Department of Physics

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A Mössbauer Study of the Black Colour in Early Cypriote and Nubian C-Group Black-Topped pottery"
(1989) Makundi, Ismail N.; Waern, Sperber. A; Ericsson, T.
Cypriot and Nubian C-Group black-topped pottery from ca. 2000 BC have been studied by Mössbauer spectroscopy in combination with carbon analysis, x-ray diffraction, thin sectioning, and oxidizing and reducing refirings. The black parts contained both an excess of Fe2+ over total iron and of free or organic carbon compared with the red parts. Thus both Fe2+ and free or organic carbon contribute to the black color. The red color is mainly due to Fe3+ ions. Although these results are consistent with most of the suggested manufacturing methods, a technique where the pots are fired reducingly seems best suited for the Cypriot and Nubian C-Group vessels studied. Analyses of Attic black gloss showed Fe2+, but no magnetite.
Aerosol Study Using Energy Dispersive X-ray Fluorescence Analysis
(1989) Koleleni, Yusuf I. A.
An Energy Dispersive X-ray Fluorescence Analysis (EDXRFA) system for quantification of thin aerosol samples is described. The detection limit is in the range of 10μ/sq. cm for thin samples and the precision is in the range of 1 to 8%. The spectrometer was used to study thin aerosol samples collected along the road site to assess pollution contribution due to exhaust and dust particles. The results are in good agreement with other techniques namely Particle Induced X-Ray Emission (PIXE), Neutron Activation Analysis (NAA) and Atomic Absorption Spectroscopy (AAS)
Suitable Filters for Analysis in Energy Dispersive X-Ray Fluorescence Spectrometry
(1990) Koleleni, Yusuf I. A.
Energy dispersive x-ray fluorescence is applied in the analysis of teflon and quartz filter material. We report on impurities observed using the two techniques and filters. These techniques have been used to analyse the concentration of a number of elements including Pb and Br and the results of the two methods give excellent agreement
Air Pollution Studies of the Highest point of the Dar es Salaam City by X-Ray Fluorescence Analysis
(1998) Koleleni, Yusuf I. A.
A survey of the environmental pollutants in the city of Dar es Salaam was conducted. Aerosol sampling was conducted using a Sierra Anderson two way impactor for particles less and greater than 10 microns. Analysis was possible with X-ray fluorescence (XRF) rube excitation. We explore the analytical parameters of the spectrometer and present aerosol results for the months of January and February 1993/94 for cites at the highest points of the Dar es Salaam. The results have local significance but are also compared to international values. Lead values is of the order of 0.004 mg/L for Dar es Salaam (DSM) while World health Organisation (WHO), United States of America (USA), Canada and European Economic Community (EEC) values stands at 0.005 mg/L.
East African Journal of Physical Sciences, Volume 1 - Part 2 April 1999
(1999) Koleleni, Yusuf I. A.
Precision Measurements with the Total Reflection X-Ray Fluorescence System in Dar es Salaam
(1999) Koleleni, Yusuf I. A.; Kondoro, John W.
Natural Radioactivity and Radiation Exposure at the Minjingu Phosphate Mine in Tanzania
(2000) Banzi, Firmi B.; Kifanga, Leonard D.; Bundala, Felician M.
In this paper the results of studies on activity and ambient radiation background around the Minjingu phosphate mine in Tanzania are presented. The outdoor dose rate in air and the activity levels of samples from and outside the mine were determined by thermoluminiscent dosimeters and a gamma spectrometer system with a Hyper Pure germanium detector system respectively. The determination of activity was made for the 226Ra, 228Ra, 228Th and 40K radionuclides. High concentrations of radium-226 were observed in phosphate rock (5760+/-107 Bq kg(-1)), waste rock (4250+/-98 Bq kg(-1)), wild leaf vegetation (650+/-11 Bq kg(-1)), edible leaf vegetation (393+/-9 Bq kg(-1)), surface water (4.7+/-0.4 mBq l(-1)) and chicken feed (4+/-0.1 Bq kg(-1)) relative to selected control sites. These findings suggest a radiation health risk particularly when the samples are ingested, because the internal exposure may give rise to an effective dose exceeding 20 mSv which is the annual limit of intake of natural radionuclides recommended by the ICRP. On the other hand, the radiation dose from ambient air over five years at the phosphate mine ranges from 1375 to 1475 nGy h(-1) with an average of 1415 nGy h(-1). The average is about 28 times that of the global average background radiation from terrestrial sources, and about 12 times the allowed average dose limit for public exposure over five consecutive years. Future investigations on the occupancy factor, external dose rate and radon and radon progeny exposure in drinking water, buildings and activity content in the locally grown foodstuffs are proposed, for the realistic quantification of the overall exposure of workers and public at Minjingu, and remedial measures for future radiation safety.
