Papers by Christos Tsabaris
HNPS Advances in Nuclear Physics
In this work, the design and initial demonstration of the KATERINA II detection system for rapid ... more 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 syst...
Journal of Marine Science and Engineering
In this study, a thermal spring located in the Gulf of Gera (Lesvos Island) is investigated in te... more In this study, a thermal spring located in the Gulf of Gera (Lesvos Island) is investigated in terms of radiotracers, water flow velocities and acoustic back-scattering properties by in situ observations. Water flow characteristics were deduced using in situ deployments of three marine sensors: an Acoustic Doppler Velocimeter (ADV), a High-Frequency Acoustic Doppler Current Profiler (ADCP), and a medium-resolution underwater gamma-ray detection system. The flow velocity combined with the activity concentration of natural radionuclides in the thermal spring provided information on the characteristics of the thermal spring in the specific gulf. The proposed methodology estimated the water supply, the residence time in the effective area of the in situ systems, and the residence time in the gulf. Eventually, the estimation of the characteristics of the discharged water source resulted from the synthetic evaluation of oceanographic measurements alongside appropriate models.
Development and application of an in-situ shipboard device for the measurement of gamma-ray emitters in seawater
Journal of Environmental Radioactivity
Distribution of dissolved 137Cs, 131I and 238Pu at Eastern Mediterranean Sea in case of hypothetical accident at the Akkuyu Nuclear Power Plant
Journal of Environmental Radioactivity
The construction and commissioning of the neutron beam line has been completed in April 2001. Aft... more The construction and commissioning of the neutron beam line has been completed in April 2001. After two touch-and-go periods of 24 hours each on April 13 and 21, the n_TOF Collaboration started on Saturday, 28th April 2001, with the first in-beam operation of the Data Acquisition system and the commissioning of the monitor, capture and fission detectors foreseen in the nTOF-02 programme. All detectors and the data acquisition system were properly working and reached the designed performance. The DAQ system, developed jointly between the Collaboration and industry, was performing without dead time even at a peak data rate of 18 MBytes/s. Data have been collected from all detectors according to the objectives of the nTOF-02 experimental campaign. Simultaneously, an off-line group started to analyse the acquired data and alarmed soon the n_TOF Collaboration on the existence of a high ambient background in the experimental area jeopardising the quality of the capture measurements and even preventing the operation of the BaF 2 calorimeter. Under these conditions part of the nTOF-02 programme has been compromised and the n_TOF Collaboration defined on May 8, 2001 a series of additional measurements in order to understand the nature and the origin of this background. Finally, the presence of this background has forced us to interrupt the data taking runs on June 11, 2001 and to request on June 1 -in agreement with the group responsible for the construction of the neutron beam -the modification of the shielding in the vicinity of the spallation target.
HNPS Proceedings, 2019
NaI(Tl) crystals are used in many marine applications for continuous measurements with buoy opera... more NaI(Tl) crystals are used in many marine applications for continuous measurements with buoy operation and autonomous in situ measurements in seawater. Monte Carlo simulations were performed using the GEANT4 code for the investigation of the γ-ray absorption in water in different spherical geometries and for the efficiency of a NaI(Tl) detector of different radionuclides in the aquatic environment. In order to test the reliability of these simulations, experimental values of the NaI(Tl) detector efficiency were deduced using a special tank filled with water and reference single gamma ray sources (99mTc, 137Cs and 40K). The cascade reference source 111In was also diluted in tank for comparison with the reproduction spectra of its cascade lines as provided with the GEANT4 code. The results are in good agreement with the simulated ones within uncertainties.
