High resolution gamma-ray spectrometry for routine measurements of environmental samples.

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.

In situ characterization using natural radio-tracers in a submarine freshwater spring, Kiveri, Greece.

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.

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.

Dispersion pattern of 226Ra and 235U using the ERICA Tool in the coastal mining area, Ierissos Gulf, Greece.

Natural radionuclides, present in mining materials, can exhibit elevated values, thus it is of great interest to study their dispersion in mining areas. Radionuclide spatial variations were determined in coastal surface sediments near the mining area of Ierissos Gulf in northern Greece. 226Ra and 235U measured concentrations were compared with the estimations of ERICA Tool, the dispersion patterns were derived and the affected region around the load-out pier area was calculated to be approximately 21 km2.

A methodology for expanding the use of NaI(Tl) based spectrometry in environmental radioactivity measurements.

A methodology that extends the usability of low and medium resolution γ-ray detectors to a wide range of energies that appear in environmental radioactivity measurements is described. Results of the implementation of the methodology in the analysis of 20 granite samples measured with a (3″ × 3″) NaI(Tl) are presented. A comparison with the activity results obtained by a high-resolution detector (HPGe) for two samples was found in good agreement, within the uncertainties, validating the results of the proposed method.

Efficiency calibration for in situ γ-ray measurements on the seabed using Monte Carlo simulations: Application in two different marine environments.

A new approach for calibrating an in situ detection system for measurements in marine sediments has been developed. The efficiency calibration was deduced on full spectral range by Monte Carlo simulations (MCNP5 code) considering a close detector-seabed geometry set-up. Moreover, the influence of the detection efficiency with respect to the variations of the sediment geological characteristics was studied through Monte Carlo simulations. The results of the theoretical approach were compared with experimental calculations in two different real test cases, yielding a satisfactory agreement (up to 10% and 20% for sites 1 and 2 respectively) in the energy range from 351 keV to 2614 keV. For the experimental measurements, the in situ detection system KATERINA was deployed both in the seawater and on the seabed in two different marine environments. The experimental determinations of the detection efficiency were performed by utilizing the acquired data of the deployments, along with additional necessary laboratory measurements. The adopted approach and the obtained results are discussed.

Radioactivity and metal concentrations in marine sediments associated with mining activities in Ierissos Gulf, North Aegean Sea, Greece.

Marine sediment samples were collected from Ierissos Gulf, N Aegean Sea, close to the coastal mining facilities. Measurements of radionuclide and metal concentrations, mineral composition and grain size distribution were performed. The concentrations of (226)Ra, (235)U and trace metals showed enhanced values in the port of Stratoni compared with those obtained near to Ierissos port. The dose rates received by marine biota were also calculated by the ERICA Assessment Tool and the results indicated no significant radiological risk.

In situ γ-ray spectrometry in the marine environment using full spectrum analysis for natural radionuclides.

The Full Spectrum Analysis approach was applied to obtain activity concentration estimations for in situ measurements in the marine environment. The 'standard spectra' were reproduced using the MCNP-CP code. In order to extract the activity concentrations, χ(2) minimization calculations were performed by implementing the MINUIT code. The method was applied to estimate the activity concentrations for measurements in the marine environment in three different test cases. The estimated activity concentrations were in good agreement with the experimentally derived ones within uncertainties.

Activity concentration and spatial distribution of radionuclides in marine sediments close to the estuary of Shatt al-Arab/Arvand Rud River, the Gulf.

Tigris and Euphrates rivers both emerge in eastern Turkey and cross Syria and Iraq. They unite to Shatt al-Arab/Arvand Rud River and discharge in Arabic/Persian Gulf. The activity concentration of natural and anthropogenic radionuclides was measured during the August of 2011 in a number of surficial sediment samples collected from the seabed along an almost straight line beginning near the estuary mouth and extending seaward. The results exhibited low activity concentration levels and an almost homogeneous spatial distribution except locations where sediment of biogenic origin, poor in radionuclides, dilute their concentrations. Dose rates absorbed by reference marine biota were calculated by the ERICA Assessment Tool considering the contribution of 40 K. The results revealed a relatively low impact of 40 K mainly to species living in, on and close to the seabed. Also, statistical association of radionuclides with selected stable elements (Ca, Ba and Sr) did not indicate presence of by-products related with oil and gas exploitation and transportation activities. Moreover, a semi-empirical sedimentology model applied to reproduce seabed granulometric facies based entirely on radionuclides activity concentrations.

Vertical distribution of (137)Cs activity concentration in marine sediments at Amvrakikos Gulf, western of Greece.

The aim of the present work is the study of (137)Cs migration in sediment column taking into account the sedimentation rate in the Amvrakikos Gulf, at the western part of Greece. Marine core sediments were collected and the measurements were performed using the high resolution gamma-ray spectrometry method. The vertical distribution of (137)Cs activity concentration, as part of anthropogenic marine radioactivity, provided averaged sedimentation rate by identifying the depths of activity concentrations due to the Chernobyl accident and the nuclear tests signals. Furthermore, (137)Cs measurements were reproduced using the proposed one-dimensional diffusion-advection model which provides mainly as an output, the sedimentation rate and the average diffusivity of (137)Cs in the sediment column. The proposed model estimates the temporal variation of (137)Cs activity concentration from 1987 (one year after the Chernobyl accident) till today (2014).