Narrow Results

Detection of antineutrinos from U and Th series decay within the Earth (geoneutrinos) constrains the absolute abundance of these elements. Marine detectors will measure the ratio over the mantle beneath the site and provide spatial averaging. The measured mantle Th/U may well be significantly below its bulk earth value of ~4; Pb isotope measurements on mantle-derived rocks yield low Th/U values, effectively averaged over geological time. The physics of the modern biological process is complicated, but the net effect is that much of the U in the mantle comes from subducted marine sediments and subducted upper oceanic crust. That is, U subducts preferentially relative to Th. Oxygen ultimately from photosynthesis oxidizes U(IV) to U(VI), which is soluble during weathering and sediment transport. Dissolved U(VI) reacts with FeO in the oceanic crust and organic carbon within sediments to become immobile U(IV). These deep marine rocks are preferentially subducted relative to Th(IV)-bearing continental margin rocks. Ferric iron from anoxygenic photosynthesis and oxygen in local oases likely mobilized some U during the Archean Era when there was very little O₂ in the air. Conversely, these elements behave similarly in the absence of life, where the elements occur as U(IV) and Th(IV), which do not significantly fractionate during igneous processes. Neither do they fractionate during weathering, as they are essentially insoluble in water in surface environments. Th(IV) and U(IV) remain in solid clay-sized material. Overall, geoneutrino data constrain the masses of mantle chemical and isotopic domains recognized by studies of mantle-derived rocks and show the extent of recycling into the mantle over geological time.

The surface chemical behavior of clean uranium metal in a hydrogen atmosphere at 80°C and 120°C has been studied using XPS and thermodynamic calculation. The main product is uranium oxide rather than hydride uranium on the uranium surface after the exposure of uranium to extremely pure hydrogen, and the U4f_7/2 binding energy of UH₃ has been found to be 378.6 ± 0.1 eV. An elevated temperature (120°C) is beneficial to the formation of UH₃ species at the same hydrogen exposures. The depth profile analysis of XPS indicates that the chemical structure of the surface layer was UO₂/UH₃/U after the exposure of hydrogen reached 1.31 × 10^-6 L (1 L = 10^-6 Torr·s). Results of thermodynamic calculations are in good agreement with the above conclusions.

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Improved environmental-particle analysis for safeguards is a continuing research goal. In this paper, we propose a modified method of fission-track analysis, employing the focused ion-beam (FIB) technique and using a single-crystal silicon substrate to carry dust particles. The use of a silicon substrate may eliminate the need to relocate identified particles of interest from the particle carrier to another substrate for mass-spectrometric analysis. FIB–SEM and SIMS were used to evaluate the efficiency of the proposed FTA method.

The ${}^{235}$U(n,f) cross section plays a key role for nuclear physics due to its widespread use as a standard reference for neutron cross section measurements and for neutron flux measurements. Recent experimental data of the fission cross section have suggested the presence of discrepancies around 6–8% with respect to the most used libraries, precisely in the range between 10 keV and 30 keV. In order to shed light on this disagreement, an accurate measurement of the ${}^{235}$U(n,f) fission cross section has been performed at n_TOF facility @CERN, using the standard reactions ⁶Li(n,t) and ${}^{10}$B(n,$\alpha )$ as reference. A custom experimental setup based on a stack of silicon detectors sandwiched between pairs of ${}^{235}$U, ⁶Li and ${}^{10}$B targets, has been installed along the neutron beam line to intercept the same neutron flux, allowing the detection of the fission fragments and the products of the reference reactions at the same time. Such a technique allows calculation of the cross section via the “ratio method”, by normalizing the ${}^{235}$U(n,f) reaction yields with respect to the reference reactions and to the recommended data in the IAEA libraries; in particular, the integral between 7.8 and 11 eV has been chosen. Accurate Monte Carlo simulations have allowed evaluation of the neutron absorption in the different layers, as well as the detection efficiency of each detector. The data are in excellent agreement with the standard values and highlight the overestimation of the ${}^{235}$U(n,f) cross section between 9 and 18 keV in the most recent libraries.

Experiments in preparation for search for uranium ternary fission by means of nuclear track emulsion are summarized. The study will be focused on the possible involvement of the unstable nucleus ⁸Be in the suggested scenario of the collinear tri-partition in the fission.

The synthesis and reactivity of uranium complexes supported by a bis(aryloxide) cyclam ligand are surveyed. The hemilability of this ligand proved to be particularly appropriate to stabilize highly reactive uranium(III) and uranium(IV) complexes that were able to activate different unsaturated molecules. Of note are the reductive cleavage of azobenzene with the unprecedented formation of a trans-bis(imido) uranium(VI) complex and its reaction with carbon dioxide to generate a trans-oxido-imido uranium(VI) complex and phenyl isocyanate. The formation of a trans-dioxido uranium(VI) (uranyl) complex was also observed in the reaction of uranium(IV) complexes with sodium nitrite. Quantum chemical computations and solution ¹⁵N NMR spectroscopy were employed to evaluate bond covalency in the three {E=U=E}²⁺ complexes (E = O, NR).

At present, exploration depth of Uranium resources is about 300-500 meters in China. It is difficult to explore the resource accurately under 500 meters. A new 3-D resistivity measuring method based on distributed system was proposed in this paper. By changing the power supply electrode and introducing “E-SCAN” observation pattern, the method can be put in pole-dipole, dipole-pole and dipole-dipole measuring mode, finally, apparent resistivity data can be acquired. This article adopts an evaluation method in which A-Kind method was combined with linear weighted method to evaluate measurement uncertainty of the resistivity measuring method. And the results of 3-D low resistance object exploration show that resistivity trends of the method in this paper is highly consistent with multi-function digital DC IP instrument WDJD-2 and Supersting R8 which are widely used in actual measurement. The maximum test error among the method and the two instruments(WDJD-2 and Supersting R8) is 6%. And the repeated average relative error is 3.90%. Besides, the result of 3-D inversion proves the method can be applied to explore the resource accurately with a large depth.

In this paper, we study the character of solute transport in in-situ leaching of uranium in some sandstone uranium deposit in Xinjiang and analyze the effect of convection, molecular diffusion, mechanical dispersion, adsorption, chemical reaction and radioactive decay on migration and distribution of solute in sandstone uranium deposit. The process of in-situ leaching of uranium in sandstone uranium deposit and shrinkage model of leaching core is divided into 3 interfaces, basic equation of solute transport of in-situ leaching of uranium in homogeneous isotropic sandstone uranium deposit is derived, based on law of mass conservation, the hydrodynamic dispersion coefficient and retardation coefficient of solute transport are determined by analysis-optimization method, the calculated values of solution concentration are consistent with the ones of fitting curve of experimental test values by analysis-optimization parameters and the efficiency of our mathematical model is verified through field test of in-situ leaching.