Laser Isotope Separation Process Research Articles

Numerical study of the laser isotope separation of optically pumped 102Pd

The feasibility of laser isotope separation of 102Pd through pulsed laser optical pumping followed by isotope selective photoionization has been studied through density matrix formalism. The effect of various parameters such as bandwidth of the excitation lasers, intensity of the lasers and Doppler broadening of the atomic ensemble on the efficiency of optical pumping and isotope selective photoionization have been evaluated. The optimum number density in the laser-atom interaction region has been derived from the studies of the effect of charge exchange collisions on the degree of enrichment. It has been shown that it is possible to enrich 102Pd up to ~ 23.7% at a production rate of 1.1 mg /h. The achievable degree of enrichment through this photoionization scheme is higher than the previously reported laser isotope separation process. The radionuclidic purity of the irradiated enriched mixture has been found to be suitable for medical applications.

Laser isotope separation of 192Ir

The following two-step isotope selective photoionization process has been studied for the separation of 192Ir isotope from natural Iridium irradiated in a medium flux reactor for 28 days.5d76s2F9/240.0cm−1→247.5871nm5d76s6p40389.83cm−1J=9/2→307.9nmIr+Density matrix formalism has been used for the investigation of laser isotope separation process. Optimum system parameters such as peak power densities of the excitation and ionization lasers, bandwidth of the excitation laser, angular divergence limit to the atomic ensemble have been derived. Effects of number density and ion travel distance prior to collection on charge exchange probability have also been studied. It has been shown that it is possible produce ∼98% enriched 192Ir at rate of 82 μg/h (27.9 GBq/h or 0.76 Ci/h) which can provide activity of 334 TBq/g or 9027 Ci/g. The enriched 192Ir can be used in both high-dose brachytherapy and high speed radiography. This is the first ever study on the laser based enrichment of Iridium isotopes.

Forensic signatures from laser isotope separation

This work introduces an analysis of the Atomic Vapor Laser Isotope Separation (AVLIS) process to assist regulatory agencies in detecting and inspecting uranium AVLIS facilities. Operating parameters of a theoretical AVLIS device are calculated based on product and tails assays. Further analysis shows a direct relationship between feed assays of minor isotopes and product assays, allowing inspectors to confirm the method of a sample’s enrichment and identify the feedstock origin due to natural variations in 234U assay. The decay of 234U into 230Th is used to estimate the time of last enrichment and increase the accuracy of feed assay calculations.

Physical characteristics of ion extraction simulation system based on gas discharge plasma jet

In an atomic vapor laser isotope separation process, the required isotope atoms are ionized selectively by a pulsed laser with a specific narrow line width, and then the produced isotope ions are extracted to the collected plates under an externally applied electromagnetic field. In the whole ion separation process, the ion extraction sub-process is one of the most important physical processes. Previous studies have shown that the key parameters of the laser-induced plasma, e.g., the initial electron number density and temperature, have a significant influence on the ion extraction features. In an actual isotope separation process, a specifically designed laser is necessary to produce the required isotope ions, which, however, leads the whole facility to have a very complicated structure, high capital cost, and especially, very narrow window of the key plasma parameters. These will, to some extent, limit a more in-depth investigation of the influences of the key plasma parameters on the ion extraction characteristics. In this paper, an ion extraction platform (ion extraction simulation experimental platform-2015, IEX-2015) is developed on the basis of a gas discharge plasma jet driven by a kilo-hertz high-voltage power supply. And an argon plasma collisional-radiative model is established to measure the electron temperature and number density in the plasma jet region. The experimental results show that the power input and driving frequency of the power supply and the argon mass flow rate can all affect the electron temperature and electron number density. The measured variation ranges of the electron number density and temperature are 109-1011 cm-3 and 1.7-2.8 eV, respectively, under a chamber pressure on the order of 10-2 Pa, which are close to the parameter levels in the actual ion extraction process. Subsequently, the preliminary ion extraction experiments are conducted under different extraction conditions including different externally applied voltages, different electrode distances and different plasma densities. The experimental results are also qualitatively consistent with those in an actual ion extraction process. The preceding preliminary experimental results show that it is feasible to conduct the ion extraction simulation study on IEX-2015. This is very helpful for systematically studying the ion extraction characteristics under different operating conditions in our future research.

