abstract: The study of high energy particle irradiation effect on Josephson junction tri-layers is relevant to applications in space and radioactive environments. It also allows us to investigate the influence of defects and interfacial intermixing on the junction electrical characteristics. In this work, we studied the influence of 2MeV Helium ion irradiation with doses up to 5.2×1016 ions/cm2 on the tunneling behavior of Nb/Al/AlOx/Nb Josephson junctions. Structural and analytical TEM characterization, combined with SRIM modeling, indicates that over 4nm of intermixing occurred at the interfaces. EDX analysis after irradiation, suggests that the Al and O compositions from the barrier are collectively distributed together over a few nanometers. Surprisingly, the IV characteristics were largely unchanged. The normal resistance, Rn, increased slightly (<20%) after the initial dose of 3.5×1015 ions/cm2 and remained constant after that. This suggests that tunnel barrier electrical properties were not affected much, despite the significant changes in the chemical distribution of the barrier's Al and O shown in SRIM modeling and TEM pictures. The onset of quasi-particle current, sum of energy gaps (2&#916;), dropped systematically from 2.8meV to 2.6meV with increasing dosage. Similarly, the temperature onset of the Josephson current dropped from 9.2K to 9.0K. This suggests that the order parameter at the barrier interface has decreased as a result of a reduced mean free path in the Al proximity layer and a reduction in the transition temperature of the Nb electrode near the barrier. The dependence of Josephson current on the magnetic field and temperature does not change significantly with irradiation, suggesting that intermixing into the Nb electrode is significantly less than the penetration depth. / Dissertation/Thesis / M.S. Materials Science and Engineering 2012

Tungsten is considered the prime candidate material for plasma facing components within fusion reactors. However, exposure of tungsten to neutron flux brings about transmutation of tungsten into by-products: Re, Os and Ta. Under increasing levels of radiation damage, irradiation induced clustering/precipitation takes place that embrittles and thus reduces lifetime of such tungsten components. This thesis was undertaken to explore this subject on a deeper level. There are three components to this study. The first part considers the effect of Re content on irradiation induced clustering. Lab-made plate W-xRe (x: 2, 5, 10 and 25at.&percnt;) alloys were exposed to 1.2, 3.9 and 33dpa, self-ion irradiated at 773K. Analysis of cluster number density and volume fraction found they increase with damage level and bulk Re content. Based on these trends and existing literature data, a hypothesis was proposed suggesting clusters originate from vacancy clusters. Also, at 33dpa, rod shaped clusters form in W-25Re alloys while spherical clusters are present in other alloys. The clusters show close correspondence with irradiation induced precipitates and appear to be precursor phase. In the second part of this thesis, the effect of Os and Ta on cluster formation and alloy mechanical properties is examined. Lab-made plate W-1Re-1Os and W-2Re-1Ta alloys were irradiated at 33dpa at 573 and 773K and compared against control W-2Re alloy. At 33dpa and 573K, the Os and Ta presence suppresses cluster formation. Both ternary alloys contain smaller cluster diameter, composition, number density and volume fraction than the W-2Re alloy. However, at 33dpa and 773K, Os and Ta have opposing effects on cluster behaviour. Os increases the cluster nucleation rate and raises irradiation hardening (compared to W-2Re). Meanwhile, Ta presence decreased cluster number density and reduced the irradiation hardening (compared to W-2Re alloy). As well, Ta showed no evidence of clustering, only Re clusters form in the W-2Re-1Ta alloy. The final aspect of the thesis analyzes the effect of material microstructure and external variables on cluster formation in W-Re alloys. Commercial wire form W-25Re alloy was irradiated at 1.2dpa at 573 and 773K as atom probe needles and bulk sample. The larger free surface on atom probe needle samples appears to act as a sink for self-interstitials and vacancies at both temperatures. The effect of grain size and dislocation density was examined by irradiating commercial W-5Re wire (0.5-1μm diameter) and plate (1-3mm diameter) samples (annealed and unannealed) to 33dpa and 573K. It was found grain boundaries and dislocations act as defect sinks at 573K. Additionally, radiation enhanced Re grain boundary enrichment was observed for first time. The effect of grain size on cluster behaviour at 773K was also analysed. Commercial wire and lab-made plate W-3Re, W-5Re and W-25Re alloys were irradiated to 33dpa at 773K. The larger grain boundary area in wire samples is suspected of acting as a sink for self-interstitials leaving more vacancies for promoting cluster formation compared to lab-made samples. The discoveries made in this thesis broaden our current understanding of irradiation induced phase formation in tungsten. Their implications on plasma facing component design are discussed as well as recommendations for improvements. Further, areas requiring further research in this field are also highlighted.

