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- ItemAngular correlation measurements with a segmented clover detector(University of Zululand, 2019) Mthembu, Sinegugu HappinessGamma-gamma angular correlation measurements are an important tool to determine (amongst other nuclear properties) the multipolarity and the mul- tipole mixing ratio of a gamma-ray transition. In this work we use for the rst time a segmented clover detector placed at close geometry to measure angular correlation functions. Gamma-gamma angular correlation analysis was carried out for the transitions of 133Ba and 60Co. It allowed to determine the angular correlation coe cients, a2 and a4, and to establish the multipole mixing ratios of several gamma-ray transitions. Codes to sort and analyze gamma-gamma angular correlation data were developed and a technique to deduce the mix- ing ratios was established. It was shown that the iThemba LABS segmented clover detector has an excellent capability for gamma-gamma angular correla- tions measurements, allowing one to determine multipole mixing ratios with high precision. The analysis of the gamma-gamma cascades of 133Ba proved that with this detector one can determine the M1+E2 multipole mixing ratios for gamma-ray transitions with precision similar to that listed in the Nuclear data tables, where the results of many di erent experiments are combined and averaged. Note that our results were produced from 12 hours of data collec- tion for each sources that were used namely 60Co and 133Ba. The analysis of the 1173 �� 1332 keV cascade in 60Co showed that using the segmented clover one can easily distinguish a stretched dipole from an unstretched quadrupole transition. Moreover, new results on the signs of the multipole mixing ratios for some transitions in 133Ba were obtained. In addition to measuring the multipole mixing ratios for the transitions in 60Co and 133Ba, an analysis was performed in order to investigate the possibility of a new 437 keV transition in 133Ba but no evidence supporting such a transition was found.
- ItemAnnealing effects on platinum coating morphology(2009) Masina, Colani John; Topic, M.; Ndwandwe, O.M.The importance of phase transformation for the physical, chemical and mechanical properties of coated systems has been of enormous scientific interest for a long time. Due to a huge application field, the metallic coatings and platinum coated systems in particular, has been studied extensively. Metallic platinum is important for many industrial applications and the demand has increased considerably in the past decade, particularly in applications such as jewellery and catalytic converters (which together account for over 80 % of platinum consumption). In addition, the applications of platinum and its alloys in fuel cells, gas sensors and MEMS are also in increased demand in the last decade. On the other hand, aluminium also plays an important role in electronics, microelectronics and many others applications. It is known that platinum and platinum alloys readily form intermetallics. Intermetallic compounds based on platinum group metals have almost unique properties. Many of them exhibit outstanding thermodynamic stability in aqueous and elevated temperature applications. Therefore, the platinum group metals base intemetallics are of particular interest as next generation high temperature materials due to their high melting temperatures and better oxidation or corrosive resistance than refractory metals. High melting temperatures of these compounds make them promising candidates for high-temperature structural materials. However, they are hard and brittle which could be a significant limitation when the surface hardness and structural integrity are of importance. Besides the applications as protective coatings and electronics, the intermetallic phases of the Pt-Al binary system can play a significant role in jewellery industry where they can contribute towards increased surface hardness without compromising the purity of platinum. However, the research on platinum/aluminium coated systems conducted in this study was concentrated onto morphological issues and thus, the effect of coating thickness, the temperature and annealing time on coating morphology was studied. Thin platinum coatings deposited on thick aluminium substrates by electron beam deposition process were used as a model system to study the effect of annealing on Pt coating morphology. Samples were annealed in a vacuum furnace at different temperatures and time. Several complementary techniques such as a scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS), Atomic force microscope (AFM), X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and Particle induced X-ray emission (PIXE) were used to characterise the coated systems in terms of surface morphology, identification of intermetallics and elemental distribution. The scanning electron microscope studies revealed that the morphology of thin platinum coatings is affected by both annealing parameters, the temperature and time. Our study showed that rumpling and increased surface roughness, flaking and thickening are the main degradation mechanisms in annealed coated systems. The investigation of phase formation by XRD and RBS revealed the formation of the following intermetallic phases: Al2Pt, Al6Pt, Al21Pt8, and Al21Pt6 when annealed at different temperatures and times. The change in coating morphology has been attributed to the formation of the platinum/aluminium intermetallic phases.
- ItemAqueous synthesis and characterization of Hematite Nanorod-based arrays for water splitting and gas sensing applications(University of Zululand, 2015) Ndlangamandla, C.L.; Maaza, M.; Ndwandwe, M.O.Hematite, a-Fe2O3, is one of the most stable oxides, with a band gap that ranges between 1.9 and 2.2 eV, and hence a prominent candidate for water splitting applications in sea water conditions. For such an application, the a-Fe2O3 particles should exhibit several singular characteristics: (i) their size should be within the nano-scale regime, (ii) their shape has to present a significant anisotropy during their growth and can be easily oriented, (iii) should be doped effortlessly. Consequentially, spatially oriented and doped a-Fe2O3 nanorods would allow an effective light trapping/harvesting combined to an efficient and a longer mean free path of the photo-induced charge carriers and hence a faster charge diffusion with a minimized excitonic recombination. The so called Vayssieres' methodology i.e. the aqueous chemical growth (ACG) process has been used in this research work as it is the ideal path to design and engineer the desired Ruthenium doped and spatially oriented a-Fe2O3 nano-rods. The thesis reports on a comprehensive set of synthesis and characterizations in view of optimizing the water splitting properties of such Ru doped and undoped a-Fe2O3 photoanodes. In addition, gas sensing potentialities of these Ru doped and undoped a-Fe2O3 have been investigated.
