Há diversas enfermidades radiossensíveis epidermotrópicas, como a micose fungóide e a síndrome de Sézary, neoplasias cutâneas originadas de linfócitos do tipo T, que apresentam grande possibilidade de erradicação quando tratadas com feixes de elétrons com energia entre 4 e 10 MeV, conforme apontam diversos estudos. No entanto, esta técnica de tratamento apresenta inúmeras dificuldades práticas, pois a doença dissemina-se por todo o corpo do paciente tornando necessário um grande campo de radiação e deposição de energia limitada à profundidade da pele. A fim de obter uma distribuição de dose uniforme, muitas técnicas já foram desenvolvidas. Com base em estudos anteriores e guiados pelo protocolo n. 23 da American Association of Physicists in Medicine (AAPM), o presente trabalho desenvolveu placas espalhadoras e degradadoras de energia e realizou toda a dosimetria (computacional e experimental), a fim de fornecer subsídios para a implementação da técnica de tratamento Total Skin Electron Therapy (TSET) no Serviço de Radioterapia do Hospital das Clínicas de São Paulo. O programa MCNP4C baseado no método de Monte Carlo foi utilizado para reconstruir o espectro energético do acelerador Varian Clinac 2100C, por meio de medidas experimentais de percentual de dose em profundidade (PDP) e perfis radiais de dose. Com estes dados, foi possível efetuar simulações computacionais para a seleção de materiais, mediante análise da distribuição radial e axial de dose, produção de raios-X e a atenuação do feixe, além da simulação de placas espalhadoras e degradadoras de energia, a serem posicionadas na saída do acelerador. Os resultados das simulações foram validados por meio de medidas experimentais a fim de obter um grande campo de radiação com 200 cm x 80 cm que atendesse as especificações do protocolo da AAPM. / There are many radiosensitive epidermotropics diseases such as mycosis fungoids and the syndrome of Sézary, coetaneous neoplasics originated from type T lymphocytes. Several studies indicate the eradication of the disease when treated with linear accelerators emitting electron beams with energies between 4 to 10 MeV. However, this treatment technique presents innumerable technical challenges since the disease in general reaches all patient´s body, becoming necessary not only a very large field size radiation beam, but also deliver superficial doses limited to the skin depth. To reach the uniformity in the dose distribution, many techniques had already been developed. Based on these previous studies and guided by the report n. 23 of the American Association of Physicists in Medi-cine (AAPM), the present study developed an energy scattering and degrading plates and made dosimetry (computational and experimental), supplying subsidies for a future installation of Total Skin Electron Therapy (TSET) at the Serviço de Radioterapia do Hospital das Clínicas de São Paulo. As part of the plates design, first of all, the energy spectrum of the 6 MeV electron beam of the VARIAN 2100C accelerator was reconstructed through Monte Carlo simulations using the MCNP4C code and based on experimental data. Once the spectrum is built, several materials were analyzed for the plates design based on radial and axial dose distribution, production of rays-x and dose attenuation. The simulation results were validated by experimental measurements in order to obtain a large field of radiation with 200 cm x 80 cm that meets the specifications of the AAPM protocol.

