Dissertations / Theses on the topic 'Shielding (Radiation)'

This thesis discusses the development, benchmarking and applications of activation dose analysis methods for fusion devices. The development and code logic of the Mesh Coupled Rigorous 2 Step (MCR2S) system is discussed. Following the development of the code, appropriate benchmarking studies were performed on the Frascati neutron generator, and revealed that the code was able to predict shutdown gamma ray doserates to within ±3% of experimentally determined values, for decay times between 3×105 and 107 seconds. The development of the Ion Cyclotron Resonance Heater (ICRH) with regards to neutronics was discussed. The ICRH went through a number of design stages and shutdown gamma ray dose rates were determined for each stage. It was determined that of all the designs analysed only one of them, the first concept design for the internally matched design did not meet the shutdown dose criteria. This was due to a flaw in the system design, brought about by a lack of consideration towards nuclear design. The ITER Light Imaging Detection and Ranging (LIDAR) system was subjected to a full shutdown nuclear analysis. It was found that the design of the LIDAR system supplied did not meet the ITER required shutdown gamma ray dose rate limit of 100 µSvhr−1, however use of the MCR2S system highlighted the components that contributed most to the shutdown gamma ray dose rate and were shown to be the mirror holder and the laser beam pipe. Future designs should include additional shielding around the beam pipe.

This study seeks to provide a novel approach for producing technologically viable new radiation shielding materials to meet the safety requirements for use in medical X-ray imaging facilities. The approach was based on dispersing micro-sized and nano-sized heavy element fillers into polymeric materials using different filler dispersion methods such as melt-mixing, ion implantation and electrospinning. These materials have high potential application for shielding of X-rays in diagnostic radiology purposes.

Beyond the protective confines of Earth's atmosphere and magnetosphere, spacecraft are subject to constant bombardment by high-energy charged particles originating from our Sun in the form of Solar Particle Events (SPEs), and from outside the solar system in the form of Galactic Cosmic Rays (GCRs). The harm these particles do can be reduced or mitigated outright through radiation shielding. Because protons and other charged particles comprise most of these radiation particles, strong magnetic fields could be generated around spacecraft to deflect incoming charged radiation particles. This thesis investigates the performance of specific configurations of toroidal superconducting solenoids to generate magnetic fields that deflect incoming energetic protons via the Lorentz force. Bulk material shielding configurations using various thicknesses of liquid water are similarly investigated, as are combination shielding configurations combining the best-performing toroidal shielding configurations with a small bulk material shield surrounding the spacecraft. The water shielding configurations tested included shields of uniform thicknesses from 1 cm to 10 cm surrounding an Apollo CSM-sized cylindrical candidate spacecraft. Water shielding was found to be very effective at reducing the SPE dose, from a 86\% reduction at 1 cm of water to a 94\% reduction at 10 cm. However water shielding was found to be minimally effective against the much higher energy Galactic Cosmic Ray protons, with no dose reduction at 1 cm and a paltry 1\% reduction at 10 cm. The toroidal shielding geometric configurations tested consisted of either 5 or 10 primary toroidal shields surrounding the candidate spacecraft, as was the addition of smaller nested toroidal shields inside the primary toroids and of toroids on the spacecraft's endcaps. The magnetic field strengths tested were 1.7 Tesla, 8.5 Tesla, and 17 Tesla. The best geometric configurations of electrodynamic shielding consisted of 5 primary toroidal shields, 5 total nested shields placed inside the primary toroids, and 2 total shields on the spacecraft's endcaps. The second best geometric configuration consisted of 10 primary toroidal shields plus two total endcap shields. These configurations at 1.7 Tesla reduced the SPE dose by 87\% and 87\%, and reduced the GCR dose by 11\% and 10\%. At 17 Tesla, these configurations both reduced the SPE dose by 90\%, and reduced the GCR dose by 76\% and 61\%. Combining these two configurations with a 1 cm-thick shield of water improved performance against SPE protons to 95\% and 93\% at 1.7 Tesla, and a 97\% and 96\% reduction at 17 Tesla. GCR dose reductions decreased slightly. Passive material shielding was found capable of providing substantial protection against SPE protons, but was minimally effective against GCR protons without very thick shielding. Electrodynamic shielding, at magnetic field strengths of 1.7 Tesla, was found to be similarly effective against SPE protons, and marginally more effective against GCR protons. Combining the best toroidal shielding configurations, at magnetic field strengths of 1.7 Tesla, with water shielding yielded high protection against SPE protons, but still marginal protection against GCR protons. Increasing the magnetic field strength to 17 Tesla was found to provide very high protection against SPE protons, and to significantly reduce the radiation dose from GCR protons. Of all shielding configurations tested, only those electrodynamic configurations with magnetic fields of 17 Tesla were able to reduce the GCR dose by more than half.

This paper focused on two significant space forces that can affect the success of a spacecraft: the radiation and micrometeoroid environments. Both are looked at in the context of the region of space between Earth and Mars. The goal was create reference environments, to provide context to results of environmental modeling, and to provide recommendations to assist in early design decisions of interplanetary spacecraft. The radiation section of this report used NASA's OLTARIS program to generate data for analysis. The area of focus was on the radiation effects for crewed missions, therefore effective dose equivalent was the metric used to compare different models of radiation and shielding. Test spheres with one, two, or three different materials layers were compared, along with modifiers such as alloys or weight vs. thickness emphasis. Results were compared to limits set by the European and Russian Space Agencies to provide context. The results hinged heavily on the intensity of the Solar Particle Events (SPEs), with testing using additional temporary radiation shielding proving to be a requirement for feasible shielding masses. Differences in shield material effectiveness were found to be negligible for thin Galactic Cosmic Rays (GCRs) and thick SPEs. Thick shields were found to perform better when the more efficient shield was on the outside of the test sphere. The micrometeoroid section used equations and programs from multiple sources to generate state vectors, flux, and finally impact models for four different case studies. Impacts v were generated with mass, velocity, and impact angle/location statistics. The mass and velocity results were run through statistical software to generate information such as mean and standard deviation with confidence intervals. Also looked at were higher mass impacts, limited to above 10-3 grams as opposed to above 10-6 for the regular case. The results of this show that very thin monolithic shields (0.1 cm-0.25 cm) could protect against the average 10-6 impact. The Ram, Nadir, and Anti-sun faces received the highest quantity of impacts and Wake received the least. When looking at the worst cases average mass and velocity for the high mass impacts significantly higher shielding was required to prevent penetration (up to 5 cm for some cases). However, the test cases had probabilities of no high mass impacts greater than 46% of the time, with shorter mission having greater chances of no high mass impacts.

