Journal Articles

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Browsing Journal Articles by browse.metadata.cluster "Environmentek"

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    Cape Point GAW Station Rn-222 detector: factors affecting sensitivity and accuracy
    (2002) Brunke, EG; Labuschagne, C; Parker, B; Van der Spuy, D; Whittlestone, S
    Specific factors of a baseline Rn-222 detector installed at Cape Point, South Africa, were studied with the aim of improving its performance. Direct sunlight caused air turbulence within the instrument, resulting in 13.6% variability of the calibration factor. Shading the instrument eliminated this effect. A residual temperature dependence of the calibration factor was reduced to negligible levels with an improved photomultiplier tube. A superior detector head permits field servicing of the instrument, and has reduced one component of the instrumental background by a factor of 2. The other component probably constitutes thoron emissions from the stainless steel walls. The detection limit of the instrument could be reduced from its current 33 to 20 mBq m(-3) if the thoron were to be eliminated.
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    Evaluating the rate of migration of an uranium deposition front within the Uitenhage Aquifer
    (1999-08-27) Vogel, JC; Talma, AS; Heaton, THE; Kronfeld, J
    The solubility of uranium in groundwater is very sensitive to changes in redox conditions. Many secondary (sandstonetype) uranium deposits have been formed when soluble U has precipitated after encountering reducing conditions in the subsurface. In the groundwater of the Uitenhage Aquifer (Cape Province, South Africa), 238U-series isotopes were used to assist in studying the history of the reducing barrier. Uranium isotopes were used to determine the present position of the barrier. Radium and radon were used to evaluate the path of migration that the front of the oxygen depletion zone has taken over the past 105 years. During this time the reducing barrier has moved, leaving in its wake a trail of U in various stages of secular equilibrium with its daughter 230Th. The 226Ra daughter of 230Th is not very mobile. Its growth upon the aquifer wall is reflected in the Rn content of the water. This in turn, due to the relatively great age of the water, indicates the extent of the 230Th ingrowth (from precipitated U) that took place before the barrier migrated.