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Properties Of Light Emitting Diodes Following Cobalt-60 IrradiationOzcan, Safak 01 September 2004 (has links) (PDF)
PROPERTIES OF LIGHT EMITTING DIODES FOLLOWING COBALT-60
IRRADIATION
Ö / zcan, Safak
M.S., Department of Physics
Supervisor: Prof. Dr. ibrahim Gü / nal
September 2004, 71 pages
The main purpose of this study is to investigate the effects of gamma radiation on the properties of the light emitting diodes. GaP and GaAsP LEDs are used in the study.
It is observed that the exposure of a light emitting diode affects its various properties. A cobalt-60 gamma-cell is used to irradiate the selected light emitting diodes. For the different total doses of gamma pre-irradiation and post-irradiation I-V characteristics and spectral responses are recorded. The capacitance characteristics are measured at 1MHz at room temperature. Gamma ray bombardment of these LEDs results in reduction of electroluminescent intensity and increase in forward current up to levels tested. In GaP diodes dominant current transport mechanism has found to be effected by irradiation. No noticeable change is observed in the series resistances. The impurity density remains same in the green LED and increases in the red one due to the irradiation, which is deduced from the C-V characteristics. Both the circuit designers and the users should be aware of these effects in order to reach a reliable application for these components in a radiation environment.
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3D field ion microscopy and atom probe tomography techniques for the atomic scale characterisation of radiation damage in tungstenDagan, Michal January 2016 (has links)
In this work, new reconstruction and analysis methods were developed for 3D field ion microscopy (FIM) data, motivated by the goal of atomic scale characterisation of radiation damage for fusion applications. A comparative FIM/ atom probe tomography (APT) study of radiation damage in self-implanted tungsten revealed FIM advantages in atomistic crystallographic characterisation, able to identify dislocations, large vacancy clusters, and single vacancies. While the latter is beyond the detection capabilities of APT, larger damage features were observed indirectly in APT data via trajectory aberrations and solute segregation. An automated 3DFIM reconstruction approach was developed to maintain reliable, atomistic, 3D insights into the atomic arrangements and vacancies distribution in ion-implanted tungsten. The new method was utilized for the automated âatom-by-atom' reconstruction of thousands of tungsten atoms yielding highly accurate reconstructions of atomically resolved poles but also applied to larger microstructural features such as carbides and a grain boundary, extending across larger portions of the sample. Additional tools were developed to overcome reconstruction challenges arising from the presence of crystal defects and the intrinsic distortion of FIM data. Those were employed for the automated 3D mapping of vacancies in ion-implanted tungsten, analysing their distribution in a volume extending across 50nm into the depth of the sample. The new FIM reconstruction also opened the door for more advanced analyses on FIM data. It was applied to the preliminary studies of the distortion of the reconstructed planes, found to depend on crystallographic orientation, with an increased variance in atomic positions measured in a radial direction to the centre of the poles. Additional analyses followed the subtle displacements in atomic coordinates on consecutive FIM images, to find them affected by the evaporation of atoms from the same plane. The displacements were found to increase with size as the distance to the evaporated atom decreased, and are likely to be the result of a convolution between image gas effects, surface atoms relaxation, and charge re-distribution. These measurements show potential to probe the dynamic nature of the FIM experiment and possibly resolve contributions from the different processes effecting the final image. Finally, APT characterisation was performed on bulk and pre-sharpened needles to determine the effect of sample's geometry on the resulting implantation profiles, and the extent to which pre-sharpened needles could be employed in radiation damage studies. While the ions depth profiles in needles were not found within a good match to SRIM simulations, the damage profiles exhibited closer agreement. Further, the concentration of implanted ions in bulk samples was found significantly higher than in the respective needle implanted samples, with excessive loss found for the light ion implantation.
