Calculations of Thermodynamic Sulfur Isotope Effect

The isotopic reduced partition function ratios (RPFR), (s/s')f, for the ³⁴S/³²S isotopic pair were calculated for 24 sulfur compounds between 10 and 2,000K. Their magnitudes were in the following sequences; at low enough temperatures at which In(s/s')f depends only on the isotopic difference in frequency-sum, SF₆>SO₂F₂>SF₅Cl>SF₅Br>SO₄ ^2->SO₂Cl₂>SO₃>NSF₃>SF₄>SOF₂>SOCl₂>Me₂SO>SOBr₂>SO₂>SPBr₃>SCBr₂>Me₂S>SPCl₃>SCCl₂>SCF₂>SPF₃>CS₂>OCS>H₂S, and at high enough temperatures at which In(s/s')f is proportional to the isotopic difference in the sum of frequencies squared, SO₂F₂>SO₄ ^2->SO₃>SF₆>SO₂Cl₂>SF₅C1>NSF₃>SF₅Br>SOF₂>SO₂>SF₄>Me₂SO>SCCl₂>SOBr₂>H₂S>Me₂S>CS₂>SCF₂>OCS<SCCl₂>SCBr₂>SPF₃>SPCl₃>SPBr₃ where Me--CH₃. Correlation of the RPFR with molecular structure and molecular forces was discussed.

The equilibrium constants K for the ³⁴S/³²S isotope exchange reactions of all the possible pairs of 19 sulfur compounds selected out of the above 24 were calculated and their temperature dependences were investigated. Two types of temperature dependences were observed; one being smooth monotonic and the other having single cross-over with no pre-inflection.     

Uranium Isotope Exchange between Uranium Hexafluoride and Uranium Pentafluoride

To aim at a better understanding of the uranium isotope exchange reaction between gaseous UF₆ and solid UF₅ experiments were done with natural UF₆ gas and solid UF₅ containing 3% ²³⁵U under different pressures of UF₆. The experimental results suggest a two-process reaction with an initial rapid increase of ²³⁵UF₆ in the gas phase followed by its slight and gradual increase. A rate equation based on a collision model is given for the two-process reaction which includes a primary exchange reaction on the solid surface and a secondary reaction participated by underlying UF₅ molecules. An analytical solution is provided for both of ²³⁵UF₆ concentration in the gas phase and ²³⁵UF₅ concentration on the solid surface, which is useful for determining the parameters characterizing the exchange reaction. A numerical analysis is also made to evaluate the influence of gas samplings. A remarkable agreement is found between the particle sizes of UF₅ estimated from the reaction parameter and from the direct observation with an electron microscope. The depletion of ²³⁵UF₅ concentration by the exchange reaction is very small when averaged over the whole solid UF₅, because the depletion is virtually limited to the solid surface due to the small reaction probability of underlying UF₅ molecules.     

Uranium Isotope Ratio Analysis of Uranium Pellet

<正>The analysis of uranium isotope ratio in uranium pellets is an important content of nuclear forensics.Thermal ionization mass spectrometry(TIMS)and multi-collector inductively coupled plasma mass spectrometry(MC-ICPMS)are high precision isotope ratio analysis methods.In this work,the isotope ratios of uranium in uranium     

Observation of Lithium Isotope Effect Accompanying Electrochemical Insertion of Lithium into Tin

Electrolysis of an organic electrolyte solution containing lithium ions was conducted to observe lithium isotope fractionation accompanying electrochemical insertion of lithium from the electrolyte to tin metal. The experimental setup consisted of a three-electrode electrolysis cell with a tin wire as cathode, lithium foils as anode and reference electrode and 1 M LiPF₆ dissolved in 1:2 volume ratio of ethylene carbonate and methylethyl carbonate as electrolyte and a power supply. The supplied electric energy was mostly consumed for the lithium insertion from the electrolyte to the tin cathode within the range of the cathode potential, relative to the reference electrode potential, from 0.05 V to 0.30 V. The single-stage separation factor increased with increasing cathode potential and seemed to asymptotically approach to the limiting value of 1.015 at 25®C, with ⁶Li being preferentially fractionated into tin metal.     

Reduced Partition Function Ratio of Uranyl Ion and Uranium Isotope Effect

Density of 30v/o tri-n-butyl phosphate-n-dodecane solution loaded with uranyl nitrate, nitric acid and water was measured. An empirical density equation was derived from regression analysis of the density data. The equation represents the density values well in a wide range of composition and temperature.     

