D. Mrdja

Public exposure to radon in drinking water in Serbia.

Radon is the main source of natural radiation that is received by population. The results of radon activity measurements in water from public drinking fountain, from bottled drinking water and from tap water in the city of Novi Sad, Serbia, are presented in this paper. The measurements were performed by RAD 7 radon detector manufactured by DURRIDGE COMPANY Inc. The corrected value of radon concentration in one sample exceeded the European Commission recommendation reference level for radon in drinking water of 100 Bql(-1). In order to make the correlation between radon and radium concentrations in the tap water and in the water from public drinking fountain, the gamma-spectrometric measurements were performed. The results of (222)Rn activity concentration measurements from soil in the city of Novi Sad using RAD 7 detector are presented.

Simple Method for Depleted Uranium Determination

When the issue of depleted uranium (DU) presence in the environment emerged, methods for analytical discrimination of DU against natural uranium should be developed. We present here a simple gamma-spectrometric method, based on the 238U–226Ra activity (non) equilibrium. The detection limit of the method for DU is of the order of magnitude of 10 Bq/kg (for about 50 ks counting), thus the method is appropriate for the determination of small amounts (≈100 Bq/kg) of DU in environmental samples. The method is tested on about 90 soil samples.

Monitoring for exposures to TENORM sources in Vojvodina region

TENORM are found in a wide variety of waste materials, some raw mineral ores and in some consumer products (in trace amounts) where molecules of radionuclides may be bound to specific minerals used in the manufacturing process and can result in increases in radiation exposures to workers and the public. The aim of this paper is to understand this problem and to develop effective ways to protect humans and the environment from harmful exposure to the radiation in TENORM materials in the Vojvodina region. The results of measurement of indoor radon concentration in schools and kindergartens and dose-rate and gamma-spectrometry measurements of the workplace with TENORM materials are presented.

NATURAL RADIOACTIVITY IN RAW MATERIALS USED IN BUILDING INDUSTRY IN SERBIA

Natural radioactivity is responsible for most of the total radiation dose received by human population. Geological materials used in building industry usually become contaminated with naturally occurring radioactive materials. They are used as mixtures in building industry (kaolin, zircon, frit, feldspar) or mechanically processed and used for covering floors and walls of the rooms (granite). In this paper, activity concentrations of 226Ra, 232Th and 40K in 6 kaolin, 11 zircon, 18 granite, 3 marble, 6 sand, 4 perlite, 4 feldspar, 5 korund and 1 frit samples imported in Serbia were determined by gamma-ray spectrometry. Activity concentration index, dose rate and annual effective dose were calculated for each of the investigated samples. Measurement of an external gamma dose rate by using a commonly available radiation survey meter can give some indication of the need for further investigations. The absorbed dose rate and annual effective doses for workers in the ceramic industry “Keramika Kanjiza Plus” in Serbia working with granite are determined.

Efficiency study of a big volume well type NaI(Tl) detector by point and voluminous sources and Monte-Carlo simulation.

The activity of environmental samples is usually measured by high resolution HPGe gamma spectrometers. In this work a set-up with a 9in.x9in. NaI well-detector with 3in. thickness and a 3in.×3in. plug detector in a 15-cm-thick lead shielding is considered as an alternative (Hansman, 2014). In spite of its much poorer resolution, it requires shorter measurement times and may possibly give better detection limits. In order to determine the U-238, Th-232, and K-40 content in the samples by this NaI(Tl) detector, the corresponding photopeak efficiencies must be known. These efficiencies can be found for certain source matrix and geometry by Geant4 simulation. We found discrepancy between simulated and experimental efficiencies of 5-50%, which can be mainly due to effects of light collection within the detector volume, an effect which was not taken into account by simulations. The influence of random coincidence summing on detection efficiency for radionuclide activities in the range 130-4000Bq, was negligible. This paper describes also, how the efficiency in the detector depends on the position of the radioactive point source. To avoid large dead time, relatively weak Mn-54, Co-60 and Na-22 point sources of a few kBq were used. Results for single gamma lines and also for coincidence summing gamma lines are presented.

Depleted uranium determination in soil samples

Publisher Summary When the issue of depleted uranium (DU) presence in the environment emerged, methods for the analytical discrimination of DU against natural uranium had to be developed. This chapter presents here a simple gamma-spectrometric method, based on the 238 U– 226 Ra activity (non) equilibrium. Preliminary calculations that are still under way lead to the result that the lower limit of detection of DU is about 10 Bq kg −1 for a 50 ks measurement and thus the method is appropriate for the determination of small amounts (≈ 100 Bq kg −1 ) of DU in environmental samples. The method is tested on about 90 soil samples. The chapter concludes that the measurements on samples collected from Novi Sad prove the absence of detectable amounts of depleted uranium. However, in the southern part of Serbia samples contaminated with depleted uranium were found. The method for depleted uranium detection can be employed for further surveying the radioactivity of the region and especially for the investigation of depleted uranium migration from the contaminated areas.

Possibility of Prompt 238U Activity Concentration Determination by Gamma-Ray Spectroscopy

Recent results on 238U/234Th disequilibria in marine studies seriously challenge the possibility of the prompt gamma-ray spectroscopic determination of 238U activity concentration in environmental samples from the gamma-ray lines of the first daughter of 238U, the nucleus 234Th. In this paper we present the results of the gamma-ray spectrometric measurements of 234Th, which were repeated using the same soil and sediment samples at least one year after the first measurement. We did not find any indication of Th activity variation due to 238U/234Th disequilibria. All the obtained results prove that the 238U and depleted uranium determination in soil and sediment samples using 234Th gamma-ray lines introduces at most a systematic error of 3% into the obtained results.

Study of Active Shielding for γ ‐ Spectrometers

The features of the ground located gamma ray spectrometer shielded passively with 12 cm of lead and actively by five 0.5m × 0.5m × 0.05m plastic veto shields are described. The detector mass related background was 0.345 C/kg s. The 511 keV annihilation line was reduced by the factor of 7 by the anticoincidence gate. It is shown that the plastic shields increase the neutron capture gamma line intensities due to neutron thermalization.

Novel approach to imaging by cosmic-ray muons

Cosmic-ray muons can be used for imaging of large structures, or high-density objects with high atomic number. The first task can be performed by measurement of muon absorption within very thick material layers, while the second approach is based on muon multiple scattering. However, the muon imaging of small structures with low atomic number and density was not yet solved appropriately. Here we show the first results of cosmic-ray muon imaging of small objects made of elements of low atomic number. This novel approach includes detection of secondary particles produced by muons, which were not used at all in previous muon imaging methods. Thus, the list of elements, as well as the range of dimensions of objects which can be imaged are significantly expanded.

Radioactivity in fertilizers and radiological impact

The contents of natural radionuclides (226Ra, 232Th and 40K) in 33 fertilizers and 50 soil samples from Vojvodina region, Serbia, were measured by low level gamma spectrometry. The obtained results showed that the averages of radiation hazard parameters for the fertilizers are higher than acceptable level for radium equivalent activity (Raeq), representative level index (Iγ), external hazard index (Hex) and absorbed dose rate (D) [1]. Based on the measured values of the activity concentration of radionuclides in soils, the activity concentrations of radionuclides for most commonly grown crops in Vojvodina were calculated.