O tratamento de câncer possui diversas modalidades. Uma delas é a utilização de fontes de radiação como principal protagonista do tratamento. A radioterapia e a medicina nuclear são exemplos desse tipo de tratamento. Por utilizarem a radiação ionizante como principal ferramenta para a terapia, há a necessidade de se efetuar diversas simulações do tratamento a fim de maximizar a dose nos tecidos tumorais sem ultrapassar os limites de dose nos tecidos sadios circunvizinhos. Os sistemas utilizados na simulação desses tipos de terapia recebem o nome de Sistemas de Planejamento Dosimétrico. A medicina nuclear e a radioterapia possuem seus próprios sistemas de planejamento dosimétricos devido a grande diversidade das informações necessárias às suas simulações. Os sistemas de planejamento em radioterapia são mais consolidados do que os de medicina nuclear e por tal motivo um sistema que aborde tanto os casos de radioterapia como de medicina nuclear contribuiria para significativos avanços na área de medicina nuclear. Dessa forma, o objetivo do trabalho foi modelar um Sistema de Planejamento Dosimétrico com o uso do código de Monte Carlo MCNP6 Monte Carlo N-Particle Transport Code que permitisse incorporar os casos de radioterapia e medicina nuclear e que fosse extensível a novos tipos de tratamentos. A modelagem desse sistema resultou na construção de um Framework, orientado a objetos, nomeado IBMC o qual auxilia no desenvolvimento de sistemas de planejamento que necessitam interpretar grandes quantidades de informações com o objetivo de escrever o arquivo base do MCNP6. O IBMC permitiu desenvolver de maneira rápida e prática sistemas de planejamento para radioterapia e medicina nuclear e os resultados foram validados com sistemas já consolidados. Ele também mostrou alto potencial para desenvolver sistemas de planejamento de novos tipos de tratamentos que utilizam a radiação ionizante. / Cancer therapy has many branches and one of them is the use of radiation sources as treatment leading method. Radiotherapy and nuclear medicine are examples of these treatment types. For using the ionization radiation as main tool for the therapy, there is the need of crafting many treatment simulation in order to maximum the tumoral tissue dose without throught the dose limit in health tissue surrounding. Treatment planning systems (TPS) are systems which have the purpose of simulating these therapy types. Nuclear medicine and radiotherapy have many distinct features linked to the therapy mode and consequently they have different TPS destined for each. The radiotherapy TPS is more developed than the nuclear medicine TPS and by that reason the development of a TPS that was similar to the radiotherapy TPS, but enough generic for include other therapy types, it will contribute with significant advances in nuclear medicine and in others therapy types with radiation. Based on this, the goal of work was to model a TPS that utilizes the Monte Carlo N-Particle Transport code (MCNP6) in order to simulate radiotherapy therapy, nuclear medicine therapy and with potential for simulating other therapy types too. The result of this work was the creation of a Framework in Java language, objectoriented, named IBMC which will assist in the development of new TPS with MCNP6 code. The IBMC allowed to develop rapidly and easily TPS for radiotherapy and nuclear medicine and the results were validated with systems already consolidated. The IBMC showed high potential for developing TPS by new therapy types.

A radioterapia é uma modalidade terapêutica que utiliza radiações ionizantes para erradicar as células neoplásicas do organismo humano. Um dos requisitos para o sucesso desta metodologia de tratamento está na utilização adequada dos sistemas de planejamento, os quais, dentre outras informações, estimam a dose a ser administrada aos pacientes. Atualmente, códigos de transporte de radiação têm proporcionado grandes subsídios a estes sistemas de planejamento, uma vez que viabilizam avaliações dosimétricas acuradas nos órgãos e tecidos específicos de um paciente. O modelo utilizado por estes códigos para descrever a anatomia humana de forma realista é denominado Objeto Simulador Segmentado (OSS), que consiste na representação das estruturas anatômicas do corpo em discretos elementos de volume (voxels), os quais são diretamente associados aos dados tomográficos. Atualmente, os OSS possíveis de serem inseridos e processados pelo código de transporte MCNP (Monte Carlo N-Particle), apresentam voxels com resoluções da ordem de 3-4 mm. No entanto, tal resolução compromete a discriminação de algumas estruturas finas do corpo, tais como a pele. Neste contexto, o presente estudo propõe a criação de uma rotina de cálculo que discrimine a região da pele, com espessura e localização próximas do real, nos OSS e os habilite para avaliações dosimétricas acuradas. A metodologia proposta consiste na manipulação dos elementos de volume dos OSS de forma a segmentá-los e subdividi-los em diferentes espessuras de pele. A fim de validar os dados obtidos por cálculos, foram realizadas avaliações experimentais de dosimetria de pele em objetos simuladores antropomórficos com dosímetros termoluminescentes. Verificou-se, ao longo deste estudo, a importância de discriminar a região da pele com localização e espessuras próximas do real, uma vez que foram encontradas diferenças significativas entre as estimativas de dose absorvida na região pelas diferentes representações. A metodologia proposta neste estudo far-se-á útil para avaliações dosimétricas acuradas da região de pele para diversos procedimentos radioterápicos, com particular interesse na radioterapia com feixe de elétrons, na qual se destaca a terapia de irradiação de corpo inteiro (TSET Total Skin Electron Therapy), procedimento radioterápico em implementação no Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HC-FMUSP). / Radiotherapy is a therapeutic modality that utilizes ionizing radiation for the destruction of neoplastic human cells. One of the requirements for this treatment methodology success lays on the appropriate use of planning systems, which performs, among other information, the patients dose distribution estimate. Nowadays, transport codes have been providing huge subsidies to these planning systems, once it enables specific and accurate patient organ and tissue dosimetry. The model utilized by these codes to describe the human anatomy in a realistic way is known as voxel phantoms, which are represented by discrete volume elements (voxels) directly associated to tomographic data. Nowadays, voxel phantoms doable of being inserted and processed by the transport code MCNP (Monte Carlo N-Particle) presents a 3-4 mm image resolution; however, such resolution limits some thin body structure discrimination, such as skin. In this context, this work proposes a calculus routine that discriminates this region with thickness and localization in the voxel phantoms similar to the real, leading to an accurate dosimetric skin dose assessment by the MCNP code. Moreover, this methodology consists in manipulating the voxel phantoms volume elements by segmenting and subdividing it in different skin thickness. In addition to validate the skin dose calculated data, a set of experimental evaluations with thermoluminescent dosimeters were performed in an anthropomorphic phantom. Due to significant differences observed on the dose distribution of several skin representations, it was found that is important to discriminate the skin thickness similar to the real. The presented methodology is useful to obtain an accurate skin dosimetric evaluation for several radiotherapy procedures, with particular interest on the electron beam radiotherapy, in which highlights the whole body irradiation therapy (TSET), a procedure under implementation at the Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo (HC-FMUSP).