Effect of Nitrogen Ion Implantation in Copper

In this study, copper samples with 99% purity implanted by N⁺ and N₂ ⁺ ions. Implantation of ions performed at 50 keV and various doses ranging from 1 × 10¹⁷ to 1 × 10¹⁸ ions/cm². Morphology of samples’ surface studied by atomic force microscopy. Microstructure of modified surfaces after ion implantation obtained using grazing incidence X-ray diffraction technique (GIXRD). Formation of both copper nitride and copper trinities confirmed by GIXRD results. Microhardness properties and corrosion behavior of implanted samples measured by Vickers and corrosion test, respectively. The maximum hardness of copper surface observed after nitrogen ion implantation at the dose of 3 × 10¹⁷ ions/cm². Moreover, the results showed that corrosion resistivity significantly increase.     

Separation of Uranium Isotope by Plasma Centrifuge

A method of centrifugal separation of isotopes by electromagnetic means is presented. The principle proposed utilizes electromagnetic acceleration by the interaction between an electric current in a slightly ionized gas and an external magnetic field. The analysis shows that an azimuthal flow of 2.6 km/sec can be realized with a magnetic field of 200 gauss and an electric current of 1.5kA. The resulting centrifugal force is large enough to permit realization of a more compact concentration cascade than the conventional mechanical centrifuge.     

Isotope Effects in Electrolytic Formation of Lithium Amalgam

Isotope effects in the lithium amalgam formation were studied by using the mercury cathode and LiOH solutions. The electrolyses were carried out at different conditions of both applied voltages 4–10 V, and the concentrations of initially charged LiOH, 0.5–5 mol/dm³. Higher efficiency of electrolytic amalgam formation was observed at higher LiOH concentrations and higher applied voltages. At these conditions, however, significant amount of solid amalgam was produced in the mercury phase. From the isotopic analyses on the samples taken during the electrolyses, it was found that the isotopic equilibrium was attained between the aqueous and the liquid amalgam phases. The isotopic equilibrium constant (isotope separation factor) was determined as 1.056 (average value for all the experiments) at 20°C.     

International Symposium on Isotope Separation and Chemical Exchange Uranium Enrichment

From the viewpoint of nuclear criticality safety, it is important to comprehend the reactivity of fuel solutions induced by oscillatory movements such as earthquakes. This paper intends to figure out the reactivity of a fuel solution system with a free surface formed by oscillation by evaluating the fluctuation of the neutron multiplication factor (k _eff ) obtained from a static calculation. To fulfill this intension, criticality calculations with reflecting fluid calculation results have been carried out. In the fluid calculations, the finite volume method and the volume of fluid (VOF) method have been applied in tracking the free surface formed by oscillation. The continuous energy Monte Carlo calculation method has been applied in the criticality calculations. As a result, it has been found that the variation patterns of the k _eff and those of the shape of fuel solutions are classified according to oscillation frequency and the ratio of solution height to the width of the tank (H/L). If a sloshing motion is generated, the k _eff fluctuates widely and has a threshold, with which we can classify the fluctuation type of the k _eff , despite the kind of reflector. If H/L is above the threshold, i.e., H/L =0.4, the k _eff fluctuates to a value below that obtained in the resting state. On the contrary, if H/L is below the threshold, the k _eff fluctuates to a value above that obtained in the resting state. This result implies the criticality calculation for a fuel solution with a free surface using the Monte Carlo method may give a slightly smaller threshold than using other approaches.     

甲烷的氢同位素交换的热力学理论计算

应用密度泛函理论(DFT)/B3LYP/6-31G**方法计算了甲烷的氢同位素交换的各反应标准摩尔生成焓、标准摩尔生成熵、标准摩尔吉布斯自由能和平衡常数.计算结果表明,温度是影响反应热力学的重要因素,较高温度有利于甲烷的氢同位素交换,但温度太高将有较多的积炭生成,欲得到较高的转化率,需要一合适的反应温度.     

Studies on Isotope Separation of Lithium by Electromigration in Fused Lithium Bromide and Potassium Bromide Mixture, (II)

Accurate knowledge on the salt composition in the anode compartment is indispensable when ⁶Li is to be highly enriched by electromigration in fused LiBr-KBr mixture. A study was made on the dependence on temperature shown by the salt composition in the anode compartment. It was observed that sustained electromigration led to a salt composition in the anode compartment that was determined by the prevailing temperature. The composition was observed for various temperatures between 380° and 740°C: In terms of the ratio Li/K in chemical equivalent, the values were 1.31 at 380°C, 1.29 at 420°C, 1.31 at 460°C, 1.41 at 500°C, 1.76 at 540°C, 1.82 at 580°C, 1.95 at 620°C, 2.16 at 680°C and 2.34 at 740°C. These results can be explained by assuming that the fused LiBr-KBr mixture is a system composed of two simple salts and their eutectic, and that at temperatures below 550°C, which is the melting point of LiBr, LiBr and KBr are dissolved in fused eutectic, while KBr is dissolved in the fused eutectic and LiBr at temperatures between 550° and 738°C, which latter is the melting point of KBr.     