- ItemBeam emittance measurements in the SPC2 injection beamline at iThemba LABS(University of Zululand, 2021) Mnikathi, NdumisoBeam emittance is a property of a charged particle beam in a particle accelerator that is used to estimate the beam quality. It is length-based measure of the average spread of particle coordinates in position and momentum phase space. This attribute makes emittance a crucial beam parameter that one requires when tuning the beam into smaller spaces in a beamline and matching the beam with the acceptance of an accelerator. At iThemba LABS, the low energy beam transport (LEBT) system required a system that measures transverse beam emittance. This beamline connects the two electron cyclotron resonance ion sources (ECRIS) to the second solid pole injector cyclotron (SPC2) and is composed of a set of solenoid and quadrupole magnets that are used to focus the beam. This layout makes it possible to use solenoid and quadrupole magnets to carry out beam emittance measurements. This thesis is aimed at presenting a developed system that can be utilized for measuring transverse beam emittance of beams emerging from the ECRIS. An analytic explanation of the techniques used and tools needed for these measurements are given. The Gauss approximation program and the emittance calculator were developed and used. During the development process, the system was validated using different beams simulated using a computer program TRANSPORT [1]. The beam widths obtained from TRANSPORT were used on the developed emittance calculator to establish if one could get the injected beam emittances. From the calculations it was clear that there is an agreement between injected and deduced emittances. This was an indication that the emittance calculator is working as expected. Thenceforth, the real beam emittance measurements were performed using 4He2+ beam with kinetic energy Ek = 12.7 keV. After analysing the helium data it was decided that a second set of measurements should be performed and this was done using 32Si5+ beam with kinetic energy Ek = 8.35 keV. The obtained results from both helium and silicon measurements were analyzed in order to compare the emittance measured in the AX-line with the one measured in the Q-line. From both set of measurements it was observed that the emittances obtained in the two beamlines had some disagreement. This disagreement between the two sets of transverse emittances violated Lioville’s theorem. In order to probe the source of disagreement the helium measurements were further investigated by performing beam widths comparison. To do this, the measured emittances were injected into TRANSPORT and the beam widths gathered were then compared with the measured widths. From the comparison results it was clear that only the beam widths from AX-line are comparable while there was disagreement in Q-line widths comparison. It was evident from these observations that one could ii rely on beam emittances obtained in the AX-line than those obtained from Q-line beamline. Upon further investigation, it was concluded that reason behind this could be associated with the fact that for AX-line measurements, instead of performing minimum number of measurements (i.e three) required to deduce the emittances, five set of measurements were utilized instead. This choice of number of measurements makes the system robust in such a way that a small error on measured beam widths will have a negligible effect on the deduced emittances. For Q-line measurements, however, the solenoids scan was performed with minimum number of beam widths measurements (i.e ten) required. This may have resulted in the solenoid scan being sensitive to errors that could occur when measuring beam widths. For much more reliable emittance measurements in the Q-line the system needs to be upgraded in order to accommodate utilization of more beam widths of measurements.
- ItemComparative of Flammable and Toxic Gas Sensing behavior for Rare-Earth Elements Substituted Cobalt based Spinel Ferrites(University of Zululand, 2021) Shozi, Euphemia Nolwazi NontobekoThere is a considerable need to design and develop a Liquid petroleum gas sensor due to its use in households and high flammability to protect human safety. Therefore, in this research work, we present a variety of cobalt-based spinel ferrites doped with 4f electron rare-earth ions to be used as flammable gas sensors. These spinel ferrites were fabricated following a glycol hydrothermal chemical-process. Due to their electronic configuration and charge dynamics, they are very sensitive and selective to integrative liquefied petroleum gases (LPG). A high response of over 730 was recorded towards 1 vol% (or 10 000 ppm) of LPG at 225 °C. The CoSm0.1Fe1.9O4 nano-ferrite meets the criteria of a potential sensor of being highly sensitive and selective with repeatability and stability that maintained a high response of 241 over 63 days. The rare-earth elements doped cobalt based ferrites were classified according to two categories in terms of overall performance. The first category were the ferrites doped with the low 4f electrons and the second category belonged to the high 4f electrons. The first category composed of solid and compact nanoparticles and proved to be better in the LPG performance while giving low photoluminescence emission intensities. This latter category had the highest combined percentages of oxygen vacancies and adsorbed oxygen. A temperature dependent tunable carrier-type transition was observed. The ferrite has p-type characteristics at 225 °C and above, otherwise n-type below this operating temperature to room temperature.
