Department of Physics

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Determination of essential and toxic elements in clay soil commonly consumed by pregnant women in Tanzania
(Elsevier, 2013) Mwalongo, D.; Mohammed, Najat K.
A habit of eating clay soil especially among pregnant women is a common practice in Tanzania. This practice known as geophagy might introduce toxic elements in the consumer's body to endanger the health of the mother and her child. Therefore it is very important to have information on the elemental composition of the eaten soil so as to assess the safety nature of the habit. In this study 100 samples of clay soil, which were reported to be originating from five regions in Tanzania and are consumed by pregnant womenwere analyzed to determine their levels of essential and toxic elements. The analysis was carried out using energy dispersive X-ray fluorescent technique (EDXRF) of Tanzania Atomic Energy Commission, Arusha. Essential elements Fe, Zn, Cu, Se and Mn and toxic elements As, Pb, Co, Ni, U and Th were detected in concentrations above WHO permissible limits in some of the samples. The results from this study show that the habit of eating soil is exposing the pregnant mothers and their children to metal toxicity which is detrimental to their health. Hence, further actions should be taken to discourage the habit of eating soil at all levels.
Natural Radioactivity in Water and Its Potential Human Health Risk in the Vicinity of Mkuju River Uranium Projectin Tanzania
(SciencePG, 2016) Banzi, Firmi B.; Msaki, Peter K.; Mohammed, Najat K.
Consistent with best practices in uranium mining, the collection and use of site characterisation data are indispensable to ensure compliance with regulations. To comply with this requirement, two samples from each of the 47 locations were collected in an area of about 1300 km2 in the vicinity and concession area of the Mkuju River Project. The samples were analysed for radioactivity using alpha spectrometry. The activity concentrations were used to estimate health risks attributable to the consumption of drinking water containing radionuclides. The range of activity concentrations (mBqL-1) were much higher in groundwater collected from the concession area for 238U (79.89 to 87.06), 234U (79.44 to 88.38), 226Ra (41.61 to 59.07), 232Th (5.32 to 9.41), and 228Ra (3.98 to 8.59) than in groundwater for 238U (20.61 to 47.21), 234U (21.70 to 49.10), 226Ra (16.80 to 43.45), 232Th (0.12 to 2.80), and 228Ra (0.10 to 2.43), and surface water for 238U (17.33 to 27.24), 234U (21.06 to 34.43), 226Ra (15.00 to 25.61), 232Th (0.16 to 2.10), and 228Ra (0.12 to 1.99) collected in the vicinity of the project. The calculated annual effective doses and carcinogenic risks resulting from the activity concentrations in drinking water were relatively marginal, since the activity concentrations were lower than the WHO permissible limits for drinking water. These findings suggest that the water resources at MRP are safe. Thus, since this study was conducted before mining activities, these data can be used as a baseline for monitoring potential future water pollution around the Mkuju River Project.
Heavy Metal Concentrations in Soil from Selected Rice Farms at Cheju, Zanzibar
(SCIENCEDOMAIN international, 2015) Mohammed, Najat K.; Makame, Rashid K.
Advancement of science and technology has enhanced the use of chemical products, such as fertilizer and pesticides, into agriculture to improve yield. Normally, these products contain metals which are detrimental to human health. These metals may be absorbed by plants and hence be introduced into food chain. In this study, samples of soil from Cheju rice farms were analyzed for heavy metals associated with agrochemicals using Energy Dispersive X-ray Fluorescence (EDXRF) Spectrometry. Sixty soil samples were collected from Cheju rice farms and 10 control samples were collected from Mwera about 25 km from Cheju. T-test to compare the mean concentrations of elements in fertilized and control soils showed that the soil samples from Cheju farms had significantly higher concentrations of most of the determined metals compared to the control sample. Higher concentrations of these elements in fertilized soil may be attributed to the repeated use of agrochemicals in farming. Analysis of rice grains from the field and other samples from the neighbouring ecosystem is recommended.
Impact of North Mara gold mine on the element contents in fish from the river Mara, Tanzania
(Springer, 2016) Mohammed, Najat K.; Ntarisa, A. V. R.; Makundi, Ismael N.; Kucˇera, J.
