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Today radioactivity monitoring in the environment is required not only around sites where the significant amounts of radioactive material are used or stored, but in a number of other processes as land remediation or decommissioning of nuclear plants. Since the end of the 20th century there has been an increasing awareness of the so-called technologically enhanced natural radioactivity and the need for its monitoring in a wide range of nonnuclear industries including oil and gas extraction, ceramic and glass industries, production of phosphoric acid, production of different phosphoric fertilizers and other chemical industries. Coal electric power plants as significant sources of ashes and other contaminants are included, too. Contrary to nuclear facilities or radioactive waste control these processes require measuring radionuclides at very low levels of radioactivity. This demands specific methodology and instrumentation and responding to the very real economic importance of classifying waste products from decommissioning and remediation processes. However, natural or man made, waste or industrial, environmental radioactivity monitoring requires adequate equipment calibrated in the full range of radionuclides likely to be encountered, as well as trained and experienced personnel. It is the task of national metrological institutions to provide radioactive reference materials and standards for calibration as pure isotopes, mixtures of isotopes or reference materials for particular applications and to supervise the processes of quality control and quality assurance. Besides primary standards and reference materials national metrological institutions should provide laboratory proficiency testing exercises to support radioactivity measurements within academic, industrial or research laboratories (Spasic, 1984; Spasic, 1985; Spasic, 1987a; Spasic et al. 1987).

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, Vinča 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.

The radioactivity monitoring in the ?Nikola Tesla?, ?Kolubara?, ?Morava? and ?Kostolac? coal-fired power plants was performed by the Radiation and Environmental Protection Laboratory, Vinca Institute of nuclear sciences in the period 2003-2010. Monitoring included the analysis of soil, water, flying ash, slag, coal and plants. This paper presents the results of the radioactivity analysis of coal, ash and slag samples. Naturally occurring radionuclides 226Ra, 232Th, 40K, 235U, 238U, and 210Pb as well as the man-made radionuclide 137Cs were determined by gamma spectrometry using HPGe detector. The concentrations of pairs of radionuclides were statistically tested to determine the correlation between them. Based on the obtained results, health effect due to the activity of these radionuclides was estimated via radium equivalent (Raeq), external hazard index (Hex), external gamma absorbed dose rate () and annual effective dose.