Radiocesium sorption-desorption processes in lake sediments

Development and characterization of a mobile γ spectrometer and its field deployment for in situ radioactivity measurements

A mobile γ–ray spectrometer (AMESOS) has been developed using a 3”×3” NaI(Tl) detector, a custom–made mounting holder, and portable electronics to perform in situ measurements of radioactivity. The spectrometer was calibrated using standard point sources and its absolute efficiency was determined. As a field test operation, AMESOS was deployed on the premises of the University of Athens Zografou campus focusing on estimating the NORM levels. Data were analyzed and used to create radiological maps for the metropolitan UoA campus for the first time. Besides natural radioactivity levels, trace concentrations of 137Cs were also detected, attributed to the Chernobyl fallout in Greece. An overall steady performance of the spectrometer was observed throughout the field operation. AMESOS is ready to be deployed for in situ studies of environmental radioactivity and radwaste management.

Sediment particle size and initial radiocesium accumulation in ponds following the Fukushima DNPP accident

This study used particle size analysis to investigate the initial accumulation and trap efficiency of radiocesium ((137)Cs) in four irrigation ponds, ~4-5 months after the Fukushima Dai-ichi nuclear power plant (DNPP) accident. Trap efficiency, represented by the inventory of (137)Cs in pond sediment to the inventory of radiocesium in soil surrounding the pond (i.e., total (137)Cs inventory), was less than 100% for all but one pond. Trap efficiency decreased as sediment particle size increased, indicating that sediments with a smaller particle size accumulate more (137)Cs. In ponds showing low trap efficiency, fine sediment containing high concentrations of (137)Cs appeared to be removed from the system by hydraulic flushing, leaving behind mostly coarse sediment. The results of this study suggest that sediment particle size can be used to estimate the initial accumulation and trap efficiency of (137)Cs in pond sediment, as well as the amount lost through hydraulic flushing.

Characterization of 210Pb and 137Cs radionuclides in sediment from Lake Shinji, Shimane Prefecture, western Japan

The characterization and chemical behaviors of (210)Pb and (137)Cs in the surface sediment (4-7 cm depth from the bottom) from Lake Shinji, Shimane Prefecture, western Japan, are studied by grain size and phase analyses. Their activities had increasing trend in silt fractions with decreasing grain size, while those in sand fractions did with increasing grain size. The (40)K content had the general increasing trend with increasing grain size. These trends might be derived from the mineral component and the adsorption mechanism of these nuclides. By using the sequential extraction technique, most of (214)Pb, (137)Cs and (40)K were proved to be contained in silicate fraction. A part of (210)Pbex presumably existed as carbonate and iron manganese oxides for coarser grains, and as iron manganese oxides for finer grains, in addition to silicate fraction. Although (210)Pb and (137)Cs may occupy the different sites and exist in different chemical phases, the bulk contents in the samples from a variety of locations within the same lake showed a generally good correlation. This result suggests their similar depositional process within a lake in a macroscopic view, being one of the evidences for the validity of sedimentation chronology in the field.