Ανάπτυξη μεθοδολογίας φασματοσκοπίας ακτίνων-γ για in-situ μετρήσεις σε θαλάσσιο ίζημα

Abstract

In the present work, the progress in developing a methodology for calculating the detection efficiency of an underwater gamma-ray spectrometer for marine sediment measurements on the seabed is presented. The experimental work was carried out at the coastal zone of Vasilikos (Cyprus) by deploying the in-situ NaI detector system ΚΑΤΕΡΙΝΑ and acquiring data from seawater (4π geometry) and from the seabed (2π geometry). Sediment samples were also collected from the same sites and subsequently measured in the laboratory, by means of high resolution gamma-ray spectrometry. The experimental full-energy peak efficiency of the in-situ system in the energy range 1400-2600 keV, was calculated for a specific site (Site 1), by combining the in-situ measurements with the laboratory reference ones. Furthermore, the efficiency results were reproduced by Monte Carlo (MC) simulations, using the MCNP5 code. The developed method was subsequently implemented for activity concentration calculations in sediments by analyzing the in-situ spectra as acquired from neighboring sites, to the reference point (Site 1), in the same region. The activity calculation results were validated using corresponding reference laboratory measurements, by means of a HPGe detector, in the same sites. Comparison results between in-situ and laboratory measurements, exhibited satisfactory agreement within statistical uncertainties. The instrumentation used and the first steps in establishing a methodology for in-situ quantitative sediment measurements are presented. Concluding, perspectives of improving experimental data and generalizations in the system efficiency calibration calculations are discussed for future applications by obtaining more data in sea beds with different geological formations.