Low-level gamma-ray spectrometry and its applications on selected issues

The gamma-ray spectrometry as an analytical method founds its application in a wide area of science disciplines. It allows to identify and to quantify the radioactivity of naturals and man- made radionuclides in different samples of environment and to monitor its variation, thereby it is applicable not only in the field of environmental studies of human activities impacts but also in the area of investigation of cosmic rays interacting with our atmosphere or radiation history of extraterrestrial objects. In special conditions, the gamma- ray spectrometry is also an efficient tool for studies of low probability nuclear processes. The first part of this work deals with the present situation of gamma-ray spectrometry. The next, experimental part of this work contains four chapters. The first one is focused on neutrinoless double electron capture on the sample of ⁷⁴Se and on a measurement of the half- time of this process using anticoincidence shielding. The limited experimental possibilities during this part of work gave us reason for more detailed study of the cosmic rays response in the semiconductor detector, due to increasing the anticoincidence shielding efficiency. Therefore, in the second chapter we describe the muon generator creation in Monte Carlo model of the HPGe detector and its use in a process of active shielding against cosmic muons configuration. The third chapter includes gamma- ray spectrometry analysis of 18 fragments of the Kosice meteorite and outlines several specific problems such as detection efficiency of irregular shape sample. In this part two different methods for detection efficiency estimation are compared and several solutions for Monte Carlo simulations are discussed. The proposed solution for Monte Carlo simulation of detection efficiency is applied on 4 fragments of the Kosice meteorite. Following a precise analysis of experimental mock- ups and theoretical models we have propose a new generalized approach to estimate the radioactivity of meteorite fragments of irregular shapes with specific parameters and a confidence level, which can simplify the evaluation of radionuclides concentration in a significant way. The last chapter contains gamma- ray spectrometry analysis of different environmental samples from the area of the crashed Chernobyl nuclear power plant, samples of materials used in the SuperNEMO experiment and an example of the long-term atmospheric aerosols sampling utilization for evidence of man- made radionuclide ¹³¹I in the air. (Author)