[Show abstract][Hide abstract] ABSTRACT: 137Cs, 241Am and Pu isotopes were analyzed in seawater, bottom sediments (BS) and suspended particulate matter samples collected in the Baltic Sea during 1997–2011. The particle size distribution and sequential extraction studies were carried out with the aim to better understand the association of radionuclides with particles and their bonding patterns in the BS. δ13Corg was applied for identification of sources of organic matter in the studied area. It has been found that massic activities of 137Cs in BS varied from 2.1 to 588 Bq/kg. High correlation of 137Cs massic activities with total organic carbon (TOC) in BS (r = 0.75) and with clay minerals (r = 0.95) was found. 239,240Pu massic activities in BS varied from 0.03 to 7.5 Bq/kg. High correlation with TOC was found for 239,240Pu (R = 0.98) as well as for 241Am (r = 0.96). δ13Corg in the studied samples ranged from −22.3 to −31.8 ‰.
Journal of Radioanalytical and Nuclear Chemistry 08/2013; 296(2):787-792. DOI:10.1007/s10967-012-2029-y · 1.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During migrations and ontogeny amphibians change their habitat and feeding, and thus are important in linking terrestrial and aquatic ecosystems. We measured δ13C and δ 15N values of early stages (egg, embryo, tadpole) and toes of adult frogs Rana temporaria, collected from a small wetland in Lithuania. We compared the isotopic composition of these tissues with potential food sources, excrements of tadpoles, and filled intestinal tracts. We found that δ 13C values in R. temporaria tadpoles were markedly depleted in comparison to adults, eggs or embryos, demonstrating a terrestrial to aquatic shift in energy sources. After the onset of feeding, tadpoles approached isotopic equilibrium with available food (algae and litter). Tadpoles had higher δ 15N than both algae and litter, differing by 3.6 and 2.4‰, respectively, and similar δ 13C to these sources. However, tadpole excrements and body tissue diverged, with mean δ 13C values of excrements (−30.3±1.6‰ SD) more similar to litter (−31.7±1.2‰ SD) and body tissue δ 13C (−34.8±0.7‰ SD) more similar to algae (−34.2±4.1‰ SD). This suggests that algal resources are critical in early life stages of this anuran, particularly at stages characterized by high growth and low development (stages: 25–35).
[Show abstract][Hide abstract] ABSTRACT: The general idea of this work is to introduce an evaluation method to restore the irradiation parameters of graphite or other carbonaceous materials using experimental and modelling results of 13C generation in the irradiated material. The method is based on coupling of stable isotope ratio mass spectrometry and computer modelling of the reactor core to evaluate the realistic characteristics of the reactor core such as the neutron fluence in any position of the reactor graphite stack or other graphite constructions.The generation of carbon isotopes 13C and 14C in the irradiated graphite of the RBMK-1500 reactor has been estimated by modelling of the reactor core with computer codes MCNPX and CINDER90. Good agreement of simulated and measured Δ13C/12C values in graphite of the central part of the reactor core indicates that the neutron flux (1.40×1014n/cm2s) is modelled accurately in the graphite sleeve of the fuel channel. The simulated activity of 14C is compared with the one measured by the β spectrometry technique. Results indicate that production of 14C from 14N in the RBMK-1500 reactor is considerable and has to be taken into account in order to make proper evaluation of 14C activity. Measured 14C specific activity values correspond to 15±4ppm impurity of 14N in graphite samples from the RBMK-1500 reactor core.