- ItemComparative study of rare- earth based ferrites for flammable and volatile organic compound gas sensors(University of Zululand, 2023) Mkwae, Prince S’busisoThe monitoring of flammables and VOCs is still a challenge. In addition, acetone (CH3CH3CO) is a one of the toxic and harmful volatile organic compounds (VOCs) commonly used as a solvent in various laboratories and industries. Its high level of inhalation and ingestion can cause low, acute and chronic poisoning. Another commonly used highly flammable gas is liquefied petroleum gas (LPG), commonly known as a cooking gas, which is widely available in almost all communities and working environments to create fires for various uses. This gas causes many fatalities due to its nature of complexities in detection and can easily ignite. This, therefore, suggests that it is one of the main air pollutants that require constant detection and monitoring. Most studies in the chemical gas sensing community focus on just the normal sensing of these gases. In an attempt to solve the long existing problem, we have undertaken this study, where MgCexFe2-xO4 (0 ≤ x ≤ 0.4) nanoparticles have been produced by the glyco-thermal technique and characterised by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy and gas sensing analyses. The X-ray diffraction results indicated that a pure cubic spinel phase was formed for samples having a low concentration of Ce, but the high Ce doping (x ≥ 0.2) of magnesium ferrite resulted in the formation of secondary phases. The crystallite size of the compounds ranged from 2.2 nm to 15.3 nm. The 57Fe Mössbauer spectra showed transformation from an ordered to a paramagnetic spin state with an increase in Ce concentration. Gas sensors fabricated from the spinel ferrites were tested towards various organic compound vapours (acetone, methanol, p-xylene, ethylbenzene, toluene, and benzene) and flammable gases (LPG, Methane, Propane, Butane and Ammonia) at an operating temperature of 225 °C. The MgCe0.2Fe1.8O4 nano-ferrites proved to possess quality sensor characteristics of high sensitivity and selectivity to acetone vapour, with a response of over 500@100 ppm concentration as well as reproducibility, reversibility, and stability of over 120 days. This sensor not only displayed high responses, but could also maintain them over 1, 3, 5, 10, 20, and 30 min of acetone exposure time. On flammable gases, the addition of cerium to magnesium ferrites proved to kill the sensing. The best performing sensor was found to be the undoped Magnesium ferrite on LPG gas. It was resilient and sensitive to an oxygen reduced, inert ambient environment. Under relative humidity, the response was reduced, but stable, due to physisorbed water molecules. In addition, this SMO sensor was tested at 200 ˚C on vegetables and fruit to evaluate their off-shelf freshness during the ripening process. These plants show a dramatic increase in the respiration rate over their maturation or ripening process over time. OKUHUNYUSHWE NGOLIMI LWESIZULU IMFINGQO Ukuqapha izinto ezivuthayo kanye nama-VOC kuseyinselelo. Ngaphezu kwalokho, i-acetone (CH3CH3CO) ingenye yezinhlanganisela eziphilayo ezinobuthi neziyingozi (VOCs) ezivame ukusetshenziswa njengesinyibilikisi kumalabhorethri nezimboni ezihlukahlukene. Izinga layo eliphezulu lokuhogela kanye nokumunca lingabangela ubuthi obuphansi, obunamandla futhi obungapheli. Enye igesi evame ukuvutha esetshenziswa kakhulu i-liquefied petroleum gas (LPG), eyaziwa ngokuthi igesi yokupheka, etholakala cishe kuyo yonke imiphakathi nasezindaweni zokusebenza ukuze kubase imililo esetshenziselwa ukusetshenziswa okuhlukahlukene. Le gesi idala ukufa kwabantu abaningi ngenxa yemvelo yayo yobunzima ekubonweni futhi ingavutha kalula. Ngakho-ke, lokhu kuphakamisa ukuthi ingenye yezinto ezingcolisa umoya ezidinga ukubonwa nokuqapha njalo. Ucwaningo oluningi emphakathini ozwa igesi yamakhemikhali lugxile ekuzwaneni nje okujwayelekile kwala magesi. Emzamweni wokuxazulula inkinga ende ekhona, senze lolu cwaningo, lapho i-MgCexFe2-xO4 (0 ≤ x ≤ 0.4) nanoparticles ikhiqizwe indlela ye-glyco-thermal futhi ibonakala nge-X-ray diffraction, i-electron microscopy, i-X-ray photoelectron spectroscopy, i-Mössbauer spectroscopy kanye nokuhlaziywa kokuzwa kwegesi. Imiphumela ye-X-ray diffraction ibonise ukuthi isigaba se-cubic spinel esihlanzekile sakhiwe amasampula ane-concentration ephansi ye-Ce, kodwa i-Ce doping ephezulu (x ≥ 0.2) ye-magnesium ferrite ibangele ukwakheka kwezigaba zesibili. Ubukhulu be-crystallite bezinhlanganisela busukela ku-2.2 nm kuya ku-15.3 nm. I-spectra ye-57Fe Mössbauer ibonise ukuguqulwa ukusuka ku-oda ukuya esimweni sokujikeleza kwe-paramagnetic kanye nokwenyuka kokugxila kwe-Ce. Izinzwa zegesi ezakhiwe ngama-spinel ferrites zahlolelwa ukushunqa inhlabathi ehlukahlukene (i-acetone, i-methanol, i-p-xylene, i-ethylbenzene, i-toluene, ne-benzene) namagesi avuthayo (LPG, Methane, Propane, Butane kanye ne-ammonia) ezingeni lokushisa elingu-225°C. I-MgCe0.2Fe1.8O4 nanoferrites ibonakale inezici zezinzwa zekhwalithi zokuzwela okuphezulu nokukhetha kumhwamuko we-acetone, nempendulo yokugxila okungaphezu kuka-500@100 ppm kanye nokuphindaphindeka, ukuhlehla, nokuzinza kwezinsuku ezingaphezu kweziyi-120. Le nzwa ayizange ibonise ukusabela okuphezulu kuphela, kodwa futhi ibikwazi ukuzigcina ngaphezu kwe-1, 3, 5, 10, 20, kanye nemizuzu engama-30 yesikhathi sokuchayeka kwe-acetone. Kumagesi avuthayo, ukungezwa kwe-cerium kuma-magnesium ferrites kufakazele ukubulala inzwa. Inzwa esebenza kahle kakhulu itholwe iyi-Magnesium ferrite engafakwanga i cerium kugesi ye-LPG. Yayikwazi ukumelana nezimo futhi izwela umoya-mpilo oncishisiwe, indawo ezungezile engenzi lutho. Ngaphansi komswakama ohlobene, impendulo yancishiswa, kodwa yazinza, ngenxa yama-molecule amanzi afakwe i-physisorbed. Ukwengeza, le nzwa ye-SMO ihlolwe ku-200 ˚C ezitshalweni nasezithelweni ukuze kuhlolwe ubusha bazo obungekho eshalofini ngesikhathi sokuvuthwa. Lezi zitshalo zibonisa ukwanda okumangalisayo kwezinga lokuphefumula phezu kokuvuthwa kwazo noma inqubo yokuvuthwa ngokuhamba kwesikhathi.
