Academic literature on the topic 'Gamma-ray spectrometry'

Spatially representative sampling of both natural and anthropogenic deposits in the environment is limited by their inherent heterogenic distribution. This problem is compounded when trying to relate ground measurements which are spatially restricted to remote sensing observations which are not. This work examined these widely experienced problems in the context of the measurement of natural (K, U and Th) and anthropogenic ( 137Cs and ' 34Cs) radioactivity through the three techniques of soil sampling with laboratory based gamma ray spectrometry, in-situ gamma ray spectrometry, and airborne gamma ray spectrometry. These three methods were applied systematically to estimate the radioactivity across a tight geometry valley in Renfrewshire. Activity estimates from field based and airborne gamma spectrometry were compared with each other and with the results of high resolution gamma spectrometry of soil samples to examine the relationship between each method under variable topographic conditions. These results demonstrated that the distribution, and post depositional migration, of activity had important influences on all measurement techniques, and affected the ability to make comparisons between them. Further detailed studies were then conducted to examine these influences. The effects of variations in soil composition and characteristics on environmental gamma ray spectrometry were evaluated by calculation and experimental determination. Corrections to standard laboratory gamma spectrometric procedures were developed to improve systematic precisio:i. These investigations also reviewed soil sampling depth for direct effective comparison with in-situ gamma spectrometry. The effects of small scale sampling errors on activity estimates were demonstrated to have a quantifiable influence on the precision of activity estimation. Lateral variability of activity distribution of natural radioactivity and anthropogenic radioactivity deposited both from the atmosphere and from marine sources has been studied in detail at a number of sites. The extent of variability depends on the nature of activity, its deposition mode and local environmental characteristics. Spatial variability represents an important constraint on the interpretation of activity estimates derived from all methods examined, and on comparisons between them. Statistically representative sampling plans were developed and applied to enable spatial comparisons to be made between soil sample derived activity estimates and in-situ and remotely sensed observations. The influence of the vertical activity distribution on in-situ and airborne measurements has been recognised as an important variable affecting calibration. The use of the information from the scattered gamma ray spectrum to quantify and correct for source burial effects was examined in a series of modelling experiments. A relationship between 'Cs source burial and forward scattering was determined and subsequently applied to a salt marsh environment which showed pronounced subsurface maxima. A spectrally derived calibration correction coefficient was shown to account for variations in source burial across a single site. This provides a potential means for surmounting one of the principal limitations of in-situ gamma spectrometry. As a result of this work it has been possible to account for important environmental factors which affect gamma ray spectrometry in the laboratory, in the field and from aircraft. This has led to the development of sound methodology for comparison between sampling, field based and remote sensing techniques.

Excited states in the transitional nucleus 160Yb have been studied using gamma-ray and conversion electron spectroscopy following the beta+/EC decay of 160Lu. Excited states in the nuclei 160Tm and 160Er have been studied following the beta+/EC decay of 160Yb and 160Tm, respectively. The data for the present study were obtained at TRIUMF in Vancouver, Canada at the ISAC-1 facility through radioactive sources moved into the combination of the 8pi gamma-ray spectrometer array and the Pentagonal Array for Conversion Electron Spectroscopy (PACES). Analysis of gamma-ray gated gamma-ray, gamma-ray gated conversion electron and conversion electron gated gamma-ray spectra resulted in the discovery of a new first excited state and the establishment of a level scheme for 160Tm which differs from the one adopted; as well as a test of the rotational characteristics of 160Er with intensity comparisons to both the spin-5 beta-decaying isomer study of by Singh et al. and the spin-parity 1- beta decay study of by Strusny et al. and Bykov et al.