Space radiation is one of the main showstoppers for human exploration of deep space. When leaving the protection provided by Earth’s atmosphere and magnetic field, the astronaut crew find themselves immersed into a complex radiation field, originated by the interaction of different high-energy radiation sources with the spacecraft’s walls, and characterized by many particle species with a broad range of energies. The biological effects of the long-term radiation exposure is largely uncertain and could give rise not only to late solid cancers and leukemia, but also to early effects to cardiac and nervous tissues, possibly undermining mission success. An available countermeasure to defend the astronauts from radiation is passive shielding, i.e. the interposition of shielding materials between the radiation sources and the exposed subjects. However, the majority of space radiation is practically impossible to completely stop: the high energetic particles constituting the space environment have the capability to penetrate several meters of materials, generating a harmful component of secondary particles, further contributing to the radiation dose. The ability of a material to attenuate the incoming space radiation and the nature of the generated secondary particles largely depends on the traversed material itself, in particular on the ratio between its charge and mass atomic numbers, Z/A. The lower is this ratio, the higher the material’s capability to attenuate the incoming radiation will be, both through electromagnetic and nuclear interactions. While the radiobiology community is focusing on the biological effects, radiation physics is trying to lower uncertainties characterizing the radiation interactions with materials, performing radiation measurements of various nature. In this framework I focused my PhD activity on the study of materials which could be used in space as shielding layers and multipurpose structures have been evaluated and selected under different criteria. At first, their ability to shield different kinds of space radiation were calculated with the aid of 1D Monte Carlo simulations, also followed by an evaluation of their structural and thermal proprieties, cost, availability and compatibility with the space environment. Simulations, in particular, were performed both to support the material selection process both to produce guidelines for design. The selected materials were then procured to be tested under different radiation beams and different set-ups, in single and multi-layers configurations, in an attempt to reproduce space exposure conditions. At the same time, the radiation tests have been reproduced by means of Monte Carlo simulations, to compare the experimental results and the simulations’ outputs, confirming the codes’ ability to reproduce radiation measurements involving High Z-number and high Energy (HZE) particles. For some materials, suggestions were provided on which nuclear model was better reproducing the data. The performed experimental campaign suggested that a candidate shielding material suitable for Galactic Cosmic Rays (GCR) should be tested with at least two beams with different characteristics, since the results indicated that some materials good at shielding 972 MeV/nuc 56Fe ions performed very poorly when irradiated with high energetic alphas. Furthermore, among the material types included in this investigation work, Lithium Hydride resulted the best option to stop space radiation, when only radiation shielding properties are considered. At the end of the experimental campaigns, on the basis of the test results, a 3D simulation activity has started and is still on-going and a modular space habitat model has been created. Monte Carlo simulations have been carried out, reproducing different Moon exposure scenarios with the goal of calculating crew radiation exposure during a Moon surface mission. This work reports results only for a standard aluminum habitat, with only Moon soil used as shielding material. However, future simulations will include Lithium Hydride and possibly others materials as shielding layers, to evaluate their effectiveness in reducing the dose in a realistic exposure scenario. Preliminary results show that even with a heavily shielded spacecraft (the habitat taken in consideration in this work is providing from every direction at least 30 g/cm2 of aluminum equivalent) radiation exposure approaches values close to the existing annual radiation exposure limits. Part of this thesis’ work was done at Thales Alenia Space, using Thales Alenia Space infrastructures and in the framework of the ROSSINI2 study. The ROSSINI2 study has been supported by European Space Agency (ESA) under the contract RFP IPLPTE/LF/mo/942.2014 and with the generous support of NASA and BNL, providing beam time at the NSRL facility.

As space technologies continue to develop rapidly, there is a common desire to launch astronauts beyond the ISS to return to the Moon and put human footsteps on Mars. One of the largest hurdles that still needs to be addressed is the protection of astronauts from the radiation environment seen in deep space. The most effective way to defend against radiation is increasing the thickness of the shield, however this is limited by strict mass requirements. In order to increase the thickness of the shield, it is beneficial to make mission critical items double as shielding material. The human rated Orion spacecraft has procedures in place for astronauts to create an emergency bunker using food and water in the event of a forewarned radiation storm. This can provide substantial support to defend against radiation storms when there is an adequate amount of warning time, however, fails to protect against Galactic Cosmic Radiation (GCR) or Solar Particle Events (SPE) without sufficient warning. Utilizing these materials as a permanent shielding method throughout the mission could be a beneficial alternative to the Orion programs current protection plan to provide constant safety to the crew. This thesis analyzes the effect in the radiation dosage seen by astronauts in the Orion Crew Module through use of on-board water as a permanent shielding fixture. The primary method used to analyze radiation is NASA’s OLTARIS (On-Line Tool for the Assessment of Radiation In Space) program, which enables users to input thickness distributions to determine a mission dosage profile. In addition this thesis further develops a ray tracing code which enables users to import male and female models into the vehicle model to produce gender specific radiation dosage results. The data suggests the permanent inclusion of water as a shielding material provides added support for GCR as well as SPE radiation that can extend the mission lifetime of humans in space.

Radiation shielding materials are an essential component of long-term space travel and habitation. The mission to Mars will require a radiation shielding material that can be produced on Mars through energy and cost-efficient means. in this study, Martian regolith simulant and hydrogen-rich polymers are used to create a radiation shielding material in the form of bricks. The bricks are capable of shielding against galactic cosmic radiation on Mars. There are three methods in which the bricks were formed: 1) a heated press, 2) a microwave oven in a CO2 atmosphere, and 3) a vacuum oven with a low CO2 pressure. Each brick varies by the type of polymer, percent of polymer, and the method in which it was made. Flexural tests were conducted on the bricks to determine the flexural strength, flexural strain, and modulus of elasticity. OLTARIS was used to estimate the effectiveness of these bricks to shield against GCR on the Martian surface.

In this study, the effects of proton irradiation on carbon nanotube (CNT)-epoxy composites are investigated for potential applications in radiation shielding for spacecraft. CNT-epoxy composites were prepared using multiwall and single wall CNTs and exposed to proton beams of energies ranging from 6 MeV to 12 MeV. The nanocomposites shielding capabilities against the different energetic proton beams were measured by tracking the beam's energy before and after penetrating the samples. The microstructures of the samples were characterized using scanning electron microscopy (FESEM). The effect of proton irradiation on the electrical resistivity was measured using a high resolution multimeter. Finally the influence of the irradiation on the mechanical properties, such as the elastic modulus and hardness, was probed using instrumented nanoindentation tests. The proton stopping power of the epoxy was shown to be unchanged by the addition of CNTs, which is a promising result since the hardness of the samples was shown to be increased by addition of CNTs. Unfortunately, however, the surface of the samples proved to be too rough for nanoindentation to yield more detailed results. This was due to the use of a diamond saw in cutting the samples to size. The addition of CNTs was shown to reduce the volume electrical resistivity of the neat epoxy by almost five orders of magnitude and the irradiation further reduced it by a factor of 2-16.
Master of Science

