A quantificação da atividade de radionuclídeos emissores de raios gama em amostras medidas por espectrometria gama com detectores HPGe depende da análise dos fotopicos presentes no espectro, especialmente da determinação exata das suas áreas líquidas. Tal análise é geralmente realizada com o auxílio de ferramentas de software proprietário. Este trabalho apresenta uma metodologia, descrição de algoritmos e um aplicativo de código aberto, denominado OpenGamma, para a busca e análise de fotopicos a fim de se obter seus parâmetros relevantes e as atividades dos radionuclídeos na amostra. A implementação computacional é distribuída sob licença aberta para o código principal e com o uso de pacotes de software aberto para o projeto da interface e para bibliotecas matemáticas. O procedimento para a busca de picos é realizado em três etapas. Primeiramente, executa-se uma pesquisa preliminar com o método da segunda diferença, que consiste na geração de um espectro derivado para a busca de picos candidatos. Na segunda etapa, calculam-se as larguras experimentais dos picos, dos quais escolhem-se aqueles bem formados e isolados para a obtenção da função de ajuste da largura vs. canal, por meio do método de Levenberg-Marquardt para ajustes não-lineares. Por fim, regiões do espectro com picos agrupados são delimitadas e novo ajuste não-linear é aplicado a cada região para a obtenção dos termos da linha de base e dos fotopicos. A partir destes termos, são calculadas as áreas líquidas dos picos. Para a determinação da atividade, curvas de calibração de eficiência previamente obtidas, bem como dados de transições gama dos radionuclídeos, são incorporadas ao código e aplicadas. O código foi escrito em linguagem C++ e a interface foi desenvolvida com a ferramenta Qt. Para as funções matemáticas e procedimentos de ajuste, foi usada a biblioteca científica GNU (GSL). A validação de código foi feita por meio da análise de: 1) espectros sintéticos de teste da AIEA, especialmente desenhados para a avaliação de desempenho de software; 2) espectros obtidos com amostras de exercícios de intercomparação e 3) espectros da rotina de trabalho do Laboratório de Radiometria Ambiental (LRA) do IPEN e analisados com o aplicativo comercial InterWinner. Os resultados obtidos são consistentes com os valores de referência e com aqueles obtidos pelo aplicativo citado, sugerindo que o código OpenGamma pode ser utilizado com segurança na espectrometria de raios gama de uso geral. / Radioactivity quantification of gamma-ray emitter radionuclides in samples measured by HPGe gamma-ray spectrometry relies on the analysis of the photopeaks present in the spectra, especially on the accurate determination of their net areas. Such a task is usually performed with the aid of proprietary software tools. This work presents a methodology, algorithm descriptions and an open source application, called OpenGamma, for the peak search and analysis in order to obtain the relevant peaks parameters and radionuclides activities. The computational implementation is released entirely in open-source license for the main code and with the use of open software packages for interface design and mathematical libraries. The procedure for the peak search is performed on a three step approach. Firstly a preliminary search is done by using the second-difference method, consisting in the generation of a derived spectrum in order to find candidate peaks. In the second step, the experimental peaks widths are assessed and well formed and isolated ones are chosen to obtain a FWHM vs. channel relationship, by application of the Levenberg-Marquardt minimization method for non-linear fitting. Lastly, regions of the spectrum with grouped peaks are marked and a non-linear fit is again applied to each region to obtain baseline and photopeaks terms; from these terms, peaks net areas are then assessed. For the activity determination, previously obtained efficiency calibration curves, as well as nuclides gamma-ray data, are incorporated in the code and applied. The code was developed in C++ language and the interface was developed with Qt GUI software toolkit. GNU scientific library, GSL, was employed to perform fitting procedures as needed. Validation of code was done by analyzing: 1) synthetic test spectra from IAEA, especially designed for software performance evaluation; 2) spectra obtained from samples of intercomparison exercises and 3) spectra from routine activities of the Environmental Radiometric Laboratory (LRA) at IPEN and analyzed with the commercial software package InterWinner. Results obtained are consistent with the reference values and with those obtained by the aforementioned package. The results suggest that the OpenGamma code could be safely used in general-purpose gamma-ray spectrometry.

