy and precision of the dating results. While the ¹⁴C dating method has proved to be useful for dating young and old wines, the ¹³⁷Cs has been effective for dating of wines originating around the ¹³⁷Cs bomb-peak observed in 1963. A new method was developed for simultaneous ¹⁴C and ¹³⁷Cs dating of wines, which helped to distinguish wines originating before or after the bomb peak. The δ¹³C values also helped to solve the ¹⁴C age ambiguity in dating of wines around the ¹⁴C bomb peak. While the ¹⁴C dating method is always destructive one, the ¹³⁷Cs method may use a radiochemical separation of cesium from wine samples when better precision of results is required, but it can be also a nondestructive one with direct gamma-spectrometry of wine samples, especially those that are very rare.

90Sr and 137Cs as tracers of oceanic eddies in the sea of Japan/East sea

Vertical distributions of ⁹⁰Sr and ¹³⁷Cs in Sea of Japan/East Sea (SOJ/ES) water in the period of 1977-2010 exhibited a typical diffusion shape with surface/subsurface maxima and decreasing values with increasing depth. Apparent vertical diffusion coefficients (AVDCs) and apparent initial surface fluxes (AIFs) of ⁹⁰Sr and ¹³⁷Cs, which were estimated using a curve-fitting method from a vertical diffusion model, showed temporal and spatial variability. A diffusion depth introduced for understanding of vertical movements of ⁹⁰Sr and ¹³⁷Cs in the SOJ/ES well correlated with corresponding AIFs, suggesting that spatial variations of the ⁹⁰Sr and ¹³⁷Cs inventories have been governed by oceanic conditions such as changes in AVDCs, which may be related with eddy field, characterizing the SOJ/ES. The temporal changes of the AVDCs suggest that the production of eddies increased during the 2000s comparing with that in the 1990s. These observations represent the first applications of radionuclides as tracers in production of oceanic eddies.

Natural radionuclides as background sources in the Modane underground laboratory

The Modane underground laboratory (LSM) is the deepest operating underground laboratory in Europe. It is located under the Fréjus peak in Savoie Alps in France, with average overburden of 4800 m w. e. (water equivalent), providing low-background environment for experiments in nuclear and particle physics, astrophysics and environmental physics. It is crucial to understand individual sources of background such as residual cosmic-ray flux of high-energy muons, muon-induced neutrons and contributions from radionuclides present in the environment. The identified dominant sources of background are radioactive contamination of construction materials of detectors and laboratory walls, radon contamination of the laboratory air, and neutrons produced in the laboratory. The largest neutron contribution has been identified from (α, n) reactions in low Z materials (10^-7-10^-4 n s^-1 Bq^-1) and from spontaneous fission of ²³⁸U (1.1× 10^-6 n s^-1 Bq^-1).

Environmental radioactivity aspects of recent nuclear accidents associated with undeclared nuclear activities and suggestion for new monitoring strategies

Recently environmental radionuclide signals were observed in the atmosphere which could be associated with undeclared nuclear activities, not directly connected with development of nuclear weapons. Large-scale contamination of European air with Ru-106 observed in 2017 may represent such an accident, which was probably associated with the Mayak nuclear fuel reprocessing facility in the Chelyabinsk region of Russia. A recently announced nuclear accident at Nyonoska in the Archangelsk region may represent an undeclared nuclear activity associated with the development of a nuclear jet engine which could be based on radionuclide energy generator or a small nuclear reactor. It is concluded that environmental radioactivity impacts associated with recent nuclear activities create new challenges for fast and reliable national and international monitoring systems which would require development of new monitoring strategies.

Impact of Saharan dust events on radionuclides in the atmosphere, seawater, and sediments of the northwest Mediterranean Sea

In February 2004, anthropogenic radionuclides (¹³⁷Cs, ²³⁶U, ²³⁹Pu and ²⁴⁰Pu), transported from the Sahara Desert, were observed in the Monaco air, and later in water and sediment samples collected at the DYFAMED site in the northwest (NW) Mediterranean Sea. While ²³⁶U and ¹³⁷Cs in Saharan dust particles showed a high solubility in seawater, Pu isotopes were particle reactive in the water column and in the sediment. The impact of the Saharan deposition was found at 0-1.0 cm of the sediment core for ²³⁶U and ¹³⁷Cs, and between 1.0 and 1.5 cm for Pu isotopes. The excess of ²³⁶U was observed more in the water column than in the sediment, whereas the ^239+240Pu total inventories were comparable in the water column and the sediment. This single-day particle event represented 72% of annual atmospheric deposition in Monaco. At the DYFAMED site, it accounted for 10% (¹³⁷Cs) and 15% (^239+240Pu) activities of sinking particles during the period of the highest mass flux collected at the 200 and 1000 m water depths, and for a significant proportion of the total annual atmospheric input to the NW Mediterranean Sea (28-37% for ¹³⁷Cs and 34-45% for ^239+240Pu). Contributions to the total ¹³⁷Cs and ^239+240Pu sediment inventories were estimated to be 14% and 8%, respectively. The Saharan dust deposition phenomenon (atmospheric input, water column and sediment) offered a unique case to study origin and accumulation rates of radionuclides in the NW Mediterranean Sea.