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Vysokoteplotní provozní zkřehnutí oceli EUROFER´97 / High temperature service embrittlement of EUROFER´97 steelStratil, Luděk January 2009 (has links)
The thesis describes effect of long-time ageing on the microstructure and properties of the Eurofer´97 steel. The ferritic-martensitic reduced activation steel Eurofer´97 is candidate structural material for in-core components of proposed fusion reactors. Thesis is focused on examination and description of brittle-fracture behaviour of the steel. Properties of the steel were investigated in as-received state and state after long-time ageing. Detailed microstructure studies were carried out by means of optical and electron microscopy and also by means of quantitative electron microscopy. Mechanical properties were evaluated also in both states by means of hardness tetsing, tensile testing and Charpy impact testing. Fractography analysis of fracture surfaces was carried out on samples after Charpy impact testing.
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Radiation Response of Nanostructured CuCuncai Fan (7036280) 02 August 2019 (has links)
Irradiation of metals with energetic particles causes heavy damage effects in microstructure and
mechanical properties, which is closely associated with irradiation conditions, presence of
impurities, and microstructural features. It has been proposed that the radiation tolerance of a
certain material can be enhanced by introducing a high density of interfaces, acting as ‘sinks’ that
can frequently involve in attracting, absorbing and annihilating defects. Nanostructured materials
with large volume fraction of interfaces, therefore, are assumed to be more radiation tolerant than
conventional materials. This thesis focuses on the radiation damage effects in nanostructured Cu
via the methods of in-situ TEM (transmission electron microscope) radiation experiments, postirradiation TEM analyses, small-mechanical tests (nanoindentation and micro-pillar compression),
and computer simulations (molecular dynamics and phase-field modeling).
We design and fabricate nanostructured Cu using direct current (DC) magnetron sputtering
deposition technique, a typica physical vapor deposition (PVD) method and a bottom-up way to
construct various nanostructured metals. High-density twin boundaries (TBs) and nanovoids (NVs)
are introduced into two distinct nanostructured Cu films, including nanovoid-nanotwinned (NVNT) Cu (111) and nanovoid (NV) Cu (110). The in-situ high-energy Kr<sup>++</sup> (1 MeV) and ex-situ
low energy He<sup>+</sup>
(< 200 keV) irradiations are subsequently preformed on the as-deposited Cu
samples. On the one hand, the in-situ TEM observations suggest that TBs and NVs can influence
the formation, distribution and stability of radiation-induced defects. Meanwhile, the preexisting
microstructures also undergo structural change through void shrinkage and twin boundary
migration. On the other hand, the ex-situ micro-pillar compression tests reveal that the Heirradiated NV-NT Cu contains less defect clusters but experiences more radiation-induced
hardening. The underlying mechanisms of void shrinkage, twin boundary migration, and radiationinduced hardening are fully discussed based on post-irradiation analyses and computer simulations.
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Comprehensive Model for X-Ray-Induced Damage in Protein CrystallographyClose, David M., Bernhard, William A. 01 July 2019 (has links)
Acquisition of X-ray crystallographic data is always accompanied by structural degradation owing to the absorption of energy. The application of high-fluency X-ray sources to large biomolecules has increased the importance of finding ways to curtail the onset of X-ray-induced damage. A significant effort has been under way with the aim of identifying strategies for protecting protein structure. A comprehensive model is presented that has the potential to explain, both qualitatively and quantitatively, the structural changes induced in crystalline protein at 100 K. The first step is to consider the qualitative question: what are the radiation-induced intermediates and expected end products? The aim of this paper is to assist in optimizing these strategies through a fundamental understanding of radiation physics and chemistry, with additional insight provided by theoretical calculations performed on the many schemes presented.
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Crystal Structure and Thermal Behavior of SbC2O4OH and SbC2O4ODKohlmann, Holger, Rauchmaul, Anne, Keilholz, Simon, Franz, Alexandra 13 April 2023 (has links)
The order of OH groups in the crystal structure of SbC2O4OH, a potential precursor in the synthesis of ternary oxides, was debated. Neutron diffraction on the deuteride SbC2O4OD revealed disordered OD groups with half occupation for deuterium atoms on either side of a mirror plane (SbC2O4OD at T = 298(1) K: Pnma, a = 582.07(3) pm, b = 1128.73(5) pm, c = 631.26(4) pm). O–H stretching frequencies are shifted by a factor of 1.35 from 3390 cm−1 in the hydride to 2513 cm−1 in the deuteride as seen in infrared spectra. SbC2O4OH suffers radiation damage in a synchrotron beam, which leaves a dark amorphous residue. Thermal decomposition at 564 K yields antimony oxide, carbon dioxide, carbon oxide, and water in an endothermic reaction. When using SbC2O4OH as a precursor in reactions, however, ternary oxides are only formed at much higher temperatures.
