A Monte Carlo model has been developed using MCNP5 to simulate the Nucletron Ir-192 HDR source in order to investigate the influence of tissue heterogeneities on dose calculations compared to the dose in homogeneous water media, as it is typically calculated by brachytherapy Treatment Planning Systems (TPS). Validity of the simulation was verified in water medium in comparison with peer reviewed results using the dosimetric parameters recommended by AAPM, Task Group-43. The dose-rates in simulated prostate, bladder and rectum were compared to those obtained in the homogeneous water phantom. Based on the resulting dose differences, it is inferred that TPS algorithms for brachytherapy dose calculations overestimate the dose to tissues like prostate and bladder by up to 49%. A clinically relevant dose underestimation of 5.5% to the rectum was also found. We recommend that further investigation using actual patient CT data as input to the Monte Carlo simulation be performed. / by Ramsâes Herrera. / Thesis (M.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

A infiltração de fluido e bactérias nos espaços internos dos implantes foi observada em pilares intermediários parafusados, tanto em situações in vitro quanto in vivo devido à microfenda existente entre o implante e o pilar intermediário. Esse fato pode estar relacionado com a inflamação dos tecidos periimplantares e também com a produção de mau odor. O objetivo do presente estudo in vitro foi avaliar e comparar a ocorrência de infiltração de fluidos pela interface implante-pilar intermediário em três sistemas de implante com conexão do tipo cone Morse, e a capacidade de vedação de um adesivo anaeróbico, utilizando o radioisótopo Tecnécio-99m como marcador. Na primeira etapa, dez conjuntos implante-pilar intermediário de cada sistema foram imersos em solução contendo esse marcador, após a aplicação do torque recomendado pelo fabricante, e foram mantidos em pressão constante de 2 atm por um minuto. Na segunda etapa, um adesivo anaeróbico foi aplicado no pilar intermediário antes do mesmo ser parafusado ao seu respectivo implante. Após a aplicação da pressão, o infiltrado presente no interior dos implantes foi coletado com pontas de papel. Esse material foi depositado em tubos de ensaio para posterior leitura da radioatividade presente. A infiltração de fluido pela interface implante-pilar intermediário mostrou ser um fenômeno mensurável em todas as amostras dos três sistemas de implante com conexão do tipo cone Morse testados. A quantidade de infiltrado variou entre os sistemas e entre as amostras. A inconstância das amostras foi observada em todos os sistemas, no entanto, foi observado que o valor de infiltrado encontrado no Grupo 1 foi significantemente maior (p<0,05) do que o encontrado no Grupo 2, e não houve diferença estatística significante entre os Grupos 1 e 3, e entre os Grupos 2 e 3. Também foi observado que, com o uso do adesivo anaeróbico, os sistemas apresentaram diminuição da quantidade de infiltrado, sendo que a análise estatística dos valores obtidos com e sem o seu uso, mostraram significância a 1%. Além disso, com o uso do adesivo anaeróbico os três sistemas de implante testados passaram a ter comportamento semelhante, não tendo sido encontrada diferença estatística significante entre eles (p=0,5451). Considerando os limites deste estudo, pode-se concluir que os três sistemas de implante com conexão do tipo cone Morse testados permitiram a passagem de fluido do meio externo para o interior dos implantes, e que o material testado não foi capaz de impedir a penetração de fluido, apesar de ter reduzido significantemente a quantidade de infiltrado em todos os sistemas. / It has been observed that in implants with screw-retained abutments, in in vitro as well as in vivo conditions, bacteria and fluids can penetrate the inner implant space as consequence of an existing microgap at the implant-abutment interface. This fact can be related to peri-implant tissue inflammation and malodor. The aim of the present study was to evaluate and compare the occurrence of fluid penetration throught implant-abutment interface in three cone Morse implant systems and sealing ability of an anaerobic adhesive using a radioisotope as trace. In the first phase, ten implant-abutment sets of each system were immersed in a solution with radioisotope, after manufacture recommended torque application. All assemblies were kept in a constant pressure of 2 atm for one minute. In the second phase, an anaerobic adhesive was applied before the abutments been torque-tightened to the same implant. After the pressure application, material inside implant bodies was colleted using a paper cone that was transferred to tubes for posterior verification of radioactivity. Fluid penetration at the implant-abutment interface was seen to be a recordable phenomenon in each assembly of the three cone Morse systems tested in this study. The quantity of infiltrated varied between systems and assemblies. The variable of the samples was observed in all systems, however, it was noted that the value of infiltrate found in Group 1 was significantly higher than that found in Group 2, and there was no statistical significant difference between the groups 1 and 3, and between groups 2 and 3. It was also noted that, using the adhesive anaerobic, the implant systems showed reduce infiltrate, and statistical analysis presented significance to 1%. Moreover, with the use of anaerobic adhesive, all three implant systems tested presented similar pattern, and no significant statistical difference was found (p=0,5451). Considering the limits of this study, the following conclusions can be drawn: the three cone Morse implant systems tested allowed the passage of fluid from external to the inside of the implants, and that the material tested was not capable of preventing the fluid penetration, despite having reduced significantly the amount of infiltrate in all systems.