In shielding design of a radiotherapy treatment room, the requirements of dose limits outside the room must be fulfilled. The primary beam from the linear accelerator, the leakage radiation from the gantry and the scattered radiation from the patient and other objects contribute to the radiation exposure outside the room. In this dissertation, we focused on the scattered radiation from the patient irradiated by the primary radiation beam including 6, 10 and 25 MV from an Elekta Precise linear accelerator. By using Monte Carlo simulations, we analysed the characteristics of the scattered radiation, so that we have better understanding of the scattered radiation when designing the shielding of a treatment room. The angular distributions and energy spectrum of the scattered radiation are presented. It was found that both the number of scatter particles and energy of the scatter particles increase with increasing primary beam energy and decreasing scatter angle. We also performed Monte Carlo simulations to collect the transmission data of scattered particles passing through the shielding wall made of the concrete commonly used in Hong Kong. The simulated results are tabulated and could be used for radiation protection purposes for the estimation of the radiation exposure behind the shielding concrete wall due to the patient scattered radiation.
published_or_final_version
Medical Sciences
Master
Master of Medical Sciences

In the following work, the MAVRIC sequence of the Scale6.1 code package was tested for its efficacy in calculating a wide range of shielding parameters with respect to HTGRs. One of the NGNP designs that has gained large support internationally is the VHTR. The development of the Scale6.1 code package at ORNL has been primarily directed towards supporting the current United States' reactor fleet of LWR technology. Since plans have been made to build a prototype VHTR, it is important to verify that the MAVRIC sequence can adequately meet the simulation needs of a different reactor technology. This was accomplished by creating a detailed model of the VHTR power plant; identifying important, relevant radiation indicators; and implementing methods using MAVRIC to simulate those indicators in the VHTR model. The graphite moderator used in the design shapes a different flux spectrum than water-moderated reactors. The different flux spectrum could lead to new considerations when quantifying shielding characteristics and possibly a different gamma-ray spectrum escaping the core and surrounding components. One key portion of this study was obtaining personnel dose rates in accessible areas within the power plant from both neutron and gamma sources. Additionally, building from professional and regulatory standards a surveillance capsule monitoring program was designed to mimic those used in the nuclear industry. The high temperatures were designed to supply heat for industrial purposes and not just for power production. Since tritium, a heavier radioactive isotope of hydrogen, is produced in the reactor it is important to know the distribution of tritium production and the subsequent diffusion from the core to secondary systems to prevent contamination outside of the nuclear island. Accurately modeling indicators using MAVRIC is the main goal. However, it is almost equally as important for simulations to be carried out in a timely manner. MAVRIC uses the discrete ordinates method to solve the fixed-source transport equation for both neutron and gamma rays on a crude geometric representation of the detailed model. This deterministic forward solution is used to solve an adjoint equation with the adjoint source specified by the user. The adjoint solution is then used to create an importance map that can weight particles in a stochastic Monte Carlo simulation. The goal of using this hybrid methodology is to provide complete accuracy with high precision while decreasing overall simulation times by orders of magnitude. The MAVRIC sequence provides a platform to quickly alter inputs so that vastly different shielding studies can be simulated using one model with minimal effort by the user. Each separate shielding study required unique strategies while looking at different regions in the VHTR plant. MAVRIC proved to be effective for each case.

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Dissertacao [Mestrado]
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares, Sao Paulo

Este trabalho de tese de doutorado visou identificar as matérias primas naturais produzidas no Brasil e possíveis de serem utilizadas na produção de concretos de elevada massa específica. Desenvolver uma metodologia para a caracterização, preparo, moldagem, ensaios para determinação do coeficiente de atenuação linear experimental, calculo do coeficiente de atenuação linear teórico, e determinação do Z efetivo, culminando com a confecção de um banco de dados embrionário para os concretos de elevada massa específica preparados com matérias primas nacionais. Para tanto foram identificadas onze matérias primas produzidas no Brasil com caracteísticas adequadas para a produção de concretos de elevada densidade. Apresentamos os fundamentos teóricos ao bom entendimento do trabalho tanto no campo da proteção radiológica como naquela dos conceitos que podem ser usados para a produção de blindagem às radiações gama e X. Preparamos vinte e dois tipos de concretos de elevada massa específica com a utilização de matérias primas naturais e nacionais. Os concretos desenvolvidos foram preparados, moldados e ensaiados com uma fonte de 137Cs, de 3,7 1010 Bq (1Ci) de atividade. Foram calculados os coeficientes de atenuação linear com a utilização das análises químicas dos concretos preparados e encontrados os coeficientes de atenução linear experimentais para comparação e avaliação da técnica proposta. Foram medidas as massas específicas dos concretos preparados em virtude de sua importância para a formação da seção de choque do composto quando da predominância do efeito Compton, e determinado o Z efetivo para a região predominante do efeito fotoelétrico. Por fim foram calculados os custos de produção levando-se em conta somente os custos das matérias primas. Para as massas específicas os concretos apresentaram uma variação de 2,74 kg/dm3 até 3,76 kg/dm3, já para o coeficiente de atenuação linear experimental a variação foi de 0,2137 cm-1 a 0,2860 cm-1, o Z efetivo variou de 19 a 25. Finalizando o trabalho foram discutidos os resultados e sugeridos preferências de concretos para utilização em blindagens com a aplicação de alguns conceitos. Comparando os resultados encontrados com vários outros publicados em trabalhos internacionais, verificamos o grau de similaridade.
This PhD thesis the natural raw materials produced in Brazil and in the production of high density concrete. Furthermore, we also develop a methodology for characterization, preparation, molding, testing to determine the linear attenuation coefficient of experimental, theoretical calculation of the linear attenuation coefficient, and determination of the effective Z, culminating with the production of an embryo stock data for the specific high density prepared with local raw materials. For this, we identified eleven raw materials produced in Brazil with suitable characteristics for the production of high density concrete. We present the theoretical understanding of radiological protection and in the fundamental concepts that can be used to produce shielding for gamma and X radiation. During the work, we prepared twenty-two concrete types of high specific weight, with the use of natural materials and domestic materials. These new concretes were prepared, molded and tested with a Cs-137 source (3.7.1010 Bq (1Ci) activity). The linear attenuation coefficients were calculated employing the chemical analyzes of the prepared concrete and the experimental linear attenuation coefficients were also determined for comparison and evaluation of the proposed technique. The specific masses of the concrete samples were determined, given their importance to the cross section for the Compton Effect predominance. The effective Z was also determined were the photoelectric effect was predominant. Finally, the production costs were considered, taking into account only the cost of the raw materials. For the specific masses, the concretes presented a variation from 2.74 kg/dm3 to 3.76 kg/dm3. In the case of the experimental linear attenuation coefficient the variation was from 0.2137 cm-1 to 0.2860 cm-1, and the effective Z varied from 19 to 25. As conclusion, the results were discussed e the preferred concretes for the shielding purposes were suggested. Comparing the results with other published international work, we find the degree of similarity.

