M. Ješkovský

Iodine-129 in Seawater Offshore Fukushima: Distribution, Inorganic Speciation, Sources, and Budget

The Fukushima nuclear accident in March 2011 has released a large amount of radioactive pollutants to the environment. Of the pollutants, iodine-129 is a long-lived radionuclide and will remain in the environment for millions of years. This work first report levels and inorganic speciation of (129)I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated (129)I concentrations in surface water were observed with the highest (129)I/(127)I atomic ratio of 2.2 × 10(-9) in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of (129)I, while stable (127)I was mainly in iodate form, reflecting the fact that the major source of (129)I is the direct liquid discharges from the Fukushima NPP. The amount of (129)I directly discharged from the Fukushima Dai-ichi nuclear power plant to the sea was estimated to be 2.35 GBq, and about 1.09 GBq of (129)I released to the atmosphere from the accident was deposited in the sea offshore Fukushima. A total release of 8.06 GBq (or 1.2 kg) of (129)I from the Fukushima accident was estimated. These Fukushima-derived (129)I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future.

Long-term variations of 14C and 137Cs in the Bratislava air – implications of different atmospheric transport processes

This study summarizes measurements of atmospheric (14)C and (137)Cs in the Bratislava air since 1976. Higher (14)C levels observed in spring and early summer months until the 1980s confirm injection of the stratospheric air into the troposphere. Later, deep winter minima were observed in (14)C concentrations, probably due to the depletion of the atmospheric (14)C levels in winter months by the injection of large quantities of fossil CO(2). Presently observed (14)C maxima in summer and minima in winter were caused by the depletion of the atmospheric (14)C in winter months, amplified by temperature inversions during winter, rather than by the injection of the stratospheric air into the troposphere. The observed (137)Cs activity concentrations also showed an impact of the stratospheric air on the (137)Cs levels until the early 1980s, documented by typical spring/early summer maxima and winter minima. The global fallout (137)Cs record was then disturbed by the Chernobyl accident (1986) when large quantities of (137)Cs were released to the atmosphere. The recent (137)Cs variations observed in the atmosphere, characterised by winter maxima and summer minima, are assumed to be mainly due to the resuspension of (137)Cs from the soil. A correlation was found between the (137)Cs activity concentration and the dust level in the air (the correlation coefficient r = 0.74), as well as an anticorrelation with the temperature (r = -0.56).

Long-term variations of radionuclides in the Bratislava air

Variations of aerosol radionuclides (2001-2015) in the ground-level air in Bratislava (Slovakia) showed 7Be maxima in spring/early summer and minima in winter, however, an inverse trend was observed for 210Pb, 137Cs and 40K. A decreasing amplitude and splitting of summer maxima for 7Be in the last years has been found. A temporal behavior of the 7Be/210Pb activity ratio showed higher levels during warm seasons due to vertical convection of air masses from higher altitudes. The 137Cs activity concentration in the surface air between 2003 and 2010 was decreasing with an effective half-life of 1.9xa0±xa00.3 years. The yearly average 137Cs concentrations during 2009-2014 were almost constant, disturbed only by the Fukushima accident in 2011. The increased atmospheric 137Cs and 40K levels observed during the autumn-winter season may be due to surface soil resuspension, biomass burning and radionuclide transport by winds. Seasonal variations of 222Rn activity concentrations were found with maxima at the end of autumn and in winter, and minima in spring. The variability of the average annual course of 222Rn has been larger than that of 210Pb. The 210Pb/222Rn activity ratio was highest at the end of winter and in the spring, while from June to December remained nearly constant. More intensive atmospheric mixing in spring months caused a decrease in the 222Rn activity concentration, while the aerosol component of the atmosphere has been affected mainly during the autumn and winter seasons. The mean residence time of aerosols in the atmosphere was calculated using the 210Pb/222Rn method to be 4.5xa0±xa00.9xa0days.

PIXE beam line at the CENTA facility of the Comenius University in Bratislava: first results

Optimization of the proton and helium beams from the alphatross ion source through the injection beam-line, the 3xa0MV Pelletron tandem accelerator, the high-energy analyzer and the PIXE chamber were carried out. Results obtained with the 4He ion beam showed better detection limits when compared with protons of the same energy and beam intensity. For detection of produced X-rays, a BEGe detector has been used, covering the energy range from 3xa0keV to 3xa0MeV. First measurements with 4He ions of 3.5xa0MeV energy included calibration runs with PIXE laboratory standards, as well as analyses of old silver coins.