<div>Detecting hidden/smuggled special nuclear materials (SNM) is one of the unsolved problems in the safeguards industry. The biggest challenge is to quantify and track SNM and prevent the use of these materials for illicit purposes. The goal is to detect smallest quantity of SNM in large cargo containers, at the ports of entry, in the shortest amount of measurement time. Currently passive detection techniques, which is based on long-lived isotopes, are used to detect hidden SNM. This technique is not very reliable, as appropriate shielding of the SNM can reduce detection signals from these long-lived isotopes. Accelerator based active interrogation methods are proposed to solve the SNM problem. Besides SNM, another challenge in the nuclear industry is to meet the demand and supply of medical radioisotopes, particularly Tc-99m (half-life 6 hours). Mo-99, which decays to Tc-99m, is one of the fission products found in nuclear reactors. Because of short half-life of 66 hours, Mo-99 cannot be stockpiled. The shutdown of various research reactors globally disrupted the supply of Mo-99. Because of the financial and regulatory burden on the nuclear reactors, accelerator-based systems can be used to produce Mo-99.</div><div><br></div><div>With the aim to solve these two major challenges, a preliminary study is done to understand the neutrons behavior on milliseconds (or shorter) time steps in an accelerator driven subcritical system. A pulsed external neutron source, i.e. Deuterium-Deuterium (DD) generator, drives the assembly. Using first principles, the transient equations are derived and the neutron population at different time stamps is calculated. The Li-6 detector’s response to the neutron population is predicted. Experiments are performed to compare the predicted behavior with the observed behavior. The model is extended further to investigate the case of no uranium fuel inside the system. Transient measurements, in the absence of the uranium fuel, are made and the neutron die-away time is determined. This die-away time is compared with the predicted time.</div>

The objective of the work described was to identify and explore a paradigm shifting solution that could offer leap-ahead capabilities to counter current and future DBHT threats while mitigating or eliminating the self-deterrence issue. A multidisciplinary approach to the problem was formulated and implemented. Systematic evaluation of DHBT defeat alternatives lead to the selection of a thermal subterrene as a hypothetical means of providing such a capability. A number of possible implementation alternatives for a thermal subterrene were investigated, resulting in the identification of the RadioIsotope Powered Thermal Penetrator (RIPTP) concept for providing an effectively unlimited, self-contained hard rock penetration capability using near-term technologies. However, the proposed approach was novel and thus required formulation and application of a physics based multidisciplinary analysis code to enable evaluation of design alternatives and analysis of performance. The following disciplinary analyses were composed into a multidisciplinary analysis code for a RIPTP: packing of RIPTP components in available volume; close-contact melting analysis; transmutation of isotope species by neutron activation; reactor neutron economy; radioisotope power generation through decay; metamodelled radiation shielding calculations for a RIPTP; and steady state thermal analyses for a RIPTP in various scenarios. Performance analysis of the identified baseline Thulium-170 RIPTP suggested that the predicted low penetration rate of about 10 meters/day could be a significant negative factor with regards to possible viability of the concept. Consequently, a survey for potentially enabling technologies was performed using an adaptation of the Technology Impact Forecasting (TIF) approach. It was found that the greatest potential for improving performance of the baseline Thulium-170 RIPTP resulted from increasing overall power density of the penetrator. Several possible technology approaches to achieving significantly increased penetration rates are proposed.

Some mounted ill. / Bibliography: leaves 203-263 / vii, 263, [52], [29] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1984

[Truncated abstract] Purpose: Permanent prostate brachytherapy (PPB) as a treatment option for prostate cancer requires implantation of 80-150 radioactive iodine-125 (I-125)

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 62-70).

Thesis (Ph.D.)--McMaster University (Canada), 1993. / Source: Dissertation Abstracts International, Volume: 55-06, Section: B, page: 2216. Adviser: R. A. Bell.

Thesis (M.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 99-104). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 116-123).