Dragana J. Todorović

Concentration measurements of 7Be and 137Cs in ground level air in the Belgrade City area

Abstract Concentrations of 7 Be and 137 Cs in ground level air in the city area (Belgrade, central Serbia) were determined in the period from 1991–1996. The average monthly concentrations of 7 Be in ground level air were in the range of 2–7 mBq/m 3 with pronounced one or two maxima in summer or early fall and a minimum in winter. The average air concentrations for 137 Cs were from 0.5–8.5 × 10−5 Bq/m 3 , with a spread maximum in the spring-summer period and a pronounced maximum during the winter. A general increase in 7 Be and 137 Cs concentrations during 1993 was recorded. The maximum seasonal indices were 1.3 for 7 Be (summers) and 2.7 (late springs and early summers) and 3.4 (winters) for 137 Cs. No correlation with the amount of precipitation and 137 Cs concentrations in air was determined, while the washout effect of rainfalls seems to be more closely related with variations in 7 Be concentrations.

Activity variations and concentration factors for natural radionuclides in a “soil-plant-honey” system

Abstract The activity of natural radionuclides (226Ra, 238U, 235U, 232Th, and 40K) was measured in soils, meadow flowers, and honey from a mountain region in West Serbia. No statistically significant differences in the contents of natural radionuclides in soil or meadow flora from different soils (shale or limestone) were obtained, although concentrations were generally higher in shale soils than in soils mainly composed of limestone rocks. Activity of 226Ra, 238U, and 235U in plants was below minimal detectable concentrations (0.4 - 0.1 Bq/kg). The content of 232Th was higher in meadow flora from shale soils. For 40K, there were no significant differences in its concentrations in plants from different soils. The activity of natural radionuclides in honey did not depend on the type of soil or meadow flora, but the variations for 238U and 235U concentrations were high. Concentration factors for “soil-honey” phase were in the range 0.01-0.07, while for “soil-plant” and “plant-honey” phase they could be calculated only for 232Th and 40K and were in the range 0.1–3.0 and 0.09-0.02, respectively.

Leaves of higher plants as biomonitors of radionuclides (137Cs, 40K, 210Pb and 7Be) in urban air

Leaves of linden (Tilia tomentosa L. and Tilia cordata Mill.) and horse chestnut (Aesculus hippocastanum L.) were analysed as biomonitors of radionuclides in urban air. Samples of soils, leaves and aerosols were collected in Belgrade, Serbia. Activities of 137Cs, 40K, 210Pb and 7Be in the samples were measured on an HPGe detector by standard gamma spectrometry. “Soil-to-leaves” transfer factors were calculated. Student’s t test and linear Pearson correlation coefficients were used for statistical analysis. Differences in local conditions at the sampling sites were not significant, and the mechanisms of the radionuclides’ accumulation in both plant species are similar. Ceasium-137 was detected in some of the leaf samples only. Transfer factors for 137Cs and 40K were (0.03–0.08) and 1.3, respectively. The concentrations of 210Pb and 7Be in leaves were higher in autumn than in spring, and there were some similarities in their seasonal patterns in leaves and in air. Weak to medium correlation was obtained for the 210Pb and 7Be activities in leaves and aerosols. Large positive correlation was obtained for the 210Pb activities in linden leaves and the mean activity in aerosols for the preceding months. Different primary modes of radionuclides accumulation in leaves were observed. Since large positive correlation was obtained for the 210Pb activity in linden leaves and the mean in aerosols for the preceding months, mature linden leaves could be used as biomonitors of recent 210Pb activity in air.

Application of GEANT4 simulation on calibration of HPGe detectors for cylindrical environmental samples

The determination of radionuclide activity concentration requires a prior knowledge of the full-energy peak (FEP) efficiency at all photon energies for a given measuring geometry. This problem has been partially solved by using procedures based on Monte Carlo simulations, developed in order to complement the experimental calibration procedures used in gamma-ray measurements of environmental samples. The aim of this article is to apply GEANT4 simulation for calibration of two HPGe detectors, for measurement of liquid and soil-like samples in cylindrical geometry. The efficiencies obtained using a simulation were compared with experimental results, and applied to a realistic measurement. Measurement uncertainties for both simulation and experimental values were estimated in order to see whether the results of the realistic measurement fall within acceptable limits. The trueness of the result was checked using the known activity of the measured samples provided by IAEA.

Determination of Symmetrical Index for 3H in Precipitation and 137Cs in Ground Level Air

The paper presents results of a long-term investigations of tritium activity concentrations in precipitation and radiocesium activity concentrations in ground level air in Belgrade, Serbia. Samples were collected at three locations in Belgrade (Meteorological Station of Belgrade MS at Zeleno Brdo (ZB), Meteorological Station MS Usek (USEK), and Vinča Institute of Nuclear Sciences (VINS)). Presented data cover the period 1985–1997. Significantly higher tritium levels were measured in samples in VINS compared with off-site location, while the impact of research reactor for 137Cs was not detected. It was found that the value of the symmetrical index n is higher for VINS in case of tritium, compared to other locations, which is in accordance with the fact that the highest average monthly concentrations of tritium were obtained in the samples from the cited place. Although the highest value of index n in case of 137Cs was also obtained for VINS, average monthly concentrations of 137Cs in ground level air for this location were the lowest. The 137Cs concentration in the ground level air is described by a kinetic equation of the first order and provides a good description of the time changes in these concentrations.

Uncertainty evaluation in radon concentration measurement using charcoal canister.

