G. Blain

Behavior of Heptavalent Technetium in Sulfuric Acid under α-Irradiation: Structural Determination of Technetium Sulfate Complexes by X-ray Absorption Spectroscopy and First Principles Calculations

The effect of α-radiolysis on the behavior of heptavalent technetium has been investigated in 13 and 18 M H2SO4. Irradiation experiments were performed using α-particles ((4)He(2+), E = 68 MeV) generated by the ARRONAX cyclotron. UV-visible and X-ray absorption fine structure spectroscopic studies indicate that Tc(VII) is reduced to Tc(V) under α-irradiation. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements are consistent with the presence of mononuclear technetium sulfate complexes. Experimental results and density functional calculations show the formation of [TcO(HSO4)3(H2O)(OH)](-) and/or [TcO(HSO4)3(H2O)2] and [Tc(HSO4)3(SO4)(H2O)] and/or [Tc(HSO4)3(SO4)(OH)](-) for 13 and 18 M H2SO4, respectively.

Behavior of heptavalent technetium in concentrated triflic acid under alpha-irradiation: technetium-triflate complex characterized by X-ray absorption fine structure spectroscopy and DFT

Abstract The nature of the Tc species produced after the alpha-irradiation of Tc(VII) in concentrated triflic acid has been investigated by X-ray absoprtion fine structure (XAFS) spectroscopy and first principles calculations. Experimental and theoretical results are consistent with the formation of Tc(V)O(F3CSO3)2(H2O)2+.

Speciation of technetium in carbonate media under helium ions and γ radiation

Abstract Technetium carbonates complexes produced by chemical, electrochemical and radiolytic methods have been studied by UV-Visible, X-ray Absorption Fine Structure (XAFS) and Density Functional Theory methods. The (NH4)2TcCl6 salt was dissolved in 2 M KHCO3. The resulting purple solution was analyzed by XAFS and UV-Visible spectroscopy. The UV-Visible spectra exhibits a band centered at 515 nm. The XAFS results were consistent with the presence of polymeric species containing the [Tc2(μ−O)2]4+ core coordinated to carbonate ligand. Concerning the electrochemical methods, the pertechnetate anion was electrochemically reduced in concentrated carbonate solution [(CO32−)=5 M and (HCO3−)=0.5 M]. For the radiolytic reduction, the speciation of Tc under Helium ions particle beam and γ radiation was examined by UV-Visible and XAFS spectroscopy in high concentrated carbonate media. In concentrated carbonate solutions, pertechnetate as Tc(VII), was not reduced under irradiation due to the formation of carbonate radical which is a strong oxidant. Then, the solution proposed was the addition of formate to the solution which can scavenge hydroxyl radical 10 times faster than carbonate and prevent re-oxidation of reduced technetium. The XANES and EXAFS spectroscopies, approved by theoretical methods, revealed that the final product of the radiolytic reduction of pertechnetate is in the +IV oxidation state. The final structure of the reduced product by He2+ radiolysis was the same as electrochemical reduction. From this complex determination and evolution vs. the dose, this study is reporting the solubility of the Tc(IV) complex.

Evolution of heavy ions (He2+, H+) radiolytic yield of molecular hydrogen vs. “Track-Segment” LET values

Abstract Ionizing radiation’s effects onto water molecules lead to the ionization and/or the excitation of them. Then, these phenomena are followed by the formation of radicals and molecular products. The linear energy transfer (LET), which defines the energy deposition density along the radiation length, is different according to the nature of ionizing particles. Thus, the values of radiolytic yields, defined as the number of radical and molecular products formed or consumed by unit of deposited energy, evolve according to this parameter. This work consists in following the evolution of radiolytic yield of molecular hydrogen and ferric ions according to the “Track-Segment” LET of ionizing particles (protons, helions). Concerning G(Fe3+) values, it seems that the energy deposited into the Bragg peak does not play the main role for the Fe3+ radiolytic formation, whereas for the G(H2) it is the case with a component around 40% of the Bragg peak in the dihydrogen production. Therefore, as main results of this work, for high energetic Helion and Proton beams, the G(Fe3+) values, which can be used for further dosimetry studies for example during the α radiolysis experiments, and the primary g(H2) values for the Track-Segment LET, which can be used to determine the dihydrogen production by α-emitters, are published.

Influence of Nitric Acid on the Helium Ion Radiolysis of Aqueous Butanal Oxime Solutions

Samples of butanal oxime in aqueous nitric acid solutions have been irradiated with the helium ion (4He2+) beam of the CEMHTI (Orléans, France) cyclotron. The consumption yield of butanal oxime has been measured by gas chromatography coupled with mass spectrometry. Gaseous products (mainly H2 and N2O) have also been monitored by micro-gas chromatography. Yields of liquid phase products (hydrogen peroxide and nitrous acid) have been determined by colorimetric methods. The influence of nitric acid on the radiation chemical behavior of butanal oxime depends on the nitric acid concentration. For a low concentration (≤0.5 mol L-1) butanal oxime is protected by the nitrate ions, which can efficiently scavenge the water radiolysis radicals. For higher concentrations, nitrous acid can accumulate in the medium, therefore leading to a strong increase of the butanal oxime degradation. The associated mechanism is an autocatalytic oxidation of butanal oxime by HNO2.