Jelena M. Stajic

Radioactivity levels and heavy metals in the urban soil of Central Serbia.

Radioactivity concentrations and heavy metal content were measured in soil samples collected from the area of Kragujevac, one of the largest cities in Serbia. The specific activities of 226Ra, 232Th, 40K and 137Cs in 30 samples were measured by gamma spectrometry using an HPGe semiconductor detector. The average valuesu2009±u2009standard deviations were 33.5u2009±u20098.2, 50.3u2009±u200910.6, 425.8u2009±u200975.7 and 40.2u2009±u200926.3xa0Bqxa0kg−1, respectively. The activity concentrations of 226Ra, 232Th and 137Cs have shown normal distribution. The annual effective doses, radium equivalent activities, external hazard indexes and excess lifetime cancer risk were also estimated. A RAD7 device was used for measuring radon exhalation rates from several samples with highest content of 226Ra. The concentrations of As, Co, Cr, Cu, Mn, Ni, Pb and Zn were measured, as well as their EDTA extractable concentrations. Wide ranges of values were obtained, especially for Cr, Mn, Ni, Pb and Zn. The absence of normal distribution indicates anthropogenic origin of Cr, Ni, Pb and Zn. Correlations between radionuclide activities, heavy metal contents and physicochemical properties of analysed soil were determined by Spearman correlation coefficient. Strong positive correlation between 226Ra and 232Th was found.

Analysis of radon and thoron progeny measurements based on air filtration

Measuring of radon and thoron progeny concentrations in air, based on air filtration, was analysed in order to assess the reliability of the method. Changes of radon and thoron progeny activities on the filter during and after air sampling were investigated. Simulation experiments were performed involving realistic measuring parameters. The sensitivity of results (radon and thoron concentrations in air) to the variations of alpha counting in three and five intervals was studied. The concentration of (218)Po showed up to be the most sensitive to these changes, as was expected because of its short half-life. The well-known method for measuring of progeny concentrations based on air filtration is rather unreliable and obtaining unrealistic or incorrect results appears to be quite possible. A simple method for quick estimation of radon potential alpha energy concentration (PAEC), based on measurements of alpha activity in a saturation regime, was proposed. Thoron PAEC can be determined from the saturation activity on the filter, through beta or alpha measurements.

Measurement of radon exhalation rates from some building materials used in Serbian construction

The rates of radon exhalation from building materials available on the Serbian market were measured using RAD7 device. Fitting the growth curves of radon activity concentration provided the information on radon exhalation rates from the samples. The results were quite low and they ranged from 1.4 to 855xa0mBqxa0m−2xa0h−1 for surface exhalation rate and from 1.3 to 11.4xa0mBqxa0kg−1xa0h−1 for mass exhalation rate. The effect of moisture on radon exhalation was confirmed. For powdered samples with dimensions smaller than radon diffusion length, the mass exhalation rate is independent of sample mass and its exhalation area.

Transfer factors of natural radionuclides and 137Cs from soil to plants used in traditional medicine in central Serbia

Transfer factors of natural radionuclides and (137)Cs from soil to plants used in traditional medicine were determined. The transfer factors (TF) were calculated as Bqxa0kg(-1) of dry plant per Bqxa0kg(-1) of dry soil. Mass activity concentrations of (226)Ra, (232)Th, (40)K and (137)Cs in soil and plant samples were measured with high purity germanium detector (HPGe). The concentrations of As, Co, Cr, Cu, Mn, Ni, Pb and Zn were determined, as well as the cation exchange capacity (CEC) and the content of exchangeable cations (Ca, Mg, K, Na). Wide ranges of values were obtained for all the metals, especially for Cr and Ni. The Absalom model was used for determination of the amount of (137)Cs transferred from soil to plant based on soil characteristics such as pH, exchangeable potassium, humus and clay contents. The estimated transfer factors were in the range from 0.011 to 0.307 with an arithmetic mean of 0.071, median of 0.050, geometric mean of 0.053 and geometric standard deviation (GSD) of 2.08. This value agreed well with that calculated from the measurements of 0.069, geometric mean 0.040 and GSD 3.19. Correlations between radionuclides, metals, physicochemical properties and transfer factors were determined by Spearman correlation coefficient. There was a strong positive correlation between (137)Cs transfer factor and the ratio of transfer factor for K and (137)Cs. Principal Component Analysis (PCA) was performed in order to identify some pattern of data.

Indoor radon and thoron concentrations in some towns of central and South Serbia.

