<p>This thesis presents MCNPX simulations of the SCANDAL set-up used at the Theodor Svedberg Laboratory for neutron scattering cross-section measurements. The thesis describes processes and data important for the upcoming off-line data analysis. In the experiment, neutrons scattered off the target are converted to protons which are stopped in scintillator crystals. The results of presented simulations include a description of the proton spectra in dependence of the neutron-to-proton conversion angle, calculation of the hit position gates and a study of the converter describing the role of its chemical composition and also the role of other plastic scintillator on the proton spectra.</p> / QC 20100520

The objective of this research was to develop a complex MCNPX model of the human head to predict absorbed dose distributions during proton therapy of ocular tumors. Absorbed dose distributions using the complex geometry were compared to a simple MCNPX model of the human eye developed by Oertli. The proton therapy beam used at Laboratori Nazionali del Sud-INFN was chosen for comparison. Dose calculations included dose due to proton and secondary interactions, multiple coulombic energy scattering, elastic and inelastic scattering, and non-elastic nuclear reactions. Benchmarking MCNPX was accomplished using the proton simulations outlined by Oertli. Once MCNPX was properly benchmarked, the proton beam and MCNPX models were combined to predict dose distributions for three treatment scenarios. First, an ideal treatment scenario was modeled where the dose was maximized to the tumor volume and minimized elsewhere. The second situation, a worst case scenario, mimicked a patient starring directly into the treatment beam during therapy. During the third simulation, the treatment beam was aimed into the bone surrounding the eye socket to estimate the dose to the vital regions of the eye due to scattering. Dose distributions observed for all three cases were as expected. Superior dose distributions were observed with the complex geometry for all tissues of the phantom and the tumor volume. This study concluded that complex MCNPX geometries, although initially difficult to implement, produced superior dose distributions when compared to simple models.

The objective of this research was to develop a complex MCNPX model of the human head to predict absorbed dose distributions during proton therapy of ocular tumors. Absorbed dose distributions using the complex geometry were compared to a simple MCNPX model of the human eye developed by Oertli. The proton therapy beam used at Laboratori Nazionali del Sud-INFN was chosen for comparison. Dose calculations included dose due to proton and secondary interactions, multiple coulombic energy scattering, elastic and inelastic scattering, and non-elastic nuclear reactions. Benchmarking MCNPX was accomplished using the proton simulations outlined by Oertli. Once MCNPX was properly benchmarked, the proton beam and MCNPX models were combined to predict dose distributions for three treatment scenarios. First, an ideal treatment scenario was modeled where the dose was maximized to the tumor volume and minimized elsewhere. The second situation, a worst case scenario, mimicked a patient starring directly into the treatment beam during therapy. During the third simulation, the treatment beam was aimed into the bone surrounding the eye socket to estimate the dose to the vital regions of the eye due to scattering. Dose distributions observed for all three cases were as expected. Superior dose distributions were observed with the complex geometry for all tissues of the phantom and the tumor volume. This study concluded that complex MCNPX geometries, although initially difficult to implement, produced superior dose distributions when compared to simple models.

This thesis presents MCNPX simulations of the SCANDAL set-up used at the Theodor Svedberg Laboratory for neutron scattering cross-section measurements. The thesis describes processes and data important for the upcoming off-line data analysis. In the experiment, neutrons scattered off the target are converted to protons which are stopped in scintillator crystals. The results of presented simulations include a description of the proton spectra in dependence of the neutron-to-proton conversion angle, calculation of the hit position gates and a study of the converter describing the role of its chemical composition and also the role of other plastic scintillator on the proton spectra. / QC 20100520

A benchmark experiment was designed and conducted that irradiated two small volume mercury targets at the Weapon Neutron Research facility at the Los Alamos Neutron Science Center with 800 MeV protons. Following irradiation the production cross sections of 53 medium and longer-lived spallation residuals using gamma spectroscopy at various decay times up to a year were determined. The measured cross sections were then compared with predicted cross sections from the MCNPX code. After acquisition of the gamma spectroscopy data the targets were drained and disassembled to study the distribution and the deposition of the spallation residuals.