The South African government’s integrated resource plan for electricity IRP2010 states that the country plans to have an additional 9.6 GW of nuclear power on the national electricity grid by 2030. In support of this, the NRF-funded SARChI Research Chair in Nuclear Engineering within the School of Mechanical and Nuclear Engineering at the North-West University recently initiated research studies focused on Light Water Reactor (LWR) systems. These studies inter alia involve coupled neutronic and thermal hydraulic analyses of selected LWR systems. This study focuses on the steady state neutronic analysis of the European Pressurised Reactor (EPR) using Monte-Carlo N-Particle (MCNP5). The neutronic model will in due course be coupled to a thermal hydraulic model forming part of a broader study of the system. The Monte Carlo neutron transport code MCNP5 has been widely used since the 1950s for analysis of existing and future reactor systems due to its ability to simulate complex fuel assemblies without making any significant approximations. The primary aim of the study was to develop an input model for a representative fresh fuel assembly of the US EPR reactor core from which the fluxes and fission power of the reactor can be obtained. There after a 3D model of full EPR core developed by the school of mechanical and nuclear engineering based on findings of this work is also tested. The results are compared to those in the US EPR Final Safety Analysis Report. Agreement in major core operational parameters including the keff eigenvalue, axial and radial power profiles and control rod worth are evaluated, from which consistency of the model and results will be confirmed. Further convergence of the model within a reasonable time is assessed. / MSc (Engineering Sciences in Nuclear Engineering), North-West University, Potchefstroom Campus, 2014

The South African government’s integrated resource plan for electricity IRP2010 states that the country plans to have an additional 9.6 GW of nuclear power on the national electricity grid by 2030. In support of this, the NRF-funded SARChI Research Chair in Nuclear Engineering within the School of Mechanical and Nuclear Engineering at the North-West University recently initiated research studies focused on Light Water Reactor (LWR) systems. These studies inter alia involve coupled neutronic and thermal hydraulic analyses of selected LWR systems. This study focuses on the steady state neutronic analysis of the European Pressurised Reactor (EPR) using Monte-Carlo N-Particle (MCNP5). The neutronic model will in due course be coupled to a thermal hydraulic model forming part of a broader study of the system. The Monte Carlo neutron transport code MCNP5 has been widely used since the 1950s for analysis of existing and future reactor systems due to its ability to simulate complex fuel assemblies without making any significant approximations. The primary aim of the study was to develop an input model for a representative fresh fuel assembly of the US EPR reactor core from which the fluxes and fission power of the reactor can be obtained. There after a 3D model of full EPR core developed by the school of mechanical and nuclear engineering based on findings of this work is also tested. The results are compared to those in the US EPR Final Safety Analysis Report. Agreement in major core operational parameters including the keff eigenvalue, axial and radial power profiles and control rod worth are evaluated, from which consistency of the model and results will be confirmed. Further convergence of the model within a reasonable time is assessed. / MSc (Engineering Sciences in Nuclear Engineering), North-West University, Potchefstroom Campus, 2014