Transport of low energy neutrons associated with the galactic cosmic ray cascade is analyzed in this dissertation. A benchmark quality analytical algorithm is demonstrated for use with B scRYNTRN, a computer program written by the High Energy Physics Division of N scASA Langley Research Center, which is used to design and analyze shielding against the radiation created by the cascade. B scRYNTRN uses numerical methods to solve the integral transport equations for baryons with the straight-ahead approximation, and numerical and empirical methods to generate the interaction probabilities. The straight-ahead approximation is adequate for charged particles, but not for neutrons. As N scASA Langley improves B scRYNTRN to include low energy neutrons, a benchmark quality solution is needed for comparison. The neutron transport algorithm demonstrated in this dissertation uses the closed-form Green's function solution to the galactic cosmic ray cascade transport equations to generate a source of neutrons. A basis function expansion for finite heterogeneous and semi-infinite homogeneous slabs with multiple energy groups and isotropic scattering is used to generate neutron fluxes resulting from the cascade. This method, called the F(N) method, is used to solve the neutral particle linear Boltzmann transport equation. As a demonstration of the algorithm coded in the programs M scGSLAB and M scGSEMI, neutron and ion fluxes are shown for a beam of fluorine ions at 1000 MeV per nucleon incident on semi-infinite and finite aluminum slabs. Also, to demonstrate that the shielding effectiveness against the radiation from the galactic cosmic ray cascade is not directly proportional to shield thickness, a graph of transmitted total neutron scalar flux versus slab thickness is shown. A simple model based on the nuclear liquid drop assumption is used to generate cross sections for the galactic cosmic ray cascade. The E scNDF/B V database is used to generate the total and scattering cross sections for neutrons in aluminum. As an external verification, the results from M scGSLAB and M scGSEMI were compared to A scNISN/P scC, a routinely used neutron transport code, showing excellent agreement. In an application to an aluminum shield, the F(N) method seems to generate reasonable results.

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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Medical radiation is estimated to contribute to over 200,000 deaths annually. Recent increases in the use of radiation-producing medical imaging examinations have led to increasing cumulative radiation dose to the general public. Multiple measures have been taken to address this alarming trend, including physician education, technologist education on dose reduction, and equipment-facilitated dose reduction techniques. Shield use can reduce the primary beam by up to 95%. Medical imaging technologists are the primary individuals responsible for applying shielding during an examination. Currently, literature shows that technologists are not shielding individuals as often as they should. After pilot testing, medical imaging technologists were recruited via email to participate in a national cross-sectional survey in September 2017. The survey contained items related to technologists’ demographics, shielding behaviors, and attitudes and beliefs measured at four social-ecological levels – intrapersonal, interpersonal, organizational, and community. The American Registry of Radiologic Technologists (ARRT) provided a list of technologists’ email addresses from their directory. One thousand six-hundred and sixty-one email notifications were sent out in the summer of 2017. Of those, 218 technologists (13%) completed the survey. Among technologists who considered their primary modality to be computed tomography (CT), organizational level factors were a positive significant predictor of shielding behavior. None of the four levels were significant in predicting shielding behavior among diagnostic radiological technologists (x-ray). Individual factors were significantly correlated to shielding behavior among radiologic technologists in the intrapersonal, organizational, and community levels. Study results indicated that interventions implemented at the organizational level may be most effective in increasing shield use among CT technologists. Additional research is needed to better understand factors affecting shield use among medical imaging technologists.

Proton therapy uses proton beams with energies of 70 – 230 MeV to treat cancerous tumours very effectively, while preserving surrounding healthy tissues as much as possible. During nuclear interactions of these protons with matter, secondary neutrons can be produced. These neutrons can have energies ranging up to the maximum energy of the protons and can thus be particularly difficult to attenuate. In fact, the rooms of a proton therapy facility are generally surrounded by concrete walls of at least ~2 m in thickness, in order to protect the members of the staff and the public from the stray radiation. Today, the design of the shielding walls is generally based on Monte Carlo simulations. Amongst the numerous parameters on which these simulations depend, some are difficult to control and are therefore selected in a conservative manner. Despite these conservative choices, it remains important to carry out accurate neutron dose measurements inside proton therapy facilities, in order to assess the effectiveness of the shielding and the conservativeness of the simulations. There are, however, very few studies in literature which focus on the comparison of such simulations with neutron measurements performed outside the shielding in proton therapy facilities. Moreover, the published measurements were not necessarily acquired with detectors that possess a good sensitivity to neutrons with energies above 20 MeV, while these neutrons actually give an important contribution to the total dose outside the shielding. A first part of this work was dedicated to the study of the energy response function of the WENDI-2, a rem meter that possesses a good sensitivity to neutrons of more than 20 MeV. The WENDI-2 response function was simulated using the Monte Carlo code MCNPX and validation measurements were carried out with 252Cf and AmBe sources as well as high-energy quasi-monoenergetic neutron beams. Then, WENDI-2 measurements were acquired inside and outside four rooms of the proton therapy facility of Essen (Germany). MCNPX simulations, based on the same conservative choices as the original shielding design simulations, were carried out to calculate the neutron spectra and WENDI-2 responses in the measurement positions. A relatively good agreement between the simulations and the measurements was obtained in front of the shielding, whereas overestimates by at least a factor of 2 were obtained for the simulated responses outside the shielding. This confirmed the conservativeness of the simulations with respect to the neutron fluxes transmitted through the walls. Two studies were then carried out to assess the sensitivity of the MCNPX simulations to the defined concrete composition and the selected physics models for proton and neutron interactions above 150 MeV. Both aspects were found to have a significant impact on the simulated neutron doses outside the shielding. Finally, the WENDI-2 responses measured outside the fixed-beam treatment room were also compared to measurements acquired with an extended-range Bonner Sphere Spectrometer and a tissue-equivalent proportional counter. A satisfactory agreement was obtained between the results of the three measurement techniques.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