<p>Gamma ray spectroscopy has provided enormous amounts of information on the behaviour and structure of atomic nuclei [SHA88, BEA92, EBE08]. Most of the major discoveries in experimental nuclear physics over the last five decades are strongly associated with improvements in detector technologies. Inorganic scintilators led to the discovery in 1963 of the first excited states of a rotational band based on the ground state of 162Dy. Improvements in peak-to-background ratios and detector resolutions obtained with germanium led to the first evidence of backbending which is associated with a two quasi-particle excitation in 162Dy [SHA88]. More recently the development of composite and highly-segmented Ge detectors has significantly increased the performance and power of detection systems. The Clover detector is such a detector system and is in use at iThemba LABS. This study concerns the evaluation of the particle transport code MCNPX 2.5.0 as a tool to model complex composite detectors such as the Clover. Lanthanum silicate (LSO) and Lead tungstate (PbWO) are also evaluated as possible suppressor shield materials. It is shown that reasonable agreement between experiment and simulation is found when the experiment is accurately reproduced. However, when complex detection modes are implemented in the detector based on the number of elements that fire, MCNPX cannot be used to model the detector performance exactly. Differences between simulated and experimental results are found in suppressed add-back mode. It is proposed that the discrepancies are due to limitations in implementation of the pulse-height and special anti-coincidence tally in MCNPX. LSO and PbWO are compared to BGO as suppressor shield materials. It is found that LSO is not an ideal material for a suppression shield. PbWO is shown to give performance values similar to that of BGO. The back-plug is shown to have no effect on the Peak-to-Total ratio but is effective at reducing the background at lower energies.</p>

Proton beam radiotherapy is an emerging treatment tool for cancer. Its basic principle is to use a high-energy proton beam to deposit energy in a tumor to kill the cancer cells while sparing the surrounding healthy tissues. The therapeutic proton beam can be either a broad beam or a narrow beam. In this research, we mainly focused on the design and simulation of the broad beam produced by a passive double-scattering system in a treatment nozzle. The NEU codes package is a specialized design tool for a passive double-scattering system in proton beam radiotherapy. MCNPX is a general-purpose Monte Carlo radiation transport code. In this research, we used the NEU codes package to design a passive double-scattering system, and we used MCNPX to simulate the transport of protons in the nozzle and a water phantom. We used "mcnp_pstudy" script to create successive input files for different steps in a range modulation wheel for SOBP to overcome the difficulty that MCNPX cannot be used to simulate dynamic geometries. We used "merge_mctal" script, "gridconv" code, and "VB script embedded in Excel" to process the simulation results. We also invoked the plot command of MCNPX to draw the fluence and dose distributions in the water phantom in the form of two-dimensional curves or color contour plots. The simulation results, such as SOBP and transverse dose distribution from MCNPX are basically consistent with the expected results fulfilling the design aim. We concluded that NEU is a powerful design tool for a double-scattering system in a proton therapy nozzle, and MCNPX can be applied successfully in the field of proton beam radiotherapy.

<p>Gamma ray spectroscopy has provided enormous amounts of information on the behaviour and structure of atomic nuclei [SHA88, BEA92, EBE08]. Most of the major discoveries in experimental nuclear physics over the last five decades are strongly associated with improvements in detector technologies. Inorganic scintilators led to the discovery in 1963 of the first excited states of a rotational band based on the ground state of 162Dy. Improvements in peak-to-background ratios and detector resolutions obtained with germanium led to the first evidence of backbending which is associated with a two quasi-particle excitation in 162Dy [SHA88]. More recently the development of composite and highly-segmented Ge detectors has significantly increased the performance and power of detection systems. The Clover detector is such a detector system and is in use at iThemba LABS. This study concerns the evaluation of the particle transport code MCNPX 2.5.0 as a tool to model complex composite detectors such as the Clover. Lanthanum silicate (LSO) and Lead tungstate (PbWO) are also evaluated as possible suppressor shield materials. It is shown that reasonable agreement between experiment and simulation is found when the experiment is accurately reproduced. However, when complex detection modes are implemented in the detector based on the number of elements that fire, MCNPX cannot be used to model the detector performance exactly. Differences between simulated and experimental results are found in suppressed add-back mode. It is proposed that the discrepancies are due to limitations in implementation of the pulse-height and special anti-coincidence tally in MCNPX. LSO and PbWO are compared to BGO as suppressor shield materials. It is found that LSO is not an ideal material for a suppression shield. PbWO is shown to give performance values similar to that of BGO. The back-plug is shown to have no effect on the Peak-to-Total ratio but is effective at reducing the background at lower energies.</p>