The environmental radioactivity monitoring programs start in the late 1950s of the 20th century following the global fallout from testing of nuclear weapons in the atmosphere, becoming a cause of concern regarding health effects. Later, the necessity of world industrialization for new energy sources led to develop national plans on electricity production from nuclear technology, initializing in this context world wide exploration for fuel minerals: uranium exploration gained a particular attention in late 1940's in USA, Canada and former USSR and in 1951 in Australia with respective national plans. Nowadays there are about 440 nuclear power plants for electricity generation with about 70 more NPP under construction giving rise to the nuclear emergency preparedness of a large number of states (like Radioactivity Environmental Monitoring (REM) data bank and EUropean Radiological Data Exchange Platform (EURDEP). Furthermore, a lot of applications in the field of geosciences are related to the environmental radioactivity measurements going from geological mapping, mineral exploration, geochemical database construction to heat -flow studies. Gamma-ray spectroscopy technique is widely used when dealing with environmental radioactivity monitoring programs. The purpose of this work is to investigate the potentialities that such a technique offers in monitoring radioactivity concentration through three different interventions in laboratory, in-situ and airborne measurements. An advanced handling of gamma-ray spectrometry method is realized by improving the performances of instruments and realizing and testing dedicated equipments able to deal with practical problems of radioactivity monitoring. For each of these gamma-ray spectrometry methods are faced also the problems of calibration, designing of monitoring plans and data analyzing and processing. In the first chapter I give a general description for the common radionuclides present in the environment having a particular interest for monitoring programs. Three categories of environmental radionuclides classified according to their origin as cosmogenic, primordial and man-made are discussed. The cosmic rays continuously produce radionulides and also direct radiation, principally high energetic muons. Cosmogenic radionuclides are originated from the interaction of cosmic rays with stable nuclides present in the Earth’s atmosphere. Primordial radionuclides are associated with the phenomenon of nucleosynthesis of the stars and are present in the Earth’s crust. Man-made radionuclides commonly present in natural environments are principally derived from radioactive fallout from atmospheric nuclear weapons testing and peaceful applications of nuclear technology like nuclear power plants for electricity generation and the associated nuclear fuel cycle facilities. A relevant contribution, generally with local implication comes from the so called non-nuclear industries which are responsible for technologically enhancement of natural radioelements producing huge amounts of naturally occurring radioactive materials (NORM/TENORM). In the second chapter is described a homemade approach to the solution of the problem rising in monitoring situations in which a high number of samples is to be measured through gamma-ray spectrometry with HPGe detectors. Indeed, in such cases the costs sustaining the manpower involved in such programs becomes relevant to the laboratory budget and sometimes becomes a limitation of their capacities. Manufacturers like ORTEC® and CANBERRA produce gamma-ray spectrometers supported by special automatic sample changers which can process some tens of samples without any human attendance. However, more improvements can be done to such systems in shielding design and detection efficiency. We developed a fully automated gamma-ray spectrometer system using two coupled HPGe detectors, which is a well known method used to increase the detection efficiency. An alternative approach on shielding design and sample changer automation was realized. The utilization of two coupled HPGe detectors permits to achieve good statistical accuracies in shorter time, which contributes in drastically reducing costs and man power involved. A detailed description of the characterization of absolute full-energy peak efficiency of such instrument is reported here. Finally, the gamma-ray spectrometry system, called MCA_Rad, was used to characterize the natural radioactivity concentration of bed-rocks in Tuscany Region, Italy. More than 800 samples are measured and reported here together with the potential radioactivity concentration map of bed rocks in Tuscany Region. In the third chapter is described the application of portable scintillation gamma -ray spectrometers for in-situ monitoring programs focusing on the problems of calibration and spectrum analysis method. In-situ γ-ray spectrometry with sodium iodide scintillators is a well developed and consolidated method for radioactive survey. Conventionally, a series of self-constructed calibration pads prevalently enriched with one of the radioelements is used to calibrate this portable instrument. This method was further developed by introducing the stripping (or window analysis) described in International Atomic Energy Agency (IAEA) guidelines as a standard methods for natural radioelement exploration and mapping. We realized a portable instrument using scintillation gamma-ray spectrometers with