137Cs and 90Sr in surface waters of the Sea of Japan: Variations and the Fukushima Dai-ichi Nuclear Power Plant accident impact

⁹⁰Sr and ¹³⁷Cs activity concentrations in surface waters of the Sea of Japan (SOJ) decreased during the period of 1993-2010 with effective half-lives of 18 and 15 y, respectively. The longer effective half-life of ⁹⁰Sr in the SOJ may suggest a surplus of ⁹⁰Sr to SOJ surface waters, however, no clear evidence of possible ⁹⁰Sr source has been found. After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, temporal variations of ¹³⁷Cs in the surface water of the SOJ have changed, while ⁹⁰Sr variations followed the pre-accident trends. The ⁹⁰Sr/¹³⁷Cs ratios reveal that increases of ¹³⁷Cs due to the FDNPP accident continued in surface waters of the SOJ until 2016.

Environmental radionuclides as contaminants of HPGe gamma-ray spectrometers: Monte Carlo simulations for Modane underground laboratory

The main limitation in the high-sensitive HPGe gamma-ray spectrometry has been the detector background, even for detectors placed deep underground. Environmental radionuclides such as ⁴⁰K and decay products in the ²³⁸U and ²³²Th chains have been identified as the most important radioactive contaminants of construction parts of HPGe gamma-ray spectrometers. Monte Carlo simulations have shown that the massive inner and outer lead shields have been the main contributors to the HPGe-detector background, followed by aluminum cryostat, copper cold finger, detector holder and the lead ring with FET. The Monte Carlo simulated cosmic-ray background gamma-ray spectrum has been by about three orders of magnitude lower than the experimental spectrum measured in the Modane underground laboratory (4800 m w.e.), underlying the importance of using radiopure materials for the construction of ultra-low-level HPGe gamma-ray spectrometers.

Potential Source Apportionment and Meteorological Conditions Involved in Airborne 131I Detections in January/February 2017 in Europe

Traces of particulate radioactive iodine (¹³¹I) were detected in the European atmosphere in January/February 2017. Concentrations of this nuclear fission product were very low, ranging 0.1 to 10 μBq m^-3 except at one location in western Russia where they reached up to several mBq m^-3. Detections have been reported continuously over an 8-week period by about 30 monitoring stations. We examine possible emission source apportionments and rank them considering their expected contribution in terms of orders of magnitude from typical routine releases: radiopharmaceutical production units > sewage sludge incinerators > nuclear power plants > spontaneous fission of uranium in soil. Inverse modeling simulations indicate that the widespread detections of ¹³¹I resulted from the combination of multiple source releases. Among them, those from radiopharmaceutical production units remain the most likely. One of them is located in Western Russia and its estimated source term complies with authorized limits. Other existing sources related to ¹³¹I use (medical purposes or sewage sludge incineration) can explain detections on a rather local scale. As an enhancing factor, the prevailing wintertime meteorological situations marked by strong temperature inversions led to poor dispersion conditions that resulted in higher concentrations exceeding usual detection limits in use within the informal Ring of Five (Ro5) monitoring network.

New ultra-sensitive radioanalytical technologies for new science

Recent developments in radiometric and mass spectrometry technologies have been associated in the radiometric sector mainly with underground operations of large volume Ge detectors, while the mass-spectrometry sector, represented mainly by accelerator mass spectrometry and inductively coupled plasma mass spectrometry has become the most sensitive technique for ultra-low-level analyses of long-lived radionuclides. These new developments have had great impact on investigations of rare nuclear processes and applications of radionuclides in environmental, life and space sciences. New scientific investigations have been carried out therefore which have not been possible before either because of lack of sensitivity or required large sample size.

Anthropogenic 137Cs on atmospheric aerosols in Bratislava and around nuclear power plants in Slovakia

Nuclear power plants (NPPs) have been one of the sources of anthropogenic radionuclides in the environment. This work combines the results from monitoring stations around NPPs in Slovakia (Mochovce and Jaslovské Bohunice) and academic measurements at the Comenius University campus in Bratislava. Most of the atmospheric ¹³⁷Cs in this region come from the resuspension of the Chernobyl-derived ¹³⁷Cs, as well as caesium produced during nuclear weapons testing. By comparison of the obtained results at NPPs with Bratislava data, radiation impacts of the NPPs on the local environments have been estimated to be negligible.