A study of the nuclei Be⁶ , Be⁹ and Cl³³ has been made. These nuclei hare been investigated by observing the neutrons emitted during or after their formation by charged induced reactions. The neutron energies have been measured by the "time of flight" technique, using both the pulsed beams and associated particle methods. The first chapter contains an outline of the Distorted Wave Born Approximation and the application of this theory to the calculation of the angular distributions of neutrons emitted from a (p,n) reaction, which is treated as a special case of inelastic scattering, and also from the single and double stripping reactions (d,n) and (He³, n). In Chapter II is a description of the pulsed beam and associated particle time of flight techniques. A detailed account of the design, construction and mode of operation of the beam pulsing device used for the (p,n) experiments is given. Also included is a description of the neutron detector used together with an account of a method of pulse shape discrimination against gamma rays. The reaction L1⁶(p,n)Be⁶ is reported in Chapter III. The reaction has been studied using the pulsed beam method with proton energies ranging from 7 MeV to 18 MeV. At all incident energies the ground state of Be was excited. For incident energies between 10.0 arid 11.3 MeV there was evidence for an excited state in Be⁶ at 1.7 MeV. Measurements with proton energies between 15.0 and 18.0 MeV confirmed this. The excitation and width of the first excited state has been found to be :-E_x = 1.67 &pm; 0.05 MeV; &Gamma; = 1.18 &pm; O.07 MeV. At incident energies of 16.55 and 18.0 MeV evidence has also been found for a second excited state in Be⁶ at an excitation of about 3 MeV. Angular distributions for the ground state neutrons have been measured at incident energies of 8.3, 9.0, 9.6, 10.0, 10.5, 15.0, 16.55 and 18.0 MeV, and for the first excited state at 15.0 MeV. The angular distributions measured at 10.5 MeV and below could be fitted very well by a series of the first three Legendre polynomials, and have been interpreted in terms of compound nucleus theory. It is concluded that for these energies the reaction proceeds through two interfering states in Be⁷ at about 10 MeV excitation with spine of &half;⁺ and ³&frasl;₂^&minus;. An attempt has been made to explain the results obtained at 15.0 MeV and above in terms of a direct reaction theory. The direct reaction theory however gave no semblance of a fit. Calculations have been made in terms of pure phase space considerations in order to explain the nature of the neutron continuum seen in the reaction. It is concluded that the continuum arises chiefly from the four body break-up reaction Li⁶ + p &rightarrow; He⁴ + p + p + n with a small contribution from the reaction Li⁶ + p &rightarrow; Li⁵ + p + n . An experiment performed to study the neutron decay of excited states in Be⁹ populated by the beta decay of Li⁹ is reported in Chapter IV. The neutron energies were measured by the associated particle time of flight technique. It has been found from this experiment that the beta decay of Li⁹ populates not only the ground state and 2.43 MeV state of Be⁹ , but also states at 3.35 and 4.6 MeV. These two states, which have not previously been observed, have been given spin assignments of &half;^&minus; and ³&frasl;₂^&minus;. Assuming that the beta decay branching ratio of Li⁹ to the 2.43 MeV state in Be⁹ is 20 per cent, the branching ratios to the 3.35 and 4.6 MeV states is found to be (7 &pm; 4) per cent and > 1.5 per cent, compared to shell model predictions of (10 &pm; 2} per cent and (12 &pm; 3) per cent. Finally, in Chapter V is reported the reaction P³¹ (Me³, n)Cl³³. This experiment was performed to measure the spin of the first T = ³&frasl;₂ state in Cl³³ . From the angular distribution of the neutrons, which is characteristic of an L = 0 angular momentum transfer, the spin of the analogue state has been found to be &half;⁺. In addition tentative spin assignments of ³&frasl;₂^&plus; and &half;⁺ have been given to two other states in Cl³³ at 6.30 and 7.45 MeV respectively.

