PuF6 Research Articles

Photophysical Dynamics and Relaxation Pathways of Ligand-to-Metal Charge-Transfer States in the 5f1 [Np(VI)O2Cl4]2- Anion.

Although several publications report on the electronic structure of the neptunyl ion, experimental measurements to detail the photophysical dynamics of this open-shell actinyl system are limited in number. Time-resolved photoluminescence has been a useful experimental approach for understanding photophysical dynamics and relaxation pathways of a variety of other molecular and ionic systems, including gaseous plutonium hexafluoride and solid-state uranyl compounds. Here, we investigate time-resolved photoluminescence emission of the 5f1 neptunyl tetrachloride ([Np(VI)O2Cl4]2-) dianion following visible excitation. Photoemission of the lowest energy neptunyl ligand-to-metal charge-transfer (LMCT) transitions to both the ground and first electronically excited states is observed. Analyses of the decay lifetimes of the excited states suggest different relaxation pathways as a function of excitation energy. Vibronic progressions associated with the Np-oxo symmetric stretching mode are measured in emission spectra, and the energies from these progressions are compared with energies of vibronic progressions associated with the excitation spectra of [Np(VI)O2Cl4]2-. This study expands our understanding of this open-shell actinyl system beyond identification of excited states, allowing characterization of photophysical properties and evidence for the electronic character of the ground state, and suggests that this approach may be applicable to more complex actinide systems.

Regularities in the Radiation Decomposition and Synthesis of Plutonium Hexafluoride

One problem of nuclear technology is stabilization of gaseous plutonium hexafluoride, which decomposes under α self-irradiation. Stabilization can be accomplished by storage in vessels with packing and dilution with inert gases as well as chemically. The first two methods have been studied quite well [1, 2]. Attempts have been made to use fluorine and krypton difluoride as chemical stabilizers. Much better stabilization is attained by using krypton difluoride, which is a donor of atomic fluorine. However, technological problems require using stabilizers, which differ very little from plutonium hexafluoride (physical and chemical properties, molecular mass, viscosity, vapor pressure). For this reason it is of interest to investigate the radiolysis of plutonium hexafluoride in the presence of completely fluorinated hydrocarbons. Trifluoromethylperfluorocyclohexane (Freon-350) and standard quality plutonium were used in the present work. The saturated vapor pressure of Freon-350 differs very little from that of plutonium hexafluoride. The molecular mass of Freon-350 is 350 amu. The hexafluoride was obtained by fluorinating plutonium dioxide in a glow discharge using the procedure described in [3] followed by purification to remove volatile impurities by repeated vacuum distillation. To investigate radiolysis, a 3.4 liters nickel cylinder was filled with plutonium hexafluoride to pressure 2.9 kPa. Next, Freon gas was added to total pressure 5.6 kPa. Radiolysis was monitored radiometrically according to the activity of the gas phase in the top part of the cylinder. The maximum error of measurement did not exceed 5%. The corresponding curve of the partial pressure versus time is displayed in Fig. 1. The degree of composition of plutonium hexafluoride in time (Fig. 2) was calculated on the basis of the experimental data. The rate of radiolysis of pure plutonium hexafluoride during the first few days is 3.2% and the average value 1.5%. The average rate of decomposition under α self-irradiation equals 0.2%/day. Thus, Freon-350 accel

Development of methods for obtaining plutonium hexafluoride

Methods for obtaining plutonium hexafluoride are examined: from high- to low-temperature using molecular and atomic fluorine and compounds – sources of atomic fluorine. It is shown that generation of atomic fluorine holds promise and plasma-chemical apparatus is desirable for obtaining plutonium hexafluoride. A schematic description is presented. The stages of model and natural tests of plasmachemical apparatus are described. A comparative assessment is given of different methods of obtaining plutonium hexafluoride.