Tritium and radiocarbon in the western North Pacific waters: post-Fukushima situation

Impact of the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident on tritium (³H) and radiocarbon (¹⁴C) levels in the water column of the western North Pacific Ocean in winter 2012 is evaluated and compared with radiocesium (^134,137Cs) data collected for the same region. Tritium concentrations in surface seawater, varying between 0.4 and 2.0 TU (47.2-236 Bq m^-3), follow the Fukushima radiocesium trend, however, some differences in the vertical profiles were observed, namely in depths of 50-400 m. No correlation was visible in the case of ¹⁴C, whose surface Δ¹⁴C levels raised from negative values (about -40‰) in the northern part of transect, to positive values (∼68‰) near the equator. Homogenously mixed ¹⁴C levels in the subsurface layers were observed at all stations. Sixteen surface (from 30 in total) and 6 water profile (from 7) stations were affected by the Fukushima tritium. Surface and vertical profile data together with the calculated water column inventories indicate that the total amount of the FNPP1-derived tritium deposited to the western North Pacific Ocean was 0.7 ± 0.3 PBq. No clear impact of the Fukushima accident on ¹⁴C levels in the western North Pacific was observed.

Determination of chemical forms of 14C in liquid discharges from nuclear power plants

Developments of radioanalytical methods for determination of radiocarbon in wastewaters from nuclear power plants (NPP) with pressurized light water reactors, which would distinguish between the dissolved organic and inorganic forms have been carried out. After preliminary tests, the method was used to process pilot samples from wastewater outlets from the Temelín and Dukovany NPPs (Czech Republic). The results of analysis of pilot water samples collected in 2015 indicate that the instantaneous ¹⁴C releases into the water streams would be about 7.10^-5 (Temelín) and 4.10^-6 (Dukovany) of the total quantity of the ¹⁴C liberated into the environment.

Temporal evolution of 137Cs, 237Np, and 239+240Pu and estimated vertical 239+240Pu export in the northwestern Mediterranean Sea

The evolution of ¹³⁷Cs, ²³⁷Np and ^239+240Pu at the DYFAMED station (NW Mediterranean) is discussed in relation to physical processes, downward fluxes of particles, and changes in the main input sources. The data set presented in this study represents the first complete ²³⁷Np vertical profiles (0.12-0.27μBqL^-1), and constitutes a baseline measurement to assess future changes. A similar behavior of Cs and Np has been evidenced, confirming that Np behaves conservatively. While the ¹³⁷Cs decrease has been driven by its radioactive decay, the vertical distribution of ²³⁷Np has not substantially changed over the last decade. In the absence of recent major inputs, a homogenization of their vertical distribution occurred, partly due to deep convection events that became more intense during the last decade. In contrast, ^239+240Pu surface levels in the NW Mediterranean waters have fallen in the past four decades by a factor of 5. This decrease in surface has been balanced by higher concentrations in the deep-water layers. A first estimate of the downward ^239+240Pu fluxes in the NW Mediterranean Sea is proposed over more than two decades. This estimation, based on the DYFAMED sediment trap time-series data and published ^239+240Pu flux measurements, suggests that sinking particles have accounted for 60-90% of the upper layer (0-200m) Pu inventory loss over the period 1989-2013. The upper layer residence time of Pu is estimated to be ~28years, twice as long as the residence time estimated for the whole western Mediterranean (~15years). This difference highlights the slow removal of Pu in the open waters of the NW Mediterranean and confirms that most of the Pu removal occurs along the coastal margin where sedimentation rates are high.

Analysis of radionuclides at ultra-low levels: A comparison of low and high-energy mass spectrometry with gamma-spectrometry for radiopurity measurements

Recent developments in high-energy accelerator mass spectrometry (AMS) and low-energy inductively coupled plasma mass spectrometry (ICPMS) made them the most sensitive techniques for ultra low-level analysis of ²³⁸U and ²³²Th. Detection limits below 1 nBq g^-1 for analysis of these radionuclides in construction materials were obtained. The most important development in the radiometric sector was operation of HPGe detectors in underground laboratories where detection limits of about 1 µBq kg^-1 were obtained. Specific features of radiometric, mass spectrometry and neutron activation techniques for ultra low-level radionuclide measurements are discussed, and obtained results for analysis of radiopure materials prepared for underground experiments are compared.