Studies on Isotope Separation of Lithium by Electromigration in Fused Lithium Bromide and Potassium Bromide Mixture, (III)

Enrichment of ⁶Li by means of electromigration was carried out in fused LiBr-KBr mixture of a composition of 1.54 (Li/K in chemical equivalent ratio).

The electromigration brought about by 847,000 C of charge transported at 520°C, produced in the cathode compartment 38.4 meq. of Li salt with an abundance ratio of the isotopes (⁷Li/⁶Li) of 7.03, as compared with the initial value of 12.58. The distribution of the total amount of salt and of the salt composition in the migration tube agreed well with the results previously obtained on the enrichment of ⁷Li. It is suggested that, in veiw of the similarity in phase diagrams between UCl₄-CaCl₂ and LiBr-KBr systems, there are logical possibilities of ²³⁵U enrichment by analogous procedure.     

Measurement of Uranium Isotope Ratio in Single Particle by SEM-LA-ICP-MS

<正>Particle analysis of single uranium-bearing particle is one of the most important techniques in environmental monitoring of nuclear safeguards.As a reliable and routine technique,fission track analysis combined with thermal ionization mass spectrometry(FT-TIMS)is complex and time-consuming.As a rapid precise analytical     

Measurement of Uranium Isotope Ratio in Single Particles by SEM-TIMS

正Particle analysis of single uranium-bearing particle is one of the most important techniques in environmental monitoring of nuclear safeguards.As a reliable and routine technique,fission track analysis combined with thermal ionization mass spectrometry(FT-TIMS)is complex     

Mean Atomic Velocities of Uranium,Titanium and Copper during Electron Beam Evaporation

Mean atomic velocities of uranium, titanium and copper during electron beam evaporation of the metal were measured by a microbalance technique as a function of evaporating metal surface temperature. In the measured temperature range, the mean velocity of uranium was up to 2.1 times the thermal mean velocity vth, corresponding to the surface temperature of the evaporating metal. Mean velocities of titanium and copper increased to 1.6 and 1.3 times vth, respectively. This meant that mean velocities of uranium and titanium exceeded the maximum flow speed of an ideal gas in adiabatic expansion, i.e. 1.4 times vth, while the mean velocity of copper was almost equal to it. The electronic states of uranium and titanium were thermally excited to higher levels, then such excited energy should be converted to kinetic energy during adiabatic expansion. However, copper was rarely excited to higher levels because of the their fewer number. As a result, mean velocities of uranium and titanium were faster than the maximum flow speed of ideal gas.     

Uranium Isotope Exchange between Gaseous UF6 and Solid UF5

A new rate equation is derived for uranium isotope exchange reaction between gaseous UF₆ and solid UF₅ by assuming the total number of UF₅ molecules on the particle surfaces to depend on time. The reaction parameters included in the equation are determined from the experimental results, and are compared with the previous ones. The rate equation given in this work satisfies the related isotopic mass balance, and includes explicitly the terms related to the UF₆ density and the mean size of UF₅ particles, both of which cause an important effect on the reaction. Since the rate equation derived in this work facilitates the simulation of the reaction under various conditions, the long term behavior of a simulated exchange reaction is studied under the condition considered to be close to that in a recovery zone of the MLIS process.     

Fluorination of Uranium Compounds by Bromine Trifluoride Vapor, (I)

The fluorination of U₃O₈ powder by BrF₃ vapor was attempted. The reaction proceeded even at 67°C and under 10 mmHg BrF₃ partial pressure, producing UF₆. The reaction rate increases with temperature up to about 220°C, and its activation energy is 0.9 kcal/mol. The reaction rate, however, decreases at temperatures slightly above 220°C and rises again after passing through a minimum at 225°–230°C.     

铀蒸发器材料耐腐蚀性能的热力学计算

本文根据自由能函数方法求出了碳化物、氮化物、硼化物和氧化物的反应自由能近似方程。同时讨论了在高温下这些物质与铀液体和铀蒸气的相容性以及作为激光分离铀同位素坩埚材料的可能性。