- ItemCross section measurements for neutron induced reactions on Bi targets using quasi mono-energetic neutron beams of 90 and 140 MeV(University of Zululand, 2017) Lamula, Thobeka Patience; Maleka, S.S; Ntshangase, S.S; Nchodu, M.RCross section measurements for 209Bi(n,3-5n)xBi reactions were performed using quasi-monoenergetic neutron beams of 90 and 140 MeV energies. Neutron beams were produced from the 7Li(p,n)7Be reaction using the neutron beam facility of iThemba Laboratory for Accelerator Based Science (LABS). Neutron activated target materials ( 209Bi) were anal-ysed for gamma-ray emission with the available HPGe gamma-ray detector system of the ERL. From the identi_ed radionuclides, their activities were determined and subsequently their production cross sections were calculated. The cross section data found from this work was compared with the existing experimental as well as the available evaluated data of the International Reactor Dosimetry Fusion File (IRDFF) library. The comparison with the reported data show good agreement. Currently, other parameters are still outstanding to finalise the comparison and finally conclude the uncertainty components. The cross section data from this work will be important for testing, improving and extending the IRDFF library since the existing experimental data for high energy neutrons are insufficient.To the IRDFF library, the current contribution from iThemba LABS will improve the Bismuth (Bi) data for high threshold energy (n,xn) reactions with cross section peaks located at 90 and 140 MeV energies.
- ItemThe design, development and fabrication of a Microwave Proton Ion Source at iThemba LABS(2006) Ndlangamandla, Ceboliyozakha Leonard; Celliers, P.J.; Ndwandwe, O.M.A low-power microwave ion source for the production of protons in the iThemba LABS Van de Graaff accelerator at Faure has been developed. The main advantages of the source are its simple construction, its low power consumption, the small number of parameters that have to be adjusted and the fact that the discharge starts easily. The construction and the operational conditions of the source are discussed. The beam intensities are compared with those of a duoplasmatron ion source in use at iThemba LABS.
- ItemDetermination of the inclusive (polarized proton, alpha) analyzing powers in the investigation of the Ca-40 (polarized proton, proton-alpha) reaction with 100 MeV polarized protons(2005) Lakaje, Tsepiso Emily; Neveling, R.; Ndwandwe, O.M.Alpha particle formation in the 40Ca nucleus was investigated by means of the (~p*,pa) reaction with a 100 MeV polarized proton beam. Coincident and singles analyzing power data were acquired for three different quasi-free angle pairs. The knocked out a particles were measured using a silicon detector telescope and the protons were measured using a K600 magnetic spectrometer. Only the singles analyzing power data for the silicon detec¬tor telescope were analyzed in this thesis. This data served as an important consistency check for the coincident results between different datasets, and it was also used in the investigation of the clustering phenomenon. The experimental analyzing power results were compared with the theoretical calcu-lations which were done using the THREEDEE computer code. This computer code is based on the Distorted Wave Impulse Approximation (DWIA). Experimental analyzing power results are not in good agreement with the theoretical analyzing power results.
- ItemDetermination of the Spectroscopic Quadrupole Moment of 40Ar(University of Zululand, 2019) Akakpo, Elijah Hornam; Ntshangase, S.S.; Orce, J. N.Coulomb excitation reorientation e ects measurement was performed at the AFRODITE vault of iThemba LABS to determine the Qs(2+1 ) of 40Ar. A beam of 40Ar at a laboratory energy of 134.94 MeV was Coulomb excited on a 194Pt target at a safe distance between nuclear surfaces of 6.5 fm. The backward scattered 40Ar particles were detected by an S3-CD double sided silicon detector at a distance of 30 mm with an angular range of 130 to 159 . Eight HPGe clover detector array ( ve at 90 and three at 135 to the beam axis) was employed to detect the de-excited -ray energy emitted by the 40Ar particles. The 40Ar particles and their corresponding -rays were collected in coincidence and stored. MTsort MIDAS was used in conjunction with an o ine sorting code to sort the coincidence data. Coulomb excitation analytical code, GOSIA, was used to extract the diagonal matrix element, h2+1 kE2k2+1 i = 0:00(4) eb. From the relation, h2+1 kE2k2+1 i = Qs 0:75793 , the Qs(2+1 ) was determined as +0:00(3) eb. This result indicates a spherical shape for 40Ar at the 2+1 state.
