Department of Physics-Journal Articles

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    Cohesive Sediment Characterization by Combined Sedimentation and Rheological Measurements
    (ASCE, 2008) Babatope, B.; Williams, B.R.; Williams, D.J.A.
    A laboratory characterization of cohesive sediment has been carried out in which data obtained from standard sedimentation and rheological measurements were combined in a determination of the critical solid concentration for the detection of elasticity in a weakly cohesive suspension. The corresponding storage modulus and shear stress are very critical in any in situ rheometry of sediments, especially in the study of mud-water surface erosion in a flume. Sedimentation results showed that particle size distribution rather than surface treatment controlled the rheological behavior of the suspension while the critical solid concentration for the appearance of three-dimensional space-filling network, showing some measurable elasticity in the suspension, occurred in the region of 0.015. This parallel between the consolidation behavior and shear rheology development for the flocculating system has been established. This technique could be an adjunct to the laboratory characterization of cohesive sediments for the estimation of critical shear stress for surface erosion, especially in a typical flume experiment under water wave pressure.
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    Continuous quantum phase transitions in the one-dimensional spin-1/2 axial next-nearest-neighbour Ising model in two orthogonal magnetic ¯elds
    (Indian Academy of Sciences, 2010-02) ADEGOKE, KUNLE; BÄUTTNER, HELMUT
    We have investigated the one-dimensional spin-1/2 axial next-nearestneighbour Ising (ANNNI) model in two orthogonal magnetic fields at zero temperature. There are four different possible ground state configurations for the ANNNI model in a longitudinal field, in the thermodynamic limit. The inclusion of a transverse field introduces quantum fluctuations which destroy the existing spin order along certain critical lines. The effects of the fluctuations in three of the four ordered regions were investigated using the finite-size scaling technique. The phase boundaries of the ANNNI model in two orthogonal magnetic fields were thus determined numerically. For certain limits of the Hamiltonian we compared the obtained results with the existing literature and our results were in good agreement with the results in the existing literature
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    Gamma Radioactivity levels of Rocks and Soils and Their Corresponding External Exposure in Navy Quarry Site, Abeokuta, South-West, Nigeria
    (Asian Journal of Applied Science, 2012) Okedeyi, A.S; Arowolo, T.A; Gbadebo, A.M; Techokosa, P
    Crystalline rocks have been observed to be rich in Naturally Occurring Radionuclides (NOR) which are the primary terrestrial sources of radiation in the environment. This study determined the activity concentrations of NOR in rocks and soils from Saunder quarry site, Abeokuta North, South-Western, Nigeria. Three rocks were randomly collected and ten soil samples comprising five surface and five sub-surface were collected by pitting to depth of interest in each location and analyzed using Nal (Tl) gamma spectrometer. The average activity concentrations of 4QK, 238U and 232Th in rock samples were 603.62±83.29, 39.70±12.57 and 62.64±20.71 Bq kg -1, respectively. The calculated average Absorbed Dose Rate (ADR) and Annual Effective Dose (AED) were 84.01 nGy h _l and 103.03 jiSv y _l. While for soils, the mean activity concentration for the two depths were 145.10*12.64 and 236.08±17.34 Bqkg -1 for 40K, 13.36±3.53 and 23.99±6.80 Bqkg -1 for 238U and 15.09±5.48 and 10.54±5.67 Bqkg -1 for 232Th, respectively. Similarly, the corresponding average ADR and AED for soil were 28.99 nGy h -1 and 35.56 jiSv y -1 for surface 33.32 nGy h -1 and 40.87 jiSv y -1 for sub-surface, respectively. The average values for AED of the sampled rock were higher than 70 jiSv y _l. Hence, the granite rock used for building and construction purpose from the study area would be rich in NOR. Routine assessment of radionuclide contents of the rocks of the quarry site was recommended
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    Low dose TL characteristics of Nigerian fluorite
    (internaltional journal of elsevier, 2011-11-08) Latif, Mouftahou .B
    Nigerian fluorite has been characterized by β-irradiation for thermoluminescence in the low dose range (40 μGy–72 mGy). The glow curves exhibit 3 peaks recorded at 111 ± 11 °C, 196 ± 2 °C and 282 ± 4 °C at the heating rate of 5 °C s−1. The two high temperature peaks exhibit a linear response over the range of study. The minimum detectable dose for each of the observed peaks has been determined and the lowest detection limit of fluorite was also determined. A complex fading pattern was observed for the phosphor and the possible source of the TL buildup has been discussed