Natural radioactivity of thermal springs and related precipitates in Gellért Hill area, Buda Thermal Karst, Hungary.

The elevated radioactivity of the thermal waters of Buda Thermal Karst (BTK), Hungary is known and studied since the beginning of the 20th century. In the recent studies, the anomalous 222Rn/226Ra ratios have drawn the attention to the existence of local 222Rn source. Biogeochemical precipitates (i.e. biofilms) in spring caves were found to have high adsorption capacity, accumulating e.g. 226Ra. Biogeochemical precipitates are ubiquitous in the thermal springs of BTK, occurring in different amount and colours (dark grey, brown, red, white), and have different microbial communities and elemental composition. The detailed investigation of the radioactivity of spring waters highlighted the different 226Ra and 222Rn activity concentrations. The present study aimed to survey the radioactivity of the thermal springs of Gellért Hill area, together with the biogeochemical precipitates and air above the water level, and to assess the evolution of the radioactivity of known-aged precipitates, formed during in situ experiments. We found that the basic physicochemical parameters of the spring waters (field parameters, major ions) do not affect the adsorption capacity of biogeochemical precipitates. It was revealed by the conducted in situ experiments, that the flow conditions influence the evolution rate of precipitates, so their adsorption capacity. The 222Rn activity concentrations of spring waters are dependent on the area of the water surface, volume of air space above the water level, ventilation of the caves/channels and presence of calcite layer on the water surface. The latter has a blocking effect on degassing.

Fallout isotope chronology of the near-surface sediment record of Lake Bolatau.

Fallout isotope (210Pbex,137Cs and 241Am) based dating has been carried out on the near-surface sediment core collected from Lake Bolatau-Feredeu (Bukovina, Romania). The motivation was to improve the chronology of this recent section in connection with significant fluctuations observed in sediment accumulation rates, particle size distribution and primordial radioisotope (i.e. 40K and 232Th) composition. Previously only an extrapolation of a broad-range OxCal age-depth model, which was based on 8 AMS radiocarbon dates from the deeper part of a parallel sediment sequence and tentatively validated for the upper part using the double peaks of the 137Cs activity concentration distribution, was available for the studied section (1-24 cm). Parallel to the previous 137Cs measurement, 210Pb and 226Ra (for a more detailed, 210Pbex-based chronology), 241Am (for an additional time-marker), as well as 40K and 232Th concentrations have also been determined by gamma-spectrometry. In case of the 210Pbex-based chronology, due to a large deviation from a pure exponential distribution, the Constant Flux (CF) model has been used for the calculation of sediment ages and accumulation rates. Although the broad-range OxCal and the CF model were broadly similar down to 22 cm, the 210Pbex-based ages are clearly superior in terms of uncertainty in the uppermost 12 cm, while the broad-range model has smaller uncertainty below 20 cm (>150 years). The CF model gave an average mass accumulation rate of (0.08 ± 0.03) g cm-2 yr-1 for sections 0-11 cm, and (0.03 ± 0.01) g cm-2 yr-1 for sections 12-22 cm, respectively. Significant changes have been observed in the depth distribution of both the particle size distribution and the elemental/isotopic composition of the sediment record, most likely related to the variation observable in the intensity and volume of precipitation in the catchment. The obtained high-resolution records of Lake Bolatau, including multiple radioisotopes, can serve as a regional benchmark for similar studies.

Fission products from the damaged Fukushima reactor observed in Hungary.

Fission products, especially (131)I, (134)Cs and (137)Cs, from the damaged Fukushima Dai-ichi nuclear power plant (NPP) were detected in many places worldwide shortly after the accident caused by natural disaster. To observe the spatial and temporal variation of these isotopes in Hungary, aerosol samples were collected at five locations from late March to early May 2011: Institute of Nuclear Research, Hungarian Academy of Sciences (ATOMKI, Debrecen, East Hungary), Paks NPP (Paks, South-Central Hungary) as well as at the vicinity of Aggtelek (Northeast Hungary), Tapolca (West Hungary) and Bátaapáti (Southwest Hungary) settlements. In addition to the aerosol samples, dry/wet fallout samples were collected at ATOMKI, and airborne elemental iodine and organic iodide samples were collected at Paks NPP. The peak in the activity concentration of airborne (131)I was observed around 30 March (1-3 mBq m(-3) both in aerosol samples and gaseous iodine traps) with a slow decline afterwards. Aerosol samples of several hundred cubic metres of air showed (134)Cs and (137)Cs in detectable amounts along with (131)I. The decay-corrected inventory of (131)I fallout at ATOMKI was 2.1±0.1 Bq m(-2) at maximum in the observation period. Dose-rate contribution calculations show that the radiological impact of this event at Hungarian locations was of no considerable concern.

Examination of the effect of particle size on the radionuclide content of soils.

Information on the distribution of radiocaesium as a function of soil particle size is fundamental for its use as tracer in soil transport. Since the processes involved in soil erosion are known to remove and transport finer particles with larger efficiency, the aim of this work was to obtain data on the particle size versus radionuclide content distribution regarding the reference site of a soil erosion study. The analysis done was based on more than 5kg of source material and the changes happened to the radionuclide content of the different size fractions between the individual separation steps have been carefully monitored. About 10% of the total amount of (137)Cs present was found to be trapped in the serrations of larger stone-fragments while another 10% is transportable only during heavier storm-events. Within the remaining 80%, physical weathering products and clay particles have a (137)Cs-activity concentration, transportability and mass ratio of about 1:10, 1:2 and 1:1, respectively.