An analysis of the kinetics of reversible A + B(s) ⇄ C reactions on porous or powdered materials

The kinetics of the A + B(s) ⇄ C reversible process in a powdered material was analyzed for the example of the F2 + PuF4(s) ⇄ PuF6 reaction. Two possibilities of performing this reaction were considered, with pressed and powdered plutonium tetrafluoride. The first possibility does not contain uncertainties and allows the rate constants of the forward and back reactions to be found using the known equilibrium constant values. Experiments with the powdered substance can be used to obtain data on the other details of the reaction. The most general problem was considered and all significant processes were taken into account. These were (1) the diffusion of fluorine and plutonium hexafluoride molecules in the powder, (2) the forward and back reactions on the surface of particles, and (3) the removal of plutonium hexafluoride molecules formed from the surface of the tetrafluoride powder. The reaction became equilibrium as the gas mixture moved over the reaction cell, and the product ceased to form. The optimum cell length was calculated. The theory developed is necessary for planning experiments with powdered materials and experimental data processing. The theory generalizes the results obtained by Zel’dovich to reactions with unstable final products (that is, reversible reactions).

Regularities in the Sorption of Plutonium Hexafluoride

When implemented, the modern methods for reprocessing nuclear fuel which are based on the volatility of fluorides are complicated by the physical adsorption of uranium and plutonium hexafluorides on inorganic compounds. The lack of the required experimental data in this field makes it impossible to describe the kinetics of the behavior of the indicated hexafluorides in the various processes involved in obtaining and reprocessing them. Consequently, the study of the adsorption of uranium and plutonium hexafluorides and the determination of the heat and entropy of adsorption are of interest from the scientific standpoint and for applications. This paper is devoted to the study of these questions.

Reduction of Plutonium Hexafluoride Using Gaseous Reagents

The direct reduction of plutonium hexafluoride to dioxide in an oxygen–methane flame with various ratios of the initial components is investigated. The basic factors which influence the residual fluorine content in plutonium dioxide and the bulk density of the latter are determined. Plutonium dioxide samples with fluorine content not exceeding 5·10–3 mass% are obtained. A mechanism is proposed for the reduction process.

Application of Physical Methods for Reducing Plutonium Hexafluoride

The exploding-wire method, the photochemical method of irradiation with a light flux from a high-pressure mercury lamp, a high-intensity spark discharge, and irradiation by a CO2 laser are used to reduce plutonium hexafluoride and to separate it from uranium hexafluoride. The dependence of the reduction of plutonium hexafluoride on the wire material, the mass of the reduced product, and the amount of input energy is investigated. It is shown that the methods presented for reducing plutonium hexafluoride and separating it from uranium hexafluoride can be used under static and dynamic conditions for preparative purposes and on a large scale.

Low-Temperature Synthesis of Plutonium Hexafluoride

Fluoridation of uranium tetrafluoride by atomic fluorine and radiolytic plutonium tetrafluoride by atomic fluorine and dioxygen difluoride are investigated. The mechanism and the limiting stages of the processes with atomic fluorine are described. It is shown that plutonium tetrafluoride is fluoridated directly by dioxygen difluoride molecules and not by the products of its thermal decomposition. Kinetic equations are obtained for the fluoridation of plutonium tetrafluoride. These equations are of first order in the gaseous reagent and the specific surface area of tetrafluoride. The effectiveness of atomic fluorine and dioxygen difluoride for synthesis and recovery of plutonium hexafluoride are compared.

