Estimation of absorbed gamma dose rate from granite by Monte Carlo simulation approach.

Apart from the continuous exposure of humans to background ionising radiation, an increased level of radiation may also originate from the use of building materials with an enhanced level of radioactivity. Thus, it is necessary to examine the content of radionuclides present in building materials, as well as the corresponding dose which may be received by residents from these materials. In this paper, particular attention was dedicated to finding the absorbed dose rate and annual effective dose caused by the presence of naturally occurring radioisotopes 226Ra, 232Th, and 40K in granite, a widely used building material, by means of Monte Carlo simulations. In addition, the obtained dose rate simulation results were compared with values estimated from commonly used simple equations, relating to the dose rate emitted by granite plates, covering the interior of a standard room. In the simulation, a room was constructed with standard dimensions (4 m × 5 m × 2.8 m), and with floor and walls covered with 3 cm thick granite. A water cylinder (approximate mass 65 kg) was positioned in the center of the room, representing a human body. The emission of the most intense gamma rays from 226Ra and 232Th progenies, as well as from 40K, emanating from the granite matrix, was simulated. The number of generated photons in each simulation (typically it was an order of magnitude of ~106) precisely represented actual activity concentrations of 226Ra, 232Th, and 40K in granite samples. All processes playing a role in the interactions of gamma photons with the granite matrix itself, the outer concrete shell, the air within the room, and the water cylinder, were taken into account by GEANT4 simulation software, after which the spectra of deposited energy inside of the water cylinder were obtained. Based on the deposited energy, the absorbed dose rate and annual effective dose were calculated for 6 analysed granite samples, each with different 226Ra, 232Th, and 40K contents. Furthermore, the effect of the position of the water cylinder in the simulated room on the absorbed dose rate was considered, as well as the distribution of the deposited energy within the water cylinder. The absorbed dose rates, and consequently annual effective dose, obtained in the simulations were found to be 30%-40% higher than the values obtained from using a standard formula.

Monte Carlo simulation of beta particle-induced bremsstrahlung doses.

It is well known that protection from the external irradiation produced by beta emitters is simpler than the corresponding shielding of radioactive sources that emit gamma radiation. This is caused by the relatively strong absorption (i.e. short range) of electrons in different materials. However, for strong beta sources specific attention should be paid to the bremsstrahlung radiation induced in the source encapsulation (matrix), especially for emitters with relatively high beta-endpoint energy (1 MeV) that are frequently used in nuclear medicine. In the present work, the bremsstrahlung spectra produced in various materials by the following beta emitters, Sr-90 (together with its daughter Y-90), P-32 and Bi-210, were investigated by Monte Carlo simulations using Geant4 software. In these simulations, it is supposed that the point radioactive sources are surrounded by cylindrically shaped capsules made from different materials: Pb, Cu, Al, glass and plastic. For the case of Y-90(Sr-90) in cylindrical lead and aluminum capsules, the dimensions of these capsules have also been varied. The absorbed dose rates from bremsstrahlung radiation were calculated for cases where the encapsulated point source is placed at a distance of 30 mm from the surface of a water cylinder with a mass of 75 kg (approximately representing the human body). The bremsstrahlung dose rate and bremsstrahlung spectrum from the Y-90(Sr-90) point source encapsulated in an Al capsule were also measured experimentally and compared with the corresponding simulation results. In addition, the bremsstrahlung radiation risk for medical staff in therapies using Y-90 was considered in simulations, relating to finger dose as well as whole-body dose during preparation and injection of this radioisotope. The corresponding annual doses were obtained for medical workers for specified numbers of Y-90 applications to patients.

Corrections of HPGe detector efficiency curve due to true coincidence summing by program EFFTRAN and by Monte Carlo simulations.

Standard reference sources, used for efficiency curve calibration of detector, often contain radionuclides with complex decay schemes (such as 60Co, 88Y, 152Eu …), introducing a potential problem in gamma-ray spectrometry, due to the appearance of coincidence summing of detected photons, in particular at a low source-detector distance. In this paper, a set of Monte Carlo simulations of an identical experimental setup were performed in order to obtain the efficiency curve of coaxial p-type HPGe detector for energy region (0-2) MeV, with the effect of true coincidence summing and without it. Obtained efficiency curves are compared with the experimental curve after applied EFFTRAN corrections. Fairly well agreement (between simulated and experimental curves with EFFTRAN corrections (with a relative deviation of 10%) proved the reliability of EFFTRAN corrections, as well as the possibility of Monte Carlo simulations for efficiency curve determination.