Radiocarbon in the Atmosphere of the Žlkovce Monitoring Station of the Bohunice NPP: 25 Years of Continuous Monthly Measurements

Radiocarbon variations in the atmosphere have been observed at the Žlkovce monitoring station of the Bohunice nuclear power plant (NPP), situated only 5 km ESE from the NPP. The observed 14 C levels provide unique evidence of a decreasing long-term impact of the Bohunice NPP on the region. Simultaneously, decreasing emissions of fossil fuel carbon dioxide in the atmosphere of the monitoring site have been found. The observed ∆ 14 C variations with time have attenuating amplitudes and decreasing mean values, showing maxima in summer and minima in winter, the latter primarily caused by increased emission of fossil CO 2 in winter months. Sporadic short-term releases of 14 C from the Bohunice NPP were observed at the Žlkovce station. The annual atmospheric ∆ 14 C variations compared with tree-ring data collected at the Žlkovce village show reasonable agreement. The observed ∆ 14 C levels after 2005 are close to the European clean-air levels as measured at the Jungfraujoch (3450 m asl) monitoring station. DOI: 10.2458/azu_rc.57.18364

A search for double-electron capture of 74Se to excited levels using coincidence/anticoincidence gamma-ray spectrometry

Abstract Evaluation of single, coincidence and anticoincidence gamma-ray spectrometry methods has been carried out with the aim to search for double-electron capture of 74Se to excited states. This process is unique, because there is probability for transition to the 2+ excited state in 74Ge (1204xa0keV), and de-excitation through two gamma-quanta cascade with energies of 595.9xa0keV and 608.4xa0keV. Long-term measurements with an anticosmic shielded HPGe (high purity Ge) spectrometer and a coincidence HPGe–NaI(Tl) spectrometer did not show any evidence for the double-electron capture in 74Se. The best limit for the half-life of the double electron capture in 74Se (both for the neutrinoless and two neutrino processes) was estimated to be >1.5×1019 yr.

Joint Bratislava–Prague studies of radiocarbon and uranium in the environment using accelerator mass spectrometry and radiometric methods

A research program has been established between Bratislava and Prague groups to study natural and anthropogenic radionuclides in the environment using both Accelerator Mass Spectrometry (AMS) and radiometric methods. The first studies have focused on 14C activity variations in the atmosphere and biosphere with the aim to evaluate an impact of Czech and Slovak Nuclear Power Plants (NPP) on the environment, and on the development of AMS technique for investigation of actinides (mainly uranium isotopes) in the environment.

Recent results from the AMS/IBA laboratory at the Comenius University in Bratislava: preparation of targets and optimization of ion sources

Developments of solid targets and optimizations of ion sources were carried out with the aim to produce high ion yields for applications of tandem accelerators as mass spectrometers. A comparison of Al− yields from different aluminum targets showed that the best results were obtained with AlN targets. Transmission studies of 9Be and 12C ions through the Pelletron accelerator showed highest efficiencies for 9Be2+ and 12C2+. First results obtained with a simplified version of the AMS line are presented as well.

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.

Radiocarbon concentration in tree-ring samples collected in the south-west Slovakia (1974–2013)

Radiocarbon measurements of tree-ring samples collected in Vysoká pri Morave were compared with tree-ring data of the Žlkovce monitoring station situated 5km south-east from the Jaslovské Bohunice Nuclear Power Plant (NPP). Radiocarbon concentrations in Vysoká pri Morave and in Žlkovce tree rings were decreasing exponentially with decay constants of 14.48±1.23 y and 17.96±1.97 y, respectively, in agreement with similar results obtained at other radiocarbon stations. The Suess effect, represented by a dilution in 14C levels by fossil fuel CO2 emissions, was observed in both tree-ring data sets. The Vysoká pri Morave 14C data were during 1974-1995 systematically lower by about 50‰ than the Schauinsland (Germany) clean air reference values due to a regional fossil-fuel impact. However, after 1996 the Vysoká pri Morave 14C data were closer to the Schauinsland data due to lower CO2 emissions as a result of closing some of the heavy industry technologies in the region.