The aim of the study was to determine element concentrations in lungfish and catfish from the river Mara with INAA and EDXF to assess the health impact of the North Mara gold mine (NMGM) in Tanzania. Twenty samples of each species were collected from two sites downstream and upstream along the river Mara in the vicinity of NMGM. The sampling sites were 70 km apart. Significantly higher concentrations (p B 0.05) of Cr, Ni, Cu, and Se in one of the species taken downstream than in those taken upstream might indicate contamination of the river Mara caused by the mining activities.
DETERMINATION OF RADIOACTIVITY IN MAIZE AND MUNG BEANS GROWN IN THE NEIGHBORHOOD OF MINJINGU PHOSPHATE MINE, TANZANIA
(College of Natural and Applied Sciences, 2014) Nkuba, Leonid L.; Mohammed, Najat K.
Two staple foods (maize and mung beans) which were cultivated in Minjingu village, where there is phosphate deposit in Tanzania, were collected directly from the farms. The activity concentrations of 226Ra, 228Th and 40K were determined in the maize and mung beans samples using γ ray spectrometry employing HPGe detector of relative efficiency of 51.0 %. The mean radioactivity level in the food samples were found to be 21.01 ± 0.8 Bq/kg (mung beans), 25.6 ± 0.7 Bq/kg (maize) for 226Ra, 62.6 ± 1.1 Bq/kg (mung beans), 72.9 ± 1.0 Bq/kg (maize) for 228Th and 542.9 ± 8.6 Bq/kg (mung beans), 434.6 ± 18.7 Bq/kg (maize) for 40K. The radioactivity content of the maize and mung beans from Minjingu village were higher than that of similar food samples collected from Bukombe district in Geita Region in Tanzania. The total annual effective dose for consumption of 226Ra and 228Th by adults was calculated to be 2.003 ± 0.044 mSv/year, which is higher than the annual dose limit of 1 mSv/year recommended by the ICRP for the general public. Hence a conclusion could be made that food crops cultivated at Minjingu village might expose the population to high radiation dose which might be detrimental to their health.
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.
Heavy Metals and Essential Elements in Selected Medicinal Plants Commonly Used for Medicine in Tanzania
(SCIENCEDOMAIN international, 2017) Nkuba, Leonid L.; Mohammed, Najat K.
Several plants in Tanzania are known to be of potential therapeutic value and are used in traditional medicine system of the country. In this paper, two medicinal plants Moringa oleifera (leaves and roots), and Hibiscus sabsdariffa (rosella calyces) were analysed for elemental concentration. Essential and non-essential heavy metals like Mg, K, Mn, Fe, Ni, Cu, Zn, Cd and Pb were quantified in selected medicinal plants by EDXRF technique. The main purpose of this study is to document the presence and the levels of heavy metals in these herbs. High Potassium contents were observed to be 20882.20 ± 253.65 mg/kg in Moringa oleifera roots, in Hibiscus sabsdariffa (rosella calyces) 15732.03 ± 191.27 mg/kg, and 14541.08 ± 206.83 mg/kg in Moringa oleifera leaves. Magnesium was the second abundant element with concentration (5058.13 ± 115.80 mg/kg in Moringa oleifera leaves, 4328.86 ± 132.85 mg/kg Hibiscus sabsdariffa and 1400.59.59 ± 72.09mg/kg in Moringa oleifera roots), followed by Iron (716.57 ± 48.05 mg/kg in Hibiscus sabsdariffa, 556.44 ± 11.77 mg/kg and 309.57 ± 8.96 mg/kg in Moringa oleifera roots and leaves respectively. Except Fe and Ni in all plant samples and Mg in leaves of Moringa oleifera and calyces of Hibiscus sabsdariffa as well as Mn in roots of Moring oleifera, the concentrations of other metals were below the permissible limits in plants set by FAO/WHO. The results presented that there is no risk associated with consumption of analysed medicinal plants. However, since Cd was not detected and it is highly toxic even at very low concentrations. Therefore, further analysis which will employ other analytical techniques and includes more samples is needed to have a definite statistical conclusion on the safety consumption of the analysed medicinal plants. The results also show that the analysed plant species are beneficial sources of appropriate and essential trace elements.
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 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.