A quantificação da atividade de radionuclídeos emissores de raios gama em amostras medidas por espectrometria gama com detectores HPGe depende da análise dos fotopicos presentes no espectro, especialmente da determinação exata das suas áreas líquidas. Tal análise é geralmente realizada com o auxílio de ferramentas de software proprietário. Este trabalho apresenta uma metodologia, descrição de algoritmos e um aplicativo de código aberto, denominado OpenGamma, para a busca e análise de fotopicos a fim de se obter seus parâmetros relevantes e as atividades dos radionuclídeos na amostra. A implementação computacional é distribuída sob licença aberta para o código principal e com o uso de pacotes de software aberto para o projeto da interface e para bibliotecas matemáticas. O procedimento para a busca de picos é realizado em três etapas. Primeiramente, executa-se uma pesquisa preliminar com o método da segunda diferença, que consiste na geração de um espectro derivado para a busca de picos candidatos. Na segunda etapa, calculam-se as larguras experimentais dos picos, dos quais escolhem-se aqueles bem formados e isolados para a obtenção da função de ajuste da largura vs. canal, por meio do método de Levenberg-Marquardt para ajustes não-lineares. Por fim, regiões do espectro com picos agrupados são delimitadas e novo ajuste não-linear é aplicado a cada região para a obtenção dos termos da linha de base e dos fotopicos. A partir destes termos, são calculadas as áreas líquidas dos picos. Para a determinação da atividade, curvas de calibração de eficiência previamente obtidas, bem como dados de transições gama dos radionuclídeos, são incorporadas ao código e aplicadas. O código foi escrito em linguagem C++ e a interface foi desenvolvida com a ferramenta Qt. Para as funções matemáticas e procedimentos de ajuste, foi usada a biblioteca científica GNU (GSL). A validação de código foi feita por meio da análise de: 1) espectros sintéticos de teste da AIEA, especialmente desenhados para a avaliação de desempenho de software; 2) espectros obtidos com amostras de exercícios de intercomparação e 3) espectros da rotina de trabalho do Laboratório de Radiometria Ambiental (LRA) do IPEN e analisados com o aplicativo comercial InterWinner. Os resultados obtidos são consistentes com os valores de referência e com aqueles obtidos pelo aplicativo citado, sugerindo que o código OpenGamma pode ser utilizado com segurança na espectrometria de raios gama de uso geral. / Radioactivity quantification of gamma-ray emitter radionuclides in samples measured by HPGe gamma-ray spectrometry relies on the analysis of the photopeaks present in the spectra, especially on the accurate determination of their net areas. Such a task is usually performed with the aid of proprietary software tools. This work presents a methodology, algorithm descriptions and an open source application, called OpenGamma, for the peak search and analysis in order to obtain the relevant peaks parameters and radionuclides activities. The computational implementation is released entirely in open-source license for the main code and with the use of open software packages for interface design and mathematical libraries. The procedure for the peak search is performed on a three step approach. Firstly a preliminary search is done by using the second-difference method, consisting in the generation of a derived spectrum in order to find candidate peaks. In the second step, the experimental peaks widths are assessed and well formed and isolated ones are chosen to obtain a FWHM vs. channel relationship, by application of the Levenberg-Marquardt minimization method for non-linear fitting. Lastly, regions of the spectrum with grouped peaks are marked and a non-linear fit is again applied to each region to obtain baseline and photopeaks terms; from these terms, peaks net areas are then assessed. For the activity determination, previously obtained efficiency calibration curves, as well as nuclides gamma-ray data, are incorporated in the code and applied. The code was developed in C++ language and the interface was developed with Qt GUI software toolkit. GNU scientific library, GSL, was employed to perform fitting procedures as needed. Validation of code was done by analyzing: 1) synthetic test spectra from IAEA, especially designed for software performance evaluation; 2) spectra obtained from samples of intercomparison exercises and 3) spectra from routine activities of the Environmental Radiometric Laboratory (LRA) at IPEN and analyzed with the commercial software package InterWinner. Results obtained are consistent with the reference values and with those obtained by the aforementioned package. The results suggest that the OpenGamma code could be safely used in general-purpose gamma-ray spectrometry.

