I. Csige

Radon transport phenomena studied in Karst caves-international experiences on radon levels and exposures

Abstract The results of radon measurements in caves obtained by using of nuclear track detectors are summarized. Mean radon concentrations are ranging worldwide from 0.1 to 20 kBqm −3 with 2.8 kBqm −3 arithmetic average. From long-term extended radon measurements in caves not only a detailed dosimetric picture can be drawn, but using radon gas as a radioactive tracer, the subsurface and near-to-surface transport processes can be studied, too. It will be shown that long-term radon monitoring by nuclear track detectors, in conjunctions with active detectors which enables detection of fast dynamic changes, offers very important information for naturally-occurring transport processes.

226Ra in geothermal and bottled mineral waters of Hungary

Abstract Geothermal waters have been used on a large scale for bathing, drinking and medical purposes, while the consumption of bottled mineral waters is increasing. In this work, radon and radium activity concentrations of thermal and bottled mineral waters, originating from different regions of Hungary, were studied by different radioanalytical methods. It was found that the thermal springs, which supply the world famous baths of Budapest along the right riverside of the Danube, have high 222 Rn and 226 Ra activity concentration: up to about 100 and 1 kBq m −3 , respectively. The radium content of some investigated geothermal waters found in the NE region of the Great Hungarian Plain is even higher: up to several kBq m −3 . The 226 Ra content of bottled mineral waters, commercially available in Hungary, was determined by gamma-spectrometric method, applying radiochemical separation. The highest value exceeded 2 kBq m −3 in the case of the Apenta mineral water, which is a popular brand in Hungary, as well as in Europe and North America.

Radon transport in fractured porous media — Experimental study in caves

The spatial and temporal variation of 222Rn concentration in three horizontal caves and in one vertical cave was measured to study the influence of different morphological and meteorological parameters on the forming of airborne radon concentrations inside. In horizontal caves, the daily mean radon concentration as a function of the daily average surface temperature showed a step-function type dependence with low winter and high summer values reflecting the main direction of underground airflows. Restriction of airflows increased winter but decreased summer radon levels. The transition pattern between the low winter and high summer values gradually linearized as the number of vertical fractures communicating with the surface increased. Contrary to horizontal caves, in the vertical cave barometric pressure variations played the most important role in controlling subsurface radon concentrations. Decreasing pressure increased radon levels, and increased pressure decreased radon levels. In the pressure-radon correlation curve, there was a small hysteresis which indicated the nonlinearity of the process.

Post-irradiation sensitization of CR-39 track detector in carbon dioxide atmosphere

Abstract The effect of post-irradiation treatment of CR-39 track detector in carbon dioxide atmosphere on the alpha particle registration sensitivity was investigated. Significant increase in etch rate ratio for 6.1 MeV 252Cf alpha particle was observed. The sensitization increasedboth as a function of trating time and as a function of carbon dioxide pressure in the treating vessel. Energy dependence of the sensitization was found to be small in the 2–9 MeV alpha particle energy interval. Fading of latent tracks after the sensitization process was slow in a one day period. Pre-irradiation treatment in carbon dioxide showed also some sensitization, though to a lesser extent than post-irradiation treatment. However, exposing CR-39 alpha particles in pure carbon dioxide atmosphere resulted in dramatic decrease in sensitivity. The role of dissolved oxygen and carbon dioxide in the primary latent track formation and in post-irradiation latent track transformation is discussed. Potential influence of the application of sensitization of CR-39 in radon, neutron and cosmic ray charged particle dosimetry is also discussed.

Temperature dependence of the calibration factor of radon and radium determination in water samples by SSNTD

Abstract The sensitivity of a 226 Ra determination method of water samples by SSNTD was measured as a function of storage temperature during exposure. The method is based on an etched track type radon monitor, which is closed into a gas permeable foil and is immersed in the water sample. The sample is sealed in a glass vessel and stored for an exposure time of 10–30 days. The sensitivity increased more than a factor of two when the storage temperature was raised from 2 °C to 30 °C. Temperature dependence of the partition coefficient of radon between water and air provides explanation for this dependence. For practical radio-analytical application the temperature dependence of the calibration factor is given by fitting the sensitivity data obtained by measuring 226 Ra standard solutions (in the activity concentration range of 0.1–48.5 kBq m −3 ) at different storage temperatures.

Determination of dissolved radon and radium content of water samples by track etch method

Abstract The authors have developed a method to determine the dissolved radon and radium content of water samples using track etch type radon monitors. The device is an immersed, small volume radon monitor with a CR-39 track etch detector. The monitor is sealed from the water by a thin radon permeable rubber foil. The dissolved radon and/or the radium content of water samples can be determined from two independent radon exposures by using the solutions of a non-steady state differential equation which describes the temporal variation of radon content of water and by using an experimentally determined calibration coefficient.

Determination of radon and radium content of water samples by SSNTD technique

We have developed a method to determine the dissolved radon and radium content of water samples using etch track type radon monitors. In two measurements the radon exposures in a freshly sealed and in a degassed water sample are determined. From the measured exposures the radon and radium content of water is calculated.

Fission products from the damaged Fukushima reactor observed in Hungary

Fission products, especially 131I, 134Cs and 137Cs, 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 131I 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 134Cs and 137Cs in detectable amounts along with 131I. The decay-corrected inventory of 131I 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.

Measurement of effective diffusion coefficient of radon in porous media with etched track radon monitors

We have developed two methods to measure the effective diffusion coefficient of radon in porous media. We used etch track type radon monitors to measure the radon exposure on both the exposure and the measuring sides. We have used a computer code to model the transport of radon through porous media. We found the effective diffusion coefficient by changing its value in the code to find the best fit of model calculation to experimental data.

Spatial distribution of radon content of soil-gas and well-waters measured with etched track radon monitors

We have measured the spatial distribution of radon content of ground-water and of soil-gas in Matraderecske village (Hungary) using etched track type radon monitors. The applicability of the used in-situ method to measure radon content of ground-water is tested and discussed. Regression analysis between ground-water radon level, soil-gas radon content and other parameters, such as temperature, pH level and the electric conductivity of water revealed no significant linear correlation between any pair of the above parameters. Surface maps of radon activity levels in soil and in ground-water were computed and compared to each other and to geological structure of the area.