Distribution of natural and anthropogenic radionuclides in northwest Mediterranean coastal sediments

The distribution of radionuclides in NW Mediterranean coastal sediments, and the processes controlling their abundance were investigated in three cores taken near the island of Porquerolles and one offshore Monaco. The sediments collected near Porquerolles were strongly anoxic due to diagenetic processes involved in the decomposition of organic matter, whereas they transitioned from oxic to anoxic at a depth of 4 cm beneath the seawater interface at Monaco. Organic carbon (OC) was more abundant in sediments at Porquerolles (by about a factor of 3-5) than at Monaco and elsewhere in the coastal NW Mediterranean. Sediment cores collected NE of Porquerolles also possessed elevated uranium concentrations that correlated with high OC content and strong reducing conditions. The ^239,240Pu and ²⁴¹Am activities in surficial sediments ranged from 1 to 5.7 Bq kg^-1 and 0.3 to 1 Bq kg^-1, respectively, while the ¹³⁷Cs activity ranged from 0.3 to 6.2 Bq kg^-1. The mean activity ratios of ²⁴¹Am/^239,240Pu and ²³⁸Pu/^239,240Pu in Porquerolles and Monaco sediments were similar to the global fallout ratios. Sediment inventories of global fallout ^239,240Pu (430-800 Bq m^-2) and ²⁴¹Am (150-285 Bq m^-2) were by about a factor of 5-10 higher at Porquerolles, whereas the inventory of ¹³⁷Cs (430-1000 Bq m^-2) was substantially lower at the investigated stations than have been reported elsewhere at similar latitudes. Specific local conditions characterised by high OC sediment loads due to the growth and mortality of Posidonia oceanica have been responsible for deposition of large amounts of seagrass tissues at the NE corner of Porquerolles, which have had a profound effect on the distribution of radionuclides in the sediments.

Carbon and Pu isotopes in Baltic Sea sediments

Distributions of ¹³⁷Cs, ^239,240Pu, Δ¹⁴C and δ¹³C measured in sediments indicated low ¹³⁷Cs and ^239,240Pu activities in the Curonian Lagoon and higher levels in the open Baltic Sea. Depleted δ¹³C_TOC values were found in the Curonian Lagoon as compared with the open Baltic Sea, while the most depleted Δ¹⁴C_TOC values were found in the Gotland Deep. The global fallout Pu dominated in the deeper zones of the Baltic Sea, while higher ²⁴⁰Pu/²³⁹Pu atom ratios were characteristic of the coastal regions.

Monte Carlo simulation of background characteristics of a HPGe detector operating underground in the Gran Sasso National Laboratory

Monte Carlo (MC) simulation of background components of an ultra-low background high purity germanium (HPGe) detector operating in a deep underground laboratory was carried out. The results show that the background of the HPGe detector is about two orders of magnitude higher than the MC prediction when accounting only for cosmic-ray induced background. The difference is due to natural radioactivity in the parts surrounding the Ge detector. To get reasonable agreement between MC simulations and the experiment, a contamination in the parts surrounding the Ge crystal from ⁴⁰K, ²⁰⁸Tl and ²¹⁴Bi of 0.1mBqkg^-1 was required to include in the simulations.

The valley system of the Jihlava river and Mohelno reservoir with enhanced tritium activities

The Dukovany nuclear power plant (NPP Dukovany) releases liquid effluents, including HTO, to the Mohelno reservoir, located in a deep valley. Significantly enhanced tritium activities were observed in the form of non-exchangeable organically bound tritium in the surrounding biota which lacks direct contact with the water body. This indicates a tritium uptake by plants from air moisture and haze, which is, besides the uptake by roots from soil, one of the most important mechanisms of tritium transfer from environment to plants. Results of a pilot study based on four sampling campaigns in 2011-2015 are presented and discussed, with the aim to provide new information on tritium transport in the Mohelno reservoir - Jihlava River - plants ecosystems.

