This study aims to reconstruct historical trends and assess environmental changes in a deep marine basin over the past 150 years using nuclear analytical methods and radiotracers. Undisturbed sediment cores are ideal for such measurements, as they preserve records of deposited material and enable the detection of contamination and past ocean geological events. A sediment core was collected with a box corer sampler from the North Cretan basin at a water depth of 1500 m. Following sample preparation, the samples were analyzed using a high-purity germanium detector, employing gamma-ray spectrometry to determine the activity concentrations of natural and artificial radionuclides. The activity concentration of 210Pbex and the mass accumulation rate were subsequently calculated. The dating of the sediment core was performed using the CF: CS model. In addition, seawater samples were obtained from various depths to determine hydrographic and radiological properties, including the activity concentration of 137Cs at the seawater–seabed interface. This information was used to estimate the site-specific sediment distribution coefficient factor Kd. The presence of a thin darker layer within the sediment core was identified based on its distinct visual characteristics relative to the adjacent layers, as well as corresponding variations in sediment density and radionuclide activity concentrations. Activity concentrations, together with grain-size (granulometric) analysis, were used for sediment characterization. In addition, the detection of 137Cs in sediment layers predating the main fallout events required the evaluation of its mobility through two diffusion models for validation. According to the model results, the darker material identified at approximately 10.5–11.5 cm depth may be associated with a transport of the darker material around 1650–1680 AD. Granulometric estimation revealed compositional differences in mean grain size in the samples adjacent to this interval, likely reflecting changes related to the formation processes. The two models that describe the 137Cs molecular diffusion in sediments exhibited satisfactory agreement. The obtained diffusion coefficients were consistent with values reported in the literature for very fine-grained sediments.

This study was realized in the frame of an IAEA Coordinated Research Project for the evaluation of sediment dynamics, applying in-situ radiometric methods accompanied with a theoretical model. The in-situ methods were validated using lab-based high-resolution gamma-ray spectrometry. Sediment dynamics assessments were performed based on the measured and mapped activity concentrations of specific 238U progenies (214Bi or 214Pb), 232Th progenies (208Tl and 228Ac), and 40K along the shoreline of the beach. The maps of the activity concentrations of natural radionuclides were produced rapidly using software tools (R language v4.5). The sediment dynamics of the studied area were also investigated through numerical simulations, applying an open source model considering land–sea interactions and meteorological conditions and the corresponding sediment processes. The assessments, which were conducted utilizing the detailed data from the natural radioactivity maps, were validated by the simulation results, since both were found to be in agreement. Generally, it was confirmed that the distribution of radionuclides reflects the selective transport processes of sediments, which are related to the corresponding processes that occur in the study area. Legrena Beach in Attica, Greece, served as a pilot area for the comparative analysis of methods and demonstration of their relevance and applicability for studying coastal processes.

A practical and comprehensive experimental approach for radioactivity measurements of voluminous environmental samples using high-resolution gamma-ray spectrometry with High Purity Germanium (HPGe) detector is presented. The radioanalytical procedure includes sample preparation, detector calibration, implemented corrections, quality control and assurance; and it is demonstrated with the determination of natural and anthropogenic radionuclides in water and soil standard samples. The methodology is verified, and the results are validated by intercomparison with the refence values provided as part of a worldwide proficiency test.

The consequences after an hypothetical nuclear accident at the Akkuyu Nuclear Power Plant in the region of Eastern Mediterranean Sea are presented. The dispersion of the radioactive plume in the sea is simulated applying a regional hydrodynamic/Lagrangian drift model and the radioecological impact is estimated after the release of 137Cs, 238Pu and 131I. The doses to marine biota and the human habitants of the affected regions are presented, while the sensitivity analysis of the results revile the most vulnerable features of this marine environment.

In this work, the design and initial demonstration of the KATERINA II detection system for rapid mapping of radionuclides in areas near to seashore is presented. A new development has been realized by integrating a GPS module in KATERINA II detection system and synchronizing its data with the acquired spectra in real-time. The new system may be used in a backpack, for areas with low activity concentration, or can be installed in an unmanned vehicle, for observing and mapping the source(s) of radioactivity, e.g. at the seashore, in areas with high contamination. A quantitative solution is provided for natural and artificial radionuclides, taking into account the characteristics of the detector, the parameters of measurement geometry and a mean beach sand/sediment composition. This paper reports field results for site characterization issues through automated analysis of gamma-ray spectra including low-level and low-energy γ-emitters. Perspectives of the future application of the system in a worldwide basis are related to radionuclides mapping and the assessment of dose rates in seashore areas that may be contaminated due to the operation of nuclear power plants, desalination plants and NORM industries, and/or due to the decommissioning of nuclear installations.

