Milica M. Rajačić

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.

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.

Distribution of natural and artificial radionuclides in chernozem soil/crop system from stationary experiments

The present paper focuses on the determination of radiological characteristics of cultivated chernozem soil and crops from long-term field experiments, taking into account the importance of distribution and transfer of radionuclides in the soil-plant system, especially in agricultural cropland. The investigation was performed on the experimental fields where maize, winter wheat, and rapeseed were cultivated. Analysis of radioactivity included determination of the gross alpha and beta activity as a screening method, as well as the activities of the following radionuclides: natural (210Pb, 235U, 238U, 226Ra, 232Th, 40K, 7Be) and artificial (90Sr and 137Cs). The activities of natural and artificial (137Cs) radionuclides were determined by gamma spectrometry, while the artificial radionuclide 90Sr was determined by a radiochemical analytical method. Based on the obtained results for the specific activity of 40K, 137Cs, and 90Sr, accumulation factors for these radionuclides were calculated in order to estimate transfer of radionuclides from soil to crops. The results of performed analyses showed that there is no increase of radioactivity that could endanger the food production through the grown crops.

Interlaboratory comparison material homogeneity testing

Abstract The homogeneity of fertilizer samples for interlaboratory γ-ray spectrometry comparison was tested by determination of the total γ count rate and the count rates for two 238U γ lines, one 40K line and one common 235U and 226Ra line. Homogeneity testing was accomplished by determination of the minimum, maximum, mean and standard deviation for each parameter and comparison of their standard deviations with predefined tolerances, by Cochran’s test, and by a one-way ANOVA. The standard deviations were all less than these tolerances. All samples passed Cochran’s test and the one-way ANOVA test for homogeneity. Graphical Abstract

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.

Quality assurance and quality control in environmental radioactivity monitoring

To assure that radiological monitoring is reasonably valid, organisations performing such measurements have found it necessary to establish quality assurance (QA) and quality control (QC) programs. These programs are needed to identify deficiencies in the sampling and measurement processes. In addition, validation of the monitoring aims to prove whether the results are acceptable. The major aim of QA and QC in analytical laboratories is to address measures used to verify the validity of the final results. In the document ISO 17025 the requirements on how to achieve QA and QC in analytical laboratories is described. All proposed measures for QC/QA are implemented in the Radiation and Environment Protection Department of Institute for Nuclear Sciences in Vinca, Belgrade. This paper presents the summarisation and analysis of QC and QA measures undertaken by the Laboratory for Environmental and Radiation Protection of the Vinca Institute of Nuclear Sciences. Total of 6 months of QC/QA charts are presented in this paper for 2 HPGe gamma spectrometry detectors and one gross alpha/beta detector. The data were analysed and conclusions were made concerning the stability of the measurement systems. In cases of unsatisfactory behaviour of the system, some correctional measures are proposed and conducted and the effect on the measurement system is discussed.