Josip Planinić

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.

Radon equilibrium factor and aerosols

Equilibrium factor values (F) were measured in the NRPB radon chamber and corresponding track densities of the bare (D) and diffusion (D0) LR-115 nuclear track detectors were determined. The obtained empirical function, F(DD0), has agreed with the theoretical one, that had been derived by using concentration equations for the radon and its short-lived decay products. Measurements of the detector track densities and aerosol concentrations (ca) made possible a fitting of the DD0(ca) function, that after introducing into the F(DD0) gave a relationship for aerosol concentration, F(ca). So, it was possible to assess a radon dose equivalent if concentrations of radon and aerosols in the air were known (measured).

Temporal variations of radon in soil related to earthquakes

A radon detector with LR-115 nuclear track film was constructed for radon concentration measurements in soil. Temporal radon variations, as well as the barometric pressure, precipitation and temperature were measured for two years. Negative correlation between radon concentration in soil and barometric pressure was found. For some of the recorded earthquakes that occurred during the observation period, soil radon anomalies may be noticed one month before the quakes.

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.

The equilibrium factor F between radon and its daughters

The theoretical relationship between the equilibrium factor F of radon and its daughters and the air exchange rate as well as the relationship between F and the track density ratio of the open (D) and filtered (D0) SSNT detector were examined. method of determining the factor F by means of the measured or given ratio DD0 was derived and an equation for the function F(DD0) was obtained. Application of the function F(DD0) to the track density measured by the detector LR-115 has given equilibrium factor values in the range from 0.14 to 0.78.

Radon anomaly in soil gas as an earthquake precursor

The mechanical processes of earthquake preparation are always accompanied by deformations; afterwards, the complex short- or long-term precursory phenomena can appear. Anomalies of radon concentrations in soil gas are registered a few weeks or months before many earthquakes. Radon concentrations in soil gas were continuously measured by the LR-115 nuclear track detectors at site A (Osijek) during a 4-year period, as well as by the Barasol semiconductor detector at site B (Kasina) during 2 years. We investigated the influence of the meteorological parameters on the temporal radon variations, and we determined the equation of the multiple regression that enabled the reduction (deconvolution) of the radon variation caused by the barometric pressure, rainfall and temperature. The pre-earthquake radon anomalies at site A indicated 46% of the seismic events, on criterion M>or=3, R<200 km, and 21% at site B. Empirical equations between earthquake magnitude, epicenter distance and precursor time enabled estimation or prediction of an earthquake that will rise at the epicenter distance R from the monitoring site in expecting precursor time T.

Radon in schools and dwellings of Osijek

Indoor radon concentrations were measured in 10 821 pupils primary schools of Osijek by means of the Radhome silicon detector. The values ranged from 15 to 300 Bq/m3 with the arithmetic and geometric means of 93.4 and 70.6 Bq/m3, respectively. Ten years continuous radon measurements performed with the LR-115 nuclear track detector in three houses of different construction and town area gave means of 27, 96 and 23 Bq/m3; the indoor Rn concentration for a heating period was a factor of 1.5 higher than for the warm season. The average effective dose equivalent for the primary school pupils was 2.8 mSv/y (with occupancy factors of 0.6, 0.2 and 0.2 for home, school and outdoors, respectively). For citizens of Osijek it was 1.7 mSv/y.

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.

Radon exposure and lung cancer

Although studies of radon exposure have established that Rn decay products are a cause of lung cancer among miners, the lung cancer risk to the general population from indoor radon remains unclear and controversial. Our epidemiological investigation of indoor radon influence on lung cancer incidence was carried out for 201 patients from the Osijek town. Ecological method was applied by using the town map with square fields of 1 km2 and the town was divided into 24 fields. Multiple regression study for the lung cancer rate on field, average indoor radon exposure and smoking showed a positive linear double regression for the mentioned variables. Case-control study showed that patients, diseased of lung cancer, dwelt in homes with significantly higher radon concentrations, by comparison to the average indoor radon level of control sample.

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.