Department of Physics

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Advances in chromogenic materials and devices
(2010-03) Granqvist, C. G.; Green, Sara V.; Niklasson, Gunnar A.; Mlyuka, N.R.; Von Kræmer, S.; Georen, Peter
Chromogenic materials allow the transmittance of visible light and solar energy to be varied under the action of an external stimulus. This paper first discusses buildings related energy savings that can be accomplished by chromogenic technologies, and their beneficial effects on comfort issues. We then summarize recent work on thermochromic VO2-based thin films with particular attention to multi-layers of VO2 and TiO2 and to new VO2:Mg films for which the doping gives significantly lowered absorption of visible light. The final part covers electrochromic materials and devices with foci on coloration efficiency and on durability issues for foil-type constructions based on films of WO3 and NiO.
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)
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.
Analysis of Heavy Metals in the Shellfish from the Neighbourhood of the Sea Port of Zanzibar
(2016-03) Koleleni, Yusuf I. A.; Haji, O. O.
Shellfish is one of the major sources of food for coastal population of Zanzibar. Toxicity of shell fish by heavy metals is of concern to consumers. This study aimed at assessing the metal concentrations of the shellfish along the coast in the neighbourhood of Sea Port of Zanzibar. Shellfish (namely oysters, mussels, clams and crabs) were collected for the assessment on effects of heavy metal contamination among the aquatic organisms. The concentrations of the shellfish were determined using Energy Dispersive X-ray Fluorescence (EDXRF). The concentrations analysed include Cr, Mn, Fe, Ni, Cu, Zn, Cd and As. The range ofCd, Cr, Ni, Mn and Zn were found to be higher in clams while Fe, Pb and Cu were found to be higher in crabs. The values of Cr, Cu, Zn, As and shellfish species appear to be higher than the values reported in the literature.
Analysis of Rock-Geological Material from Places in Tanzania by Wavelength Dispersive X-ray Fluorescence Spectrometer
(2009) Koleleni, Yusuf I. A.
A number of precious stones and minerals in Tanzania are found either just on the ground surface or unexplored inside the earth. Principally, those found at the surface differ in their source of origin from those found inside the earth. Some of these stones are coming from the rocks in their present locations (primary deposits) while others are transported from other places (secondary deposits). The mechanism of transportation may be rivers, sea or wind. The distribution of these valuable stones is geographically irregular in Tanzania and in some of the regions the deposits are higher compared than others. In several parts of the country such information is completely unavailable and in many cases unexplored. In order to provide this information to the decision makers and investors, Wavelength Dispersive X-ray Fluorescence (WDXRF) Analysis has been used with objective of identifying the composition of some of these stone and rock samples. The samples identified and reported in this paper include: Iron ore, Green Aventurine, Amethyst, Red Garnet, Sapphire nuts, Green Opal, Blue Kymete, Black Tormaline, White opal, Aquamarine and Granite. The samples were prepared as pellets after mixing with boric acid or fused as discs for analysis. Typical results for the Iron Ore in % are SiO2 (0.97), Al2O3 (0.57), Fe2O3 (77.5), MnO (0.35), MgO (0.35), CaO (0.16), Na2O (< 0.01), K2O (0.04), TiO2 (19.1), P2O5 (< 0.01), SO3 (0.14) and that of the Amethyst SiO2 (97.8), Al2O3 (0.11), Fe2O3 (1.37), MnO (< 001), MgO (< 0.01), CaO (< 0.01), Na2O (< 0.01), K2O (< 0.01), SO3 (0.33). The results show that Tanzania is a very rich country in minerals but are currently unexplored either because of lack of information or investment capital.