Random coincidence and angular correlation corrections in the sum-peak method using Monte Carlo simulations.

The sum-peak method is a technique for measuring the absolute activity of gamma cascade emitting sources with a single gamma spectrometer. The effects of angular correlations and random coincidences, if not taken into account, can significantly reduce the accuracy of the method. However, we show that Monte Carlo simulations can reproduce the spectral data with a sufficient quality to perform the required corrections. In this work, we introduced a novel approach for data corrections for angular correlations and pile-up using Monte Carlo simulations. Furthermore, the new method for forming the count rate equations leads to a new formula for the sum-peak method, including random coincidences of any order.

Simple coincidence technique for cosmic-ray intensity exploration via low-energy photon detection.

Changes in cosmic-ray intensity can significantly influence the search for rare events or processes in nuclear and astroparticle physics through corresponding variations in detector background count rate. In this work, we present an approach to explore cosmic-ray intensity and corresponding cascade production of secondary particles in the detector vicinity using low-energy photon background spectra induced by cosmic rays at the earth's surface. The coincidence system based on a plastic scintillator and an extended range HPGe detector, including a multiparameter device, was used for the acquisition of low-energy photon spectra. This system was also simulated by the GEANT4 toolkit, and the simulated and experimental spectra were compared. Single aperiodic events, as well as possible periodic behavior of low-energy photon emission were searched for.

A new Certified Reference Material for radionuclides in Irish sea sediment (IAEA-385).

A new Certified Reference Material (CRM) for radionuclides in sediment (IAEA-385) is described and the results of the certification process are presented. Eleven radionuclides ((40)K, (137)Cs, (226)Ra, (228)Ra, (230)Th, (232)Th, (234)U, (238)U, (238)Pu, (239+240)Pu and (241)Am) have been certified and information mass activities with 95% confidence intervals are given for seven other radionuclides ((90)Sr, (210)Pb((210)Po), (235)U, (239)Pu, (240)Pu and (241)Pu). Results for less frequently reported radionuclides ((60)Co, (99)Tc, (134)Cs, (155)Eu, (224)Ra and (239)Np) and information on some activity and mass ratios are also reported. The CRM can be used for quality assurance/quality control of the analysis of radionuclides in sediment samples, for the development and validation of analytical methods and for training purposes.

Indoor radon in rural dwellings of the South-Pannonian region.

The results of indoor radon survey in the South-Pannonian Province Vojvodina (Serbia and Montenegro) are presented. The sampling strategy was oriented towards suburban and urban regions in the Province. For the dwellings typical for such regions the geometric mean annual radon activity concentration of 76.1 Bq m(-3) is measured (1000 measurements). This result leads to the annual dose estimate of 4.3 mSv y(-1), which is above the recommended action limit of ICRP. For urban dwellings in Novi Sad (the Province capital), the annual mean value of 54 Bq m(-3) (220 measurements) is obtained. By comparison of these two results it is concluded that radon surveys based on measurements in urban environment may seriously underestimate the radon-related health risk. The elevated radon levels could not be explained by elevated uranium levels of surface soil.

Correlations between soil characteristics and radioactivity content of Vojvodina soil.

During the years 2001 and 2010, the content of 238U, 226Ra, 232Th, 40K and 137Cs in agricultural soil and soil geochemical characteristics were measured on 50 locations in Northern Province of Serbia - Vojvodina. The locations for sampling were selected so that they proportionately represent all geomorphologic units in the region. The content of clay and humus varied within wide limits depending on soil type and influence the activity concentrations of radionuclides. In this paper we analyzed correlations between radionuclides content and geochemical characteristics of the soil. Possible influence of fertilizers on 238U content in soil was discussed. The main conclusion is that measured maximal activity concentrations for 238U (87 Bq/kg), 226Ra (44.7 Bq/kg), 232Th (55.5 Bq/kg) and 137Cs (29 Bq/kg) at 30 cm depth could not endanger the safety of food production. The process of genesis of soil and cultivation mode plays a dominant role on the characteristics of the soil. The most significant correlation was found between the activity concentrations of 40K and clay content in agricultural soil.

Correlation analysis of the natural radionuclides in soil and indoor radon in Vojvodina, Province of Serbia.