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Overcoming wound healing complications following radiotherapy in human breast dermal fibroblasts, through the influence of preadipocytes from the stromal vascular fractionTrevor, Lucy V. January 2021 (has links)
Radiotherapy has major therapeutic benefits for cancer patients, but ionizing
radiation causes damage of surrounding healthy tissues with poor wound
healing a common side effect. Therefore, further oncoplastic, reconstructive
surgery is challenging and often problematic. Current research models use
normal human dermal fibroblasts irradiated in vitro to mimic radiation
damage, but this is not comparable to ionising radiation and only measures
acute changes. Since radiotherapy may induce epigenetic changes leading
to alterations in dermal fibroblast phenotype, the first aim of this study was to
compare fibroblasts cultured from irradiated skin with non-irradiated skin. As
mesenchymal stem cells isolated from adipose tissue may offer beneficial
effects in the regenerative capacity of irradiated tissue, the second part of
this study was to compare those cultured from non-irradiated and irradiated
breast tissue.
Histological changes in the structural organisation of breast tissue in situ
from donors exposed to radiotherapy was compared to untreated breast.
Primary cultures of dermal fibroblasts from irradiated and non-irradiated
breast skin were established and comparisons quantitated in proliferation
(CyQuant), metabolism (Alamar Blue), migration (scratch-wound assay),
collagen production (Sircol), levels of proteases and protease inhibitors
(human protease/protease inhibitor array) and gene expression of COL1A1,
COL3A1, MMP1, MMP2, TIMP1 and PPAR-γ mRNA (qPCR). Cells from the
stromal vascular fraction (SVF) were cultured and characterised by
immunocytochemistry and compared to human preadipocytes sourced
commercially. The secretion of FGF, adiponectin and VEGF by the preadipocyte and the SVF mesenchymal cells was compared and the ability
of their secretome to modulate dermal fibroblast proliferation, metabolism
and migration was evaluated.
Radiotherapy caused extensive disorganisation of the reticular dermis and
flattening of the epidermal-dermal junction. Dermal fibroblasts cultured from
irradiated skin had a pronounced spindle shaped morphology with longer
thinner projections and took approximately twice as long to explant and grow.
They had a lower proliferative and higher basal metabolic rate and did not
respond to FGF-2. While they secreted similar amounts of total collagen they
demonstrated distinct differences in proteolytic enzyme and protease inhibitor
expression. This is the first report to culture cells from the SVF of irradiated
breast tissue. The cells expressed the preadipocyte markers CD10, CD73 and
CD105 and no CD45 (negative marker). SVF cells cultured displayed a typical
ASC fibroblastoid morphology. Analysis of the secretome identified the
presence of FGF, adiponectin and VEGF, while functional analysis
demonstrated a stimulatory effect on normal dermal fibroblast migration,
although irradiated dermal fibroblasts were unresponsive.
Radiotherapy induces long term, detrimental changes in breast skin. This is
the first quantitative characterisation of dermal fibroblasts and mesenchymal
cells from the SVF, subjected to ionising radiation in situ. Changes in their
phenotype that alter their function will impact on wound healing. Further
characterisation of these cells may explain their dysfunctional behaviour, and
lead to therapies to reverse or reduce this deleterious side-effect and
significantly improve treatments facilitating wound healing following radiation
injury. / Plastic Surgery and Burns Research unit
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Radiation Damage in GMR Spin ValvesCarroll, Turhan Kendall 22 October 2010 (has links)
No description available.
