Inorganic arsenic speciation by differential pulse anodic stripping voltammetry using thoria nanoparticles-carbon paste electrodes.

Two novel thoria (ThO2) nanoparticles-carbon paste electrodes were used to evaluate an anodic stripping voltammetric method for the direct determination of arsenite and total inorganic arsenic (arsenite plus arsenate) in water samples. The effect of Ag((I)), Cu((II)), Hg((II)), Sb((III)) and Se((IV)) ions on the electrochemical response of arsenic was assayed. The developed electroanalytical method offers a rapid procedure with improved analytical characteristics including good repeatability (3.4%) at low As((III)) concentrations, high selectivity, lower detection limit (0.1 µg L(-1)) and high sensitivity (0.54 µA µg(-1) L). The analytical capability of the optimized method was demonstrated by the determination of arsenic in certified reference materials (trace elements in natural water, trace elements in water and coal fly ash).

Thorotrast: analysis of the time evolution of its α activity concentration, in the 70 years following the chemical purification of Thorium.

We simulate the α-activity of the Thorium series elements present in the contrast medium named Thorotrast, used until 1960 and cause of certified deaths until today. Assuming, as active components at t=0, (232)Th and (228)Th in the same relative concentration they have in nature, α-activity oscillates for some decades before reaching a stationary value that in absence of biological depletion would be AST =24000Bq/g. Our Montecarlo code generates the nuclear decays of the Thorium series with and without in-vivo biological depletion, arriving to three kinds of results for the activity: 1) Theoretical activity concentration (no biological depletion). Our result is fitted by: A(t)=A(ST).{[1-exp(-t/10)]+[exp(-t/tB)(1-0.8exp(-t/tA))]}, with t in years, tA=1.07.10(-2) years, and tB=2.38 years. 2) Weak biological depletion (228Ra/232 Th equilibrium activity ratio 0.6, 224Ra/228Ra e.a.r 0.9, 10% excretion for 220Rn). The ratio of the activity concentration to the theoretical activity concentration is fitted by: A weak (t)/A(t)=0.61+0.29 exp[-(t/15)2] (t in years). 3) Strong biological depletion (228Ra/232Th e.a.r 0.4, 224Ra/228Ra e.a.r. 0.8, 10% excretion for 220Rn). The ratio of the activity concentration to the theoretical activity concentration is fitted by A(strong)(t)/A(t)=0.44+0.4 exp[-(t/13)2](t in years). We also report fluctuation calculation for two cases where standard statistical behavior is not expected.

A novel approach for preferential recovery of Sr from (Sr, Th)O2.

Quantitative leaching of Sr from homogeneous and calcined (Th,Sr) O(2) in dilute perchloric acid medium suggests the possibility of reducing the hazardousness of discharged nuclear fuel by separation of (90)Sr, a prominent fission product at dissolution stage itself rather than the conventional approach of its recovery from high level nuclear waste. Apart from mitigating the radiotoxicity of the nuclear waste, recovered (90)Sr can be employed as a compact heat source and as parent radionuclide for (90)Y (used in therapy radiopharmaceuticals), provided it can be made available at desired high purity. Leaching behavior of few other fission products was also investigated to quantify their contamination in leached Sr. Feasibility of employing extraction chromatography using Sr selective resin was explored in perchloric acid medium. In this context, the distribution coefficients of (85)Sr(II), Th (IV), Zr(IV), Y(III), Pd(II) as well as (152)Eu(III) and (137)Cs (I) were determined under varying nitric acid/perchloric acid concentration and under varying loading conditions of metal ions. Perchloric acid medium appears better than nitric acid medium for preferential leaching of Sr from (Th,Sr)O(2) as well as for uptake of Sr by Sr selective chromatographic resin.

Atomistic models to investigate thorium dioxide (ThO2).

Thorium dioxide (ThO(2)) is of great interest to energy research as thorium-based nuclear fuel offers the promise of increased proliferation resistance, longer fuel cycles, higher burn-up and improved wasteform characteristics in the generation of nuclear power. However, understanding of ThO(2) as a nuclear fuel is not as comprehensive as UO(2). In order to improve the atomic level understanding of thorium-based fuels, we have developed eight interatomic potential descriptions of ThO(2) by fitting the experimental lattice parameter, elastic constants and static dielectric constants. Using these interatomic potentials, we have calculated the structural and elastic properties, phase stability, defect formation energies, defect binding energies and complexes as well as the energetics of low-index surfaces. A critical assessment of all the potentials is performed by comparing the predicted properties with available experimental and first-principles calculations.

Communication: The permanent electric dipole moment of thorium monoxide, ThO.

The optical Stark spectrum of the E(0(+)) - X(1)Σ(+) (1,0) band of thorium monoxide, ThO, was recorded and analyzed to determine the permanent electric dipole moments, µ, for the E(0(+)) (v = 1) and X(1)Σ(+) (v = 0) states. Values of 2.782 ± 0.012 D (X) and 3.534 ± 0.010 D (E) were obtained. The uncertainties are 2σ statistical error. The systematic errors are estimated to be less than 1%. The experimental results are used to access the quality of electronic structure calculations of the properties of the X(1)Σ(+) (v = 0) state.