- ItemDetermining the Radon Emanation Coefficient for Soil Samples(University of Zululand, 2020) Phefo, LebogangExposure to high concentrations of radon and radon decay products are known to increase lung cancer in humans. This study is in preparation for a national indoor radon survey to be conducted in South Africa. The aim of this study is to determine the radon emanation coefficient for soil samples collected in various areas in South Africa. The radon emanation coefficient is important for identifying areas with high radium concentrations which emanate radon which could lead to high levels of radon in houses. The areas of interest for this study include Paarl and Saldanha (having granite outcrops), Kloof and Boksburg mine dumps, Centurion, West Coast and Richards Bay Minerals where high radon levels are expected. The soil samples were collected and analysed in the laboratory. Both alpha and gamma spectrometry were used for determining the radium activity concentration of the soil samples and the radon released by the soil from which the radon emanation coefficient can be found. The samples were sealed for a period of 21 days to achieve secular equilibrium between radium and radon and then counted using a NaI(Tl) detector to measure the radium activity using a 214Bi full-energy peak. The radon concentration was determined using an active radon monitor, the RAD7 which measures the alpha particles emitted from the radon progenies, 218Po and 214Po. The values obtained for the radium activity concentration varied in the range of 9.206 × 103, 94 - 1146, 339 - 368, 64 147, 72, 18 - 34 and 11 Bq.kg−1 for West Coast, Boksburg, Kloof, Paarl, Richards Bay Minerals, Saldanha and Centurion samples, respectively. The radon concentration values built up in the accumulation chamber (of 10 litres) to values of 233, 175 - 596, 225 - 352, 218 - 223, 358, 61 - 99, 58 Bq.m−3 in West Coast, Boksburg, Kloof, Paarl, Richards Bay Minerals, Saldanha, and Centurion for soil samples having the mass of about 0.256 kg, respectively. Finally, the emanation coefficient was determined as the fraction of the radon atoms created that is exhaled into the air and the radium activity. The values of the emanation coefficient obtained in this study for sample mass of 0.256 kg ranges from, 0.073 - 0.146, 0.063 - 0.313, 0.214 - 0.541, 0.276 - 0.847, 0.812, 0.765 and 0.004, in Kloof, Boksburg, Paarl, Saldanha, Centurion, Richards Bay Minerals and West Coast, respectively. The radon emanation coefficient for sample mass of 0.512 kg are in the ranges from 0.092 - 0.108, 0.139 - 0.326, 0.171 - 0.572, 0.169 - 0.774, 0.188, 0.003, in Kloof, Boksburg, Paarl, Saldanha, Centurion, Richards Bay Minerals and West Coast, respectively. The radon emanation for the final sample mass to be investigated ranges from 0.089 - 0.113, 0.139 - 0.275, 0.245 - 0.373, 0.296 - 0.738, 0.686, 0.157, 0.003, Kloof, Boksburg, Paarl, Saldanha, Centurion, Richards Bay Minerals and West Coast, respectively. These values of the emanation coefficient are in line with wide ranging values of 0.01 - 0.8 reported in the UNSCEAR 2000 report. These values will help to choose the distribution of houses that should be measured in the planned survey of radon in houses.
- ItemDevelopment of a laser ionization test bench for radioactive ion beams(University of Zululand, 2013) Makhathini, Lucky Maxwell; Bark, R.A.; Ndwandwe, O.M.This thesis aims to develop the technique for selective laser ionization of atoms and the role it can play in the production of radioactive ion beams. The theory of the production of radioactive ion beams and resonant laser ionization using different techniques will be discussed. Furthermore, the Isotope Separation On-Line method will be comprehensively discussed and the requirements needed for the development of a laser ion source will be summarized. The selective laser ionization of atoms will be demonstrated using two different techniques, laser-enhanced ionization in gas and using a time-of-_flight mass spectrometer. In laser-enhanced ionization in gas, atoms will be ejected into a flame via a device called a nebulizer where the atoms will be excited by two-step excitation followed by collisional ionization in the flame. The signal obtained will be fed onto a "boxcar" for data processing and analysing. In time-of-flight mass spectroscopy, a collimated beam of stable atoms will be created and the detailed design and construction of the atomic beam source and the time-of-flight mass spectrometer will be shown. Two-step ionization of atoms will be used to ionize the created beam and the ionized atoms will be accelerated twice by electric fields, after which they will enter a free-field region and they will be separated according to their mass to charge ratio. The interpretation of the results obtained will conclude the thesis and future prospects for the project will be given.
- ItemDevelopment of fission suppression devices for afrodite(2005) Hlatshwayo, Thulani Thokozani; Bark, R.A.; Ndwandwe, O.M.The discovery of the third minimum in various heavy mass nuclei, for example, in the U-Th region, has developed interest in the nuclear physics community to study the behaviour of the nucleus in this minimum. The nuclear shape that is predicted to exist in this minimum is known as a hyperdeformed shape, which corresponds to 3:1 major to minor axis ratio. A hyperdeformed nucleus could be created when a heavy target is bombarded with a light beam, for example, when an a-particle beam bombards 232Th. However in such a reaction, the strongest channel is fission, which occurs almost 99% of the time. Due to the high fission background, which reduces the experimental sensitivity for picking out y decay of hyperdeformed states from the background, many experiments have failed to observe hyperdeformed bands in this minimum. Therefore, this thesis focuses on the development of two fission suppression devices, namely a recoil detector and a solar cell array at iThemba LABS (South Africa).