Active charcoal detectors are used for testing the concentration of radon in dwellings. The method of measurement is based on radon adsorption on coal and measurement of gamma radiation of radon daughters. The contributions to the final measurement uncertainty are identified, based on the equation for radon activity concentration calculation. Different methods for setting the region of interest for gamma spectrometry of canisters were discussed and evaluated. The obtained radon activity concentration and uncertainties do not depend on peak area determination method.

Depth Distribution of 137Cs in Anthrosol from the Experimental Field "Radmilovac" near Belgrade, Serbia

Abstract This is a preliminary study of the depth distribution of 137Cs radionuclides in cultivated anthrosol soil of a 15-year old peach tree plantation at the experimental field “Radmilovac” near Belgrade. Before planting, the soil was ploughed at the depth of 1 m. The soil had not been annually ploughed, irrigated and treated with mineral fertilizers for three years before sampling. Activity concentration for 137Cs ranged from 1.8 Bq kg-1 to 35 Bq kg-1. Along the soil depth it varied highly, reaching as high a total variation coefficient as 83 %. Radiocaesium distribution patterns depended on the extent of soil mixing in the plough layer, as it was mechanically transferred from the surface to the lower soil layers during cultivation. 137Cs was associated with humus content and fixation to clay fractions in the soil. Our results single out soil’s hygroscopic water as a valuable parameter for 137Cs behaviour that could be used commonly if the measurement is standardised. Sažetak RASPODJELA 137Cs U ANTROSOLU OGLEDNOG POLJOPRIVREDNOG DOBRA “RADMILOVAC” KOD BEOGRADA Ovo je preliminarno istraživanje dubinske raspodjele radionuklida 137Cs u kultiviranome zemljištu tipa Antrosol 15 godina starog voćnjaka pod zasadom breskvi koje pripada oglednom poljoprivrednom dobru “Radmilovac” u blizini Beograda. Dubokim oranjem do dubine od 1 m zemljište je pripremljeno za postavljanje zasada breskvi. Tri godine prije uzorkovanja zemljišta prekinuta je obrada voćnjaka odnosno godišnje oranje (do 40 cm dubine), navodnjavanje i unos mineralnoga gnojiva. Koncentracija aktivnosti 137Cs kretala se od 1,8 Bq kg-1 do 35 Bq kg-1 i bitno varirala s povećanjem dubine zemljišta te dostigla ukupni koeficijent varijacije od 83 %. Obrasci raspodjele radiocezija po dubini zavisili su od stupnja obrade zemljišta u prethodnom razdoblju, s obzirom na to da je mehanička manipulacija zemljišta dovela do njegove prisutnosti i u nižim slojevima. 137Cs izravno je korelirao sa sadržajem humusa i bio je fiksiran za glinovitu frakciju zemljišta, što upućuje na njegovu povezanost s česticama zemlje. Unatoč tome što se sadržaj higroskopske vlage u zemljištu pokazao korisnim parametrom za opis ponašanja cezija, za njezino određivanje još uvijek nije utvrđena standardna metoda mjerenja.

Natural radionuclides in cigarette tobacco from Serbian market and effective dose estimate from smoke inhalation

The activity concentrations of natural radionuclides ((40)K, (210)Pb, (210)Po, (226)Ra and (228)Ra) in 17 most frequently used cigarette brands in Serbia and corresponding effective doses due to smoke inhalation are presented. The mean annual effective doses for (210)Pb and (210)Po were estimated to be 47.3 and 724 µSv y(-1) for (210)Pb and (210)Po, respectively. Serbia currently has the highest smoking rate in the world. The results of this study indicate the high contribution of the annual effective dose due to smoke inhalation to the total inhalation dose from natural radionuclides. The more effective implementation of actions for reducing smoking prevalence in Serbia is highly needed.

Semiempirical Efficiency Calibration in Semiconductor HPGe Gamma-Ray Spectroscopy

One of the main problems in quantitative gamma-ray spectroscopy is the determination of detection efficiency, for different energies, source-detector geometries, and composition of samples or sources. There are, in principle, three approaches to this issue: experimental, numerical, and semiempirical. Semiempirical approach is based on the calculation of the efficiency for the measured sample on the basis of an experimental efficiency measured on the same detector, but with a calibration source that can be of different size, geometry, density, or composition—the so-called efficiency transfer. The aim of this paper is to analyze the semiempirical approach, using EFFTRAN and MEFFTRAN software as a typical example. These software were used in the Department of Radiation and Environmental Protection, Vinca Institute of Nuclear Sciences, on three HPGe detectors. The results were compared to the experimentally obtained efficiency, and further validation is performed by measuring reference materials issued within the framework of several interlaboratory intercomparisons. The analysis of the results showed that the efficiency transfer produces good results with the discrepancies within the limits of the measurement uncertainty. Also, for intercomparison measurement, utest criterion for the trueness of the result was applied showing that the majority of the obtained results were acceptable. Some difficulties were identified, and the ways to overcome them were discussed.

Comparison of two methods for high purity germanium detector efficiency calibration for charcoal canister radon measurement

The charcoal canister method of radon measurement according to US Environment Protection Agency protocol 520/5-87-005 is widely used for screening. This method is based on radon adsorption on coal and measurement of gamma radiation of radon daughters. For the purpose of gamma spectrometry, appropriate efficiency calibration of the measuring system must be performed. The most usual method of calibration is using standard canister, a sealed canister with the same matrix and geometry as the canisters used for measurements, but with the known activity of radon. In the absence of standard canister, a different method of efficiency calibration has to be implemented. This study presents the results of efficiency calibration using the EFFTRAN efficiency transfer software. Efficiency was calculated using a soil matrix cylindrical secondary reference material as a starting point. Calculated efficiency is then compared with the one obtained using standard canister and applied to a realistic measurement in order to evaluate the results of the efficiency transfer.