Development of a small scintillation detector with an optical fiber for fast neutrons.

To investigate the characteristics of a reactor and a neutron generator, a small scintillation detector with an optical fiber with ThO(2) has been developed to measure fast neutrons. However, experimental facilities where (232)Th can be used are limited by regulations, and S/N ratio is low because the background counts of this detector are increase by alpha decay of (232)Th. The purpose of this study is to develop a new optical fiber detector for measuring fast neutrons that does not use nuclear material such as (232)Th. From the measured and calculated results, the new optical fiber detector which uses ZnS(Ag) as a converter material together with a scintillator have the highest detection efficiency among several developed detectors. It is applied for the measurement of reaction rates generated from fast neutrons; furthermore, the absolute detection efficiency of this detector was obtained experimentally.

Studies of the EPR parameters and defect models for three Er3+ impurity centers in ThO2 crystals.

The electron paramagnetic resonance (EPR) parameters (g factors and hyperfine structure constants of the ground state, and g factors of the first excited state) of three (one cubic and two trigonal) Er(3+) centers in fluoride-type ThO(2) crystal are studied from a diagonalization (of energy matrix) method. In the method, the Zeeman and hyperfine interaction terms are added to the classical Hamiltonian, and a 52 x 52 energy matrix concerning the ground multiplet (4)I(15/2) and the first to third excited multiplets (4)I(13/2), (4)I(11/2) and (4)I(9/2) is established for a 4f(11) ion in trigonal crystal field and under an external magnetic field. From the studies, the EPR parameters for three Er(3+) centers in ThO(2) are reasonably explained, the defect models for the two trigonal Er(3+) centers suggested in the previous paper are confirmed and the defect structures of the two trigonal centers are obtained. The results are discussed.

Oxygen-17 hyperfine structures in the pure rotational spectra of SrO, SnO, BaO, HfO and ThO.

Hyperfine structures arising from the couplings of the nuclear spin angular momentum of (17)O (I = 5/2) with the end over end rotation of several metal-containing diatomic monoxides have been observed using a Fourier transform microwave spectrometer. The molecules have been produced by reacting (17)O(2) with laser ablated metal atoms. The oxygen-17 nuclear quadrupole coupling constants have been determined for the title molecules and are interpreted in terms of a simple Townes-Dailey model. Also, the oxygen-17 nuclear spin-rotation constants have been determined and used to calculate the oxygen-17 shieldings for each molecule.

EPR g factors of trigonal Dy(3+) center in ThO(2) crystal.

The perturbation formulas of EPR g factors g(parallel) and g( perpendicular ) for the lowest Kramers doublet of 6H(15/2) of a 4f(9) ion in trigonal symmetry are established in this paper. In these formulas, besides the contribution due to the interaction within the lowest 6H(15/2) manifolds considered in the previous papers, the contributions due to the J-mixing among the 6H(15/2), 6H(13/2) (first excited state) and 6H(11/2) (second excited state) via crystal-field interaction, the admixtures among the states with the same J value via spin-orbit coupling interaction and those between the lowest Kramers doublet Gammagamma and other Kramers doublets Gamma(X) within the states 6H(J) (J=15/2,13/2,11/2) via crystal-field and orbital angular momentum interactions are included. From these formulas, the g factors g(parallel) and g( perpendicular ) for the trigonal Dy(3+) center in ThO(2) crystal are calculated. The results are discussed.

Raman scattering investigations of nanocrystalline thorium oxide.

Raman scattering investigations are carried out on nanocrystalline thorium oxide powders. Shift and broadening of the Raman peak associated with F2g phonons are observed for the nanocrystalline samples as compared with those of the bulk. The peak shift and broadening are found to increase further as the particle size decreases. A quantitative analysis of the Raman line shape is carried out with a Gaussian confinement model, and the estimated size is found to be consistent with that obtained from X-ray diffraction and transmission electron microscopy.

[Selective excitation spectra and energy level structure of Dy3+:ThO2 crystal].

Dy3+:ThO2 crystal was grown by the flux technique for the first time. The emission spectra, excitation spectra and fluorescence decay curves were measured and discussed. By using emission spectra obtained under selective dye laser excitation at 12 K, together with the crystal-field theory, the site symmetry of Dy3+ ions in ThO2 was determined as C3 nu and its energy level structure was tabulated. The lifetime of radiative level 4F9/2 was also determined as 0.40 ms.

In vitro dissolution characteristics of aged and recrystallised high-fired 232ThO2.

The dissolution characteristics of 232Th from ThO2 in the lung have been determined in an in vitro study. Two types of ThO2 were examined to determine if the age of the material had any effect; an aged high-fired ThO2 that had its progeny in secular equilibrium, and a recently recrystallised and high-fired ThO2 in disequilibrium. The results show the amount of 232Th that dissolved from the aged ThO2 was approximately 10 times greater than the amount that dissolved from the recrystallised and fired ThO2 which was the result of recoil damage to the crystal structure of the aged material. A model based on nuclear track theory was developed to relate the size of the observed rapidly soluble fraction of 232Th to the age of the material and its experimentally determined surface area.