- ItemThe effect of capping layers, diffusion barriers on TiSi2 phase formation(2002) Nkosi, M.M.; Ndwandwe, O.M.; Theron, C.C.Metal silicides continue to be an important part of the design philosophy in semiconductor technology due to their application as contacts or interconnect. Among these silicides, titanium disilicide is currently the most widely used as it possesses the lowest resistivity (\4\in~cm) of all silicides, a low contact resistance and a good thermal stability. Titanium-silicide formation with and without capping layers, through diffusion barrier layers and on stressed Si (100) substrate was studied. The oxidation of titanium makes accurate kinetics measurements very difficult. Capping layers, namely Al203 and MgO, and sandwich technique were used in attempting to limit the unwanted oxidation. It was found that both capping layers reduced the oxygen concentration in the unreacted Ti film by 30% compared to the uncapped samples. It was also found that the reaction was faster in the MgO capped samples and slower in the Al203 capped samples. In the sandwich technique, the oxygen concentration was found to be less by 35% and the reaction was fast at high temperatures compared to the silicide formation in the unsandwiched samples. In attempting to control the metal concentration at the growth interface diffusion barrier layers were used. Cr and Zr were used as diffusion barrier layers. Both barrier layers were found to react with silicon to form CrSi2 and ZrSi2 respectively. It was found that both barrier layers moved deeper into the samples as more silicide was formed on top, which indicates that Si is the dominant diffusing species during Ti-silicide formation. Both barrier layers delayed the formation of TiSi2. Tensile and compressive stresses were induced by depositing different thicknesses of Si3N4 and Si02 on the backside of Si{100) wafers. The reflection of laser light was used to measure the radius of curvature which was related to stress using Stoney's equation. It was found that the silicide phase formation was faster in samples under tensile stress and slower in samples under compressive stress. The cube root of time gave the best fit to the data for all sample groups. Therefore the TiSi2 formation kinetics was neither diffusion nor reaction limited.
- ItemEffects of particles’ size and composition on magnetic properties of substituted ferrite nanoparticles(University of Zululand, 2024) Majozi, Prince Phathizwe; Msomi, J. Z. and Jili, T. P.This project presents the effects of particle size and composition on the magnetic properties of ferrites investigated by magnetization and electron spin resonance (ESR) spectroscopy. CuxMn1−xFe2O4, (Zn, Cd)Fe1.2Al0.8O4, NixCo1−xFe2O4 and Cu0.5Ni0.5Fe2O4 nanoferrites were produced by glycol-thermal reaction under a low reaction temperature of 200 ◦C. Structural properties were analysed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). For CuxMn1−xFe2O4, the majority of the XRD peaks were indexed to the cubic spinel phase. However, a small impurity peak at 2θ ≈ 52◦ attributed to α-Fe2O3 and Mn2O3 phases for samples 0.4≤ x ≤ 0.8 was observed. The particle sizes varied between 8 nm and 16 nm. The particle size for the sample x = 0.3 (Cu0.3Mn0.7O4), which did not show any impurity phases was about 8 nm. The reduction of lattice parameters as a function of increasing Cu content is attributed to the smaller Cu replacing Mn ions. Magnetization data revealed superparamagnetic Cu0.3Mn0.7Fe2O4 fine particles and spin-glass behaviour. Enhanced magnetization and coercive fields at 10 K were explained by the core-shell model and spin freezing. An attempt to produce (Zn, Cd)Fe1.2Al0.8O4 was made. The XRD spectrum of the Cd-based sample showed impurity phases. XRD analysis showed clean ZnFe1.2Al0.8O4 with a particle size of about 6 nm. TEM images revealed nearly spherical particles with a reasonably narrow distribution of particle size which compared well with the value estimated from XRD data. ESR measurements showed a single-line signal indicative of dominant superexchange interactions. A small peak at very low magnetic field (about -500 ≤ H ≤ 500 G) was observed for the Zn- based oxide annealed at 1000 ◦C. This anomalous peak may be due to the low field microwave absorption(LFMA) phenomenon that is not fully understood in magnetic materials. NixCo1−xFe2O4 were successfully indexed to the cubic spinel. An additional peak associated with α-Fe2O3 was observed for samples with 0.7 ≤ x ≤ 0.9. XRD spectra revealed crystallite sizes ranging from 8 nm to 13 nm. There was no significant change in lattice parameters with increasing Ni concentration due to the small difference in their atomic radii. The ESR results showed single-line signals. Additional resonances were observed at low fields which need further measurements. We suspect these additional resonance peaks to be due to LFMA. The Land´e g-values varied between 1.98 and 3.6. Nanosized Cu0.5Ni0.5Fe2O4 fine particles with particle sizes of about 12 nm were produced. XRD did not show any impurity phases. The as-prepared oxide was annealed from 500 ◦C to 1100 ◦C to investigate particle size effects. Grain growth to about 46 nm was observed after annealing at 900 ◦C. ESR data revealed enhanced magnetization on the sample annealed at 900 ◦C due to the large ferromagnetic domains.
- ItemFullerene C60 based nanostructures by self-assembly and molecular recognition(University of Zululand, 2012) Mtshali, Christopher Bongani; Maaza, M.; Ndwandwe, O.M.The drive to have biological compatibility, light weight and low cost materials and hard coating which can withstand hard environments such as those in space and nuclear reactors has met with a lot of challenges such as radiation and heat. These challenges pose a threat to the function of expensive components used in space and nuclear reactors. Therefore, Carbon- Carbon composites been an alternative choice for fusion reactor plasma facing components because of their low atomic number, superior thermal shock resistance, higher melting temperature (graphite sublimes at ~3600K), high thermal conductivity and low neutron activation. So, studying how irradiation changes the structure and properties of solid targets is necessary in order to understand the irradiation-induced degradation of components in the nuclear reactors. Although carbon structures have been studied quite extensively, fullerene C60 nanostructures have not received much attention. Furthermore, carbon nanostructures experience a self-healing process when subjected to intense conditions, this created a scope to explore and investigate the effects of such conditions on the nanostructures of fullerene with an additional aim of discovering new properties. Indeed this study has discovered that C60 nanostructures cannot withstand reactor conditions but new vital properties such as magnetism were discovered forming a long term project in the creation of biocompatible light weight room temperature magnets to be applied in electronics.