ASSESSMENT OF HEAVY METAL AND RADIOACTIVITY LEVELS IN SPINACH (Spinacia oleracea) GROWN AT BAHI WETLANDS IN DODOMA REGION
(College of Natural and Applied Sciences, 2018) Mohammed, Najat K.; Haule, Boniface
This study reports on the levels of heavy metals and radionuclides in Spinach (Spinacia oleracea) grown in Bahi wetlands in Dodoma Region. The farm soil in Bahi wetland has been reported to contain elevated concentrations of 238U, 232Th and 40K due to the existence of shallow uranium deposit in the area. In this study, spinach (Spinacia oleracea) grown in three zones of Bahi district were analyzed for heavy metals and radioactivity associated with the uranium deposit in the area. The concentrations of elements were determined by Energy Dispersive X-ray Analysis (EDXRF) of Tanzania Atomic Energy Commission, Arusha. The activities of the radionuclides were calculated from their concentration in μg/g. The concentrations of Pb and Cd in all samples were found to be higher than the maximum tolerable limits recommended by Codex 2015. The results show that, the mean activities of 232Th (10.8 Bq/kg) and 40K(686.9 Bq/kg)in the samples are lower than the maximum tolerable limits (1000 Bq/kg) recommended by WHO/FAO, yet higher than their activities in samples of spinach collect from a control area. Hence, regular monitoring of heavy metals and radioactivity level in farm soils and agricultural products is recommended.
ASSESSMENT OF HEAVY METAL CONCENTRATION IN WATER AROUND THE PROPOSED MKUJU RIVER URANIUM PROJECT IN
(College of Natural and Applied Sciences, 2015) Banzi, Firmi B.; Msaki, Peter K.; Mohammed, Najat K.
Effective verification for compliance with water quality standards in uranium mining in Tanzania requires data sensitive to monitor heavy metal concentration in water around the Mkuju River Uranium Project before mining commences. The area susceptible for pollution by the project was estimated using AERMOD dispersion model and found to cover about 1300 km2. Thirty one surface and groundwater samples were collected and analysed for heavy metals and physicochemical properties using ICP-MS and standards techniques, respectively. The physicochemical properties for water samples analysed ranges from 5.7 to 7.8 for pH, 2.8 to 80.2 mg/L for TDS and 15 to 534.5 mS/cm for EC. These values show that the water in the vicinity of the Mkuju River Uranium Project is normal. The ranges of concentration of heavy metals (μgL-1) determined in water ranges were: Al(2 to 9049), Cr(0.2 to 19.96), Mn (0.1 to 1452),Fe(2 to 53890),Co(0.02 to 27.63), Ni(0.2 to 9.7), Cu(2 to 17), Zn(2 to 62.94), As(0.4 to 19.17), Cd(0.02 to 0.14), Pb (0.02 to 78.68), Th (0.002 to 1.73),U(0.002 to 29.76). These values are below the tolerance levels of concentrations set by different International organisations. Therefore heavy metal toxicity in the study area is marginal. The parameters that could serve as baseline data because of their enhanced sensitivity to pollution were (i) concentration of chromium, cobalt, nickel, copper, zinc, arsenic, cadmium and lead in water (ii) pH, TDS and EC for water, (iii) TDS ratio for surface to ground water values and (iv) correlation coefficients between the heavy metals. However, since TDS values are season dependent, this indicator can serve as baseline data when measured during the dry season as was the case in the study.
Assessment of Heavy Metal Concentration in Water around the Proposed Mkuju River Uranium Project in Tanzania
(2015) Banzi, Firmi B.; Msaki, Peter K.; Mohammed, Najat K.
Effective verification for compliance with water quality standards in uranium mining in Tanzania requires data sensitive to monitor heavy metal concentration in water around the Mkuju River Uranium Project before mining commences. The area susceptible for pollution by the project was estimated using AERMOD dispersion model and found to cover about 1300 km2 . Thirty one surface and groundwater samples were collected and analysed for heavy metals and physicochemical properties using ICP-MS and standards techniques, respectively. The physicochemical properties for water samples analysed ranges from 5.7 to 7.8 for pH, 2.8 to 80.2 mg/L for TDS and 15 to 534.5 mS/cm for EC. These values show that the water in the vicinity of the Mkuju River Uranium Project is normal. The ranges of concentration of heavy metals (µgL-1 ) determined in water ranges were: Al(2 to 9049), Cr(0.2 to 19.96), Mn (0.1 to 1452),Fe(2 to 53890),Co(0.02 to 27.63), Ni(0.2 to 9.7), Cu(2 to 17), Zn(2 to 62.94), As(0.4 to 19.17), Cd(0.02 to 0.14), Pb (0.02 to 78.68), Th (0.002 to 1.73),U(0.002 to 29.76). These values are below the tolerance levels of concentrations set by different International organisations. Therefore heavy metal toxicity in the study area is marginal. The parameters that could serve as baseline data because of their enhanced sensitivity to pollution were (i) concentration of chromium, cobalt, nickel, copper, zinc, arsenic, cadmium and lead in water (ii) pH, TDS and EC for water, (iii) TDS ratio for surface to ground water values and (iv) correlation coefficients between the heavy metals. However, since TDS values are season dependent, this indicator can serve as baseline data when measured during the dry season as was the case in the study.