sodium iodide detector. An alternative calibration method using instead well-characterized natural sites, which show a prevalent concentration of one of the radioelements, is developed. This procedure supported by further development of the full spectrum analysis (FSA) method implemented in the non-negative least square (NNLS) constrain was applied for the first time in the calibration and in the spectrum analysis. This new approach permits to avoid artifacts and non physical results in the FSA analysis related with the χ2 minimization process. It also reduces the statistical uncertainty, by minimizing time and costs, and allows to easily analyze more radioisotopes other than the natural ones. Indeed, as an example of the potentialities of such a method 137Cs isotopes has been implemented in the analysis. Finally, this method has been tested by acquiring gamma Ombrone -ray spectra using a 10.16 cm×10.16 cm sodium iodide detector in 80 different sites in the basin, in Tuscany. The results from the FSA method with NNLS constrain have been compared with the laboratory measurements by using HPGe detectors on soil samples collected. In the forth chapter is discussed the self-construction of an airborne gamma-ray spectrometer, AGRS_16.0L. Airborne gamma-ray spectrometry (AGRS) method is widely considered as an important tool for mapping environmental radioactivity both for geosciences studies and for purposes of radiological emergency response in potentially contaminated sites. Indeed, they have been used in several countries since the second half of the twentieth century, like USA and Canada, Australia, Russia, Checz Republic, and Switzerland. We applied the calibration method described in the previous chapter using well -characterized natural sites and implemented for the first time in radiometric data analysis FSA analysis method with NNLS constrain. This method permits to decrease the statistical uncertainty and consequently reduce the minimum acquisition time (which depend also on AGRS system and on the flight parameters), by increasing in this way the spatial resolution. Finally, the AGRS_16.0L was used for radioelement mapping survey over Elba Island. It is well known that the natural radioactivity is strictly connected to the geological structure of the bedrocks and this information has been taken into account for the analysis and maps construction. A multivariate analysis approach was considered in the geostatistical interpolation of radiometric data, by putting them in relation with the geology though the Collocated Cokriging (CCoK) interpolator. Finally, the potential radioelement maps of potassium, uranium and thorium are constructed for Elba Island.

La spectrométrie gamma est une des techniques principales pour la mesure de la radioactivité, qui permet d'identifier et quantifier les radionucléides. L'objectif de la thèse est de développer de nouvelles méthodes d’analyse des spectres gamma afin d'améliorer les limites de détection. Dans ce contexte, la première contribution est la proposition de nouvelle approches statistiques pour l'estimation des activités en spectrométrie gamma par le démélange spectral, qui consiste à décomposer un spectre gamma mesuré en spectres individuels des radionucléides. Contrairement aux méthodes standard, cette approche permet de traiter un spectre gamma dans sa globalité et prendre en compte la statistique Poisson du processus de détection. En modélisant l'estimation des activités comme un problème inverse sous la contrainte de non-négativité, le démélange spectral parcimonieuse est étudié pour estimer conjointement l'ensemble des radionucléides actifs et leurs activités. La deuxième contribution est l'utilisation métrologique du démélange spectral étudié, qui nécessite en plus l'évaluation des limites caractéristiques pour la prise de décision et l'étalonnage des instruments pour l'analyse quantitative<br>Gamma-ray spectrometry is one of the main techniques used for the measurement of radioactivity, which allows identifying and quantifying radionuclides. The objective of this thesis is to develop new spectrum analysis methods to improve the detection limits. In this context, the first contribution is investigating the activity estimation in gamma-ray spectrometry with spectral unmixing, which decomposes a measured spectrum into individual radionuclides' spectra. Contrary to standard methods, this approach allows accounting for the full spectrum analysis of a gamma-ray spectrum and the Poisson statistics underlying the detection process. By formulating the activity estimation as an inverse problem under non-negativity constraint, the sparse spectral unmixing is investigated to estimate the subset of active radionuclides and their activities jointly. The second contribution is the metrological use of the investigated spectral unmixing method, which further necessitates the evaluation of characteristic limits for decision making purposes and the instruments' calibration for quantitative analysis

