P. P. Povinec

Dispersion of Fukushima radionuclides in the global atmosphere and the ocean

Large quantities of radionuclides were released in March-April 2011 during the accident of the Fukushima Dai-ichi Nuclear Power Plant to the atmosphere and the ocean. Atmospheric and marine modeling has been carried out to predict the dispersion of radionuclides worldwide, to compare the predicted and measured radionuclide concentrations, and to assess the impact of the accident on the environment. Atmospheric Lagrangian dispersion modeling was used to simulate the dispersion of (137)Cs over America and Europe. Global ocean circulation model was applied to predict the dispersion of (137)Cs in the Pacific Ocean. The measured and simulated (137)Cs concentrations in atmospheric aerosols and in seawater are compared with global fallout and the Chernobyl accident, which represent the main sources of the pre-Fukushima radionuclide background in the environment. The radionuclide concentrations in the atmosphere have been negligible when compared with the Chernobyl levels. The maximum (137)Cs concentration in surface waters of the open Pacific Ocean will be around 20 Bq/m(3). The plume will reach the US coast 4-5 y after the accident, however, the levels will be below 3 Bq/m(3). All the North Pacific Ocean will be labeled with Fukushima (137)Cs 10 y after the accident with concentration bellow 1 Bq/m(3).

Resuspension processes controll variations of 137Cs activity concentrations in the ground-level air

The 137Cs activity concentration in the surface air between 1977 and 2007 was decreasing with an ecological half-life of 3.4xa0years, however, during 2007–2010 the yearly averaged 137Cs activity concentrations were almost constant. The increased atmospheric 137Cs and 40K levels observed during the winter may be due to surface soil resuspension and radionuclide transport by winds, particularly from open agricultural areas, as confirmed by high correlation coefficient between 137Cs and 40K atmospheric levels (Rxa0=xa00.84), and similar 137Cs/40K activity ratios in aerosols (0.07) and soils (0.05).

Tritium analysis with an ethane-filled proportional counter

An apparatus for natural tritium concentration measurement using an ethane-filled proportional counter with anticoincidence shielding is described. The counter characteristics and the counter calibration with internal tritium and external137Cs standards are discussed. Results of tritium analysis of Bratislava rains are presented.

Environmental radionuclides as contaminants of HPGe gamma-ray spectrometers: Monte Carlo simulations for Modane underground laboratory

The main limitation in the high-sensitive HPGe gamma-ray spectrometry has been the detector background, even for detectors placed deep underground. Environmental radionuclides such as 40K and decay products in the 238U and 232Th chains have been identified as the most important radioactive contaminants of construction parts of HPGe gamma-ray spectrometers. Monte Carlo simulations have shown that the massive inner and outer lead shields have been the main contributors to the HPGe-detector background, followed by aluminum cryostat, copper cold finger, detector holder and the lead ring with FET. The Monte Carlo simulated cosmic-ray background gamma-ray spectrum has been by about three orders of magnitude lower than the experimental spectrum measured in the Modane underground laboratory (4800u202fm w.e.), underlying the importance of using radiopure materials for the construction of ultra-low-level HPGe gamma-ray spectrometers.

Ultra-sensitive radioanalytical technologies for underground physics experiments

Assessment of radioactive contamination of construction materials used in deep underground experiments has been carried out using ultra-sensitive analytical methods such as radiometrics, inductively coupled plasma mass spectrometry (ICPMS), accelerator mass spectrometry (AMS), and neutron activation analysis. The lowest detection limits,u2009<u20091xa0nBqxa0g−1, has been obtained with ICPMS and AMS techniques.

The 137Cs distribution in sediment profiles from the Yangtze River estuary: a comparison of modeling and experimental results

It has been generally accepted when estimating sedimentation rates using the 137Cs dating method that the position of the 137Cs maximum in a sediment profile represents the year 1963. In this paper we validated this approach by developing a model in which the annual 137Cs global fallout flux for the Yangtze River estuary was established on the basis of the Tokyo flux corrected for precipitation rates observed in Shanghai. As the 137Cs maxima in the sediment deposition profiles depend on the sedimentation rates, the sub-sampling intervals were calculated accordingly. Higher measured than the calculated values were found in some cores, what may be due to fluctuating sedimentation rates and an additional deposition of 137Cs from land-based sources. The study provides useful information on the reliability of the measured 137Cs maxima in sediment profiles frequently used for dating of sediments in marine (coastal regions, open seas) as well as in terrestrial (lakes) environments.

Anthropogenic 137 Cs on atmospheric aerosols in Bratislava and around nuclear power plants in Slovakia

Nuclear power plants (NPPs) have been one of the sources of anthropogenic radionuclides in the environment. This work combines the results from monitoring stations around NPPs in Slovakia (Mochovce and Jaslovské Bohunice) and academic measurements at the Comenius University campus in Bratislava. Most of the atmospheric 137Cs in this region come from the resuspension of the Chernobyl-derived 137Cs, as well as caesium produced during nuclear weapons testing. By comparison of the obtained results at NPPs with Bratislava data, radiation impacts of the NPPs on the local environments have been estimated to be negligible.