<p>This thesis presents experimental data on the fragmentationof gas phase sulfur hexafluoride (SF6) and deutheromethane(CD4) molecules after their interaction with synchrotronradiation in the energy range of 70-200 eV. The data wasobtained using coincidence spectroscopy between energy resolvedelectrons and ions (EREICO).</p><p>Degradation of the molecular bond upon selective ionizationof different molecular orbitals has been studied by measuringionic fragments in coincidence with energy selected electrons.Besides the direct ionisation of the orbitals also the indirectprocess, in which the hole is created by the decay of a highlyenergetic core-excited state, was studied. The differencesdetected in the fragmentation after the direct and indirectionisation of a selected orbital can be related, in some cases,with the relaxation of the nuclei in the potential energysurface of the core excited state during its lifetime, thusproviding information on the neutral core excited state.</p><p>An experimental set-up capable of photon inducedfluorescence spectroscopy (PIFs) studies of core excitedmolecules in the visible range has been constructed. Thistechnique can yield complementary information to the EREICOdata about the energy distribution in the fragmentation sincethe internal energy of excited emitted fragments that decay inthe visible can be measured. It also allows the detection ofpossible neutral fragments.</p>

This thesis presents experimental data on the fragmentationof gas phase sulfur hexafluoride (SF6) and deutheromethane(CD4) molecules after their interaction with synchrotronradiation in the energy range of 70-200 eV. The data wasobtained using coincidence spectroscopy between energy resolvedelectrons and ions (EREICO). Degradation of the molecular bond upon selective ionizationof different molecular orbitals has been studied by measuringionic fragments in coincidence with energy selected electrons.Besides the direct ionisation of the orbitals also the indirectprocess, in which the hole is created by the decay of a highlyenergetic core-excited state, was studied. The differencesdetected in the fragmentation after the direct and indirectionisation of a selected orbital can be related, in some cases,with the relaxation of the nuclei in the potential energysurface of the core excited state during its lifetime, thusproviding information on the neutral core excited state. An experimental set-up capable of photon inducedfluorescence spectroscopy (PIFs) studies of core excitedmolecules in the visible range has been constructed. Thistechnique can yield complementary information to the EREICOdata about the energy distribution in the fragmentation sincethe internal energy of excited emitted fragments that decay inthe visible can be measured. It also allows the detection ofpossible neutral fragments.

Neutron coincidence counting is an important passive Nondestructive Assay (NDA) technique widely used for qualitative and quantitative analysis of nuclear material in bulk samples. During the fission process, multiple neutrons are simultaneously emitted from the splitting nucleus. These neutron groups are often referred to as coincident neutrons. Because different isotopes possess different coincident neutron characteristics, the coincident neutron signature can be used to identify and quantify a given material. In an effort to identify unknown nuclear samples in field inspections, the Portable Neutron Coincidence Counter (PNCC) has been developed. This detector makes use of the coincident neutrons being emitted from a bulk sample. An in-depth analysis has been performed to establish whether the nuclear material in an unknown sample could be quantified with the accuracy and precision needed for safeguards measurements. The analysis was performed by comparing experimental measurements of PuO2 samples to the calculated output produced using MCNPX and the Neutron Coincidence Point Model. Based on the analysis, it is evident that this new portable system can play a useful role in identifying nuclear material for verification purposes.

Neutron coincidence counting is an important passive Nondestructive Assay (NDA) technique widely used for qualitative and quantitative analysis of nuclear material in bulk samples. During the fission process, multiple neutrons are simultaneously emitted from the splitting nucleus. These neutron groups are often referred to as coincident neutrons. Because different isotopes possess different coincident neutron characteristics, the coincident neutron signature can be used to identify and quantify a given material. In an effort to identify unknown nuclear samples in field inspections, the Portable Neutron Coincidence Counter (PNCC) has been developed. This detector makes use of the coincident neutrons being emitted from a bulk sample. An in-depth analysis has been performed to establish whether the nuclear material in an unknown sample could be quantified with the accuracy and precision needed for safeguards measurements. The analysis was performed by comparing experimental measurements of PuO2 samples to the calculated output produced using MCNPX and the Neutron Coincidence Point Model. Based on the analysis, it is evident that this new portable system can play a useful role in identifying nuclear material for verification purposes.

Neutron coincidence counting is an important passive Nondestructive Assay (NDA) technique widely used for qualitative and quantitative analysis of nuclear material in bulk samples. During the fission process, multiple neutrons are simultaneously emitted from the splitting nucleus. These neutron groups are often referred to as coincident neutrons. Because different isotopes possess different coincident neutron characteristics, the coincident neutron signature can be used to identify and quantify a given material. In an effort to identify unknown nuclear samples in field inspections, the Portable Neutron Coincidence Counter (PNCC) has been developed. This detector makes use of the coincident neutrons being emitted from a bulk sample. An in-depth analysis has been performed to establish whether the nuclear material in an unknown sample could be quantified with the accuracy and precision needed for safeguards measurements. The analysis was performed by comparing experimental measurements of PuO2 samples to the calculated output produced using MCNPX and the Neutron Coincidence Point Model. Based on the analysis, it is evident that this new portable system can play a useful role in identifying nuclear material for verification purposes.

Neutron coincidence counting is an important passive Nondestructive Assay (NDA) technique widely used for qualitative and quantitative analysis of nuclear material in bulk samples. During the fission process, multiple neutrons are simultaneously emitted from the splitting nucleus. These neutron groups are often referred to as coincident neutrons. Because different isotopes possess different coincident neutron characteristics, the coincident neutron signature can be used to identify and quantify a given material. In an effort to identify unknown nuclear samples in field inspections, the Portable Neutron Coincidence Counter (PNCC) has been developed. This detector makes use of the coincident neutrons being emitted from a bulk sample. An in-depth analysis has been performed to establish whether the nuclear material in an unknown sample could be quantified with the accuracy and precision needed for safeguards measurements. The analysis was performed by comparing experimental measurements of PuO2 samples to the calculated output produced using MCNPX and the Neutron Coincidence Point Model. Based on the analysis, it is evident that this new portable system can play a useful role in identifying nuclear material for verification purposes.