A coupled hydrodynamic/lagrangian particle drift model was applied to obtain the distribution of key radionuclides that are dispersed at the surface water (upper 100 m) of Eastern Mediterranean Sea, in case of an accident of Nuclear Power Plant at Akkuyu. The model was applied to simulate the dispersion of key artificial radionuclide concentration, in case of a hypothetical accident to assess issues related to sea health and potential hazards. The released radionuclide was found to have a favorable westward direction, following the prevailing currents. The variability of the predicted pattern is interpreted according to the near surface circulation patterns in the study area. The dispersion of key radionuclides (137Cs, 238Pu and 131I) was studied in a spatial and temporal manner at the neighboring coasts of the location of the NPP. Furthermore, the fate of the plume was predicted for each month after the accident date close to the areas of Akkuyu, namely Cyprus, Rhodes Island, North Cretan coast, Cyclades and Syrian Coast. The annual study revealed that the radioactive plume is present with high concentration (maximum values of 1200 Bq m- 3 for the long lived isotopes and 600 Bq m- 3 for 131I) in the location of the plant for short period of time (1-2 months), while the other areas are affected during the whole year with low level of activity concentration (20-50 Bqm- 3). The ERICA Assessment Tool was also used to evaluate dose rates to common marine biota at the studied areas.

Tiran and Sanafir are coastal ecosystem islands located in the fragile environment of the Red Sea. The importance of the islands has always been bordering security for Egypt and Saudi Arabia. In the last decade, an economic value has been added to the border islands and has grown a significant importance to be the focal point between the two countries’ trade lines. The study is aiming at the temporal analysis of the SAR data phase estimation to map the island’s vertical displacement for the last 5 years. Temporal datasets of SAR images were collected from the European Space Agency, and dataset collection started from November 2016 until May 2020 to comprehend the objectives of the research study. The SAR interferometry techniques were implemented to estimate the phase displacement for 15 SAR data sets of the border islands. Consequently, the temporal analysis demonstrated the trend of the phase displacement during the study timeframe. Results indicated that the maximum island subsidence (−0.417 m) was estimated from the scene acquired on 21 Feb 2018, while the maximum uplift (0.708 m) value was conducted from the scene acquired on 17 Nov 2017. Moreover, the trend analysis showed an instability behavior among the successive SAR datasets. The current study’s findings are crucial to the decision-makers from Egypt and Saudi Arabia in realizing the predictability of the island’s displacement mitigations to ensure the sustainability of the incoming socioeconomic activities.

Recent spatial and vertical distributions of 137Cs activity concentration in the Aegean Sea are presented almost 30 years after the Chernobyl accident. The study aims to provide the current radioactivity levels of 137Cs in the Aegean Sea and to combine the 137Cs activity concentration with typical oceanographic parameters (T, S) in order to utilize them as tracers to identify/validate the different water masses that are present in the Aegean Sea. This work was performed in the frame of the “KRIPIS” project in 2017 for continuous investigations of the deep basins from all over the Aegean Sea and includes samplings from the water column layers of seven stations. The 137Cs activity concentrations were determined via lab-based gamma ray spectroscopy after appropriate chemical pre-concentration of 137Cs, while the salinity and temperature of the water column were obtained by in-situ measurements. The activity concentration values of 137Cs varied from 1.6 to 5.5 Bq m−3. Clear distinction of the Black Sea and Levantine Waters was obtained based on the combination of temperature and salinity values with 137Cs activity concentration. Furthermore, including 137Cs as a supplementary tracer, the Transitional Subsurface Aegean Waters were identified at the Myrtoan and Antikythera Straits, combining the salinity, temperature and 137Cs activity concentration.

A review of the evolution of 137Cs activity concentrations in the Aegean Sea is presented almost 34 years after the Chernobyl accident. The data from field measurements are interpreted considering the different water masses present in the Aegean Sea, for better understanding of 137Cs spatial and temporal variation. The last 15 years, a lot of effort is given in the study of the vertical advection of 137Cs and the related processes in the deep basins of the Aegean Sea. These results provided significant information about the average values along with depth of the velocity and diffusion parameters. The role of 137Cs as a circulation and mixing tracer is undergoing a gradual weakening, since the gradient of its activity concentration between the water masses is small. 137Cs is proved to be a valuable radiotracer for identifying the Black Sea Water masses since they are still enriched with higher values of 137Cs compared to the background values in the Mediterranean Sea.