Results from this study, which has investigated the impact of the treatment technologies of chlorination, ozonation and UV irradiation on pool water quality are reported. The aim of the study was to evaluate the effect of these technologies in an unbiased way using a unique protocol, and to calculate a mass balance across the pool system. Data refer to a protocol based on operation of a 2.2m (cubed) capacity pilot swimming pool, which allows the comparison of technologies applied with reference to the propensity to generate the chlorinated disinfection by-products (DBPs) of chloramines and trihalomethanes (THMs). The protocol makes use of a specially developed body fluid analogue (BFA), containing simulant endogenous organic matter, with a soiling analogue consisting of commercial humic acid (HA). Using this analogue, levels of organic carbon (OC) and chloramines similar to those recorded in real pools have been obtained, along with somewhat lower levels of THMs. Results revealed conventional chlorination leads to steady-state TOC and DBP levels following an equilibrium period of 200-600 hours, with concentration values which are dependent on BFA loading rate. Following equilibration nitrate is the only DBP accumulating in the pool water, accounting for between 4% and 28% of the ammoniacal nitrogen loaded into the pool depending upon the operating conditions (primarily the Cl:N ratio). Both UV irradiation and ozonation, the latter combined with downstream adsorption, provide a similar efficacy in reducing chloramine levels, with their effect on THM and nitrate formation being highly dependent on the pH level and chlorine dose rate. This study builds on previous experimentation by including a more rigorous analysis of ozone-GAC with respect to DBP formation, a unique analysis of UV irradiation and a more comprehensive mass balance calculation of C, Cl and N across the pool. The study has established that no accumulation of carbon takes place in the pool, contrary to postulations made in previous published studies, and that the balance between the chloramines and THM DBPs is significantly affected by the HA loading.

abstract: Concrete is relatively brittle, and its tensile strength is typically only about one-tenth of its compressive strength. Regular concrete is therefore normally uses reinforcement steel bars to increase the tensile strength. It is becoming increasingly popular to use random distributed fibers as reinforcement and polymeric fibers is once such kind. In the case of polymeric fibers, due to hydrophobicity and lack of any chemical bond between the fiber and matrix, the weak interface zone limits the ability of the fibers to effectively carry the load that is on the matrix phase. Depending on the fiber’s surface asperity, shape, chemical nature, and mechanical bond characteristic of the load transfer between matrix and fiber can be altered so that the final composite can be improved. These modifications can be carried out by means of thermal treatment, mechanical surface modifications, or chemical changes The objective of this study is to measure and document the effect of gamma ray irradiation on the mechanical properties of macro polymeric fibers. The objective is to determine the mechanical properties of macro-synthetic fibers and develop guidelines for treatment and characterization that allow for potential positive changes due to exposure to irradiation. Fibers are exposed to various levels of ionizing radiation and the tensile, interface and performance in a mortar matrix are documented. Uniaxial tensile tests were performed on irradiated fibers to study fiber strength and failure pattern. SEM tests were carried out in order to study the surface characteristic and effect of different radiation dose on polymeric fiber. The interaction of the irradiated fiber with the cement composite was studied by a series of quasi-static pullout test for a specific embedded length. As a final task, flexural tests were carried out for different irradiated fibers to sum up the investigation. An average increase of 13% in the stiffness of the fiber was observed for 5 kGy of radiation. Flexural tests showed an average increase of 181% in the Req3 value and 102 % in the toughness of the sample was observed for 5 kGy of dose. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2018

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