INDOOR RADON CONCENTRATION LEVELS AND ANNUAL EFFECTIVE DOSES FOR RESIDENCE OF HOUSES NEAR URANIUM DEPOSIT IN BAHI DISTRICT, DODOMA, TANZANIA
(College of Natural and Applied Sciences, 2018) Mohammed, Najat K.; Focus, Erasto
The objective of this study was to determine the levels of indoor radon concentration in houses in Bahi District situated in the neighbourhood of uranium deposit. The study aimed also to assess the annual effective dose due to indoor radon exposure to individuals residing in the houses as a step to control the radon exposure in Tanzania. Two villages were involved in this study; Bahi Makulu, which is within the proximity of Uranium deposit and Bahi Sokoni, which is about 7 km from the deposit. The Indoor radon concentration levels were detected using Alpha Guard radon monitor and the obtained mean concentration levels are presented and compared with the mean concentrations levels published in literature. The results revealed that 78% of the houses involved in this study have concentration levels of indoor radon above the reference level of 100 Bq/m3 set by WHO 2009. The levels are higher in traditional houses which are mostly built with poor ventilation than the modern houses with good ventilation. Out of the two villages involved in this study, Bahi Makulu which is closer to the uranium deposit has significantly higher (p<0.01) concentrations of indoor radon than Bahi Sokoni. The calculated annual effective doses for the population in both villages are higher than the dose reference level of 1 mSv/y.
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.
Concentration Levels and the Associated Health Risks of Elements in Food Crops Grown in the Neighbourhood of Minjingu Phosphate Mine, Tanzania
(SCIENCEDOMAIN international, 2017) Mohammed, Najat K.; Nkuba, Leonid L.
The concentration levels of heavy metals in food crops (maize and mung beans) grown in the neighbourhood of Minjingu Phosphate mine were analyzed using EDXRF. The metal concentrations in both food crops followed the following pattern Fe > Zn > Cu > Cd > Cr > Pb > As. Maize accumulated higher levels of all analyzed elements than mung beans. The concentration level of metals in maize and mung beans from Minjingu were higher than those from the control site. Except for Cd in both types of samples, the concentration levels of all other metals were below the FAO/WHO recommended limits. The risk assessment showed that consumption of mug beans from Minjingu is without any safety risk while there is a risk in consumption of maize due to the concentration of Cd. However, the number of samples was not sufficient enough to make a definite conclusion; therefore, there is need for further analysis to include more data.
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.
Heavy Metal Concentrations in Soil and Green Vegetables (Vigna unguiculata) around Volcanic Mountain of Oldoinyo Lengai, Arusha, Tanzania
(SCIENCEDOMAIN international, 2015) Amour, Khamis O.; Mohammed, Najat K.
The aim of this work was to assess heavy metal concentrations of samples collected from areas around a volcanic mountain in Tanzania. Fifty five soil samples and 10 samples of bean leaves were analysed using Energy Dispersive X- ray Fluorescence spectrometry (EDXRF). The concentrations of heavy metals in the samples are presented, statistical analysed and compared with control. The concentration in bean leaves are also compared with the maximum tolerable limits set by FAO/WHO to assess their safety for consumption. The results from this study show that high concentration of elements in both soils and bean leaves samples from Oldoinyo Lengai areas might be associated with frequently eruptions of the volcanic mountain of Oldoinyo Lengai. Hence, farming in Oldoinyo Lengai areas is introducing heavy metals in the food chain.
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.
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.
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.
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.
Magnesium Diboride Nanobridges Fabricated by Electron-Beam Lithography
(2005-12) Malisa, Anayesu B.; Charlebois, S.; Lindström, T.
MgB2MgB2 nanobridges were fabricated by e-beam lithography and Ar-ion beam milling. Nanobridges of widths ranging from 60 nm to 1μm1μm and 3μm3μm in length were realized by Ar-ion beam milling using amorphous carbon as etching mask. The processing did not harm the superconductingproperties appreciably. High values of the critical current density, more than 10MA/cm210MA∕cm2, were measured for bridges with widths down to 60 nm. Current-voltage (I‐V)(I‐V)characteristics showed a behavior typical of a bridge going normal, after the critical current is exceeded, and remaining normal as the current is decreased to a lower switch back value due to Joule heating. We could also observe switching behavior in some bridges indicating formation of normal hotspots in the bridges before they returned to their superconducting state. Alternative explanations may include natural grain boundaries in the film or the movement of Abrikosov vortices. The current-voltage (I‐V)(I‐V)characteristics showing critical current densities up to 5×107A/cm25×107⁢A∕cm2 indicates excellent filmproperties in the nanobridges.

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