- ItemGas sensing properties of doped copper oxide (CuO) thin films and nanostructures.(University of Zululand, 2021) Mnethu, Ongezwap-xylene is a harmful volatile organic compound that needs to be tested for indoor air quality detection. We report on the sensing characteristics of CuO and Zn doped CuO nanoplatelets of various concentrations that were prepared by hydrothermal synthesis, against nine different gases. These CuO and Zn based nanoplatelets were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence emission and vibrating sample magnetometer measurements. CuO and 0.1 at. % Zn doped CuO samples were most sensitive and selective to p-xylene gas with relatively high responses (Ra/Rg ratio) of about 42 and 53 at an operating temperature of 150 °C, respectively. These responses were about six times higher compared to the other 8 tested interfering gases. All these samples further exhibited a paramagnetic behavior at room temperature, due to small traces of point defects, such as oxygen vacancies. Both these sensor materials did not show green luminescence at room temperature that is normally associated with oxygen vacancies. However, temperature dependent photoluminescence (PL) measurements for the 0.1 at. % Zn doped CuO showed broad visible emission, including green luminescence, which increased with temperature up to 150 °C and coincided with the gas sensing temperature. The pure CuO, however, showed a rapid quenching in PL emission with an increase in the temperature up to 150 °C. Nevertheless, both pure CuO and 0.1 at. % Zn doped CuO based sensors were highly sensitive to the p-xylene gas. The mechanism associated to the xylene superior sensing was considered in terms of point defects and surface area as active sites for adsorption of gas molecules.Keywords: CuO, Gas sensor, Thin films and nanostructures, Gas sensing properties.
- ItemGreen synthesis of Europium (III) Oxide nanoparticles using Hibiscus sabdariffa flower extract(University of Zululand, 2018) Kweyama, ZamaveziNowadays there is a need to develop eco-friendly processes, inexpensive and nontoxic chemical use in the synthesis protocol in order to obtain biocompatible and harmless nanoparticles. Green chemistry approach is the eco-friendly process which has taken the researchers attention globally due to its advantages over conventional methods. This ecological method has potential in transforming the inorganic metal ions into metal oxides NPs via the bio-reduction of molecules present in the particular organism. This contribution reports on the synthesis, the main physical and optical properties of Europium (III) oxide (Eu2O3) nanocrystals synthesized for the first time by a completely green physical-chemistry process using Hibiscus sabdariffa (HB) natural flower extract and Europium nitrate pentahydrate (Eu(NO3)3.5H2O) salts as a precursor. The HB natural extract solution was used as a reducing agent for the production of Eu2O3 nanoparticles. The 1 g of EuN3O9.5H2O was dissolve in 100 ml of HB extract solution. The precipitate obtained was dried in the oven set at 100oC and thereafter annealed for 2 hrs at various temperature; 300oC, 500oC and 700oC using a standard furnace. The structural and optical properties of such biosynthesis nanocrystals were analyzed using High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM), Electron Dispersive X-rays Spectroscopy (EDS), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Raman Spectroscopy, Ultraviolet and visible spectrometer (UV-Vis-NIR) as well as room temperature photoluminescence (PL). The HRTEM and SEM results showed the images of small NPs formed, which indicated that the Eu2O3 NPs are nano-scaled with a mixed population of crystalline particles. The TEM and XRD analysis showed grain size of nanoparticles ranging between 14 nm and 25 nm. The XRD results confirmed the characteristic body centered cubic (BCC) structure of Eu2O3 nanoparticles and the UV-Vis proved that Eu2O3 absorbs in a wide range of electromagnetic wave from ultraviolet region. The luminescence properties of such cubic were characterized by an intense red emission centered at 614.93 nm (5D0-7F2). It was observed that a biosynthesized cubic Eu2O3 nanocrystal is an efficient luminescence material due to a very good luminescent response with potential application as red phosphors. These results represent an important step forward in the investigation of Eu2O3 nanoparticles properties synthesized via green chemistry process. It is a promising cost-effective path and energy wise non-consuming with zero waste end products for highly stable and well-characterized nanoparticles. The green synthesized Eu2O3 nanoparticles would be beneficial for the development of nontoxic, clean and environmentally friendly biosynthesis procedure.