The research activity moves from a partnership between the Department of Structural and Transportation Engineering of the University of Padova and the National Institute of Nuclear Physics (INFN), National Laboratories of Legnaro (Padova), aimed at the design of the SPES project (Selective Production of Exotic Species), for the construction at the INFN laboratories of Legnaro of a next-generation nuclear facility, dedicated to the production of a special kind of radioactive ion beams called exotic species. Their study is expected to provide advances in physics and astrophysics and a possible medical application of these beams is foreseen, as well. The topic of our study is the concrete shielding surrounding such a facility and the deeper understanding of the physical aspects involved in the radiation exposure of concrete to nuclear radiation generated by the fission reactions due to a primary proton beam impinging a uranium-carbide target. The study can be ideally subdivided into three phases: a) a bibliographic research within the scientific production in the field of nuclear physics and concrete behaviour (articles and manuals); b) the numerical implementation and validation within an ad hoc finite element code of a damage law, experimentally based, for concrete under neutron radiation; c) the application of the numerical model developed so far to the SPES project, provided the boundary conditions for the exposed concrete have been defined, in accordance with the design work specifics of the facility. This phase has required the combined use of the Monte Carlo technique and the FEM model. The previous bibliographic investigation has lead mainly to define the status of the art of the shielding materials employed in nuclear engineering and collect experimental data of irradiated concrete samples. As for the first point, the use of some improved mixtures has been envisaged to be of interest in the common practice so that some special concretes have been considered, in addition to ordinary Portland concrete; they differ basically for the presence of hydrous aggregates in the mixture, which are able to retain their water content even at high temperature, or heavy aggregates (iron-based or barytes aggregates, mainly). The former are known to assure good shielding properties against neutrons, since the atoms of hydrogen in the water molecules can easily absorb a huge amount of the incident kinetic energy of neutrons in a few scattering events; the latter provide, generally, good shielding properties against gamma rays, unsought by-product of atom-neutron reactions. The second point of the study allowed us to better understand the degradation mechanisms for concrete under an irradiated environment and quantify the threshold value for neutron fluence, marking the beginning of the macroscopic decay in the mechanical properties, in terms of compression and tension strength and Young modulus. The required damage law has been defined based on the enveloping curve of several empirical data describing the behaviour of the Young modulus of exposed concrete, with respect to that proper of the virgin material, in function of the neutron fluence; this macroscopic parameter for defining radiation damage has been chosen in agreement with the effective stress theory by Kachanov. The damage law here introduced has been implemented in a research FEM code able to solve the coupled hygro-thermo-mechanical problem in multiphase porous systems like concrete. Concrete is modeled by the code in its visco-elastic behaviour, taking into account damage effects due to mechanical loads, thermal loads and, thanks to the upgrade, a surrounding radiation field. The validation of the code has been accomplished by reproducing a particular irradiation test found in the scientific literature and involving serpentinitic concrete samples subject to two different neutron fluences; the overall stress-strain trend numerically simulated is found in good agreement with the data of the empirical investigation. A comparative analysis has followed the validation phase, aimed at studying the shielding performance of ordinary concrete, with respect to that of the improved mixtures, for a given radiation field, which is assumed to follow the simplified one-dimensional model known as diffusive model for thermal neutrons; a similar model is defined for high energy neutrons, i.e. fast neutrons, based on the so-called two-group theory. The one-dimensional simplification above mentioned is meant to be acceptable if the attenuation of radiation is considered to happen along the thickness of a wall, which is the geometry under analysis in the following: as explained later on, a portion of the directly impinged wall has been modeled with the FEM code and the attenuation process has been studied along the beam direction. The incident flux being equal, the comparative analysis has shown higher damage values for concrete specimens under fast neutrons than thermal and, as expected, better shielding characteristics have been found for the special concretes than ordinary Portland. The third phase of our work has focused the target room, the most critical area of the facility under design for the National Laboratories of Legnaro, dedicated to the fission reactions; it has been modeled in a Mote Carlo environment through a special software developed by CERN and INFN of Milan; the statistical tool is able to handle 3D radiation transport calculations and it has been exploited for our purposes to define the radiation and the temperature field from the design specifics of the SPES facility. The combined use of the Monte Carlo technique and the FEM code, upgraded to take into account the radiation exposure effects on concrete, has allowed us to identify in the thermal aspect, i.e. the temperature rise in the shielding due to radiation energy deposition, the most severe factor for prescribing a work scenario consistent with concrete durability. The numerical have allowed us to quantify an admissible irradiation profile of up to 6-7 months per year, for five years, under the design characteristics of the accelerating system and of the primary beam, not considering any protective device, such as outer metallic liners working as coats for the biological shield or the presence of a cooling systems inside the walls.
L’attività di ricerca si inserisce nell’ambito di una collaborazione del Dipartimento di Costruzioni e Trasporti dell’Università di Padova con l’Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Legnaro (Padova), finalizzata alla messa a punto del progetto SPES (Selective Production of Exotic Species), per la costruzione nei suddetti laboratori di un impianto nucleare di ultima generazione per la produzione di speciali fasci di ioni radioattivi, detti specie esotiche, a scopi di ricerca in campo fisico, astrofisico e auspicabile applicazione in campo medico. L’argomento di studio è il rivestimento in calcestruzzo per un impianto di questo tipo e le problematiche connesse all’irraggiamento da neutroni a seguito delle reazioni di fissione nucleare generate dalla collisione di un fascio primario di protoni su un elemento bersaglio in uranio-carbonio. Lo studio può suddividersi idealmente in tre fasi: a) una prima fase di ricerca nella letteratura scientifica di settore (articoli e manuali); b) una successiva fase di implementazione numerica e validazione in apposito codice agli elementi finiti di una legge di danno da radiazione sul calcestruzzo, basata su sperimentazione; c) una terza fase di applicazione del modello numerico al caso di studio, il progetto SPES, con la necessaria definizione delle condizioni al contorno per il calcestruzzo esposto, dovute alle condizioni di progetto del macchinario. Ciò ha richiesto un uso congiunto della tecnica Monte Carlo e del modello FEM. L’iniziale indagine bibliografica ha coinvolto la definizione dello stato dell’arte sui materiali di schermatura impiegati in campo nucleare e la raccolta di dati sperimentali di irraggiamento neutronico su campioni in calcestruzzo. Il primo punto ha permesso di considerare, a fianco del calcestruzzo ordinario, l’impiego di altri impasti migliorati per la presenza o di aggregati idrati, in grado di ritenere il loro contenuto d’acqua anche ad alte temperature, o di aggregati pesanti (di natura ferritica o baritica soprattutto); la prima caratteristica garantisce una buona capacità schermante nei confronti dei neutroni, essendo in grado l’idrogeno contenuto nelle molecole d’acqua di assorbire dopo pochi eventi di scattering una grande aliquota dell’energia incidente di un neutrone; la seconda caratteristica è indice di una buona prestazione schermante nei confronti dei raggi gamma, indesiderato prodotto secondario delle reazioni atomi-neutroni. Il secondo punto ha condotto alla comprensione dei meccanismi di deterioramento del calcestruzzo sotto un ambiente irraggiato e alla quantificazione della soglia di flusso neutronico oltre la quale si hanno le prime manifestazioni macroscopiche di perdita di resistenza del materiale, valutata in termini di resistenza a compressione, a trazione e modulo elastico. La legge di danno ricercata è stata definita come la curva di inviluppo del decadimento del modulo elastico di calcestruzzo esposto, rispetto al materiale vergine, proveniente da diversi tests, in diverse condizioni sperimentali, che, tuttavia, hanno permesso di identificare un trend univoco, in funzione del flusso di neutroni, di questo parametro macroscopico (il modulo elastico), scelto in accordo alla teoria dello stress effettivo di Kachanov. La legge è stata implementata in un preesistente codice FEM che numericamente risolve il problema termo-igro-meccanico accoppiato per i mezzi porosi multifase, come si configura il calcestruzzo. Il materiale è qui modellato nel suo comportamento visco-elastico danneggiato, in cui le forme di danno possibili provengono dal carico meccanico, dal carico termico e, grazie all’upgrade prefissato, dal campo di radiazione nucleare. La validazione è stata fatta sulla base di una prova di irraggiamento reperita in letteratura per calcestruzzo serpentinitico, sottoposto a due diversi flussi neutronici; nel complesso la risposta del materiale irraggiato è ben colta dal modello numerico, in termini di legame tensioni-deformazioni. A questa ha seguito un’analisi comparativa sulla bontà di schermatura del calcestruzzo ordinario, rispetto a provini fatti di impasti migliorati individuati anch’essi da letteratura, nell’ipotesi che il campo di radiazione spazialmente segua un modello semplificato monodimensionale, nella fattispecie noto in letteratura come modello diffusivo per i neutroni a bassa energia o termici; un modello analogo è definibile per i neutroni ad alta energia o veloci, sulla base della cosiddetta teoria dei due gruppi, che assume la suddivisione dello spettro neutronico reale in due soli livelli energetici, in una logica di semplificazione computazionale della teoria generale del trasporto della radiazione nella materia. L’evoluzione monodimensionale è accettabile se si analizza l’attenuazione della radiazione lungo lo spessore di una parete uniformemente investita, geometria che non si discosta dal caso di studio, il quale considera una porzione di parete orientata in direzione del fascio, per la quale la sezione trasversale è la faccia esposta e l’attenuazione avviene lungo lo spessore. A parità di flusso incidente, l’analisi comparativa ha messo in luce valori di danno superiori in presenza di neutroni veloci, rispetto a quelli dati da neutroni termici e ha permesso di quantificare le migliori prestazioni degli impasti speciali, rispetto al calcestruzzo ordinario. Successivamente si è preso in considerazione l’elemento sensibile dell’impianto in progetto per i Laboratori Nazionali di Legnaro, ovvero il vano ospitante l’elemento bersaglio e sede delle reazioni di fissione. La geometria dell’impianto è stata ricreata in un codice Monte Carlo di ricerca, un brevetto CERN-INFN di Milano in grado di effettuare calcoli 3D di trasporto della radiazione, allo scopo di ricavare i campi di radiazione e temperatura attesi per SPES nelle condizioni di lavoro di progetto per il macchinario. L’uso congiunto della tecnica Monte Carlo con il codice FEM, modificato per tenere in conto gli effetti del campo di radiazione nel materiale, ha consentito di definire l’aspetto termico, ossia lo sviluppo di calore interno al materiale per effetto del deposito di energia da radiazione, il fattore limitante per descrivere uno scenario di lavoro compatibile con la durabilità del calcestruzzo. Le simulazioni hanno condotto alla definizione di un profilo di irraggiamento ammissibile di cicli continuativi al più di 6-7 mesi all’anno, per un quinquennio, alle specifiche di progetto del sistema di accelerazione e del fascio primario sull’elemento fissile, in assenza di ulteriori provvedimenti o dispositivi di attenuazione del fronte termico, come ad esempio predisposizione di liners metallici all’intradosso delle pareti direttamente investite della camera di fissione o impianti di raffreddamento annegati in parete.