The most dominant source of indoor radon is the underlying soil, so the enhanced levels of radon are usually expected in mountain regions and geology units with high radium and uranium content in surface soils. Laboratory for radioactivity and dose measurement, Faculty of Sciences, University of Novi Sad has rich databases of natural radionuclides concentrations in Vojvodina soil and also of indoor radon concentrations for the region of Vojvodina, Northern Province of Serbia. In this paper we present the results of correlative and multivariate analysis of these results and soil characteristics in order to estimate the geogenic radon potential. The correlative and multivariate analysis were done using Toolkit for Multivariate Analysis software package TMVA package, within ROOT analysis framework, which uses several comparable multivariate methods for our analysis. The evaluation ranking results based on the best signal efficiency and purity, show that the Boosted Decision Trees (BDT) and Multi Layer Preceptor (MLP), based on Artificial Neural Network (ANN), are multivariate methods which give the best results in the analysis. The BDTG multivariate method shows that variables with the highest importance are radio-nuclides activity on 30 cm depth. Moreover, the multivariate regression methods give a good approximation of indoor radon activity using full set of input variables. On several locations in the city of Novi Sad the results of indoor radon concentrations, radon emanation from soil, gamma spectrometry measurements of underlying soil and geology characteristics of soil were analyzed in detail in order to verify previously obtained correlations for Vojvodina soil.

Pollution of the Begej Canal sediment--metals, radioactivity and toxicity assessment.

The Begej Canal is one among a large number of canals in Vojvodina (Northern Province of Serbia and Montenegro). The paper describes a study of metal and radioactivity contamination of the Begej Canal sediment. It is also concerned with the evaluation of sediment acute toxicity based on standard test species Daphnia magna and simultaneously extracted metals and acid volatile sulfides. The quality of sediment was assessed according to Dutch standards, but the results were also compared with some Canadian and USEPA (United States Environmental Protection Agency) guidelines for sediment quality. The results showed severe pollution with chromium, copper, cadmium and zinc, whereby the anthropogenic origin of these contaminants was indicated. The tests of toxicity of sediment pore water to D. magna, gave no indication of the presence of substances in acutely toxic concentrations to this species. It can be speculated that, despite of high metal contents, the observed toxicity was low because of the high contents of clay and iron, as well as sulphide. Also, based on a comparison with the Danube sediment and Vojvodina soil in general, the data of the Begej sediment contamination with 238U and 137Cs. The 137Cs data were used for approximate dating of the sediment. No traces of contamination by nuclear power plants in the region were found, while the presence of technologically enhanced naturally occurring radioactive materials (TENORM) was proved. Conclusions based on different criteria for sediment quality assessment were in some cases contradictory. Study also showed that radioactivity aspects can be useful in sediment quality surveys. The obtained results will be invaluable for the future activities regarding integrated water management based on EC Water Framework Directive (2000/60/EC) in the Danube basin, and particularly in the region of crossborder water body of the Begej Canal.

An improved formula for determination of the activity via the sum-peak method.

The sum-peak method principally enables determination of the absolute activity of gamma cascade emitting sources based only on the use of spectral data, without knowledge of the detector efficiencies. However, to achieve better accuracy of the activity results, corrections due to pile-up, accidental coincidences, electronic noise and angular correlations must be introduced into the proposed method. Such corrections usually require the collection of a few gamma spectra and additional extrapolations, thereby further complicating the experimental procedures. In this paper, it is shown that by using pile-up peaks for corrections of accidental coincidences, Monte Carlo techniques for angular correlation, and LLD corrections, the source activity can be measured with accuracy and reproducibility below 1% using only one gamma spectrum, without any additional extrapolations.

Radioactivity of the soil in Vojvodina (northern province of Serbia and Montenegro).

The widespread public belief that during the bombardment of Vojvodina (Yugoslavia) this region was contaminated by depleted uranium has recently raised public concern with respect to the potential contamination of agricultural products due to soil radioactivity. Based on the gamma-spectrometric analysis of 50 soil samples taken from the region of Vojvodina we concluded that there is no increase of radioactivity that could endanger the food production. Taking into account the transfer factors of 137Cs to plants, the measured activity concentrations of this isotope should not endanger the health safety of the produced food. No traces of depleted uranium have been found. The natural radioactivity levels are compared with the results form other countries.

Radioactivity of the Bega sediment-case study of a contaminated canal.

The Bega canal is one among many heavily polluted canals in Vojvodina (the northern province of Serbia and Montenegro). In the framework of the revitalization of this canal, the radionuclide content of the sediment was investigated in order to support the safe deposition after excavation. It was found that, in comparison with the Danube sediment and Vojvodina soil, the Bega sediment is contaminated with (238)U and (137)Cs. The origin of this contamination is discussed. No traces of contamination by nuclear power plants in the region were found, while the presence of technologically enhanced, natural occurring radioactive materials (TENORM) was proved.

Evaluation of bremsstrahlung spectra generated by a 4-MeV linear accelerator.