A 3-D hydrodynamic model, coupled with a Lagrangian drift model, was applied to simulate the dispersion of derived 137Cs activity concentration in case of a nuclear accident in Akkuyu Nuclear Power Plant (NPP) located at the East Mediterranean Sea. The simulated near surface circulation presented a good skill in reproducing observed patterns from satellite altimetry data and existing literature. The dispersion pattern of dissolved 137Cs was investigated on an annual and seasonal basis. In all seasons the dominant pathway of released 137Cs had a westward direction, following the prevailing currents. The different dispersal patterns are mainly related to the intensity of the Asia Minor Current and the local circulation in the vicinity of the Akkuyu NPP. 137Cs was transported during the first month to the neighboring coasts of the NPP, while after the fourth month the distribution of the plume was extended in areas of the Eastern Aegean Sea (including East Crete and Rhodes Islands), as well as at the Antalya coastline. After the 3rd month, the plume reaches areas in the Eastern Aegean Sea (including the Crete Island and Cyclades plateau) while after the 6th month it is spread gradually to the Ionian Sea and Levantine basin. At the end of the annual simulation, the plume appears significantly diluted, with relatively high concentrations found still in Dodecanese Islands and along the Aegean Turkish coast. The 137Cs activity concentration starts to decline after the 9th month in most of the studied areas at the East Mediterranean Sea. The particulate 137Cs was diminished within a month from the accident, due to sinking and its fast transformation to dissolved, showing a similar westward dispersion pattern.

Radionuclides are characterized by their nuclear and chemical behavior. Additionally, the geochemical characteristics of radionuclides result in their accumulation in the sediments via sorption processes. In this work the radionuclide activity concentrations obtained by gamma-ray spectrometry (HPGe detector) were converted to metal concentrations as described in [1]. The results were compared with the measured metal concentrations obtained by atomic spectrometry (X-ray fluorescence system-XRF). The samples originate from the coastal environment of two Greek areas, characterized by elevated values of natural radionuclides (e.g. 226Ra) and metals. The preliminary study revealed a good agreement among the concentrations of potassium calculated via activity concentrations of 40K and those of XRF measurement, while a great divergence was observed for the thorium case. These differences can be attributed to the low statistics, as well as to the calibration set-up of Th XRF measurement.

The measurement of radiotracers is recognized as a major tool for the investigation and characterization of submarine groundwater discharges, while the use of underwater gamma-ray spectrometry has been proved a robust solution for the qualitative and quantitative determination of radionuclides in the aquatic environment. The capability of online continuous monitoring of submarine springs by means of gamma-ray spectrometry for direct estimation of SGD velocity and discharge is presented. The quantification of SGD flux rate is based on radon progenies time-series provided by two spectrometers placed above the seabed and near the water surface respectively, coupled with water level and meteorological data. The proposed methodology has been applied for a 5-month period in a coastal karstic system where multiple submarine springs occur at Anavalos-Kiveri, Greece. The estimated flux rates derived from the measured activities revealed significant SGD temporal variations with the mean discharge of 12 m(3) s(-1) being compatible with previous measurements. The advantages and limitations of direct SGD estimation via underwater gamma-ray monitoring are also discussed.

Radioactivity and metal concentration measurements are provided at coastal areas of the Aegean Sea, assessing the anthropogenic impact as well as investigating natural phenomena. A summary of representative analysis combining the concentration of metals and radionuclides (including the measuring methods) is described to assess in temporal basis the contamination status at the coastal areas. The work is focused on recently obtained results in (a) Lavrio and Ierissos Gulf where coastal mining activities occur, (b) Elefsis Gulf and Thermaikos Gulf (Thessaloniki Bay) which are affected by two major urban areas, and (c) Gulf of Corinth and Litochoro Bay which both are characterized by dynamic natural phenomena. The radiological assessment was estimated via dose rate calculations using the ERICA assessment tool and the metal risk assessment via the enrichment factors and the pollution load index analysis. Furthermore, the percentage reduction of the 137Cs inventory was calculated to evaluate the deposition on the marine sediment of the anthropogenic cesium released by nuclear weapon tests and accidents. Also, erosion/accretion patterns were calculated in a temporal basis according to the existing radiotracing method based on the ratio of two natural radionuclides of radium (226Ra/228Ra).