A Relativistic Density Functional Study on the Uranium Hexafluoride and Plutonium Hexafluoride Monomer and Dimer Species

A study on the UF6 monomer and dimer was carried out within the density functional method. The U-F distance in the UF6 monomer was optimized at different levels of theory, pointwise, assuming octahedral geometry, (1) by using an all-electron basis for both U and F in a nonrelativistic calculation; (2) by using a relativistic effective core potential (RECP) on U and nonrelativistic effective core potential (ECP) on the fluorines; and (3) by using RECP on the U atom and an all-electron basis on the F atoms. Atomization energies of 23.11, 33.92, and 35.66 eV were obtained at the three levels, respectively. Relativistic effects lead to about a 50% increase in the atomization energy. For the UF6 dimer, the potential energy curve, as a function of the intermolecular U-U distance, was computed at level 2, and the rotational barrier between the two monomers was determined. Similar calculations were performed on the corresponding PuF6 species. Comparisons are made with experiment and other theoretical studies, where available.

Plutonium hexafluoride decomposition under the action of laser radiation

The action of a CO 2 laser on a mixture of gases (plutonium hexafluorides and sulphur) has been studied. For the analysis a gaseous addition of sulphur hexafluoride has been used. The additive absorbs laser light, is inert to the plutonium hexafluoride and undergoes no chemical changes under laser radiation (10.6 μm). Dependence of the rate of plutonium hexafluoride decomposition on the laser beam intensity and on the partial pressure of sulphur hexafluoride has been investigated. The dependence of the rate of plutonium hexafluoride decomposition on the radiation intensity within the laser power range of 30–60 W is of a linear character and in the strong absorption range it depends only insignificantly on the sulphur hexafluoride pressure. The gas temperature in the tray has been estimated at 500 K on the beam input. The reaction mechanism has been interpreted. The resultant powder obtained after the plutonium hexafluoride decomposition has been identified as plutonium tetrafluoride.

A study of plutonium tetrafluoride interaction with krypton difluoride

Solid-state interaction between plutonium tetrafluoride and krypton difluoride has been investigated with the help of an experimental plant. The work presents the experimental results on the influence of temperature (in the temperature range of 273–333 K) and of reagent relations on the fluorination rate. The reaction rate constant and the activation energy have been determined, the latter equal to 20–25 kJ/mol. The major parameter defining the rate of interaction of plutonium tetrachloride with krypton difluoride has turned out to be the contact surface of the reagents. The specific role of krypton difluoride in the reaction of plutonium hexafluoride production has been estimated. On the basis of experimental data a flow chart of the process is suggested.

Vibronic states of plutonium hexafluoride in the visible and near infrared spectral regions

The entire absorption spectrum of PuF6 in the near IR and visible regions has been obtained at 0.5 cm−1 or higher resolution. A detailed analysis of the vibronic energy levels is presented and spectroscopic assignments of all observed transitions are made. The energy levels obtained from these spectroscopic measurements of the gas phase PuF6 molecule are the most accurate values available. A comparison is shown of our assignments and results with the matrix-isolation experiment and available theoretical studies.

Energy flow and branching ratios between the low-lying electronically excited states of PuF6

Measurements of the rise and decay times, relative intensities, and pressure dependence of the 1.0, 1.9, and 2.3 μm laser-induced fluorescence (LIF) of plutonium hexafluoride (PuF6) excited at 795 nm are reported. Einstein A coefficients of the transitions are also determined. Then, all these quantities are used to determine many of the rate constants of the kinetics of energy flow and also the relative quantum yields into the low-lying electronically excited states of PuF6. In addition, the data indicate that both radiating and nonradiating states are involved in the relaxation.

ChemInform Abstract: PRESSURE DEPENDENCE OF THE 2.3 μM LASER‐INDUCED FLUORESCENCE (LIF) OF ROOM TEMPERATURE PLUTONIUM HEXAFLUORIDE

Chemischer InformationsdienstVolume 16, Issue 25 Physical Inorganic Chemistry ChemInform Abstract: PRESSURE DEPENDENCE OF THE 2.3 μM LASER-INDUCED FLUORESCENCE (LIF) OF ROOM TEMPERATURE PLUTONIUM HEXAFLUORIDE W. W. RICE, W. W. RICESearch for more papers by this authorJ. E. II BAREFIELD, J. E. II BAREFIELDSearch for more papers by this author W. W. RICE, W. W. RICESearch for more papers by this authorJ. E. II BAREFIELD, J. E. II BAREFIELDSearch for more papers by this author First published: June 25, 1985 https://doi.org/10.1002/chin.198525001Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue25June 25, 1985 RelatedInformation