A modified method for the evaluation of bremsstrahlung spectra on the basis of transmission measurements is presented. The method is tested for two 4 MeV therapy accelerators. The calculated spectra are compared with other experimental results and Monte Carlo simulation.

115In as a probe for the characterization of therapy bremsstrahlung beams and the detection of photoneutrons.

Variation of the photoactivation rate across radiation fields of three different bremsstrahlung beams of two medical accelerators has been measured, making use of the photonuclear reactions in natural indium probes: 115In(y,y')115mIn and 115In(y,n)114mIn. The third nuclear reaction, 115In(n,y)116mIn, was used to detect the presence of neutrons in the photon beam and to estimate the spatial distribution of thermal and fast neutrons in the patient plane as a function of collimator opening.

Investigation of cosmic-ray muon induced processes by the MIREDO facility.

The MIREDO (Muon Induced Rare Event Dynamic Observatory) spectrometer system is primarily developed for the study of cosmic muon induced processes in different materials. Exploration of such interactions can be important for ultra-low background experiments. The system is based on the 100% relative efficiency ultra-low-background HPGe spectrometer. With the addition of two plastic scintillators and a fast-slow coincidence circuit, the coincidence events between the plastic detectors and the HPGe spectrometer have been investigated. First results derived for a CaO powder sample, placed in a Marinelli beaker, are presented and discussed.

Granulation effects on the radon emanation rate.

The radon emanation and the granulation effect on the emanation rate of several building materials (ceramic plates, sand, red brick and siporex brick) with different (226)Ra concentrations were investigated. A ball mill was used to achieve different granulations of the materials. The particle size distributions were determined by a particle size analyser (Mastersizer 2000). The increase in the (222)Rn concentration inside a closed chamber (volume ≈5.4 × 10(-3) m(3)) due to emanation from each material with different granulations was measured by an alpha spectrometer (RAD7). Thus, time-dependent curves for radon concentrations were obtained. The highest radon emanation coefficient (27 %) was obtained for the siporex sample with the smallest grain size (0.34 µm). For the ceramic pads, the granulation effect was negligible and the emanation coefficient was very low (∼0.4 %). The strongest influence of granulation on the radon emanation rate was found for the siporex brick sample.

Temporal variations of 7Be, 210Pb and 137Cs in moss samples over 14 month period.

Concentrations of (210)Pb, (7)Be and (137)Cs in moss samples were continuously measured, using low-background HPGe spectrometer at Novi Sad, Serbia (45 degrees 14'45''N, 19 degrees 51'35''E). Weekly data collected over 14 month period from January 2007 to March 2008 are presented and discussed. Measured values of (7)Be activity concentrations in dry moss samples are ranged from 201 to 920 Bq/kg showing prominent increase in summer and autumn season. Data for (210)Pb, ranged from 347 to 885 Bq/kg do not show such trend. The average concentration of (137)Cs is 8.9 Bq/kg. It is shown that yield of (7)Be can be estimated using average values of activity concentrations. Precipitation amount and duration of precipitation are measured and their possible influence on activity concentrations measured in moss samples was considered.

[Importance of studying exposure of the population to radon and its daughters]. / Znacaj istrazivanja izlozenosti stanovnistva radonu i njegovim potomcima.

INTRODUCTION: Radon and thoron are naturally-occurring radioactive gases, which are products of uranium and thorium decay series, respectively. Uranium and thorium occur widely in the environment, in rocks, soil, air, water, building materials, humans, etc. Radon daughters in the air are predominantly attached to aerosols. A minor part, normally less than 10%, occurs as unattached atoms or ions. The relative distribution of attached daughters in indoor air and equilibrium factor depend on many variables, such as the decay constant, the concentration and size distribution of aerosols and ventilation rates. Increased ventilation decreases the concentration of radon and daughters in the air. OCCURRENCE: Concentration of radon, thoron and their decay products in the air indoors, in mines or houses, is higher than outdoors. In houses, the level of radon daughters may be enhanced by radon from radium rich building materials, landfill, soil and bedrock under the house, radon rich water and by poor ventilation. CONCLUSION: In recent years, several evaluations of human health risks and estimations have been made in regard to the dose-response relationship and lung cancer risk attributable to inhaled radon daughters. Inhalation of radon and thoron daughters leads to deposition in the human respiratory tract and consequent irradiation. Deposition depends on various factors, such as the size distribution of aerosols to which the daughter products of radon are attached, and fraction of unattached daughters. On average, the dose to the basal cell layer in the lung is about 5 to 8 times higher than the dose in the pulmonary region.