Assessment of heavy metal contamination in vegetables consumed in Zanzibars
(Scientific Research, 2012-01) Mohammed, Najat K.; Khamis, Fatma
Samples of amaranth and cabbage from Zanzibar were analyzed for heavy metal concentrations using Energy Dispersive X-ray Fluorescence spectrometry (EDXRF) of Tanzania Atomic Energy Commission (TAEC) in Arusha. Thirty samples of amaranth and twenty five samples of cabbage were collected from four farms and two markets at Urban West Region in Zanzibar. The concentrations of Al, Cl, Cr, Mn, Fe, Ni, Zn, Cu, Ag, I, Br, Cd and Pb are presented and discussed. Amaranth had significant (P < 0.05) higher concentrations of Zn, Fe, Cr and Mn than cabbage, whilst Cd, Ni and Pb were significantly (P < 0.05) higher in cabbage than amaranth. Although the mean concentrations of the essential elements were in the range reported in literature, Pb and Cd were in concentrations above FAO/ WHO maximum tolerable limits.
Assessment of Natural Radioactivity in Soil and its Contribution to Population Exposure in the Vicinity of Mkuju River Uranium Project in Tanzania
(Science Technol, 2016) Banzi, Firmi B.; Msaki, Peter K.; Mohammed, Najat K.
The level of 226Ra, 232Th and 40K was established in soil collected in an area about 1,300 km2 in the vicinity of Mkuju uranium project in Tanzania and selected points in the concession using HPGe spectrometer and associated exposure risks to population were estimated. The radioactivity concentration in the vicinity range (Bqkg-1) for 226Ra (24.94 to 53.50), 232Th (20.86 to 47.14), and 40K (344.50 to 697.54). Whereas, radioactivity in the concession range for 226Ra (2430.00 to 4200.00), 232Th (130.00 to 220.00), and 40K (1293.30 to 1466.10). On average the radioactivity in the concession were about 89, 5 and 3 times high than those in the vicinity. Based on the measurements, the hazards attributable to use of soil from the vicinity for different purposes is marginal. However, the hazards indices indicate that soils from the concession have relatively a significantly risk by range of factors about 27 to 29 and 40 to 42 times high than in the vicinity for the external and internal hazards, respectively. Also the radium equivalent radioactivity, dose rate and effective dose tend to be significantly high in the concession than in the vicinity by range of factors from 27 to 29, 23 to 25 and 23 to 25, respectively. These findings reveals that soils in the vicinity of the project could pose less radiological risk to human health when compared to soil in the concession.
ASSESSMENT OF RADIOACTIVITY LEVELS IN COAL AND COAL ASH IN KIWIRA COAL MINE USING GAMMA-RAY SPECTROMETRY
(College of Natural and Applied Sciences, 2018) Makundi, Ismael N.; Nyaki, Mungubariki M; Mohammed, Najat K.
This study aimed to assess the radioactivity levels and associated dose rates from the naturally occurring radionuclides 226Ra, 232Th and 40K in coal and coal ashes at Kiwira coal mine. The radioactivity of 40 representative coal, fly ash samples were measured using gamma spectroscopy of the Tanzania Atomic Energy Commission (TAEC) in Arusha, Tanzania. The activity concentrations of 226Ra, 232Th and 40K in coal and coal ashes from Kiwira were higher by several orders of magnitude than their worldwide average values. The calculated radium equivalent activity, the air absorbed dose rate, external hazard index and the average annual effective dose rate in fly ashes were 1335 ± 60 Bq kg-1, 610 ± 29 nGy h-1, 4 ± 0.4, 738 ± 52 μSv y-1 which were higher than the international recommended values of 370 Bq kg-1, 57 nGy h-1, and 70 μSv y-1 for fly-ashes respectively. The results provide information for the radiation protection when the coal and its by-products in the vicinity of Kiwira coal field is used. The data can be used by the authorities to design an appropriate method for handling wastes and implement intervention measures to protect the miners, the public as well as the environment.