Dissertation (Ph.D.)--Worcester Polytechnic Institute.
Keywords: nuclear physics, particle physics, phyiscs, resonance, nuyclear fragmentation, nucleon-nucleon interactions, radiation shileding, heavy-ion physics, space radiation. Includes bibliographical references (leaves 163-141).

The purpose of this study is to improve spacecraft shielding from radiation in space. It focuses on the evaluation of shielding efficiency of different materials. The efficiency of a shield is evaluated by the dose profile within the shield and the amount of dose absorbed by a target using the Monte Carlo transport code called FLUKA. The output of this code is validated by recreating the experiments from published papers and comparing the results. Once the FLUKA’s output is validated, the efficiency of sixteen materials, subject to SPE and GCR sources, are evaluated. The efficiency comparison is made by fixing the area density of a shield. It was found that polyethylene, water, carbon and silicon outperform aluminum – the primary metal used in spacecraft. In case of composite shield, made of layers of different materials, the 3Carb-9Al combination has better performance than the shield made just of aluminum. This holds true for both Solar Particle Events (SPEs) and Galactic Cosmic Ray (GCR). However, the choice of material is more efficient at shielding from SPE particles rather than from GCR. In case of GCR, the choice of materials is found to have rather small effect on the efficiency of a shield. The percent difference between the rate of dose absorption by a target, shielded by different materials, is within about 9%. Secondary particles make a significant contribution to the target’s dose. For SPEs, the secondary particles are primarily electrons and neutrons. For GCRs, the secondary particles are primarily pions, α-particles and electrons. Protons contribute more than 50% to the target’s dose in both cases.

The main objective of this research is: (1) to develop a model and perform numerical simulations to evaluate the radiation field and the resulting dose to personnel and activation of materials and structures throughout the IRIS nuclear power plant, and (2) to confirm that the doses are below the regulatory limit, and assess the possibility to reduce the activation of the concrete walls around the reactor vessel to below the free release limit. IRIS is a new integral pressurized water reactor (PWR) developed by an international team led by Westinghouse with an electrical generation capacity of 335 MWe and passive safety systems. Its design differs from larger loop PWRs in that a single building houses the containment as well as all the associated equipment including the control room that must be staffed continuously. The resulting small footprint has positive safety and economic implications, and the integral layout provides additional shielding and thus the opportunity to significantly reduce the activation, but it also leads to significantly more challenging simulations. The difficulty in modeling the entire building is the fact that the source is attenuated over 10 orders of magnitude before ever reaching the accessible areas. For an analog Monte Carlo simulation with no acceleration (variance reduction), it would take many processor-years of computation to generate results that are statistically meaningful. Instead, to generate results for this thesis, the Standardized Computer Analyses for Licensing Evaluation (SCALE) with the package Monaco with Automated Variance Reduction using Importance Calculations (MAVRIC) will be used. This package is a hybrid methodology code where the forward and adjoint deterministic calculations provide variance reduction parameters for the Monte Carlo portion to significantly reduce the computational time. Thus, the first task will be to develop an efficient SCALE/MAVRIC model of the IRIS building. The second task will be to evaluate the dose rate and activation of materials, specifically focusing on activation of concrete walls around the reactor vessel. Finally, results and recommendations will be presented.