Journal of Marine Science and Engineering
In recent years, the environmental effects of both active and legacy mining activity have motivat... more In recent years, the environmental effects of both active and legacy mining activity have motivated many research groups worldwide through the use of a variety of methods that have been conducted among diverse environments. In this study, we measured radionuclide concentrations at two coastline locations of the Northern Aegean Sea: Stratoni and Ierissos. We deployed KATERINA II, an in situ gamma ray spectrometer. Our results indicate that the activity concentration for 238U progenies (214Bi), 232Th progenies (208Tl and 228Ac) and 40K vary by up to (33 ± 4) Bq kg−1, (19 ± 3) Bq kg−1, and (420 ± 30) Bq kg−1, respectively. The activity concentration of the 137Cs in Stratoni and Ierissos beach sands were (8.1 ± 2.2) and (3.9 ± 1.2) Bq kg−1, respectively. Lab-based measurements were also collected prior to the in situ data collection for the determination of radionuclide and metal concentrations. The lab-based data were found to be (800 ± 40) μg g−1 and (12 ± 1) μg g−1, for As, (1200 ± 6...
Journal of Marine Science and Engineering
Recent spatial and vertical distributions of 137Cs activity concentration in the Aegean Sea are p... more 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 ...
Could atmospheric carbon be driving sedimentation?
Journal of Soils and Sediments
HNPS Proceedings, 2019
The coastal area of Piraeus is an environmentally aggravated region since many decades due to per... more The coastal area of Piraeus is an environmentally aggravated region since many decades due to persistent pollution sources as the international port of Piraeus, a coastal fertilizers plant, the Athens sewage outfall and the industrial zone of Eleusis Bay. Recent sediment samples from the seabed of NW Salamina strait (upper Saronikos Gulf) were collected and analyzed for radionuclides and heavy metals composition. Measurements of 22 samples were performed including gralunometrical analyses using wet sieving treatment, radiological measurements using high resolution gamma-ray spectrometry and determination of main heavy metals concentrations using the XRF technique. The activity concentrations of all radionuclides exhibited values expected in natural sediments, while the heavy metals concentrations are locally far above the sediment quality guidelines values. The most contaminated area is the small harbor of the ex fertilizers plant at Sfageion Bay, where discrepancy from the linear c...
Deep Sea Research Part II: Topical Studies in Oceanography, 2019
In-situ and laboratory data of radioisotopes were acquired and interpreted for the Olimpi field, ... more In-situ and laboratory data of radioisotopes were acquired and interpreted for the Olimpi field, Mediterranean Sea. Standard oceanographic parameters and in-situ radon progeny profiles were analysed for four different sites, utilizing a state-of-the-art gamma-ray spectrometer optimized for deep sea research. In addition, a sediment core recovered from the Gelendzhik mud diapir plateau was analysed by means of high resolution laboratory gamma-ray methods providing vertical distribution of excess lead 210 Pb, potassium 40 K, and caesium 137 Cs. Water column profiles of radon progenies revealed higher concentrations above mud volcano areas/structures in comparison to the selected reference site. This increase is likely attributed to higher emanation rates of radon gas in areas which are affected by the local diapirism. In all cases the concentration of radon progeny almost linearly decreased toward the surface due to radioactive decay and dilution processes, however differences in the concentration slopes between sites indicates a continuous release of fluids in the Moscow and Milano sites. The profile of the excess 210 Pb in the Gelendzhik sediment core revealed two different accumulation rates. Using two local maxima of 137 Cs, two dating points were used to suggest that an intense mud flow event took place during 1963-1986. Also, as the activity concentration of 40 K increased by almost 30% during this period, and the chemical constituent of the accumulated material differed from the underneath layers, a material of different origin is presumed. Moreover, in the period 1986-2016 the accumulation rate was much lower indicating the absence of other, more recent, intense mud flow events in the neighbouring area of the core sampling.
Applied Radiation and Isotopes, 2016
In situ γ-ray Spectrometry in the Marine Environment using Full Spectrum Analysis for natural rad... more In situ γ-ray Spectrometry in the Marine Environment using Full Spectrum Analysis for natural radionuclides, Applied Radiation and Isotopes,
HNPS Proceedings, 2020
In this work, core sediment samples up to 50 cm have been collected from three different marine e... more 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.