ASSESSMENT OF RADIOACTIVITY OF 226Ra, 232Th AND 40K IN SOIL AND PLANTS FOR ESTIMATION OF TRANSFER FACTORS AND EFFECTIVE DOSE AROUND MKUJU RIVER PROJECT, TANZANIA
(2017) Banzi, Firmi B.; Msaki, Peter K.; Mohammed, Najat K.
Purpose. To establish pre-mining indicators to assess radiological impact as a result of release of radionuclides to environment during uranium mining at Mkuju River Project radioactivity of 226Ra, 232Th and 40K in soil, plants, fruits and cereals. Methods. The High Purity Germanium detector was used to determine the radioactivity and the data were subsequently used to establish soil to plant transfer factors and annual effective dose. Findings. The results revealed a strong positive correlation (r) of 0.947 and 0.950 for 226Ra and 232Th, respectively, between values determined in soils and plants. Implicit in these finding is that the distribution of radionuclides in soils is directly proportional to the corresponding radionuclides in plants. Originality. The roots of wild grass had the highest specific radioactivity (Bqkg-1) for 226Ra (2.15 ± 0.02), 232Th (1.43 ± 0.02) and 40K (198.16 ± 1.72) and the roots of cabbage had the highest values for 226Ra (1.38 ± 0.04), 232Th (1.34 ± 0.03) and 40K (146.12 ± 1.02) among the food crops, an indication of a higher ability to uptake radionuclides from soil. Similarly, since the TFs were found higher in wild grass for 226Ra (0.0533 ± 0.04), 232Th (0.0374 ± 0.002) and 40K (0.5297 ± 0.05) and cabbage for 226Ra (0.0362 ± 0.03), 232Th (0.0360 ± 0.001) and 40K (0.4173 ± 0.05). Practical implications. It is an evident that these plants can serve as good bio indicators to assess release of radionuclides from inside the mining site to the public domain. Moreover, the annual effective dose (mSvy-1) for 40K (0.23 ± 0.02), 226Ra (0.046±0.004) and 232Th (0.073 ± 0.006) in edible crops when consumed in the vicinity of the MRP before the mining operations were, as expected, insignificant.
ASSESSMENT OF THE ESSENTIAL AND TOXIC ELEMENTS IN COMPLEMENTARY FOODS FOR UNDER FIVE CHILDREN IN TANZANIA USING EDXRF SPECTROSCOPY
(College of Natural and Applied Sciences, 2016) Paschal, Catherine; Mohammed, Najat K.
In this study, the commonly used complementary foods (Unga wa Lishe) for children 0-5 years in Tanzania were analyze for essential and toxic elements in order to assess their nutritional levels. 60 samples were purchased from shops in Dar es Salaam, Moshi and Arusha regions and analyzed using Energy Dispersive X-Ray Fluorescence Spectroscopy (EDXRF). The concentrations of the essential elements were referenced to the Recommended Nutrient Intake (RNI) values for 6-12 months old children while the levels of toxic elements were compared to the Maximum Tolerable Limits (MTL) set by WHO 2004. The nutrient intake for Fe, Zn, Cu and Ca obtained in the complementary foods were less than the RNI values of 11.6 mg/day, 8.3 mg/day, 0.56 mg/day and 500 mg/day respectively set by Joint FAO/WHO and Codex. On the other hand, the concentrations of the toxic elements Ni and As were higher than the MTL (0.2 μg/g and 11 μg/g, respectively) for these elements recommended by EC and WHO 2004, respectively. Further analysis of the complementary foods in Tanzanian is needed to produce more data which will be a guide for the appropriate measures to reduce mineral malnutrition in Tanzania.
Assessment of the Lake Gendabi salt for trace elements and toxic heavy metals by energy dispersive X-ray fluorescence spectrometry
(Springer Netherlands, 2012-08) Lugendo, Innocent; Mohammed, Najat K.; Mussa, L. M.; Spyrou, Nicholas M.
