Development of new methodologies for the measurement of radionuclides by gamma-ray spectrometry using detectors

The environmental impact caused by pollutants, like radionuclides, released from different pollution sources, is currently of general concern, making controls for radioactivity levels be more exhaustive. Moreover, the potential radiological risk caused by the exposure to radiation is also an issue that has become more important in the last decades. This makes strict regulations have to be generally applied to different working places and building materials, and for that the analysis of radionuclides is essential to assess the radiological risks associated to the human activities. Therefore, this Thesis aims to develop new methodologies to determine both natural and artificial radionuclides by gamma-ray spectrometry for a wide variety of sample matrices and geometries. For this, a new and comprehensive calibration method to obtain the full-energy peak efficiency (FEPE) for volume samples in the case of cylindrical geometries, at each gamma emission energy (Eγ), as a function of the thickness (h), apparent density (ρ) and matrix composition has been developed for an extended range (XtRa) HPGe detector. The selected certified calibration standards contain only natural radionuclides belonging to the 238U series and 232Th series as well as 40K; codes RGU-1, RGTh-1 and RGK-1 from the International Atomic Energy Agency (IAEA). For well-type detectors, a novel methodology for the efficiency calibration has also been developed, based on obtaining a general FEPE function varying the apparent density and composition of the calibration standards, keeping h constant. For this, RGU-1, RGTh-1, KCl, PbS and activated carbon were used. To properly obtain the FEPE for problem samples whose chemical compositions and apparent densities were very different from those related to calibration samples, corrections due to self-absorption effects were needed. For this, the self-absorption correction factor (fa) was used, which made necessary to obtain a general function for the mass attenuation coefficient. To calculate fa, it was also ...