Association of Iron Sulphides with Gold in Lake Victoria Gold field in Tanzania: A preliminary study
(2000) Banzi, Firmi B.
There is a resumed gold rush in Tanzania following liberalization of the private sector in 1993. Therefore, the need for finding mineral association with gold for quick location of gold rich areas is particularly high. Although such signatures already exist in some regions, their theoretical basis is still ill defined. The aim of this work is to resolve this problem by collecting and analyzing several rock samples obtained from different area around Lake Victoria gold field. The Energy Dispersive X-Ray Fluorescence technique was used to identify and quantify mineral elements and X-ray Diffraction was employed to identify phases of minerals. The preliminary results from XRF indicated that only five out of the expected gold associated mineral elements are found in Lake Victoria gold field: Fe (1- 24%), Co (4-67ppm), Cu (1-49 ppm), Pb (3-76 ppm) and As (15-88 ppm). Of particular interest is Pb element, which was found in all samples containing gold but gold was not found in all samples containing lead. The results from XRD showed that gold in Lake Victoria occurs in close association with chalcopyrite, pyrite and pyrrhotite. Work is in progress to identify mineral elements and phases, which can be used for quick location of gold rich area in the Lake Victoria gold field.
Radioactivity in Products Derived from Gypsum in Tanzania
(Nuclear Technology Publishing, 2000) Msaki, P.; Banzi, Firmi B.
Scientific investigations have long concluded that prolonged exposure to low dose radiation can induce deleterious effects in humans. The aim of this paper is to investigate the radioactivity of gypsum and gypsum derived products as part of a bigger project aimed at establishing radiation levels in materials or/and products suspected to have natural radioactivity radiation risk in Tanzania. In response to the concern expressed by the users of chalk sticks in some schools in Arusha municipality, it was found necessary to establish levels of radioactivity in this product and associated radiation risk. Natural radioactivity content was determined in chalk dust, natural gypsum and normal background soil using a hyper pure germanium spectrometer (HPGe). The soil measurements were used as control. Results have shown that the concentration of 226Ra and 228Ra nuclides found in chalk dust were 24.25 Bq.kg21 and 22.86 Bq.kg21 , respectively. These levels were lower or comparable to the corresponding 34.2 Bq.kg21 and 21.5 Bq.kg21 , respectively, found in soil. However, the radioactivity levels found in the chalk dust were five times higher than that found in the gypsum 5 Bq.kg21 for 226Ra and 4 Bq.kg21 for 228Ra. These values compare well with the value recorded for natural gypsum in Denmark of 7 Bq.kg21 for 226Ra and 4 Bq.kg21 for 228Ra by UNSCEAR. The calculated external (0.21) and internal (0.31) hazard indices due to radioactivity in chalk dust were respectively, lower than (0.26 and 0.35) hazard indices calculated for normal background soil. In both cases, the hazard indices were lower than the acceptable limits (<1) recommended for building materials. This study has shown that natural gypsum and gypsum derived products have traces of radioactivity. However, the associated levels are not detrimental to health.
Effects of Impurities on the Structural and Magnetic Properties of Natural Iron Sulphides from the Lake Victoria Gold Field
(2001) Banzi, Firmi B.
In this thesis three techniques, namely, X-ray Fluorescence, X-ray diffraction and Moessbauer spectroscopy were used to study the effects of impurities on the structural and magnetic properties of natural iron sulphides from the lake Victoria gold field. Pyrite and pyrrhotite being the main component of the iron sulphide in this area were investigated.
A study of heavy metal pollution in Lake Victoria sediments by Energy Dispersive X-Ray Fluorescence
(2001-02) Makundi, Ismael
Sources of heavy metal pollution of Lake Victoria is of interest due to its economic and domestic implication in East Africa. Sediments from the shore of Lake Victoria and from some streams flowing into the lake have been analyzed for their heavy metal content using Energy Dispersive X-Ray Fluorescence (EDXRF) analysis. The samples were collected from seventeen different locations around the Municipality of Mwanza divided into three zones according to their activities. The results show that sediments from Mwanza North, which is least in anthropogenic activities, contains Cr and Co in addition to metals of terrestrial origin (K, Ca, Ti, Mn, Fe, Rb, Sr, Y, and Zr), samples from Mwanza Central, which is the town center, contains high concentrations of V, Cu, Zn and Pb, and samples collected from Mwanza South, which is the industrial area, contains the highest concentrations of V, Cu, Zn, As and Pb. It is concluded that the industrial and sewage wastes discharged into the lake are the main sources of the heavy metal contamination of Lake Victoria. Further studies will be required to assess detriments of these pollutants to human and aquatic life before policy for the factories responsible is put in place.