This study presents the results of indoor radon and thoron activity concentrations of some municipalities in central and south part of Serbia: Krusevac, Brus, Blace and Kursumlija. Measurements were carried out in 60 dwellings during the winter season. Passive discriminative radon-thoron detectors known as UFO detectors were used. The mean values of indoor radon and thoron concentrations were 82xa0Bqxa0m-3 and 42xa0Bqxa0m-3, respectively. Population-weighted mean values were 76xa0Bqxa0m-3 and 40xa0Bqxa0m-3, respectively. 26.7% of dwellings had radon concentration higher than 100xa0Bqxa0m-3 (one location had even more than 300xa0Bqxa0m-3). There are no statistically significant correlations of indoor radon and thoron concentrations neither with the period of house construction, nor with the existence of a basement. The results of this study represent the first step of investigating radon and thoron levels in these parts of Serbia and therefore could be the basis for creating a radon map.

Computer program for the sensitivity calculation of a CR-39 detector in a diffusion chamber for radon measurements

Computer software for calculation of the sensitivity of a CR-39 detector closed in a diffusion chamber to radon is described in this work. The software consists of two programs, both written in the standard Fortran 90 programming language. The physical background and a numerical example are given. Presented software is intended for numerous researches in radon measurement community. Previously published computer programs TRACK_TEST.F90 and TRACK_VISION.F90 [D. Nikezic and K. N. Yu, Comput. Phys. Commun. 174, 160 (2006); D. Nikezic and K. N. Yu, Comput. Phys. Commun. 178, 591 (2008)] are used here as subroutines to calculate the track parameters and to determine whether the track is visible or not, based on the incident angle, impact energy, etching conditions, gray level, and visibility criterion. The results obtained by the software, using five different V functions, were compared with the experimental data found in the literature. Application of two functions in this software reproduced experimental data very well, while other three gave lower sensitivity than experiment.

The accuracy of radon and thoron progeny concentrations measured through air filtration.

The accuracy and the optimization of determining radon and thoron progeny concentrations in air using air filtration followed by alpha activity measurements were investigated in details. The effects of radon and thoron concentrations, filtering duration and the choice of measuring intervals on relative standard deviations were analyzed. Obtaining satisfactory results by this method should be expected only in the case of high radon and thoron progeny concentrations in air. The optimization process also showed up to be dependent on the progeny concentration. Determinant of the system matrix and its effect on the sensitivity of the results were investigated.

Environmental radioactivity with respect to geology of some Serbian spas

This study was performed in order to investigate gamma dose rates, radon exhalation rates and soil radioactivity with respect to geology. Fifteen locations in three Serbian spas were under investigation. Gamma dose rate was measured by Radex RD1503+ monitor. GIS technology was applied for the interpretation of the results. HPGe detector was used for gamma-spectrometry determination of soil radioactivity. Radon exhalation rate was determined using RAD7 device. The correlation was examined between radon exhalation rate and 226Ra. No correlation was found between calculated effective dose from radionuclides in soil and measured ambient gamma dose rate.

Is high indoor radon concentration correlated with specific activity of radium in nearby soil? A study in Kosovo and Metohija

This paper presents indoor radon concentrations and specific activities of natural radionuclides measured in soils of Kosovo and Metohija. The measurements of radon concentration were performed during two consecutive 6-month periods in two rooms of 63 houses using CR-39 detectors. The annual radon concentration ranged from 30 to 810xa0Bqxa0m−3 with the average value of 128xa0Bqxa0m−3. Almost 15% of the houses had radon concentration higher than 200xa0Bqxa0m−3. The difference between radon concentrations measured in the two 6-month periods was analyzed, showing, as expected, a slightly higher radon concentration in the “winter period” than in the “summer period”. The variation between different rooms of the same houses was also analyzed, showing that 20% of the dwellings had a significantly higher radon concentration (>100xa0Bqxa0m−3) in one room compared to the other (the coefficient of variation ranged up to 96%). The specific activities of natural radionuclides in the nearby soil were determined by gamma spectrometry. The estimated average value (and standard deviation) of 226Ra, 232Th, and 40K specific activities were 32 (13), 35 (16), and 582 (159)xa0Bqxa0kg−1, respectively. The correlation between indoor 222Rn and 226Ra content in soil was investigated. Only a weak correlation was found (Spearman’s rhoxa0=xa00.220) indicating that other factors might affect diffusion and accumulation of radon indoors, as confirmed also by the high variability between the rooms of the same houses.