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The gamma spectrometry of environmental samples poses a series of specific problems for the practitioner. The determination of full energy peak efficiencies is, in the case of environmental samples, one of the greatest challenges. In this paper, the calibration of two HPGe detectors for environmental samples in Marinelli beakers was performed using the newly developed MEFFTRAN software. The results obtained with MEFFTRAN were compared to the experimental efficiencies measured using the calibration sample produced at the Laboratory for Radiation and Environment Protection, Institute for Nuclear Sciences Vinca, Belgrade, in order to confirm the validity of the calculation. It is shown that calculated and experimental efficiencies are in good agreement with the discrepancies from -3.9% to +1.5%. The results were also validated by measuring secondary reference materials provided by the IAEA within several interlaboratory proficiency tests. The activity concentration of the radionuclides in the secondary reference materials was determined using the efficiency obtained by MEFFTRAN and compared with the target value given by the IAEA. All the results in materials provided by the IAEA were acceptable except one, proving, that MEFFTRAN produces satisfactory results. (C) 2016 Elsevier Ltd. All rights reserved.

Determination of full energy peak efficiency is one of the most important tasks that have to be performed before gamma spectrometry of environmental samples. Many methods, including measurement of specific reference materials, Monte Carlo simulations, efficiency transfer and semi empirical calculations, were developed in order to complete this task. Monte Carlo simulation, based on GEANT4 simulation package and EFFTRAN efficiency transfer software are applied for the efficiency calibration of three detectors, readily used in the Environment and Radiation Protection Laboratory of Institute for Nuclear Sciences Vinca, for measurement of environmental samples. Efficiencies were calculated for water, soil and aerosol samples. The aim of this paper is to perform efficiency calculations for HPGe detectors using both GEANT4 simulation and EFFTRAN efficiency transfer software and to compare obtained results with the experimental results. This comparison should show how the two methods agree with experimentally obtained efficiencies of our measurement system and in which part of the spectrum do the discrepancies appear. The detailed knowledge of accuracy and precision of both methods should enable us to choose an appropriate method for each situation that is presented in our and other laboratories on a daily basis. (C) 2014 Elsevier B.V. All rights reserved.

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. (C) 2013 Elsevier Ltd. All rights reserved.

During 2005 and 2006, soil samples were collected from different regions in the Republic of Srpska, in order to evaluate their radioactivity. During the war that lasted from 1994 to 1995, it is known that some locations in the Republic of Srpska were imposed upon by NATO forces. Sampled locations were chosen far away from the bombed places in order to check whether the depleted uranium was dispersed over long distances. The activity concentrations of radionuclides in soil samples were determined by gamma spectrometry (HPGe detector, relative efficiency 23%). Results showed the presence of natural radionuclides 226 Ra , 232 Th , 40 K , 235 U , 238 U as well as the produced radionuclide 137 Cs (from the Chernobyl accident and nuclear probes). In order to evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity, the gamma-absorbed dose rate, the annual effective dose rate and the external hazard index have been calculated.

The paper presents the results of indoor radon concentration survey in 201 homes and offices in Niska Banja (the Spa of Nis), a well-known health resort and a spa in the South-East of Serbia. Radon indoor concentrations were determined by active charcoal method, according to standard EPA procedure. The indoor radon concentrations were in the range of up to 200 Bq/m3 (47%), from 200–600 Bq/m3 (26%) and over 600 Bq/m3 (27%). Three areas of extremely high average radon concentrations were found (1340–4340 Bq/m3), with a maximum above 13,000 Bq/m3.The content of natural radionuclides (226Ra, 214Pb, 214Bi, 235U, 228Ac, 212Pb, 212Bi, 208Tl, 40K) and 137Cs, as well as the content of total uranium, thorium and potassium in mud used in peloidotherapy in the Health Institute “Niska Banja” was determined, too. The activities of the radionuclides were determined on an HPGe detector, by standard gamma spectroscopy. The results indicated considerably high amounts of total uranium and thorium (0.021 g/kg mud and 0.003 g/kg mud, respectively), due to the karsts origin of the soil. Keywords: Radon in air, Radionuclides, Soil, Spa, Gamma spectroscopy

7Be to 210Pb concentration ratios in ground level air on two monitoring stations (MS1 and MS2) in Belgrade area were determined from 1996 to 2001. The average monthly concentrations of 7Be in ground level air were in the range of 0.6-18.3 mBq/m3 and exhibited one or two summer/early fall maxims and one minimum in winter. The maximum concentrations for 210Pb were generally observed in the fall, with the average concentrations in the range of 1.09 x 10(-4) to 30.9 x 10(-4) Bq/m3. The 7Be/210Pb ratios were in the range of 1.7-12.7 (MS1) and 1.8-11.3 (MS2), with summer maxims and late fall/winter minimums. The mean Radionuclides Loading Indices values approach zero except for 1996/1997 (MS1) and 2001 (MS2) due to higher concentrations of 7Be and 210Pb. The mean monthly concentrations of both radionuclides exhibited lognormal distributions. There is significant correlation between the 7Be/210Pb activities ratio and the air stability classes A + B + C for both monitoring stations (correlation coefficients 0.61-0.65), and no correlation with D class and E + F classes. Correlation was found between the activity of 7Be and air stability classes A + B + C (0.46-0.68), and E + F (0.38 for MS1), while for 210Pb, a moderate correlation (0.38-0.40) was found with the E + F air stability classes.

A phenomenological model of a tumor interacting with the relevant cells of the immune system is proposed and analysed. The model has a simple formulation in terms of delay-differential equations (DDEs). The critical time-delay, for which a destabilising Hopf bifurcation of the relevant fixed point occurs, and the conditions on the parameters for such bifurcation are found. The bifurcation occurs for the values of the parameters estimated from real data. Local linear analyses of the stability is sufficient to qualitatively analyse the dynamics for small time-delays. Qualitative analyses justify the assumptions of the model. Typical dynamics for larger time-delay is studied numerically.

Concentrations of 210 Pb in ground level air in the city area (Belgrade, Central Serbia) were measured in the period from 1985 to 1996. The activity of 210 Pb in air filters was determined on a HPGe detector by standard gamma spectrometry. Total standard error of the method was estimated to be below 25%. The average monthly concentrations of 210 Pb in the ground level air in the period from 1985 to 1996 were in the range of 0.30–3.17 mBq m−3 with the maxima in fall–winter periods and minimums in springs and early summers. The seasonal indices were 1.12–1.59 for fall–winter and 0.77–0.92 for spring–summer periods. The ratios of maximum-to-minimum concentrations in each year were relatively stable over the period, with slight increase in 1985, 1989 and 1995. The investigations are part of the long-term measurements of natural and man-made radionuclides in the ground-level air in the region.

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.

The effect of tropopause height on the content of Cs-137 and total beta activity in surface atmosphere was considered for the period of intensive nuclear weapon tests, from 1968-1971. The activity of Cs-137 in monthly air filter samples was measured by gamma spectrometry and total beta activity was determined by 2 pi proportional counters. The results were correlated with data on tropopause height. The results indicate that the movement of radioactive debris from the stratosphere into the troposphere occurs simultaneously with the changes in tropopause height. The content of long lived radionuclides in the troposphere follows the changes with a certain delay due to meteorological conditions in surface air and due to the location of sampling. (C) 1997 Elsevier Science Ltd.

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.