- ItemGrowth and characterization of carbon nanostructures on zinc oxide nanostructures(University of Zululand, 2012) Mbuyisa, Puleng Nontobeko; Ndwandwe, M.O.; Cepek, C.The research work of this thesis is aimed to explore the possibility to synthesize different hybrid materials based on ZnO and carbon hierarchical nanostructures, and to test their performances when used as chemiresistors to detect low doses (~ ppm) of polluting gases, like ammonia and acetone. Nanostructures of ZnO and carbon, including carbon nanotubes, exhibit on their own exceptional qualities, which can be enhanced when they are combined in hybrids, extending their possible practical applications further. In this thesis it is shown that, it is possible to grow different CNs/ZnO hybrid nanostructures which present higher sensitivity to ammonia if compared to other carbon-based and ZnO-based chemiresistors. The hybrids have been grown by combining different growth techniques, like magnetron sputtering, hydrothermal process, electron beam deposition and chemical vapour deposition. The grown samples were studied by using a variety of experimental techniques, also in-situ, which allowed us to deeply understand their structural and chemical properties. In particular the chemical analysis was done by ultra violet and X-ray photoelectron spectroscopy (UPS and XPS, respectively, also using synchrotron radiation), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX). The morphology of the samples have been analysed, ex-situ, by scanning electron microscopy (SEM) and their fine atomic structure by high resolution transmission electron microscopy (HRTEM). The synthesis of aligned ZnO nanorods was done following the procedure below. Zinc oxide films were first deposited on Si <100> substrates using DC magnetron 4 sputtering at different chamber pressures, using oxygen to fully oxidize the films. Vertically oriented ZnO nanorods were then grown using the hydrothermal method on the resultant films. The pristine ZnO films were characterized by SEM, AFM, EDX and XRD. The films transparency and grain size were found to be pressure dependent: as the pressure was increased from the recommended sputtering pressure of 3x10-3 to 6x10-2 Torr the films became more transparent due to the decreases in the films grain size and thickness. The resultant nanorods were found to be highly dense with nonuniform dimensions due to the different grain sizes within the individual film samples. At a chamber pressure of 9x10-3 Torr we were able to grow c-axis oriented and crystallized miniature rods directly using DC sputtering, of approximately 250 ± 10 nm in length. This method of growing the nanorods directly from sputtering may lead to a simple way of growing ZnO nanorods, by eliminating the hydrothermal growth step and allowing in-situ growth in cases where ZnO rods are used as a substrate. Our work show that chemical vapour deposition (CVD) done on the so grown vertically aligned ZnO nanorods can synthesize different carbon nanostructures (CNs), whose morphology is driven by the ZnO nanorods and whose dimensions and structure change as a function of the process temperature. The grown CNs range from amorphous carbon cups, completely covering the nanorods, to highly dense one dimensional carbon nanodendrites (CNDs), which start to appear like short hairs on the ZnO nanorods. The nanorods are partially etched when the process is done at 630- 740 °C, while they are completely etched at high temperatures (> ~ 800 °C). In the later case the CNDs are preferentially aligned along the location of the pristine nanorods and emerge from a porous carbon sponge formed at the substrate interface. When the CVD process was done on Fe coated ZnO NRs at 580-630 °C, in addition 5 to the previously described CNs, we observed randomly oriented CNTs. The CNs/ZnO hybrids were characterised by ex-situ SEM, TEM and Raman spectroscopy, and in-situ XPS and UPS. We further found that, when used as a chemiresistor, the CND/ZnO nanostructures have a higher sensitivity to ammonia compared to chemiresistors made from the bare ZnO nanorods, other one-dimensional CNs, like carbon nanotubes or other metal/metal-oxides hybrid CNs. The absorption and desorption of ammonia gas on the bare ZnO NRs and the CNs/ZnO hybrids were studied by fast acquisition XPS using synchrotron radiation. Ammonia gas was found to chemisorb on the hybrid structure by forming amine groups, while on the NRs physisorbed on the NRs surface. The hybrid showed a ~ 4.5 higher sensitivity to ammonia as compared to the ZnO NRs sensor but a slower recovery time. The enhanced response and slow desorption of the CNs/ZnO hybrid can be attributed to the strong interaction of the hybrid with ammonia gas i.e. the different adsorption surface chemistry of C (chemisorption) and ZnO (physisorption) and also to the increased surface to volume ratio of the CNDs. The ZnO NRs were sensitive to both ammonia and acetone while the hybrid was ammonia selective.
- ItemHydrothermally grown Pb2+ doped ZnOnanorods for hydrogen and acetylene gas sensing(2008) Ngqondo, Sipho Tumi; Ndwandwe, O.M.Randomly orientated ZnO nanorods were deposited hydrothermally on Si <100> wafers. The precursor solutions used for ZnO nanorods deposition were zinc chloride + aqueous ammonia and Zinc nitrate + HMT. ZnO nanorods were deposited on Si<100> wafers to establish the optimal PH and concentration which yield the best substrate coverage for each precursor solution. ZnO thin films were deposited on glass substrates using pulsed laser deposition. These thin films were used for both gas sensing and as seed for orientated ZnO nanorods deposition. Rutherford Backscattering was used to measure the thickness and stochiometry of the deposited ZnO films. Orientated ZnO nanorods were then deposited on glass slides with ZnO thin films using the optimal PH and concentration for reagents established when Si<100> wafers were used as substrates. Pb doped ZnO nanorods were prepared by adding Lead (II) Nitrate as the Lead source into Zinc nitrate + HMT precursor solution. These Pb doped ZnO nanorods were then deposited on glass substrates with a ZnO thin film. The crystal structure and preferred plane orientation of all samples was studied using X-ray diffraction. Morphological and elemental analysis of samples was investigated using Scanning Electron Microscopy equipped with EDX. All samples showed good ZnO stochiometry with no foreign atoms except the samples with Pd doped ZnO nanorods. Ag contacts were deposited on the samples using EDWARDS vacuum coater. The gas sensing characteristics were investigated on all samples using 20% hydrogen and acetylene as test gases while 80% nitrogen was used as a carrier gas. ZnO thin films were found be at optimum for hydrogen gas sensing in the range 300-350oC, the minimum temperature for acetylene sensing was 400oC. Orientated ZnO nanorods also operated at their optimum in the 300- 350oC range like thin-films, however they exhibited better sensitivity in this range than thin films. ZnO nanorods started sensing acetylene at 350oC, slightly lower than ZnO thin films. Pb doped ZnO nanorods were able to sense hydrogen with 67% sensitivity at 250oC. These Pb doped ZnO nanorods were also found to be cable of sensing acetylene in the whole temperature range.
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