Laser Isotope Separation of Zirconium for Nuclear Transmutation Process

Laser isotope separation process of zirconium based on polarization selection rules has been investigated using three dye lasers and a 1.06μm Nd:YAG laser in relation to nuclear transmutation process in the fast reactor. A high selectivity larger than a hundred between odd and even isotopes has been obtained by keeping the laser fluence lower than 0.4mJ/cm2. A highly selective photoionization scheme employing only two dye lasers has been newly found. The process includes the excitation from the ground state by a 573.7 nm dye laser and the subsequent three-photon ionization by a 578.1 nm laser.

Isotopically selective collisional vibrational energy transfer in CF3H

The authors investigate here the mechanism of collisionally enhanced isotopic selectivity observed in infrared multiple photon dissociation (IRMPD) of vibrationally preexcited CF3H by Boyarkin et al. [J. Chem. Phys. 118, 93 (2003)]. For both the carbon-12 and carbon-13 isotopic species they measure the dependence of the IRMPD yield on the time delay between the preexcitation and the dissociation pulses at different dissociation frequencies as well as its dependence on the initial isotopic composition of the sample. The results reveal that the collisional increase in isotopic selectivity originates not only from that of IRMPD itself but also from the isotopic selectivity of vibrational energy transfer, with the latter making the major contribution under their experimental conditions. They suggest that the observed isotopic selectivity in collisional energy transfer arises from the difference in overlap between the absorption spectra of the nu5 mode in the 12CF3H acceptor molecule with emission spectra of the same mode in the two isotopically different donors. Understanding the origin of this collisional effect has important implications for optimization of laser isotope separation processes.

Selectivity and Efficiency of Laser Isotope Separation Processes of Gadolinium

Isotopic selectivity and ionization efficiency are discussed in the isotope separation processes of Gd based on polarization selection rules and based on isotope shift. Enrichment of 157Gd to 90% was experimentally demonstrated using both methods together. The features of the absorption spectra of Gd in yellow-red and blue regions were summarized. Absorption spectra that are suitable for separation process using isotope shift were examined and an obtainable selectivity and efficiency are quantitatively calculated.

Selectivity and Efficiency of Laser Isotope Separation Processes of Gadolinium

Selectivity and Efficiency of Laser Isotope Separation Processes of Gadolinium

Infrared Laser Chemistry of Trichlorosilane in View of Silicon Isotope Separation

With a view toward laser isotope separation of Si, we have studied infrared multiphoton dissociation (IRMPD) of room temperature trichlorosilane, SiHCl3. Over the wavelength range investigated, multiphoton dissociation of the room temperature species exhibits a maximum efficiency at 12.6 μm and a threshold fluence of only ∼1 J/cm2. Vibrational overtone preexcitation of SiHCl3 to the first SiH-stretch overtone (2ν1) prior to IRMPD results in a 10-fold increase of the dissociation yield compared to molecules with only thermal excitation. In an effort to collect the nascent SiCl2 dissociation fragments, we have tested a number of different molecules that could serve as a scavenger to convert them into a stable gaseous compound. Several of these molecules react directly with trichlorosilane after being decomposed by collisional energy transfer from vibrationally excited SiHCl3 and therefore are not suitable for a laser isotope separation process. Of the compounds tested, we find that only BCl3 scavenges SiCl2 without significant reaction with the starting material.

Measurement of Condensation Onset in Steady Supersonic Laval Nozzle Flow for the Molecular Laser Isotope Separation Process.