Master of Science / Department of Mechanical and Nuclear Engineering / William L. Dunn / This report investigates the feasibility of a standoff interrogation method to identify nitrogen-rich explosive samples shielded by other materials (“clutter”) using neutron beams from Cf-252 and deuterium-tritium (D-T) generator sources. Neutrons from the beams interact with materials in the target to produce inelastic-scatter gamma rays, and, after slowing down to thermal energies, prompt-capture gamma rays. By detection of these gamma rays, a response vector is formed that is used to calculate a figure-of-merit, whose value is dependent upon the contents of the target. Various target configurations, which include an inert-material shield and a sample that may or may not be explosive, were simulated using the MCNP5 code. Both shielding and collimation of 14.1-MeV neutron beams were simulated to produce effective neutron beams for target interrogation purposes and to minimize dose levels. Templates corresponding to particular target scenarios were generated, and their effectiveness at nitrogen-rich explosive identification was explored. Furthermore, methods were proposed yielding more effective templates including grouping target responses by density and composition. The results indicate that neutron-based interrogation has potential to detect shielded nitrogen-rich explosives. The research found that using a tiered filter approach, in which a sample must satisfy several template requirements, achieved the best results for identifying the explosive cyclonite (RDX). A study in which a 14.1-MeV neutron beam irradiated a target containing a shielded sample, which could either be explosive (RDX) or inert, yielded no false negatives and only 2 false positives over a large parameter space of clutter-sample combination.

Master of Science / Department of Mechanical and Nuclear Engineering / Jeremy Roberts / The reactivity method is an indirect nondestructive technique to estimate integral burnup in fuel elements. In this method, the assumption is made that reactivity worth of a fuel element is a known function of burnup, often a linear relationship. When a fuel element burns, reactivity is reduced due to depletion of fissile actinides and generation of neutron-absorbing fission products. Currently, there is a lack of experimental data to verify the current composition of the KSU TRIGA (Training Research Isotopes General Atomics) fuel. Moreover, the KSU TRIGA Mark II staff method of estimating burnup is admittedly inaccurate due to its simple approximations. This work presents the positive period technique as convenient method use only the excess reactivity of the KSU core to compute reactivity via the inhour equation. Period measurements are determined via extraction and manipulation of the time dependent power data in the measurements. MCNP and Serpent modeling codes are both used extract the neutron kinetics parameters necessary in the inhour equation. Seven axial discretization of the KSU fuel was modeled, which minimizes the reactivity biases as function of burnup. Moreover, two unit cell models of the KSU TRIGA fuel were investigated. Modeled reactivity worths were computed using the KCODE in MCNP for comparative analysis. The burnup steps using two power peaking factor methods were developed to account for the biases introduced initial burnup of fuel prior to installation at KSU. By using the error distribution given by the two method to generate 200 test cases of the burnup steps can yield to reactivity worths as a function of burnup with quantifiable uncertainties. Finally, the results suggest that validation from another nondestructive technique such as gamma spectroscopy is necessary to asses the reactivity biases observed for higher burnup fuel elements due to unknown radial orientations. This work ultimately supports the production of a high-fidelity model of the KSU reactor.