The anthropogenic radionuclide 137Cs is used as a valuable oceanographic tracer for the study of sea water masses identification and water movement. In the present work, 137Cs activity concentrations have been investigated in deep basins of Aegean Sea. Seawater samples were collected from five different sampling stations, during scientific oceanic campaigns from the period March to April 2008. The applied methodology was based on the adsorption of radiocaesium from dissolved AMP (Ammonium Phosphomolybdate Hydrate) in 20 L water samples. Moreover, during the pre- concentration procedure, the 134Cs was used as reference tracer for determining the chemical efficiency and consequently to measure the activity concentration in a High Purity Ge detector. In terms of vertical records, the activity concentration in the selected basins ranged between 3-8.5 Bq/m3, depending on the region and the depth of the basins. The higher concentration (8.5 Bq/m3) was found in the region between Lemnos Island and the narrows of Dardanelles. The maximum concentrations were observed at the North Aegean Sea basins, between 20 and 40 m of depth, caused by the water masses coming from the Black Sea. At the Cretan Sea the vertical activity concentration of 137Cs was homogeneous down to 2000 m depth, with an exception at the 800 m where it was decreasing significantly due to the transient deep-water masses from Adriatic Sea.

The calibration of an underwater spectrometer, consisting of a CeBr3 crystal, is performed for sediment sample measurements, via experimental data and Monte Carlo simulations. The system was implemented for activity concentration measurements in marine sediment samples in the laboratory. The results were compared with corresponding high resolution measurements and showed that the system provides accurate results, but relatively high uncertainties. Different measurement geometries are theoretically studied via Monte Carlo simulations in order to improve the system performance for such measurements.

In this work, core sediment samples up to 50 cm have been collected from three different marine environments; Gulf of Corinth, Gulf of Thermaikos, specifically from Litochoro Coast and Lake Uluabat from the wider region of Black Sea. Natural (210Pb) and anthropogenic (137Cs) radionuclides in the samples were measured using an HPGe detector, calibrated for sediments geometry. The vertical distribution of 137Cs and 210Pb was used to determine the sedimentation rate. The results were 0.56 cm/year for the Gulf of Corinth and 0.54 cm/year for the coast of Litochoro. In the case of the lake Uluabat the sedimentation rate was 0.41 cm/year.

A radiological box model of the Aegean Sea has been developed simulating the dispersion and fate of radionuclides in the marine environment. The model incorporates all transfer processes within abiotic and biotic compartments in combination with appropriate site-specific information. The model was calibrated using empirical radiological data, with the simulation of 137Cs dispersion after the Chernobyl. Environmental sensitivity analysis has been carried out based on Chernobyl 137Cs fallout, in terms of doses to representative marine organisms (fish, crustacean and molluscs) and human population. Comparison of the results with doses from natural sources and sensitivity estimations for shallow marine environments has been performed in order to reveal the vulnerability of each sub-region. The main characteristics and parameters controlling the radioecological processes are also discussed.

A new medium resolution (based on a 2″x2″CeBr3 crystal) gamma-ray spectrometer named “GeoMAREA” was developed and applied for measuring radioactivity in aquatic environments. The system is capable for qualitative and quantitative measurement of radionuclides in aquatic environments with maximum depth of deployment up to 600 m. A special software is developed to fulfill different demands of the end-users in order to: a) provide real time data using the cable mode, b) perform communication tasks with a data center transferring (near) real time data, c) provide time series in sequential buffers for continuous monitoring in a stand-alone mode and d) provide profile data and subsequently maps using mobile vehicles (underway mode). The spectrometer was calibrated first using point sources for energy, energy resolution and efficiency. The system offers activity concentrations of all detected gamma-ray emitters in Bq/m3 using the marine efficiency calibration, which is reproduced via the MCNPX code [1]. Two experimental points were used for validation of the theoretical estimation obtained by two reference sources (137Cs and 40K) diluted in a water-filled tank. Currently, GeoMAREA is deployed in a closed aquatic system where groundwater discharges (Anavalos, Kiveri, Greece). A first estimation of the intrinsic background of the crystal at the emission energy area of 40K is estimated. Additionally, an inter-comparison exercise with the low resolution system KATERINA II [2], is also described.

Radionuclides are characterized by their nuclear and chemical behavior. Additionally, the geochemical characteristics of radionuclides result in their accumulation in the sediments via sorption processes. In this work the radionuclide activity concentrations obtained by gamma-ray spectrometry (HPGe detector) were converted to metal concentrations as described in [1]. The results were compared with the measured metal concentrations obtained by atomic spectrometry (X–ray fluorescence systemXRF). The samples originate from the coastal environment of two Greek areas, characterized by elevated values of natural radionuclides (e.g. 226Ra) and metals. The preliminary study revealed a good agreement among the concentrations of potassium calculated via activity concentrations of 40K and those of XRF measurement, while a great divergence was observed for the thorium case. These differences can be attributed to the low statistics, as well as to the calibration set–up of Th XRF measurement.