<p>Dissertation in Environmental Physics to be publicly examined in Häggsalen (Ångström Laboratory), Uppsala University, on Friday, November 8, 2002 at 10:00 am for the degree of doctor of philosophy in Physics. The examination will be conducted in English. </p><p>Gamma spectrometry is one of the tools commonly used for the measurement of various environmental radionuclides. Simultaneous determination of the absolute activity of gamma emitting radiotracers in a wide range of environmental matrices and fractions necessitates proper and accurate evaluation of the sample-to-detector efficiency. Several radiotracers require, in addition, the use of sub-routines for self-absorption corrections. </p><p>Gamma spectrometry is an important and elegant tool for assessing environmental changes. Optimisation of ultra low-level gamma spectrometry for reliable assessment of such changes requires harmonisation of laboratory needs with sampling and site conditions.</p><p>Different aspects of the calculation of sample-to-detector efficiencies using empirical and Monte Carlo approaches are discussed here, including the uncertainties related to the simulation of the performance of different HPGe detectors and the effects of the incomplete collection of charges in Ge-crystals. Various simulation codes for the computation of peak efficiencies in planar and well Ge-detectors have been developed from scratch. The results of the simulations have been tested against experimental data and compared to other simulation results obtained with the Monte Carlo N-Particle code (MCNP). The construction of calibration sources with improved absorption and collimation characteristics have been, also, described in this work. These sources have been especially designed for the efficiency calibration of Ge-detectors at energies below 100 keV. </p><p>Flexible, fully tested and prototype approaches for the evaluation of self-absorption corrections, based on Monte Carlo simulations, are described. Special consideration is given to the problems related to the sample's variability in size, density and composition. Several examples of the absolute and simultaneous determination of environmental multitracers which benefited from self-absorption corrections and the optimised efficiency calibration algorithms are, also, presented and discussed. These examples include, among other things, a comprehensive analysis of the gamma spectrometry of ²³⁴Th in a wide range of matrices and the speciation of several radionuclides in sediments from a hard-water lake.</p>

Dissertation in Environmental Physics to be publicly examined in Häggsalen (Ångström Laboratory), Uppsala University, on Friday, November 8, 2002 at 10:00 am for the degree of doctor of philosophy in Physics. The examination will be conducted in English. Gamma spectrometry is one of the tools commonly used for the measurement of various environmental radionuclides. Simultaneous determination of the absolute activity of gamma emitting radiotracers in a wide range of environmental matrices and fractions necessitates proper and accurate evaluation of the sample-to-detector efficiency. Several radiotracers require, in addition, the use of sub-routines for self-absorption corrections. Gamma spectrometry is an important and elegant tool for assessing environmental changes. Optimisation of ultra low-level gamma spectrometry for reliable assessment of such changes requires harmonisation of laboratory needs with sampling and site conditions. Different aspects of the calculation of sample-to-detector efficiencies using empirical and Monte Carlo approaches are discussed here, including the uncertainties related to the simulation of the performance of different HPGe detectors and the effects of the incomplete collection of charges in Ge-crystals. Various simulation codes for the computation of peak efficiencies in planar and well Ge-detectors have been developed from scratch. The results of the simulations have been tested against experimental data and compared to other simulation results obtained with the Monte Carlo N-Particle code (MCNP). The construction of calibration sources with improved absorption and collimation characteristics have been, also, described in this work. These sources have been especially designed for the efficiency calibration of Ge-detectors at energies below 100 keV. Flexible, fully tested and prototype approaches for the evaluation of self-absorption corrections, based on Monte Carlo simulations, are described. Special consideration is given to the problems related to the sample's variability in size, density and composition. Several examples of the absolute and simultaneous determination of environmental multitracers which benefited from self-absorption corrections and the optimised efficiency calibration algorithms are, also, presented and discussed. These examples include, among other things, a comprehensive analysis of the gamma spectrometry of 234Th in a wide range of matrices and the speciation of several radionuclides in sediments from a hard-water lake.

Abstract My thesis examines the measurement optimalization when the semiconductor HPGe detectors with a low background and a high relative efficiency are used for achieving low values of MDA (minimum detectable activity). I conducted my research in the Department of Spectrometry of SÚRO (National Radiation Protection Institute) in Prague. In this laboratory the standard geometries of detectors with lower efficiency are used. The aim of this thesis is to offer a proposal of new geometry, sizes and shapes of measurement cells which will better correspond with the demand for higher efficiency of updated detectors. The assignment was to find the best mathematical function to descibe the correlation between efficiency and the direction of the radiation point source towards the detector. This function is derived from experimentally obtained data. To conduct measurements, three kinds of detectors with high relative efficiency used for activity measurements at different geometries were selected. As the source of gamma radiation, the point sources with energies of 46 keV, 661 keV, 1332 keV in different distances and positions were used. The function was applied separatelly to each of the three detectors and to the areas above the detector and sidewards of the detector. The objective of the research was to project new measurement geometries or to optimalize the current ones which could be used also in other detectors with high efficiency. After integrating the function in the cylindrical area above the detector and the annular area sidewards of the detector, areas contributing substantially to the overall efficiency were determined. These areas may be considered to be the optimal sizes for new geometries in given positions. After combining all the optimal areas above the detector, sidewards of the detector and for selected energies and the detector, optimal sizes of a new geometry were found. The function can be used both in the front part and the side part of the detector but its validity is limited. The value of MDA for the particular geometry is in indirect proportion to the efficiency square root and thus this new geometry should lead to minimum values of MDA.

