A methodology for the determination of the radionuclide contents and activity of samples

γ-Spectrometry has been used in the Department of Radiological Protection and Nuclear Safety of ITN (the Nuclear and Technological Institute, in Lisbon, Portugal) to identify and quantify radionuclides in samples from radiological monitoring of radioactive waste discharges. Real samples from radiological monitoring are characterized by a range of different geometries and heterogeneous matrices, therefore, requiring a diversified range of calibration sources to correctly calibrate the measuring system. Moreover, there are cases when due to the geometry or type of matrix, none of the system calibrations is adequate to correctly measure the sample representing a major problem in the accurate determination of samples’ radionuclide concentration. Two detection systems were used, one consisting of a 3″×3″ NaI(Tl) detector and the other consisting of a HPGe5030. Both detection systems are complete by the associated shielding and calibration sources. The Monte Carlo method was used in support of a methodology to assess the radionuclide contents and activity of the real samples previously mentioned. The efficiency curves measured experimentally from three calibration sources were compared with the corresponding computational ones, obtained by Monte Carlo simulation in order to validate the method and providing the crucial tool needed to simulate any samples’ geometry and matrices. The method is then used to analyze unknown samples with different matrix materials. Results from the measurements performed and their comparison with the computational results obtained are presented. Improvements in the understanding of the behavior of the experimental setup, namely the efficiency versus matrix material and geometry are explained.