Low temperature synthesis of plutonium hexafluoride using dioxygen difluoride

The preparation of PuF/sub 6/ by the action of dioxygen difluoride (O/sub 2/F/sub 2/) on plutonium fluorides, oxides, and oxyfluorides at room temperature or below is described. Previously, direct synthesis of PuF/sub 6/ could only be achieved by high temperature (>300/sup 0/C) fluorination and by microwave or photolytic generation of fluorine atoms. Six experiments are described that illustrate the potency of O/sub 2/F/sub 2/ which is the property of this compound that indicates potential application in the nuclear industry.

Absorption cell with fiber optics for concentration measurements in a flowing gas stream

To facilitate the connection of the fiber optics to the experimental apparatus, the optical system was kept simple. Delicate alignments were avoided since the apparatus was contained in a glovebox and access to the monitor cells was limited. Changing the analysis site from one monitor cell to another was a trivial operation, allowing a single light source and detector assembly to service all experimental configurations. The in-line absorption cell was utilized to study the preparation of uranium and plutonium hexafluorides in a flowing system.

ChemInform Abstract: FLUORESCENCE STUDIES OF NEPTUNIUM AND PLUTONIUM HEXAFLUORIDE VAPORS

Chemischer InformationsdienstVolume 13, Issue 25 Physical Inorganic Chemistry ChemInform Abstract: FLUORESCENCE STUDIES OF NEPTUNIUM AND PLUTONIUM HEXAFLUORIDE VAPORS J. V. BEITZ, J. V. BEITZSearch for more papers by this authorC. W. WILLIAMS, C. W. WILLIAMSSearch for more papers by this authorW. T. CARNALL, W. T. CARNALLSearch for more papers by this author J. V. BEITZ, J. V. BEITZSearch for more papers by this authorC. W. WILLIAMS, C. W. WILLIAMSSearch for more papers by this authorW. T. CARNALL, W. T. CARNALLSearch for more papers by this author First published: June 22, 1982 https://doi.org/10.1002/chin.198225002AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue25June 22, 1982 RelatedInformation

Reactivity of transition metal fluorides—XII: Plutonium hexafluoride

In a continuing study of the relative chemical reactivities of the higher fluorides of the d- and ‖-transition elements, oxidation-reduction reactions of plutonium hexafluoride with a selected series of non-metal fluorides in low oxidation states have been examined. This investigation has also included reactions with hydrogen and with various covalent chlorides and bromides. The results of this study have been correlated with those from previous investigations, and the reactivity of plutonium hexafluoride is considered in the light of plutonium as an ‖-transition element. Special techniques were developed for thestudy of compounds of this radioactive element, and a new procedure for the preparation of plutonium hexafluoride has been devised which requires apparatus very much simpler than previously reported.

Isotope effects in the molecular spectrum of plutonium hexafluoride

The first evidence for an isotope shift in the near infrared region of the spectrum of an actinide molecule, PuF6, is reported. Using samples of 239PuF6 and 242PuF6, isotope shifts were found in the absorption region near 8000 Å. Shifts of 0.3 to 1.2 cm−1 were observed. The data are interpreted as indicating that some of the absorption bands in this region are vibronically induced electronic transitions which result from coupling of one or more quantum changes in the asymmetric ν3(F1u) and ν4(F1u) vibrations to electronic states of the nonbonding 5f electrons in the molecule.

Thermodynamical estimation of the processes involved in the separation of uranium and plutonium hexafluorides by selective chemical reducing agents

Thermodynamical estimation of the processes involved in the separation of uranium and plutonium hexafluorides by selective chemical reducing agents