When astronauts travel in space, their primary health hazards are high-energy cosmic radiations from galactic cosmic rays (GCR). Most galactic cosmic rays have energies between 100 MeV and 10 GeV. For occupants inside of a space shuttle, the structural material is efficient to absorb most of the cosmic-ray energy and reduce the interior dose rate to below 1.2 mGy per day. However, the biological effects of prolonged exposure to low-dose radiation are not well understood. The purpose of this research was to examine the feasibility of constructing a low-dose irradiation facility to simulate the uniform radiation field that exists in space. In this research, we used a pre-manufactured incubator, specifically the Thermo Scientific Forma Series II Water Jacketed CO2 Incubator, to act as shielding and simulate the exterior of the space shuttle. To achieve the desired dose rate (< 1 mGy/h) inside the incubator volume, the computer code MCNPX was used to determine required source activity and distance between the shielding and source. Once the activity and distance were calculated, an experiment was carried out to confirm the simulation results. The confirmation used survey meters and thermoluminescence dosimeters (TLDs) to map the radiation field within the incubator.

Submitted by Almir Azevedo (barbio1313@gmail.com) on 2018-04-25T12:46:52Z No. of bitstreams: 1 dissertação mestrado ien 2018 William Luna Salgado.pdf: 2344749 bytes, checksum: ea9367443eda44509d009585d80f788c (MD5) / Made available in DSpace on 2018-04-25T12:46:52Z (GMT). No. of bitstreams: 1 dissertação mestrado ien 2018 William Luna Salgado.pdf: 2344749 bytes, checksum: ea9367443eda44509d009585d80f788c (MD5) Previous issue date: 2018-02 / Os oleodutos são sistemas de dutos interconectados utilizados no transporte de grandes quantidades de petróleo e seus derivados, são mais econômicos, eliminam a necessidade de estocagens e, além disso, apresentam grande segurança na operação minimizando a possibilidade de perdas ou roubos. Em muitos casos, especialmente na indústria petroquímica, a mesma linha de transporte é usada para transportar mais do que um tipo de produto (poliduto), tais como: gasolina, diesel e querosene. Na operação de um poliduto existe uma sequência de produtos a serem transportados e durante a troca do produto, ainda existem frações de volume do produto anterior ocorrendo, desta forma, contaminações. A solução tradicional é descartar todo este volume, no entanto é importante identificar precisamente esta região visando reduzir os custos de reprocessamento e tratamento dos produtos descartados. Este trabalho apresenta uma metodologia para avaliar a sensibilidade da técnica de densitometria gama na identificação precisa da região de interface aperfeiçoando o transporte de subprodutos do petróleo em polidutos. O estudo considerou uma geometria composta por uma fonte de 137Cs, uma tubulação de acrílico medindo 8,0 cm de diâmetro e um detector de NaI(Tl) 1x1” ”, um posicionado diametralmente oposto a fonte de radiação para medir o feixe transmitido. Utilizando simulações computacionais por meio do método de Monte Carlo com o código MCNPX foi proposta uma geometria de medição que apresentasse a maior sensibilidade para o cálculo das frações de volume. Os dados técnicos pertinentes (dimensões e materiais) para realizar a simulação dos detectores foram baseadas em informações obtidas a partir da técnica de gamagrafia. O estudo teve uma validação teórica por meio de equações analíticas e os resultados mostram que é possível identificar a região de interface com precisão de equivalente a 1%. / Pipelines are interconnected ducts systems used to transport large quantities of petroleum and its by-products, are more economical, eliminate the need for stocks and, in addition, present great safety in operation minimizing the possibility of loss or theft. In many cases, especially in the petrochemical industry, the same transport line is used to carry more than one type of product (poliduct), such as: gasoline, diesel and kerosene. In the operation of a poliduct there is a sequence of products to be transported and during the exchange of the product, there are still fractions of volume of the previous product thus occurring contaminations. The traditional solution is to discard all this volume; however it is important to identify precisely this region in order to reduce the costs of reprocessing and treatment of discarded products. This work presents a methodology to evaluate the sensitivity of the gamma densitometry technique in the precise identification of the interface region by optimizing the transportation of petroleum by - products into polyducts. The study considered geometry composed of a source of 137Cs, an acrylic tubing measuring 8.0 cm in diameter and a 1x1 "NaI (T1) detector, a position diametrically opposed to a radiation source to measure the transmitted beam. Using computational simulations using the Monte Carlo method with the MCNPX code, measurement geometry with the highest sensitivity for the calculation of volume fractions was proposed. The pertinent technical data (dimensions and materials) to perform the simulation of the detectors were based on information obtained from the gammagraphy technique. The study had a theoretical validation through analytical equations and the results show that it is possible to identify the interface region with an accuracy of 1%.