This study has analyzed samples of salts from Lake Gendabi, located in the northern part of Tanzania for metal contamination using the EDXRF spectrometry. The aim of the study was to assess the suitability of the salt from Lake Gendabi for human consumption. Seventy-five samples of salt were collected from the Lake Gendabi floor and grouped into five grades (G1, G2, G3, G4 and G5) depending on the position of the salt from the lake shore. In addition to Na and Cl, concentrations of 17 more elements were determined in all five grades of salt. These included seven toxic metals which are Al, Ni, Cr, Cd, Pb as well as Th and U which are both toxic and radioactive. The concentrations of all toxic elements found in the samples were higher than their Maximum tolerable limits set by international organizations. As this salt is used in many parts of Tanzania, it is proposed that the salt should be thoroughly purified before entering the market. Further research to include salt samples from other salt production areas in Tanzania is recommended.
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.
Band gap widening in thermochromic Mg-doped VO2 thin films: Quantitative data based on optical
(2013-10) Li, S.-Y.; Mlyuka, N.R.; Primetzhofer, Daniel; Hallén, Anders; Possnert, Goran; Niklasson, Gunnar A.; Granqvist, C. G.
hermochromic Mg-doped VO2 films were deposited by reactive DC magnetron sputtering onto heated glass and carbon substrates. Elemental compositions were inferred from Rutherford backscattering. Optical band gaps were obtained from spectral transmittance and reflectance measurements—from both the film side and the back side of the samples—and ensuing determination of absorption coefficients. The band gap of Mg-doped films was found to increase by 3.6 ± 0.6 eV per unit of atom ratio Mg/(Mg + V) for 0 < Mg/(Mg + V) < 0.21. The presence of ~0.45 at.% Si enhanced the band gap even more.
Ca-doped Ba2Cu3O7–δ Bicrystal Junctions Fabricated on Asymmetric SrTiO3 Substrates
(2005-07) Malisa, Anayesu B.
Bicrystal grain–boundary Josephson junctions of Ca–doped YBa2Cu3O7–δ that is Y0.7Ca0.3Ba2Cu3O7–δ were fabricated on three bicrystal SrTiO3 (001) substrates with asymmetric 30°, 40° and 45° orientations. An enhancement of the critical current density in these Ca–doped junctions was observed when compared with normal YBCO grain–boundary junctions with similar angular orientations. The observed increase in the critical current density is large for the junctions fabricated on the asymmetric 30° bicrystal substrate and small or negligible, for those on the asymmetric 45° bicrystal substrate. The critical current was modulated by a magnetic field applied in the plane of the junctions. However, the Fraunhofer pattern observed due to the applied magnetic field deviates from the ideal one.
Challenging Issues in Regulating Uranium Mining in Tanzania
(Springer International Publishing, 2014-09) Banzi, Firmi B.; Msaki, Peter; Mohammed, Najat K.
Experiences have shown that unregulated uranium mining practices have led to significant radiological risk to workers, public and the environment. Tanzania is about to start uranium mining in different parts of the country. Although the legislation and regulations to control doses to workers, public and the environment are in place, there are challenges to adequately address best practice requirements during and after the mining operations. This paper provides an overview of the challenges in addressing the regulatory compliance
Chromogenics for Sustainable Energy: Some Advances in Thermochromics and Electrochromics
(2010-10) Granqvist, C. G.; Green, Sara V.; Li, S.-Y.; Mlyuka, N.R.; Niklasson, Gunnar A.; Avendaño, E.
Chromogenic materials are able to change their optical properties in response to external stimuli such as temperature (in thermochromic materials) and electrical charge insertion (in electrochromic materials). Below we review some recent advances for these types of materials. Specifically we first discuss the limitations of thermochromic VO2 films for energy efficient fenestration and show from calculations that nanocomposites containing VO2 can have superior properties and display high luminous transmittance and large temperature-dependent solar transmittance modulation. Even better results may be found for nanoparticles of VO2:Mg. In the second part of the paper we survey some recent progress for electrochromic devices and show that W oxide films have increased coloration efficiency when some Ni oxide is added. We also present initial results for flexible electrochromic foils produced by roll-to-roll coating and continuous lamination.
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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