Magnesium-zinc reduction is effective in preparation of metals

Uranium, thorium, and plutonium are effectively prepared by magnesium-zinc reduction, using uranium oxides, thorium dioxide, and plutonium dioxide as starting materials. This technique is also useful in performing reduction of metals such as zirconium and titanium

Electrochemical behaviour of thorium(IV) in molten LiF–CaF2 medium on inert and reactive electrodes

The electrochemicalbehaviour of the Th(IV)/Th system was examined in moltenLiF–CaF2medium on inert (molybdenum), reactive (nickel) and liquid (bismuth) electrodes in the 810–920 °C temperature range by several electrochemical techniques. Experimental results showed that (i) thorium fluoride was reduced in a single step exchanging 4 electrons and limited by thorium ions diffusion in the solution, (ii) the oxide ions induce the precipitation of Th(IV) in the form of thorium oxide (ThO2), in a process involving as intermediate compound a soluble oxifluoride (ThOF2), (iii) the reduction of thorium ions on reactive (Ni and liquid Bi) electrodes yields compounds Ni–Th and Bi–Th with a potential shift of around 0.7 V (for Ni and Bi) more anodic than the reduction of Th(IV) on inert substrate

Thorium Energy Futures

The potential for thorium as an alternative or supplement to uranium in fission power generation has long been recognised, and several reactors, of various types, have already operated using thorium-based fuels. Accelerator Driven Subcritical (ADS) systems have benefits and drawbacks when compared to conventional critical thorium reactors, for both solid and molten salt fuels. None of the four options – liquid or solid, with or without an accelerator – can yet be rated as better or worse than the other three, given today's knowledge. We outline the research that will be necessary to lead to an informed choice

Spectrometric study of condensed phase species of thorium and palladium-based modifiers in a complex matrix for electrothermal atomic absorption spectrometry

The chemical and morphological transformations of condensed phase species of a thorium-based modifier were studied over the temperature range 200–2500 °C, without and with the presence of aluminium and silicon as matrix components, and in some instances, arsenic as an analyte element. A similar study was also conducted with palladium as the modifier, for comparison. Results were derived using scanning electron microscopy (SEM), energy dispersive (ED) X-ray spectrometry, Raman microanalysis and attenuated total reflectance (ATR) Fourier transform-infrared (FT-IR) spectrometry. Comparable results were found using pyrolytic and non-pyrolytic graphite platforms, with processes occurring at slightly higher temperatures on the pyrolytic graphite platform. With thorium as the modifier, metal oxides were the predominant species on the platform surface at relatively low temperatures (<1500 °C), whereas metal phases became prevalent at high temperatures, when thorium and aluminium tended to behave independently from one other. Some spatial variations in the composition of the salt residues on different regions of the platform were observed (from the region closest to the slot in the tube, to the region furthest from the slot). Nonetheless, thorium metal remained on the graphite platform to higher temperatures than did aluminium metal. In the presence of arsenic, the existence of mixtures of thorium and arsenic oxides, just before the appearance temperature of gas phase arsenic atoms, was confirmed by SEM studies, ED X-ray spectra and Raman microanalysis. This suggests that any modifying effect of thorium on arsenic occurs while the modifier is in the oxide phase rather than in the metal phase. The presence of silicon added as silica, did not influence significantly the thermochemical behaviour of mixtures of thorium and aluminium. However, coexistence of silicon and arsenic oxides at the appearance temperature of the atomic absorption signal of arsenic was obtained, confirming that silicon can act as an internal modifier for arsenic. In the presence of palladium, aluminium exhibited greater interaction with the modifier; consequently, aluminium metal was retained on the platform surface to higher temperatures than thorium, which could explain how interference effects of aluminium on e.g. arsenic are avoided or reduced. Similarly, there was evidence for interaction of palladium and arsenic in the reduced state. However, when aluminium and silicon were present, the transformation of the palladium oxide to the metallic state was affected, which could diminish the modifying benefits of palladium for arsenic in the presence of aluminium

Experimental studies of thorium ions implantation from pulse laser plasma into thin silicon oxide layers

We report the results of experimental studies related to implantation of thorium ions into thin silicon dioxide by pulsed plasma fluxes expansion. Thorium ions were generated by laser ablation from a metal target, and the ionic component of the laser plasma was accelerated in an electric field created by the potential difference (5, 10 and 15 kV) between the ablated target and SiO2/Si(001) sample. Laser ablation system installed inside the vacuum chamber of the electron spectrometer was equipped with YAG:Nd3+ laser having the pulse energy of 100 mJ and time duration of 15 ns in the Q-switched regime. Depth profile of thorium atoms implanted into the 10 nm thick subsurface areas together with their chemical state as well as the band gap of the modified silicon oxide at different conditions of implantation processes were studied by means of X-ray photoelectron spectroscopy (XPS) and Reflected Electron Energy Loss Spectroscopy (REELS) methods. Analysis of chemical composition showed that the modified silicon oxide film contains complex thorium silicates. Depending on local concentration of thorium atoms, the experimentally established band gaps were located in the range of 6.0 - 9.0 eV. Theoretical studies of optical properties of the SiO2 and ThO2 crystalline systems have been performed by ab initio calculations within hybrid functional. Optical properties of the SiO2/ThO2 composite were interpreted on the basis of Bruggeman effective medium approximation. A quantitative assessment of the yield of isomeric nuclei in "hot" laser plasma at the early stages of expansion has been performed. The estimates made with experimental results demonstrated that the laser implantation of thorium ions into the SiO2 matrix can be useful for further research of low-lying isomeric transitions in 229Th isotope with energy of 7.8(0.5) eV