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Soft X-ray Spectromicroscopy of Radiation Damaged Perfluorosulfonic AcidMelo, Lis GA January 2018 (has links)
Climate change has propelled the development of alternative power sources that minimize the emission of greenhouse effect gases. Widespread commercialization of polymer electrolyte membrane fuel cell (PEM-FC) technology for transportation and stationary applications requires
cost-competitiveness with improved durability and performance. Advantages compared to battery electric vehicles include fast refueling and long distance range. One way to improve performance and minimize costs of PEM-FC involves the optimization of the nanostructure of the catalyst layer. The rate limiting oxygen reduction reaction occurs at a triple-phase interface in the cathode catalyst layer (CL) between the proton conductor perfluorosulfonic acid, PFSA, the Pt catalyst particles decorating the electron conductor carbon support and gaseous O2 available through the porous framework of the carbon support. Visualization and quantitation of the distribution of
components in the CL requires microscopy techniques. Electron and X-ray microscopy have been used to characterize the distribution of the PFSA relative to the carbon support and porosity in CLs. Understanding and limiting the analytical impact of radiation damage, which occurs due to
the ionizing nature of electrons and X-rays, is needed to improve quantitation, particularly of PFSA. This thesis developed scanning transmission X-ray microscopy (STXM) methods for quantitation of damage due to electron and soft X-ray irradiation in PFSA materials. Chemical
damage to PFSA when irradiated by photons and electrons is dominated by fluorine loss and CF2-CF2 amorphization. The quantitative results are used to set maximum dose limits to help optimize characterization and quantitation of PFSA in fuel cell cathode catalyst layers using: analytical electron microscopy, X-ray microscopy, spectromicroscopy, spectrotomography, spectroptychography and spectro-ptycho-tomography. / Thesis / Doctor of Philosophy (PhD) / Polymer electrolyte membrane fuel cells are an alternative, environmentally friendly power
source for transportation and stationary applications. Major challenges for mass production
include cost competitiveness, improved durability and performance. A key component to enhance
the performance and lower costs involves understanding and improving the spatial distribution of
the perfluorosulfonic acid (PFSA) polymer in the catalyst layer. The ionizing nature of electrons
and X-rays used in microscopy characterization tools challenges PFSA characterization since this
material is radiation sensitive. This thesis developed measurement protocols and methods for
quantitative studies of radiation damage to PFSA and other polymers using scanning transmission
X-ray microscopy. The chemical changes to PFSA films irradiated with photons, electrons and
ultraviolet (UV) photons were studied. The quantitative results identify limits to analytical
electron and soft X-ray microscopy characterization of PFSA. The results are used to optimize
methods for soft X-ray microscopy characterization of PFSA in fuel cell applications.
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Nonlinear ultrasound for radiation damage detectionMatlack, Kathryn H. 01 April 2014 (has links)
Radiation damage occurs in reactor pressure vessel (RPV) steel, causing microstructural changes such as point defect clusters, interstitial loops, vacancy-solute clusters, and precipitates, that cause material embrittlement. Radiation damage is a crucial concern in the nuclear industry since many nuclear plants throughout the US are entering the first period of life extension and older plants are currently undergoing assessment of technical basis to operate beyond 60 years. The result of extended operation is that the RPV and other components will be exposed to higher levels of neutron radiation than they were originally designed to withstand. There is currently no nondestructive evaluation technique that can unambiguously assess the amount of radiation damage in RPV steels. Nonlinear ultrasound (NLU) is a nondestructive evaluation technique that is sensitive to microstructural features such as dislocations, precipitates, and their interactions in metallic materials. The physical effect monitored by NLU is the generation of higher harmonic frequencies in an initially monochromatic ultrasonic wave, arising from the interaction of the ultrasonic wave with microstructural features. This effect is quantified with the measurable acoustic nonlinearity parameter, beta. In this work, nonlinear ultrasound is used to characterize radiation damage in reactor pressure vessel steels over a range of fluence levels, irradiation temperatures, and material composition. Experimental results are presented and interpreted with newly developed analytical models that combine different irradiation-induced microstructural contributions to the acoustic nonlinearity parameter.
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