Environmental Air Degradation in Dar es Salaam by X-Ray Fluorescence
(Taylor and Francis, 2002) Koleleni, Yusuf I. A.
In Dar es Salaam a study of the aerosol contents was conducted and particulate matter on the filters were collected using an AndersenTM PM10 impactor to determine the environmental air pollution. The contents were determined by X-ray fluorescence analysis. In this study sources of environmental degradation and the concentrations were named as follows: Combustion processes with range of Br from 10 to 800 ng/m3, Pb from 30 to 790 ng/m3. Industrial processes with range of Fe from 37 to 883 ng/m3, Cu from 14 to 310 ng/m3, Zn from 6 to 820 ng/m3. Top soil activities with range of K from 20 to 540 ng/m3, Ca from 24 to 3805 ng/m3, Ti from 2 to 59 ng/m3, Mn from 10 to 386 ng/m3. Marine processes with range of Cl from 20 to 310 ng/m3, S from 72 to 134 ng/m3.
A survey of background radiation dose rates and radioactivity in Tanzania
(2002-02) Banzi, Firmi B.; Msaki, P.; Makundi, Ismael
Potential terrestrial sources of naturally occurring elevated radiation levels have been identified in Tanzania. Thus, efforts are currently being undertaken to create a natural radiation database, in the form of a radiation level map of natural radioactivity, to be used to assess the associated radiation risk to public and workers. Background radiation dose rate was determined with thermoluminescent dosimeters for 7 y (1993-1999) in five stations. The average background radiation dose rates for these stations were as follows: Tropical Pesticides Research Institute (TPRI) (102 +/- 7 nGy h(-1)), Same (98 +/- 2 nGy h(-1)), Namanga (98 +/- 5 nGy h(-1)), University of Dar Es Salaam (99 +/- 2 nGy h(-1)), and Kilimanjaro Christian Medical Center (121 +/- 3 nGy h(-1)). These stations were found convenient from an economic point of view since the project has no funds to cover wider and/or more remote areas in Tanzania. For the sake of comparison, similar measurements were made for the same period at Minjingu phosphate mine. The mine was one of the suspected areas with elevated levels of natural radioactivity. The radiation dose rate measured in this mine was about fourteen times higher (1,415 +/- 28 nGy h(-1)) than the average value obtained in northern Tanzania (98 nGy h(-1)). The high average activity levels of phosphate (5760 +/- 107 Bq kg(-1) for 261Ra, 497 +/- 5 Bq kg(-1) for 228Ra, 350 +/- 6 Bq kg(-1) for 228Th, and 280 +/- 5 Bq kg(-1) for 40K) and radiation dose rate recorded show that Minjingu phosphate mine has higher values than the highest radioactivity in phosphate compiled by the United Nations Scientific Committee on the Effect of Atomic Radiation. In view of these findings, a comprehensive risk-management strategy for reduction of radiation risk to the public and mine workers should be put in place. Efforts are currently being made to seek support to improve the background radiation database for subsequent assessment of radiation risk to miners and the societies in the
Superconductivity in Magnesium Diboride Thin Films
(2002-04) Ivanova, Z.; Malisa, Anayesu B.; Johansson, L. -G; Komissinski, P. V.
Mg–B thin films were grown in situ on (1 0 0) SrTiO3 substrates by pulsed laser deposition. Targets pressed from a commercial MgB2 powder had a superconducting transition temperature of 37 K. Films were characterized by atomic force microscopy and susceptibility measurements. First samples showed superconducting onset at 30 K and became superconducting at about 20 K. Films were patterned into microbridges 4–100 μm wide by Ar ion beam milling. Films had large contact resistances, of the order of 500 Ω cm2 in the temperature range 4.2–300 K.
Levels of Aerosol in Dar Es Salaam, Tanzania, Compared to Some Cities
(2003) Koleleni, Yusuf I. A.
The aerosol concentrations in the city of Dar es Salaam were found with aim of investigating pollution levels. The aerosol samples were collected on the sites of Tanzania Oxygen Limited (TOL) which is purely an industrial area, Ocean Road Cancer Research Institute (ORCRI) located along the sea shore at the port exit, and Dar es Salaam International Airport (DIA) far from the city center. The PM10 dichotomous impactor was used for sample collection. The analysis of the samples was conducted with x-ray fluorescence spectrometer. The values obtained for Dar es Salaam aerosol samples are compared to similar samples of aerosol data available for the cities of Kinshasa and Butare in the republic of Congo and Rwanda respectively. The elements found in the aerosol samples include Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Br, Rb, Sr, Zr, Pb and Se. The variations of the minimum and maximum values of the elemental concentration in the sample for these elements are given for the months between September 1996 and May 1997. The elemental variation was affected by seasonal weather parameters like rain, wind speed and their directions. Temperatures varied between 29 and 32°C; rainfall between 5 and 70 mm while wind speed varied between 5 and 20 m/s.