Environmental gamma-ray spectroscopy provides a powerful tool that can be used in environmental monitoring given that it offers a compromise between measurement time and accuracy allowing for large areas to be surveyed quickly and relatively inexpensively. Depending on monitoring objectives, spectral information can then be analysed in real-time or post survey to characterise contamination and identify potential anomalies. Smaller volume detectors are of particular worth to environmental surveys as they can be operated in the most demanding environments. However, difficulties are encountered in the selection of an appropriate detector that is robust enough for environmental surveying yet still provides a high quality signal. Furthermore, shortcomings remain with methods employed for robust spectral processing since a number of complexities need to be overcome including: the non-linearity in detector response with source burial depth, large counting uncertainties, accounting for the heterogeneity in the natural background and unreliable methods for detector calibration. This thesis aimed to investigate the application of machine learning algorithms to environmental gamma-ray spectroscopy data to identify changes in spectral shape within large Monte Carlo calibration libraries to estimate source characteristics for unseen field results. Additionally, a 71 × 71 mm lanthanum bromide detector was tested alongside a conventional 71 × 71 mm sodium iodide to assess whether its higher energy efficiency and resolution could make it more reliable in handheld surveys. The research presented in this thesis demonstrates that machine learning algorithms could be successfully applied to noisy spectra to produce valuable source estimates. Of note, were the novel characterisation estimates made on borehole and handheld detector measurements taken from land historically contaminated with 226Ra. Through a novel combination of noise suppression and neural networks the burial depth, activity and source extent of contamination was estimated and mapped. Furthermore, it was demonstrated that Machine Learning techniques could be operated in real-time to identify hazardous 226Ra containing hot particles with much greater confidence than current deterministic approaches such as the gross counting algorithm. It was concluded that remediation of 226Ra contaminated legacy sites could be greatly improved using the methods described in this thesis. Finally, Neural Networks were also applied to estimate the activity distribution of 137Cs, derived from the nuclear industry, in an estuarine environment. Findings demonstrated the method to be theoretically sound, but practically inconclusive, given that much of the contamination at the site was buried beyond the detection limits of the method. It was generally concluded that the noise posed by intrinsic counts in the 71 × 71 mm lanthanum bromide was too substantial to make any significant improvements over a comparable sodium iodide in contamination characterisation using 1 second counts.

O Laboratório de Análise por Ativação com Nêutrons (LAN) do Instituto de Pesquisas Energéticas e Nucleares (IPEN), utiliza esta técnica analítica multielementar, baseada na irradiação de uma amostra por um feixe de nêutrons oriundos de um reator nuclear, que induz a radioatividade; que é medida em um espectrômetro de raios gama, para a obtenção dos espectros de raios gama. Neste trabalho é implementado um software denominado de SAANI (Software Análise por Ativação com Nêutrons Instrumental) para análise de espectros de raios gama, desenvolvido para os usuários do laboratório LAN-IPEN, com a filosofia de software livre, para a substituição do software existente VISPECT/VERSÃO 2, e tem como características principais: tornar a interface mais amigável; facilitar a padronização dos procedimentos realizados pelos pesquisadores, estudantes e técnicos; ser extensível com a utilização da tecnologia de plugins; multiplataforma; código livre. O software foi desenvolvido utilizando a linguagem de programação Python, a biblioteca gráfica Trolltech Qt e algumas de suas extensões científicas. Os resultados preliminares obtidos utilizando o software SAANI foram comparados aos obtidos com o software existente e foram considerados bons. Algumas diferenças encontradas foram verificadas oriundas de erros de precisão na implementação do software. O software SAANI está instalado nos computadores de usuários selecionados para a execução de rotinas de análise para uma maior verificação de sua robustez, precisão e usabilidade.<br>This study developed a specific software for gamma ray spectra analysis for researchers of the Neutron Activation Laboratory (LAN), which was named SAANI (Instrumental Neutron Activation Analysis Software). The LAN laboratory of the Institute for Research and Nuclear Energy (IPEN-CNEN/SP), uses a multielementar analytical technique, based on irradiation of a sample by a flux of neutrons from a nuclear reactor, which induces radioactivity. The sample is then placed in a gamma-ray spectrometer, to obtain the spectrum. With free software philosophy in mind, this software will replace the existing software VISPECT / VERSION 2. The new software´s main features are: a friendlier interface; easier standardization procedure carried out by LAN staff and researchers; adapted to the use of plug technology; multiplatform and code free. The software was developed using the programming Python language, the library Trolltech Qt graphics and some of their scientific extensions. Preliminary results using the SANNI software were compared to those obtained with the existing software and were considered good. There were some errors in accuracy during the implementation of the software. The SAANI software has been installed in selected computers to be used for routine analysis in order to verify its strength, accuracy and usability.