A method based on laser light scattering is presented for the observation of the condensation of working molecules in a steady-state-flow supersonic Laval nozzle operating in a closed loop. The distribution of scattered light from droplets formed by condensation along the flow direction is measured from photographs to determine the point of condensation onset. The temperature and density at the onset point are obtained from the values of static pressure based on the equations of isentropic flow.

Energy level effects during multiphoton dissociation and the laser separation of closely spaced isotopes

A novel approach for enhancing the selectivity of the desired isotope in the molecular laser isotope separation (MLIS) process is presented. The scheme consists of simultaneously applying two laser beams with frequencies corresponding to those between the ground and the first energy excitation level and the ground and the second energy excitation level, respectively. Practical relations on the properties of the spherical-top molecules are derived and a semiclassical analysis of the electromagnetic interaction within the limits of the experimental conditions applied in actual MLIS experiments shows that the selectivity, defined as the ratio of the absorption cross sections of the two isotopes, increases by a factor of 10–20 times in the case of the uranium isotopes. In addition, it is demonstrated that during the multiphoton absorption process energy-level splittings due to induced magnetic dipoles and induced electric quadrupoles are by no means negligible. They become significant during multiphoton processes where two or more photons are lost during the interaction process. At high pumping powers they become dominant and inhibit selectivity. They cancel out during interaction processes where there is no change in the total number of photons, such as scattering. These effects can be avoided by applying the laser beams to the molecular gas in arrangements which in principle are equivalent to a Mach–Zehnder interferometer with the molecules substituted for the reuniting beam splitter. Moreover, the induced electric quadrupoles (E2) are fully exploited. The application of the results and the concepts described herein can render the MLIS process the most economic and practical method for the commercial separation of the uranium isotopes.

Ion extraction and charge exchange in laser isotope separation

In the atomic vapor laser isotope separation (AVLIS) process, a vapor is ionized by pulsed laser beams, and the ions are extracted by negatively biased collectors. We compute the unsteady dynamics of the photoplasma using a two-dimensional (2-D) particle-in-cell (PIC) code. Collisions between ions and neutral species are simulated by a Monte Carlo technique. The plasma dynamics is visualized by snapshots of particle positions showing the directions of their velocities. The three kinds of particles (electrons, photo-ions, and ions created by charge exchange) are marked by different colors. The graphic outputs illustrate the motion of the electrons toward the anodes, the vertical drift of the plasma, its erosion by the transient ion sheath, and nonselective ionization by charge exchange.

Analysis of Laser Beam Propagation Effects in Atomic Laser Isotope Separation

In the atomic laser isotope separation process, the laser beams propagate through the atomic vapor over a long distance. It has been shown that the laser-atom interactions significantly modify the laser pulse shape and propagation velocity, resulting in degradation of the isotope separation efficiency. These propagation effects have been analyzed quantitatively, and a simple scaling formula has been derived to estimate the necessary laser energy for such optically thick atomic vapor. The optimum conditions of incident laser pulse have also been discussed.

Limitation of CO<inline-formula><sup><roman>2</roman></sup></inline-formula> laser-induced gas breakdown

To obtain economical extraction of ²³⁵U in the molecular laser isotope separation (MLIS) process, 16-μm laser beams must be generated in a parahydrogen Raman cell with high repetition rates and sufficient intensity. Because the intensities of the 16-μm laser beams are dependent on the intensity of the incoming pump laser beams, the intensity of the CO₂ lasers must be kept as high as possible. The maximum intensity has, however, been found to be controlled by the onset of gas breakdown in the Raman cell at too low a level for efficient Raman conversion. Through tests, the origin of gas breakdown in a 2-kHz-repetition-rate Raman cell is identified as particle contamination. The effect of the degree of contamination is determined and compared with experimental results. Conditions are set and modifications implemented on the Raman cell to ensure efficient Raman conversion.