A geoneutrino experiment at Homestake

A significant fraction of the 44TW of heat dissipation from the Earth's interior is believed to originate from the decays of terrestrial uranium and thorium. The only estimates of this radiogenic heat, which is the driving force for mantle convection, come from Earth models based on meteorites, and have large systematic errors. The detection of electron antineutrinos produced by these uranium and thorium decays would allow a more direct measure of the total uranium and thorium content, and hence radiogenic heat production in the Earth. We discuss the prospect of building an electron antineutrino detector approximately 700m^3 in size in the Homestake mine at the 4850' level. This would allow us to make a measurement of the total uranium and thorium content with a statistical error less than the systematic error from our current knowledge of neutrino oscillation parameters. It would also allow us to test the hypothesis of a naturally occurring nuclear reactor at the center of the Earth.Comment: proceedings for Neutrino Sciences 2005, submitted to Earth, Moon, and Planet

Use of 15N NMR spectroscopy to probe covalency in a thorium nitride.

Reaction of the thorium metallacycle, [Th{N(R)(SiMe2)CH2}(NR2)2] (R = SiMe3) with 1 equiv. of NaNH2 in THF, in the presence of 18-crown-6, results in formation of the bridged thorium nitride complex, [Na(18-crown-6)(Et2O)][(R2N)3Th(μ-N)(Th(NR2)3] ([Na][1]), which can be isolated in 66% yield after work-up. Complex [Na][1] is the first isolable molecular thorium nitride complex. Mechanistic studies suggest that the first step of the reaction is deprotonation of [Th{N(R)(SiMe2)CH2}(NR2)2] by NaNH2, which results in formation of the thorium bis(metallacycle) complex, [Na(THF) x ][Th{N(R)(SiMe2CH2)}2(NR2)], and NH3. NH3 then reacts with unreacted [Th{N(R)(SiMe2)CH2}(NR2)2], forming [Th(NR2)3(NH2)] (2), which protonates [Na(THF) x ][Th{N(R)(SiMe2CH2)}2(NR2)] to give [Na][1]. Consistent with hypothesis, addition of excess NH3 to a THF solution of [Th{N(R)(SiMe2)CH2}(NR2)2] results in formation of [Th(NR2)3(NH2)] (2), which can be isolated in 51% yield after work-up. Furthermore, reaction of [K(DME)][Th{N(R)(SiMe2CH2)}2(NR2)] with 2, in THF-d 8, results in clean formation of [K][1], according to 1H NMR spectroscopy. The electronic structures of [1]- and 2 were investigated by 15N NMR spectroscopy and DFT calculations. This analysis reveals that the Th-Nnitride bond in [1]- features more covalency and a greater degree of bond multiplicity than the Th-NH2 bond in 2. Similarly, our analysis indicates a greater degree of covalency in [1]- vs. comparable thorium imido and oxo complexes

A new wavelength calibration for echelle spectrographs using Fabry-Perot etalons

The study of Earth-mass extrasolar planets via the radial-velocity technique and the measurement of the potential cosmological variability of fundamental constants call for very-high-precision spectroscopy at the level of \updelta\lambda/\lambda<10^{-9}. Wavelength accuracy is obtained by providing two fundamental ingredients: 1) an absolute and information-rich wavelength source and 2) the ability of the spectrograph and its data reduction of transferring the reference scale (wavelengths) to a measurement scale (detector pixels) in a repeatable manner. The goal of this work is to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise spectral information of a Fabry-P\'erot-based calibration source. On the basis of calibration frames acquired each night since the Fabry-P\'erot etalon was installed on HARPS in 2011, we construct a combined wavelength solution which fits simultaneously the thorium emission lines and the Fabry-P\'erot lines. The combined fit is anchored to the absolute thorium wavelengths, which provide the `zero-point' of the spectrograph, while the Fabry-P\'erot lines are used to improve the (spectrally) local precision. The obtained wavelength solution is verified for auto-consistency and tested against a solution obtained using the HARPS Laser-Frequency Comb (LFC). The combined thorium+Fabry-P\'erot wavelength solution shows significantly better performances compared to the thorium-only calibration. The presented techniques will therefore be used in the new HARPS and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.Comment: 15 pages, 8 figure