OpenPET was developed to be a scalable and flexible design for data acquisition and signal processing in Positron Emission Tomography (PET) systems. The OpenPET hardware design is mature, but the control software and firmware need further development. In this thesis we developed a software application to connect a host PC with an OpenPET system. We also developed data acquisition firmware that allows data transfer to the host PC. A novel design for an OpenPET coincidence detection processor was proposed, with its basic functionality implemented and validated. A novel method to process PET events in real time was also introduced and validated using simulated data. The feasibility of implementation of this method using Field Programmable Gate Arrays (FPGAs) was demonstrated for our OpenPET system.

OpenPET was developed to be a scalable and flexible design for data acquisition and signal processing in Positron Emission Tomography (PET) systems. The OpenPET hardware design is mature, but the control software and firmware need further development. In this thesis we developed a software application to connect a host PC with an OpenPET system. We also developed data acquisition firmware that allows data transfer to the host PC. A novel design for an OpenPET coincidence detection processor was proposed, with its basic functionality implemented and validated. A novel method to process PET events in real time was also introduced and validated using simulated data. The feasibility of implementation of this method using Field Programmable Gate Arrays (FPGAs) was demonstrated for our OpenPET system.

The Comprehensive Nuclear Test Ban Treaty verification regime mandates atmospheric monitoring for the four radioxenon isotopes that are produced in high abundance in a nuclear explosion: [superscript 131m]Xe, [superscript 133m]Xe, [superscript 133g]Xe, and [superscript 135g]Xe. This mandate has driven the development of improved xenon detectors, including a phoswich detector, which has potential to replace the ARSA detector in the International Monitoring System. In this experiment, the four relevant radioxenon isotopes were produced through neutron activation and the phoswich detector was used to attain spectra from the gas. Spectral characteristics and resolution of the phoswich spectra were compared to an ARSA-type [beta]-[gamma] coincidence detector to perform an overall evaluation of the phoswich detector. The results indicated that spectral characteristics and resolutions for the phoswich were comparable to the ARSA-type detector, with slightly improved beta detection. As an additional test of the new detector's capabilities, a tailored spectrum designed to mimic a nuclear explosion signature was produced and analyzed with the detector. / text

Este trabalho apresenta os métodos de padronização de 111In e 99mTc, em sistemas de coincidências 4&pi;&beta;-&gamma;. O 111In foi produzido em cíclotron pela reação 111Cd(p, n)111In; decai com uma meia vida de 2,8 dias pelo processo de captura eletrônica populando os níveis excitados do 111Cd, emitindo raios gama de 171 keV e 245 keV. O 99mTc decai com uma meia vida de 6,007 h por transição isomérica do decaimento radioativo do 99Mo . A padronização do 111In foi feita no sistema 4&pi;&beta;-&gamma; constituído de um detector proporcional em geometria 4&pi; acoplado a dois cristais cintiladores de NaI(Tl) com eletrônica convencional. A radiação gama selecionada para medida em coincidência foi de (171 + 245) keV. A escolha da janela gama foi baseada na análise da previsão da curva de extrapolação obtida na simulação de Monte Carlo. A padronização do 99mTc foi feita num sistema 4&pi;&beta;-&gamma; usando um contador proporcional de janela fina acoplado a um cristal de cintilação NaI (Tl). A eficiência beta foi variada por discriminação eletrônica, usando sistema de coincidências por software (SCS). A padronização do 99mTc foi feita pela seleção de dois intervalos gama, um no pico de absorção total de 140 keV e outro no pico de absorção total dos raios X de 20 keV. O resultado da atividade experimental de duas soluções de 111In concorda com o resultado obtido pela simulação de Monte Carlo. As atividades experimentais do 99mTc para os dois intervalos gama selecionados estão de acordo dentro da incerteza experimental, indicando que a metodologia adotada é adequada. / The 111In and 99mTc standardization in a 4&pi;&beta;-&gamma; coincidence system is described. The 111In was produced by the reaction of 111Cd (p, n) 111In in the cyclotron. The 111In decays with a half life of 2.8 days by electron capture process, populating the excited levels of 111Cd, emitting two main gamma rays with energies of 171 keV and 245 keV. The 99mTc decay with a half life of 6.007 h for isomeric transition, from the radioactive decay of 99Mo . 111In standstand ardization was carried out in a 4&pi;&beta;-&gamma; system, consisted of a system, consisted of a system of a gas flow proportional counter with 4flow proportional counter with 4&pi; geometry coupled to a pair of NaI(Tl) scintillation counter with conventional electronics. The gamma window was set comprising the (171 keV + 245 keV) total absorption energy peaks. The choice of the window was based on the analysis of the extrapolation curves prediction, obtained by Monte Carlo simulation. The 99mTc standardization has been accomplished by the 4&pi;&beta;-&gamma; coincidence method using a thin window proportional counter in a 4&pi; geometry coupled to a single NaI(Tl) scintillation counter. The beta efficiency was varied by electronic discrimination using a software coincidence counting system (SCS). Two windows were selected for the gamma channel: one at 140 keV gamma ray and the other at 20 keV X ray total absorption peaks. The result of the experimental activity of 111In two solutions agree with the results obtained by Monte Carlo simulation. The experimental activities of 99mTc for the two gamma windows are in agreement within the experimental uncertainty, indicating that the adopted methodology is adequate.