High precision measurements of a weak interaction decay were conducted to search for possible variation of the decay rate parameter caused by an antineutrino flux. The experiment searched for variation of the ⁵⁴Mn electron capture decay rate parameter to a level of precision of 1 part in ∼10⁵ by comparing the difference between the decay rate in the presence of an antineutrino flux ∼3×10¹² cm^-2sec^-1 and no flux measurements. The experiment is located 6.5 meters from the reactor core of the High Flux Isotope Reactor (HFIR) in Oak Ridge National Laboratory. A measurement to this level of precision requires a detailed understanding of both systematic and statistical errors. Otherwise, systematic errors in the measurement may mimic fundamental interactions. <div><br></div><div>The gamma spectrum has been collected from the electron capture decay of ⁵⁴Mn. What differs in this experiment compared to previous experiments are, (1) a strong, uniform, highly controlled, and repeatable source of antineutrino flux, using a reactor, nearly 50 times higher than the solar neutrino flux on the Earth, (2) the variation of the antineutrino flux from HFIR is 600 times higher than the variation in the solar neutrino flux on the Earth, (3) the extensive use of neutron and gamma-ray shielding around the detectors, (4) a controlled environment for the detector including a fixed temperature, a nitrogen atmosphere, and stable power supplies, (5) the use of precision High Purity Germanium (HPGe) detectors and finally, (6) accurate time stamping of all experimental runs. By using accurate detector energy calibrations, electronic dead time corrections, background corrections, and pile-up corrections, the measured variation in the ⁵⁴Mn decay rate parameter is found to be δλ/λ=(0.034±1.38)×10^-5. This measurement in the presence of the HFIR flux is equivalent to a cross-section of σ=(0.097±1.24)×10^-25cm². These results are consistent with no measurable decay rate parameter variation due to an antineutrino flux, yielding a 68% confidence level upper limit sensitivity in δλ/λ <= 1.43×10^-5 or σ<=1.34×10^-25cm² in cross-section. The cross-section upper limit obtained in this null or no observable effect experiment is ∼10⁴ times more sensitive than past experiments reporting positive results in ⁵⁴Mn.</div>

Neutron-rich rare-earth nuclei are among the most collective nuclei that can be found in nature. In particular, the doubly mid-shell nucleus 170Dy is expected to be the nucleus where the collective structure is maximized. This has implications for the astrophysical r-process, since it has been suggested that the collectivity maximum plays an important role in the abundances of the rare-earth elements that are created in supernova explosions. In this work, the collective structure of the five nuclei 168,170Dy and 167,168,169Ho are studied and different theoretical models are used to interpret the evolution of collectivity around the mid-shell. In order to produce and study even more neutron-rich nuclei in this mass region, new radioactive ion beam facilities will be a valuable tool. These facilities, however, require advanced instruments to study the weak signals of exotic nuclei in a high background environment. Two of these instruments are the γ-ray tracking spectrometer AGATA and the neutron detector array NEDA. For AGATA to work satisfactorily, the interaction position of the gamma rays must be determined with an accuracy of at least five millimetres. The position resolution is measured in this work using a model independent method based on the Doppler correction capabilities of the detector at two different distances between the detector and the source. For NEDA, one of the critical parameters is its ability to discriminate between neutrons and γ rays. By using digital electronics it is possible to employ advanced and efficient algorithms for pulse-shape discrimination. In this work, digital versions of the common analogue methods are shownto give as good, or better, results compared to the ones obtained using analogue electronics. Another method which effectively distinguishes between neutrons and γ rays is based on artificial neural networks. This method is also investigated in this work and is shown to yield even better results.