Ivan Kobal

Systematic indoor radon and gamma-ray measurements in Slovenian schools.

Abstract—During the winter months of 1992/93 and 1993/94, instantaneous indoor radon concentrations and gamma dose rates were measured in 890 schools in Slovenia attended in total by about 280,000 pupils. Under “closed conditions,” the room to be surveyed was closed for more than 12 h prior to sampling, the air was sampled into alpha scintillation cells with a volume of 700 cm3, and alpha activity was measured. An arithmetic mean of 168 Bq m−3 and a geometric mean of 82 Bq m−3 were obtained. In 67% of schools, indoor radon concentrations were below 100 Bq m−3, and in 8.7% (77 schools with about 16,000 pupils) they exceeded 400 Bq m−3, which is the proposed Slovene action level. In the majority of cases, radon concentrations were high due to the geological characteristics of the ground. Approximately 70% of schools with high radon levels were found in the Karst region. Gamma dose rates were measured using a portable scintillation counter. An arithmetic mean of 102 nGy h−1 and a geometric mean of 95 nGy h−1 were obtained. No extraordinarily high values were recorded.

Systematic indoor radon and gamma measurements in kindergartens and play schools in Slovenia

Systematic measurements of indoor radon concentrations and gamma dose rates were carried out in the 730 kindergartens and play schools in Slovenia that, together, care for 65,600 children. The main method for indoor radon measurement was direct sampling in alpha scintillation cells, but in cases with an increased instantaneous radon concentration, the additional methods of track-etch detectors and alpha spectroscopy were applied. In 528 kindergartens and play schools (72%), radon concentrations were below 100 Bq m-3, with a geometric mean of 58 Bq m-3. In 16 kindergartens and play schools (2.2%), radon concentrations exceeded 800 Bq m-3. In all cases, the main reason for a high indoor radon concentration was the geological structure of the soil. Gamma dose rates were measured with a portable scintillation counter, but in the Ljubljana region thermoluminescence dosimeters were also exposed. The results ranged from 30 to 295 nGy h-1, with a geometric mean of 88 nGy h-1.

Soil radon monitoring in the Krsko Basin, Slovenia.

In order to support the safe operation of the Krsko Nuclear Power Plant (Westinghouse, 676 MWe PWR), the seismotectonic structure of the Krsko basin has been thoroughly investigated. As part of a wider study, a study on radon in soil gas was started in April 1999. Combined barasol detectors buried in six boreholes, two along the Orlica fault and four on either side of it, measure and record radon activity, temperature and pressure every 60 min. The results have been evaluated and the possibility of a correlation with seismic activity is discussed. Correlation between radon concentration and barometric pressure has been observed for all barasols. Preliminary results show that, at one location, the correlation coefficient between radon and barometric pressure changed sign before earthquakes.

Long-term radon investigation in four selected kindergartens in different geological and climate regions of Slovenia

During a one year-and-a-half period in 1993 and 1994 indoor radon concentrations were measured with complementary measurement techniques in four selected kindergartens in different geological and climate regions in Slovenia. This study was performed to obtain more information how local geology, climate, building materials and occupational patterns affect radon concentration in a kindergarten. In addition, the advantages and disadvantages of different measurement techniques were critically appraised. It was found that average working hours radon concentrations, calculated on the basis of continuous radon measurements, are significantly lower than whole day averages obtained by track-etch detectors. The ratio might be as large as two.

Radon in the spa of Bizovac

The radon concentration in the air and water of the Bizovac spa was measured by the Radhome silicon detector and the average values were obtained as 70 Bq/m3 in the indoor pool, 40 Bq/m3 in the hotel room, 135 Bq/m3 in the closed therapeutic bathroom, but the geothermal water had a Rn concentration of 25.3 kBq/m3 and the potable one 2.7 kBq/m3. The Rn transfer factor (f) from water to air in the indoor pool and therapeutic bathroom was 10 and 40 times higher than for normal dwellings (fn=10−4), respectively. The effective equivalent dose of inhaled radon for permanent personnel under the worst conditions in the spa was 5.4 mSv/y, but visitors spending two weeks in the spa could receive the dose of 77 μSv.

Tracing depositional consequences of environmental radionuclides (137Cs and 210Pb) in Slovenian forest soils

Depth distribution profiles of environmental radionuclides (137Cs and 210Pb) have been investigated in soil to elucidate the underlying environment of semi-natural temperate deciduous and/or coniferous forest soils in Slovenia (Žirovski vrh, Idrija, Kočevski Rog, Pohorie, Gorišnica and Rakitna). Surface enrichment of both nuclides was observed at all the sites investigated in this study, suggesting that the soils had undergone little natural or anthropogenic disturbance for at least the last several decades. Apparent annual burial rates of 137Cs (0.1–0.2 cm y−−1) were estimated to be about 1.3 times higher than those of 210Pb at individual sites of different lithology, which suggests strong affinity of 210Pb to soil organic matter. Variability of the vertical distribution profiles of these nuclides depends not only on “in situ” pedology but also on geographical and meteorological conditions, especially precipitation and wind direction.

Two desorption components of product CO2 in steady-state CO oxidation on Pd(110)

The velocity and angular distributions of desorbing product CO2 were studied in steady-state CO oxidation on Pd(110) by means of cross-correlation time-of-flight techniques. CO2 desorption was always collimated along the surface-normal direction. The velocity distribution curves involved two desorption components, a fast one and a slow one. The former showed translational temperatures above 2300 K and was suddenly suppressed above a critical CO pressure at which CO retarded the reaction. On the other hand, the latter showed a Maxwellian distribution at the surface temperature and was not suddenly suppressed around the critical CO pressure, decreasing slowly at higher CO pressures. Below the critical CO pressure, the fraction of this component was around 0.3, and above it, the value abruptly increased to approximately 0.9. The slow component appears to be formed on sites which are suitable for oxygen dissociation, such as structural defects.

Radon level reduction in two kindergartens in Slovenia.

Remedial actions were carried out in two kindergartens with average heating season radon concentrations of about 2,000 Bq m-3. The first kindergarten is built on sedimentary gravel and the second one on fly ash and cinder fill. In both cases, radon accumulated in a sub-floor channel (service tunnel). The channels were opened at both ends. Natural ventilation of the tunnels did not produce a sufficient reduction in radon concentration. A fan was mounted in one kindergarten to ventilate the channel for 20 min three times each day, thus reducing radon levels to an acceptable value.

Correlation between Short-Term and Long-Term Radon Measurements

Abstract In selected kindergartens and schools, long-term average indoor air radon concentrations were measured by twomonth exposure of etched track detectors. Short-term average concentrations were obtained from 7–10 day continuous radon recordings during the exposure of etched track detectors. Only in about 1/3 of cases both averages did agree within ± 20%; otherwise they differ considerably. The assumption that short-term results can substitute for long-term data, which is sometimes made to correct radon exposure estimated on the basis of concentrations obtained by etched track detectors, should therefore be treated with caution.

Nitrogen-15 and oxygen-18 kinetic isotope effects in the catalytic decomposition of N2O over MgO

The 15N kinetic isotope effects (KIE) in the catalytic decomposition of nitrous oxide on MgO powder were determined in the temperature range 675–875 K, and the following temperature dependence was found: KIE(15N)=(0.231±0.149)+(1353±114)/T. At initial pressures of N2O between 40 and 60 kPa, the reaction is of the order of +1 in N2O and has an apparent activation energy of 125±4 kJ mol−1. According to the Bigeleisen formalism, the rate-determining and isotope fractionation governing step was well represented by two transition states: a bent product-like NNO and a fork-type NNOO.