The computational ability to accurately predict the dynamic behavior of a nuclear reactor core in response to reactivity-induced perturbations is an important subject in the field of reactor physics. Space-time and point kinetics methodologies were developed for the purpose of studying the transient-induced behavior of the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor’s (HFIR) compact core. The space-time simulations employed the three-group neutron diffusion equations, which were solved via the COMSOL partial differential equation coefficient application mode. The point kinetics equations were solved with the PARET code and the COMSOL ordinary differential equation application mode. The basic nuclear data were generated by the NEWT and MCNP5 codes and transients initiated by control cylinder and hydraulic tube rabbit ejections were studied. The space-time models developed in this research only consider the neutronics aspect of reactor kinetics, and therefore, do not include fluid flow, heat transfer, or reactivity feedback. The research presented in this dissertation is the first step towards creating a comprehensive multiphysics methodology for studying the dynamic behavior of the HFIR core during reactivity-induced perturbations. The results of this study show that point kinetics is adequate for small perturbations in which the power distribution is assumed to be time-independent, but space-time methods must be utilized to determine localized effects. En route to developing the kinetics methodologies, validation studies and methodology updates were performed to verify the exercise of major neutronic analysis tools at the HFIR. A complex MCNP5 model of HFIR was validated against critical experiment power distribution and effective multiplication factor data. The ALEPH and VESTA depletion tools were validated against post-irradiation uranium isotopic mass spectrographic data for three unique full power cycles. A TRITON model was developed and used to calculate the buildup and reactivity worth of helium-3 in the beryllium reflector, determine whether discharged beryllium reflectors are at transuranic waste limits for disposal purposes, determine whether discharged beryllium reflectors can be reclassified from hazard category 1 waste to category 2 or 3 for transportation and storage purposes, and to calculate the curium target rod nuclide inventory following irradiation in the flux trap.

A new model for an adult human gastrointestinal tract (GIT) has been developed for use in internal dose estimations to the wall of the GIT and to the other organs and tissues of the body from radionuclides deposited in the lumenal contents of the five sections of the GIT. These sections were the esophagus, stomach, small intestine, upper large intestine, and the lower large intestine. The wall of each section was separated from its lumenal contents. Each wall was divided into many small regions so that the histologic and radiosensitive variations of the tissues across the wall could be distinguished. The characteristic parameters were determined based on the newest information available in the literature. Each of these sections except the stomach was subdivided into multiple subsections to include the spatiotemporal variations in the shape and characteristic parameters. This new GIT was integrated into an anthropomorphic phantom representing both an adult male and a larger-than-average adult female. The current phantom contains 14 different types of tissue. This phantom was coupled with the MCNP 4C Monte Carlo simulation package. The initial design and coding of the phantom and the Monte Carlo treatment employed in this study were validated using the results obtained by Cristy and Eckerman (1987). The code was used for calculating specific absorbed fractions (SAFs) in various organs and radiosensitive tissues from uniformly distributed sources of fifteen monoenergetic photons and electrons, 10 keV - 4 MeV, in the lumenal contents of the five sections of the GIT. The present studies showed that the average photon SAFs to the walls were significantly different from that to the radiosensitive cells (stem cells) for the energies below 50 keV. Above 50 keV, the photon SAFs were found to be almost constant across the walls. The electron SAF at the depth of the stem cells was a small fraction of the SAF routinely estimated at the contents-mucus interface. Electron studies showed that the “self-dose” for the energies below 300 keV and the “cross-dose” below 2 MeV were only from bremsstrahlung and fluorescent radiations at the depth of the stem cells and were not important.

Tritium is a radioactive hydrogen isotope that is typically produced via neutron interaction with heavy water (D2O), producing tritiated water (DTO). As a result of this, tritium accounts for roughly a third of all occupational exposures at a CANDU type nuclear power plant. This identifies a need to study the biological effects associated with tritium (and low energy electrons in general). However, there are complications regarding the dosimetry of tritium, as well as difficulties in handling and using tritium for the purposes of biophysics experiments. To avoid these difficulties, an experiment has been proposed using photons to mimic the beta decay energy spectrum of tritium. This would allow simulation of the radiation properties of tritium, so that a surrogate photon source can be used for biophysics experiments. Through experimental and computational means, this work has explored the use of characteristic x-rays of various materials to modify the output spectrum of an x-ray source, such that it mimics the tritium beta decay spectrum. Additionally, the resultant primary electron spectrum generated in water from an x-ray source was simulated. The results from this research have indicated that the use of characteristic x-rays is not a viable method for simulating a tritium source. Also, the primary electron spectrum generated in water shows some promise for simulating tritium exposure, however further work must be done to investigate the slowing down electron spectrum. / UOIT