HNPS Proceedings, 2019
Chronology models based on radiotracers are useful for dating aquatic sediments influenced by ind... more Chronology models based on radiotracers are useful for dating aquatic sediments influenced by industrialization. Among the many natural (e.g. 7Be, 234Th,210Pb) and artificial (e.g. 137Cs,238,239,240Pu) radiotracers, the proper ones to study the industrial impact and reconstruct past events during the last 100 years, are 210Pb and 137Cs. Mining belongs to the industries with great ecological impact in the aquatic environment, as mines are situated near environmental sensitive areas such as coasts, rivers and lakes. Additionally, the accurate historical reconstruction may provide information regarding the mine footprint in the aquatic environment so as to assess the previous or the remaining contamination, in case of on-going or abandoned mines. In the present study, the retrospective investigation in a coastal area of Lavrio, near an abandoned metallic mine is attempted, using the 210Pb and 137Cs methodologies and the emerged difficulties are discussed.
HNPS Proceedings, 2019
Chronology models based on radiotracers are useful for dating aquatic sediments influenced by ind... more Chronology models based on radiotracers are useful for dating aquatic sediments influenced by industrialization. Among the many natural (e.g. 7Be, 234Th,210Pb) and artificial (e.g. 137Cs,238,239,240Pu) radiotracers, the proper ones to study the industrial impact and reconstruct past events during the last 100 years, are 210Pb and 137Cs. Mining belongs to the industries with great ecological impact in the aquatic environment, as mines are situated near environmental sensitive areas such as coasts, rivers and lakes. Additionally, the accurate historical reconstruction may provide information regarding the mine footprint in the aquatic environment so as to assess the previous or the remaining contamination, in case of on-going or abandoned mines. In the present study, the retrospective investigation in a coastal area of Lavrio, near an abandoned metallic mine is attempted, using the 210Pb and 137Cs methodologies and the emerged difficulties are discussed.
Applied Radiation and Isotopes, 2018
The KATERINA system is upgraded for quantitative measurements at the deep ocean. • MC simulations... more The KATERINA system is upgraded for quantitative measurements at the deep ocean. • MC simulations using MCNP5 reproduced experimental energy spectra and efficiency.
In situ characterization using natural radio-tracers in a submarine freshwater spring, Kiveri, Greece
Journal of Environmental Radioactivity, 2021
A medium resolution underwater gamma ray spectrometer was deployed in the submarine groundwater s... more A medium resolution underwater gamma ray spectrometer was deployed in the submarine groundwater spring of Anavalos and was combined with conductivity and temperature sensors for continuous measurements of natural radioactivity, salinity and water temperature, respectively. The activity concentrations of radon progenies varied from (5-40) kBq m-3, exhibited reverse dependence with salinity and were found above the guideline proposed by Environmental Protection Agency (11 kBq m-3). Their ratio was above unity indicating radon gas escape to the atmosphere. Time-series of the activity concentration together with their ratios were provided enabling the system configuration for long term monitoring applications. The in-situ method proved to be an effective tool to study the radioactivity levels of the spring and the groundwater - seawater interaction process. Furthermore, the proposed tool provides cost-effective measurements in terms of real-time and long-term requirements and, it is characterized by flexibility in terms of sensor integration in different platforms to perform submarine groundwater studies in a temporal and spatial manner.
Calibration of a CeBr3 based γ-spectrometer for onsite and laboratory radioactivity measurements in sediment samples
Applied Radiation and Isotopes, 2020
The calibration of an underwater spectrometer, consisting of a CeBr3 crystal, is performed for se... more 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.
HNPS Proceedings, 2020
The anthropogenic radionuclide 137Cs is used as a valuable oceanographic tracer for the study of ... more 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 Is...
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Papers by Christos Tsabaris