Long-term variations of radionuclides in the Bratislava air

Variations of aerosol radionuclides (2001-2015) in the ground-level air in Bratislava (Slovakia) showed ⁷Be maxima in spring/early summer and minima in winter, however, an inverse trend was observed for ²¹⁰Pb, ¹³⁷Cs and ⁴⁰K. A decreasing amplitude and splitting of summer maxima for ⁷Be in the last years has been found. A temporal behavior of the ⁷Be/²¹⁰Pb activity ratio showed higher levels during warm seasons due to vertical convection of air masses from higher altitudes. The ¹³⁷Cs activity concentration in the surface air between 2003 and 2010 was decreasing with an effective half-life of 1.9 ± 0.3 years. The yearly average ¹³⁷Cs concentrations during 2009-2014 were almost constant, disturbed only by the Fukushima accident in 2011. The increased atmospheric ¹³⁷Cs and ⁴⁰K levels observed during the autumn-winter season may be due to surface soil resuspension, biomass burning and radionuclide transport by winds. Seasonal variations of ²²²Rn activity concentrations were found with maxima at the end of autumn and in winter, and minima in spring. The variability of the average annual course of ²²²Rn has been larger than that of ²¹⁰Pb. The ²¹⁰Pb/²²²Rn activity ratio was highest at the end of winter and in the spring, while from June to December remained nearly constant. More intensive atmospheric mixing in spring months caused a decrease in the ²²²Rn activity concentration, while the aerosol component of the atmosphere has been affected mainly during the autumn and winter seasons. The mean residence time of aerosols in the atmosphere was calculated using the ²¹⁰Pb/²²²Rn method to be 4.5 ± 0.9 days.

Impact of the Fukushima accident on tritium, radiocarbon and radiocesium levels in seawater of the western North Pacific Ocean: A comparison with pre-Fukushima situation

Tritium, radiocarbon and radiocesium concentrations in water column samples in coastal waters offshore Fukushima and in the western North Pacific Ocean collected in 2011-2012 during the Ka'imikai-o-Kanaloa (KoK) cruise are compared with other published results. The highest levels in surface seawater were observed for ¹³⁴Cs and ¹³⁷Cs in seawater samples collected offshore Fukushima (up to 1.1 Bq L^-1), which represent an increase by about three orders of magnitude when compared with the pre-Fukushima concentration. Tritium levels were much lower (up to 0.15 Bq L^-1), representing an increase by about a factor of 6. The impact on the radiocarbon distribution was measurable, but the observed levels were only by about 9% above the global fallout background. The ¹³⁷Cs (and similarly ¹³⁴Cs) inventory in the water column of the investigated western North Pacific region was (2.7 ± 0.4) PBq, while for ³H it was only (0.3 ± 0.2) PBq. Direct releases of highly contaminated water from the damaged Fukushima NPP, as well as dry and wet depositions of these radionuclides over the western North Pacific considerably changed their distribution patterns in seawater. Presently we can distinguish Fukushima labeled waters from global fallout background thanks to short-lived ¹³⁴Cs. However, in the long-term perspective when ¹³⁴Cs will decay, new distribution patterns of ³H, ¹⁴C and ¹³⁷Cs in the Pacific Ocean should be established for future oceanographic and climate change studies in the Pacific Ocean.

Impact of Saharan dust events on radionuclide levels in Monaco air and in the water column of the northwest Mediterranean Sea

Characterization of atmospheric aerosols collected in Monaco (2004-2008) and in sediment traps at 200 m and 1000 m water depths at the DYFAMED (Dynamics of Atmospheric Fluxes in the Mediterranean Sea) station (2004) was carried out to improve our understanding of the impact of Saharan dust on ground-level air and on the water column. Activity concentrations of natural (²¹⁰Pb, ²¹⁰Po, uranium and radium isotopes) and anthropogenic (¹³⁷Cs, ²³⁹Pu, ²⁴⁰Pu, and ^239+240Pu) radionuclides and their isotopic ratios confirmed a Saharan impact on the investigated samples. In association with a large particulate matter deposition event in Monaco on 20 February 2004, the ¹³⁷Cs (∼40 Bq kg^-1) and ^239+240Pu (∼1 Bq kg^-1) activities were almost a factor of two higher than other Saharan deposition dust events. This single-day particle flux represented 72% of the annual atmospheric deposition in Monaco. The annual deposition of Saharan dust on the sea was 232-407 mBq m^-2 for ¹³⁷Cs and 6.8-9.8 mBq m^-2 for ^239+240Pu and contributed significantly (28-37% for ¹³⁷Cs and 34-45% for ^239+240Pu) to the total annual atmospheric input to the northwest Mediterranean Sea. The ¹³⁷Cs/^239+240Pu activity ratios in dust samples collected during different Saharan dust events confirmed their global fallout origin or mixing with local re-suspended soil particles. In the sediment trap samples the ¹³⁷Cs activity varied by a factor of two, while the ^239+240Pu activity was constant, confirming the different behaviors of Cs (dissolved) and Pu (particle reactive) in the water column. The ¹³⁷Cs and ^239+240Pu activities of sinking particles during the period of the highest mass flux collected in 20 February 2004 at the 200 m and 1000 m water depths represented about 10% and 15%, respectively, of annual deposition from Saharan dust events.