This thesis collected data on radiation dose to staff and patients during fluoroscopically guided cardiovascular procedures. The dose measurements were compared and procedural variables which contributed to higher levels of dose were identified. This investigation has informed clinically based practice and provides evidence-based recommendations for easily implemented actions to reduce both patient and staff radiation dose.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Thesis (MEng)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Within a complex electronic system, sub-system communication forms the backbone of the functionality of any satellite. It allows multiple processors to run simultaneously and data to be shared amongst them. Without it, a single processor would have to control the entire satellite. Not only would such a design then be overly complicated, but the processor would also not have sufficient capacity to service all the components efficiently. Furthermore the detrimental effects that radiation have on integrated circuits are well documented and can be anything from a single bit flip to a complete integrated circuit failure. If not repaired, a failure on a sub-system communication bus could lead to the loss of the entire satellite. Die goal is to create more radiation resistant Controller-Area-Network (CAN) node. Since a full triple modular redundant design will have a large footprint and high power consumption, a combination of techniques will be applied and tested. The goal is to achieve improved footprint utilisation over triple modular redundancy, while still maintaining good resistance to Single Event Upsets (SEU). By applying simulation, it was sufficiently proven that the implementation of the individual techniques used functioned according to expectations. These techniques included error detection and correction using Hamming Codes, single event transient filter and triple modular redundancy. Having applied these mitigation techniques, the footprint of the CAN controller increased by only 116%. Simulation showed that the Error Detection and Correction and Triple Modular Redundancy worked effectively with the CAN controller, and that the CAN controller could function as originally intended. Using radiation testing, the design proved to be more resistant to SEUs than the unmitigated CAN controller. It was thus shown that through using a combination of mitigation techniques, it is possible to develop an optimal design with a high level of resistance against Single Event Upsets, utilizing a smaller footprint than implementing Triple Modular Redundancy.
AFRIKAANSE OPSOMMING: Sub-stelsel kommunikasie vorm die basis van die funksionaliteit in ’n komplekse elektroniese stelsel soos ’n satelliet. Dit skep die vermoë om veelvoudige verwerkers gelyktydig te laat funksioneer en inligting tussen hulle te deel. Sonder sub-stelsel kommunikasie, sal ’n enkele verwerker die hele sateliet moet beheer. Dit sal nie net die hele ontwerp oorkompliseer nie, maar die verwerker sal ook nie genoeg kapisteit hê om al die komponente effektief te diens nie. Die newe-effekte van bestraling op geïntegreerde stroombane is goed gedokumenteer en kan wissel van ’n enkele omgekeerde bis, tot die vernietiging van die geïntegreerde stroombaan. Indien die fout in die kommunikasiestelsel nie herstel word nie, kan dit lei tot die verlies van die hele sateliet. Die doel is om ’n meer bestraling bestande Controller-Area-Network (CAN) nodus te skep. Aangesien ’n volle drie-dubbele-modulêre-oortollige ontwerp ’n baie groot area beslaan en hoë krag verbruik het, gaan ’n kombinasie van versagting tegnieke toegepas en ge-evalueer word. Die doel is om beter area benutting as die drie-dubble-modulêre-oortollige ontwerp te kry, terwyl ’n goeie weerstand teen foute behoue bly. Deur middel van simulasies is voldoende bewyse gelewer dat die implimentasie van die individuele versagting tegnieke soos verwag funktioneer. Hierdie tegnieke sluit in, fout opsporing en regstelling deur middel van Hamming kodes, enkele geval oorgangs verskynsel filter asook drie-dubbele-modulêre-oortollige ontwerp. Nadat versagting meganismes toegepas is, het die area verbruik van die CAN beheerder toegeneem met slegs 116%. Simulasies het bewys dat Fout Opsporing en Regstelling en Drie-Dubbele-Modulêre-Oortollige ontwerp tegnieke binne die CAN beheerder korrek funktioneer, terwyl die CAN beheerder self funktioneer soos dit oorspronklik gefunksioneer het. Deur middel van bestralingstoetse, is dit bewys dat die ontwerp meer bestand is teen foute geïnduseer deur bestraling as die onbeskermde CAN beheerder. Dit is dus bewys dat deur gebruik te maak van verskeie versagting tegnieke dit moontlik is om ’n optimale ontwerp te implimenteer, met ’n hoë weerstand teen foute, maar met ’n laer area verbruik as die van ’n Drie-dubbele-Modulêre-Oortollige ontwerp.

Composite materials have wide application areas in industry. Boron Carbide is an important material for nuclear technology. Silicon carbide is a candidate material in the first wall and blankets of fusion power plants. Titanium diboride reinforced boron carbide- silicon carbide composites which were produced from different titanium diboride particle sizes and ratios were studied for searching of the behaviour against the gamma ray. Cs-137 gamma radioisotope was used as gamma source in the experiments which has a single gamma-peak at 0.662 MeV. Gamma transmission technique was used for the measurements. The effects of titanium diboride particle size on radiation attenuation of titanium diboride reinforced boron carbide-silicon carbide composites were evaluated in related with gamma transmission and the results of the experiments were interpreted and compared with each other. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20849

Composite materials have wide application areas in industry. Boron Carbide is an important material for nuclear technology. Silicon carbide is a candidate material in the first wall and blankets of fusion power plants. Titanium diboride reinforced boron carbide- silicon carbide composites which were produced from different titanium diboride particle sizes and ratios were studied for searching of the behaviour against the gamma ray. Cs-137 gamma radioisotope was used as gamma source in the experiments which has a single gamma-peak at 0.662 MeV. Gamma transmission technique was used for the measurements. The effects of titanium diboride particle size on radiation attenuation of titanium diboride reinforced boron carbide-silicon carbide composites were evaluated in related with gamma transmission and the results of the experiments were interpreted and compared with each other. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20918

Radiation is defined as ionizing if it has enough energy to remove electrons from atoms or molecules when it passes through or collides with matter. This ability implies potentially detrimental effects on living tissue. Ionizing radiation shielding is therefore a discipline of great practical importance. The thesis builds upon the author's previous work on the topic and widens the scope of discussion with theoretical and practical issues of advanced shielding calculations. The theoretical part of the thesis describes several approaches to calculating fluence or absorbed dose at an arbitrary point in space. Point-kernel methods provide sufficiently accurate results for simpler shielding problems. In many practical cases, however, calculations based on the transport theory are necessary. There are two basic types of transport calculations: deterministic transport calculations in which the linear Boltzmann equation is solved numerically, and Monte Carlo calculations in which a simulation is made of how particles migrate stochastically through the problem geometry. Advantages and disadvantages of both methods are discussed. In the practical part are the results of radiation shielding calculations performed with a major Monte Carlo code - MCNP6, compared with those obtained in the experiments, which were carried out at the Ionizing Radiation Laboratory at Department of Electrical Power Engeneering, FEEC BUT. The experiments consisted of placing a cobalt-60 radioisotope source at three different positions inside a lead collimator, and counting pulses with two different scintillation detectors positioned in front of the opening of the collimator, alternately with or without lead shield located between the source and the used detector. Agreement of the calculations and the data from the measurements is reasonable, given the inherent uncertainties of the experimental set-up. Performed sensitivity analysis shows relative importances of different parameters used as inputs in simulations, such as densities of materials, or dimensions of the scintillation crystals. Annotated MCNP input files used for simulation are also part of the thesis.

This thesis investigates and develops a number improvements to a category of radiation therapy called stereotactic radiotherapy, most notably for spinal tumours. By careful consideration of planning parameters, treatment delivery accuracy can be improved and skin toxicity reduced for patients receiving this treatment. Improvements to patient safety and departmental efficiency with stereotactic radiotherapy can also be increased by matching treatment machines to each other. In addition, better patient access to this treatment can be afforded through improved design of the concrete bunkers that house these machines.