Josephson Junctions Fabricated by Focused Ion Beam from Ex Situ Grown MgB2 Thin Films
(2004-03) Malisa, Anayesu B.; Valkeapää, M.; Johansson, L. -G; Ivanov, Zdravko
We prepared MgB2 thin films on SrTiO3 (1 0 0) and Al2O3 (1 1̄ 0 2) substrates by e-beam evaporation of MgB2 pellet. The films were deposited at room temperature and post-annealed at 900 °C in Mg vapour for 5–30 min. Superconducting transition temperatures were observed between 22 and 30 K. Structure and surface morphology of the films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM). The films grown on Al2O3 substrates are c-axis oriented while a film grown on SrTiO3 substrate is aligned with the (1 0 1) direction normal to the substrate planes. The films have grain sizes of about 70 nm. The films were patterned into 4 and 8 μm wide microbridges. The microbridges were observed to carry large critical current densities of approximately 1 MA/cm2 at 6.7 K. Focused ion beam (FIB) was used on the bridges in order to fabricate Josephson junctions. A cut 50 nm in width was made across the microbridges followed by an in situ platinum (Pt) deposition into the cut made. SNS-like weak-link junctions were formed in the process.
Josephson Effects in Magnesium Diboride Based Josephson Junctions
(2004-04) Malisa, Anayesu B.; Valkeapää, Markus; Johansson, Lars G.; Ivanov, Zdravko
We report on Josephson effects in Josephson junctions fabricated from magnesium diboride (MgB2) thin films using a focused ion beam (FIB) milling technique. The films were deposited on SrTiO3(100) and {\mathrm {Al_2O_3}}(1\bar 102) substrates at room temperature using e-beam evaporation of MgB2 with a post-annealing stage in Mg vapour. Conventional photolithography and Ar-ion-beam milling were used to pattern the films into 4 and 8 µm wide microbridges. A focused ion beam was used to narrow the microbridges to 2 µm. The narrowed microbridges were thinned by making 50 nm wide cuts across them. The depth of each cut was calibrated to remove 75% of the film thickness. A thin MgB2 layer remained on the substrate after this process. The current–voltage (I–V) characteristics of junctions made using this technique show that the junctions carry excess current. The first Shapiro step was observed when one of the junctions was irradiated with a microwave field of frequency f = 8.92 GHz. The Shapiro step appeared at a voltage value V = hf/2e = 18.445 µV.
Ultrasound Use for the Placement of Dialysis Catheters
(Wiley, 2005) Prasad, B. T.; Kumwenda, Mwingereza J.; Stiff, Rhianwen E.
In Situ Superconducting MgB2 Films Grown by Co-evaporation Technique
(2005) Malisa, Anayesu B.
Superconducting thin films of MgB2 were grown in situ by co-evaporation of magnesium and boron on MgO (111), SiC (0001) and Al2O3 (0001) substrates at ∼300 °C. The films showed transitions to the superconducting state in the temperature range of 33–37 K. The widths of the superconducting transitions were less than 1 K. The films exhibited growth in the c-axis and absence of other phases. Optimization of the growth parameters enabled films with smooth surface morphology and root-mean-square (RMS) roughness of 2 nm to be grown. The low RMS roughness value indicates that the technique can be used to grow MgB2 films useful for junctions and multilayer devices. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Colossal magnetoresistance effect in epitaxially grown La2/3Ca1/3MnO3 perovskite-like manganite thin films
(2005-02) Malisa, Anayesu B.; Ivanov, Z.
We report in this work, study on colossal magnetoresistance (CMR) effect in epitaxial La2/3Ca1/3 MnO3 thin films grown on SrTiO3 (0 0 1) substrates by pulsed laser deposition (PLD) technique. The films were grown on as-received SrTiO3 substrates and on SrTiO3 substrates prepared by HF etching (Koster et al., Appl. Phys. Lett. 73 (1998) 2920; V. Leca et al., Wet etching methods for perovskite substrates, University of Twente, MESA+ Research Institute, Low Temperature Division). Two of the samples were annealed in different conditions to investigate the films heat treatment effect on electric and magnetic properties. Electrical resistance was done using the four-probe method at temperatures in the range of 2–375 K without a magnetic field and in an external field of 5 T applied in the film plane. Resistance-magnetic field (R vs. H) at 77 K for the two annealed samples was done in a 5 T sweep magnetic field. The surface morphology and structural information of the films were obtained using atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. Secondary ion mass spectroscopy (SIMS) analysis was performed on the annealed samples to investigate any possible chemical reaction between La2/3Ca1/3MnO3 thin films and SrTiO3 substrate.

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