Small cell experiments for electrolytic reduction of uranium oxides to uranium metal using fluoride salts

Electrolytic reduction of uranium oxide was proposed for the preparation of uranium metal feed for the atomic vapor laser isotope separation (AVLIS) process. A laboratory cell of 25-cm ID was operated to obtain additional information in areas important to design and operation of a pilot plant cell. Reproducible test results and useful operating and control procedures were demonstrated. About 20 kg of uranium metal of acceptable purity were prepared. A good supply of dissolved UO2 feed at the anode is the most important controlling requirement for efficient cell operation. A large fraction of the cell current is “nonproductive” in that it does not produce a metal product nor consume carbon anodes. All useful test conditions gave some reduction of UF4 to produce CF4 in addition to the reduction of UO2, but the fraction of metal from the reduction of UF4 can be decreased by increasing the concentration of dissolved UO2. Operation of large continuous cells would probably be limited to current efficiencies of less than 60 Pct, and more than 20 Pct of the metal would result from the reduction of UF4.

Detuning from intermediate resonance dependence of the atomic three-step pulse photo-ionization selectivity in powerful laser fields

The selectivity of three-step pulse photo-ionization of atoms versus the detuning delta of exciting radiation frequencies from intermediate resonance is investigated in powerful laser fields where the power broadening of the resonant transitions is at least of the order of isotope shifts. The Doppler broadening of the resonant transitions is taken into account and it is assumed that the sum frequency of both exciting laser radiations is tuned to the line centre of the two-photon transition of a selected isotope. It is shown that in this situation the photo-ionization selectivity increases so greatly with the absolute detuning mod delta mod that even in such strong fields the process of photo-ionization can be highly selective. The optimization of selective photo-ionization of atoms is discussed in connection with the decrease in the selective isotope yield with increase of the absolute detuning mod delta mod . Analytical consideration of selective three-step pulse photo-ionization in powerful laser fields, based on the density matrix formalism, is presented together with the results of numerical simulation of the 40Ca-48Ca laser isotope separation process as an example.

Process Modeling of Laser Photochemical Reactor

The applicability of conventional process engineering terms like value function, separative work unit, etc. to the laser isotope separation process has been established through appropriate formulation of the problem. The value function developed in this paper has been shown to be useful in arriving at guidelines for optimal design and operation of an isotope separation plant. A direct and simple model has been developed for a single-phase single-component laser photoreactor stage. This model, incorporating the key features and constraints of the laser isotope separation process, can provide an analysis and design basis to the process engineer.

Laser isotope separation

Abstract This work describes the atomic route to laser isotope separation. This is a process which uses intense pulsed lasers to photoionize one isotopic species of a chemical element, after which these ions are extracted electromagnetically. The paper describes only the isotopic enrichment of uranium for nuclear fuel cycles. It makes brief mention of the traditional cascade processes used at present, and then turns to the atomic physics of laser photoionization. The principles of the laser isotope separation process, important spectroscopic experiments and considerations which determine the design of a plant are described. This review concentrates on the laser ionization process, few details of vaporization of uranium metal or the extraction of ions are given.

Shortcut Method for the Analysis of Reaction Characteristics in Infrared Multiphoton Dissociation

It has been shown that the fluence dependence of the fractional conversion per pulse (which is often called the reaction characteristics) of infrared multiphoton dissociation is very useful in designing and evaluating the laser isotope separation processes. It was reported in our preceding works that it was possible to obtain this reaction characteristics through the procedure we proposed. In this note, this procedure is improved for promptanalysis using both numerical expressions and approximating equations for generalized relations between the dimensionless reaction volume and the dimensionless fluence.

Uranium optogalvanic laser spectroscopy

When laser radiation is sent into a hollow cathode lamp and the radiation wavelength is tuned on an absorption line of a species which is present in the lamp, the discharged impedence does changed. This optogalvanic effect can be used to obtain spectroscopic information about the cathode elements and/or the buffer gas. This technique is particularly powerful for refractory elements since it associates the efficiency of sputtering evaporation to a straightforward and very sensitive detection means. We use this technique in order to study the uranium spectrum, detect new atomic energy levels and measure physical parameters useful for a laser isotope separation process.