Transport Of Thorium Research Articles

Finite difference model of thorium transport in tungsten

A finite difference model of thorium transport in tungsten electrodes and its effect on the thermionic emission current is presented. Lattice, grain boundary and surface diffusion, grain boundary and surface segregation, evaporation, limited solubility and the rate of formation of thorium metal from thorium oxide are included. From the view of thermionic emission, the “ideal” grain size depends on the operation temperature of the electrode. High operation temperatures ( T > 2300 K) favor larger grain sizes. Low operation temperatures ( T < 2000 K) favor smaller grain sizes. The emission current is sensitive to the prior thermal treatments that the electrode has seen.

228Ra and 228Th in coastal waters

Typically, the waters above the continental shelf contain higher concentrations of 228 Ra but lower concentrations of 228 Th than do the surface waters of the open ocean. The vertical profiles of 228 Ra concentration in the shelf waters of the Middle Atlantic Bight suggest that the shelf sediments are the chief source of 228 Ra, but that the sediments of bays and estuaries are a significant secondary source. In the mid-shelf and outer shelf waters of the Bight, the 228 Ra concentration increases and the 228 Th/ 228 Ra activity ratio decreases from the region bordering Nova Scotia to the region uust north of Cape Hatteras. The mean residence time of thorium in the surface waters of the Bight, calculated from the 228 Th/ 228 Ra activity ratios, ranges from 4 months in the slope waters and outer shelf waters and 1·5 months in the inner shelf waters of the region bordering Nova Scotia to 1·5 months in the slope waters, 20 days in the outer shelf waters and 10 days in the inner shelf waters of the region just north of Cape Hatteras. The vertical profiles of 228 Th concentration in the surface mixed layer and thermocline of the open ocean qualitatively resemble the profiles of concentrations of nutrients, such as phosphate. The process most likely to produce the observed rapid transport of thorium out of the surface waters probably involves uptake of thorium by phytoplankton, ingestion of the phytoplankton by zooplankton, and inclusion of the thorium in rapidly settling fecal pellets.

The significance of lead isotopes in detrital feldspar with respect to chemical differentiation within the earth's mantle

On a continental scale, leads in K-feldspars from North America were found to deviate from closed system evolution such that there is an excess of Pb 206 and, in lesser extent, Pb 208 which increases as the age of the feldspar decreases. This effect can be shown to result from the transport of uranium and thorium, over long periods in the past, from the interior of the earth to an outer mantle layer which functioned as a source of segments of continental crust that were formed and isolated at different times and locations. The effect is decisive in defining, as a function of time, the rates of transport of uranium, thorium and lead from the inner mantle to the outer mantle : there was a sharp decrease in the rates of transport of these three elements during the first one hundred m.y. after the earth was formed; during the remaining aeons, lead transport became essentially zero while uranium and thorium transport remained appreciable. The effect also suggests that the bulk of the North American continent was formed during the interval 3500-2500 m.y. ago.

The chemistry of thorium—VIII some electrochemical characteristics of andhydrous thorium chloride in anhydrous ethylenediamine

Abstract Anhydrous thorium chloride dissolves vigorously and readily in anhydrous ethylenediamine. The resulting solutions show the conductance behaviour of solutions of weak electrolytes. Electrolysis of such solutions gives cathodic evolution of hydrogen and transport of thorium to the anode compartment, but does not give cathodic deposition of thorium metal.