This thesis deals with the problem of shielding ionizing radiation which is a beam that has enough energy to ionize an atom or a molecule of an irradiated substance. This radiation can occur in nuclear facilities such as a nuclear power plant, a particle accelerator, or in X-rays in healthcare. Until now, standard shielding materials, most often lead or concrete, have been used to protect against ionizing radiation. New trends are therefore trying to replace these materials with lighter, more effective and harmless materials. The practical part is focused on measure the data to obtain the basic properties of shielding materials, such as the attenuation factor and the buildup factor. A measuring platform is described here, which can be used to measure the data needed to calculate the attenuation factor and the buildup factor. The measurement results are compared with tabular values to determine the accuracy of the measurements. Furthermore, the results of measurements of five concrete materials from the company MICo, spol. s r.o. To obtain theoretical values, the simulation program MCNP6 was used, in which it is possible to create a model of the measuring platform, which was used in practical measurements. Next the shielding material, source and detector are defined. The result lead again to the data needed to determine the attenuation factor. The results of measurement and simulation data in MCNP6 are evaluated and graphically processed into such a form that it is possible to compare the properties of shielding materials with each other.

This master’s thesis deals with the problematics of influence of ionizing radiation on semiconductor devices and their properties. The aim of the thesis is to analyze the different types of radiation that can occur in the areas of application of these components. In the second part, the degradation processes are explored, with emphasis on the influence caused by the radiation dose. Also, the displacement damage and SEE effects are described, but just slightly, because they are not part of this work. The third part describes the device design process and harmful effects, that have to be considered during the design phase. In the forth and the fifth parts of this work were done modeling of radiation effects (influence of dose rate, Single-Event Upset and Total Ionizing Dose) in PSpice program and was carried out the possibility of designing a simple dosimeter with silicon diode. In conclusion, the results of the thesis are summarized and evaluated.

This study investigated the use of modulated solar shielding in the context of solar radiation control in hot-dry and semi-arid climates. Solar shielding refers to the solar protection of the entire or large parts of the building's external fabric and not just those elements which directly transmit solar radiation. The study was undertaken with particular reference to the hot semi-arid climate of northern Nigeria. A conceptual and climatic analysis provided a contextual background for the work. A study of the use of shading devices indicated that their strength in some climates may be their weakness in others, especially the hot dry and semi and climates. A multiplicity of inherent climatic and environmental elements were not fully addressed by formal shading techniques. The concept of solar shielding was conceived from the interplay of the climatic and environmental factors of hot dry and semi-axid lands. Lack of measured solar radiation data in the reference climate necessitated the development of an interactive computer program to generate this and other relevant design data. A literature review provided a theoretical foundation un- derpining a series of full scale field measurements, scale model experimentation and thermal simulation studies. Fill scale measurements in a building were instructive on a possible impact of solar shielding on indoor thermal conditions. Model scale wind tunnel tests on the reference building and studies on full size louvres, using a pressurisation test facility, culminated in the development of airflow models through louvres. Finally, parametric thermal modelling studies enabled not only the optimisation of the technique but also a comparison with formal shading methods. Measured and simulated data portrayed not only a significant agreement but also indicated that solar shielding could have a higher solar protection efficiency than shading devices.

Thesis (D. Tech.) -- Central University of Technology, Free State, 2009
Superficial cancerous lesions are commonly treated through low energy X-ray or electron radiation in radiotherapy. The treatment units that produce the radiation are equipped with square, rectangular and round applicators of different sizes. These applicators attach to the treatment units and define the radiation field size applied during treatment. An applicator is chosen to fit the shape of the cancerous lesion on the patient as closely as possible. Since cancerous lesions are irregular in shape, there will always be an area of healthy tissue between the edge of the lesion and the edge of the standard field shape. This healthy tissue will be irradiated along with the lesion during treatment which is undesirable since the cancer wound heals through reparative growth of the surrounding healthy tissue after treatment. Traditional techniques that were developed to shield this healthy tissue and thus shape the radiation field to the shape of the lesion present various shortcomings. This study introduces a new thermal-spray process for producing radiation field shaping shields which overcomes most of the shortcomings encountered with the traditional field shaping techniques. Since none of the commercially available thermal-spray equipment could be used to produce field shaping shields, new thermal-spray equipment was designed and fabricated tailor made to the application. Different techniques to determine the contours of the treatment area on the patient were investigated. These included a patient contact technique using a plaster bandage impression and a non-contact technique using 3D laser scanning. From the plaster bandage impression a plaster model can be produced onto which a high density low melt material such as Wood’ s alloy can be thermally sprayed to produce a field shaping mask. A model can also be produced from the 3D laser scanning data through laser sintering (LS) in nylon polyamide powder or through computer numerical controlled (CNC) milling in a block of low density polyurethane. The thermal-spray technique was evaluated by comparing the field shaping ability of radiation shields produced through the technique to the field shaping ability of shields produced through the traditional techniques. Radiographic film was used for this purpose and the results are presented in the form of isodensity charts. The required thicknesses of thermal-sprayed field shaping masks to shield radiation of various energies were also determined. The thicknesses were determined through radiation transmission measurements of known thicknesses of sprayed sheets of Wood’ s alloy. X-ray imaging showed that there were no defects present within thermal-sprayed layers of Wood’ s alloy that may negatively affect the shielding ability of masks produced through the technique.

Thesis submitted in partial fulfilment of the requirements for the degree Doctor of Technology: Electrical, Electronic and Computer Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology
This research investigates the effects of sub-10 MeV protons on coatings obtained from the pulsed laser ablation of W2B5/B4C. This is in an attempt to extend the bullet proof applications of W2B5/B4C to space radiation shielding applications, offering low cost and low mass protection against radiation including X-rays, neutrons, gamma rays and protons in low Earth orbit. The focus in this research, however, is on low energy protons. The associated problems addressed in this work are solar cell degradation and Single Event Upsets in high density semiconductor devices caused by low energy protons. The relevant constraints considered are the necessity for low cost, low mass and high efficiency solutions. The work starts with a literature review of the space environment, the interaction of radiation with matter, and on pulsed laser deposition as a technique of choice for the coating synthesis. This paves the way for the pulsed laser ablation of W2B5/B4C. The resulting coating is a solid solution of the form WC1-xBx which contains crystalline and amorphous forms. Two proton irradiation experiments are carried out on this coating, and the resulting effects are analysed. The effects of 900 keV proton irradiation were the melting and subsequent growing of nanorods on the surface of the coating, the lateral transfer of the proton energy across the coating surface, and the lateral displacement of matter along the coating surface. These effects show that the coating is a promising cost effective and low mass radiation shield against low energy protons. The effects of 1 MeV protons on this coating are the three-stage melting of rods formed on the coating surface, and further evidence of lateral transfer of energy across the coating surface. Optical measurements of this coating show that it is about 73% transparent in the Ultraviolet, Visible and near Infrared range. This allows it to be used as radiation shielding for solar cells, in addition to high density semiconductor devices, against low energy protons in low Earth orbit. Simulations show that based on coulombic interactions alone, the same level of protection coverglass offers to solar cells can be achieved with about half the thickness of WC1-xBx or less.