Laser Isotope Separation Research Articles

Ionization yield and isotopic selectivity of three-step photoionization of atoms by pulsed lasers

Estimate of ionization yield and selectivity in multi-step photoionization is of interest in studies related to trace analysis and laser isotope separation. Analytical expressions of ionization yield for the desired and interfering isotopes have been derived by solving rate equations for three-step photoionization. The partial overlap of absorption lines of the isotopes and the charge exchange of the ions of the desired isotope with the atoms of the interfering isotope have been considered. The ionization yield and the isotopic selectivity of the photoionization process are calculated for ytterbium isotopes, considering various atomic and laser parameters. Numerical results have been discussed, showing the effect of both factors on the ionization yield and the isotopic selectivity of the process.

Researches on Laser Isotope Separation of Gadolinium and Boron

Laser isotope separation experiments of Gd and B by atomic and molecular methods, respectively, have been performed. Gadolinium-157 was selectively photoionized by means of three linearly polarized dye lasers, the excitation process of which is based on the polarization selection rules. The effect of magnetic field on isotopic selectivity was discussed. 10BCl3 was selectively photodissociated through IR multiphoton dissociation by the irradiation of TEA CO2 laser or free electron laser (FEL). Selectivity was improved by two-color laser irradiation.

Isotope separation required in SCNES and future subjects

In the SCNES studies it has been confirmed that transmutation of radioactive nuclides and of net energy generation can be attained simultaneously. In order to realize the SCNES, material separation, isotope separation of the FP's and future subjects to be solved are discussed. In this paper we discuss about the required energy for a scheme of atomic vapor laser isotope separation (AVLIS) of FP's, the practical isotope separation system and the combination of AVLIS, plasma separation process and gas centrifugation methods for SCNES. And also we discuss about the future subject to guide to shift to SCNES smoothly in future concerning with waste management in the intermediate period to the SCNES. Consequently, the SCNES can be the ultimate goal of the nuclear energy development and it is very important to make effort to development in the intermediate period to SCNES.

High Enrichment of 28Si by Infrared Multiple Photon Decomposition of Si2F6

High enrichment of 28Si has been carried out using the laser isotope separation technique based on the isotopically selective infrared multiple photon decomposition of Si2F6. When about 2 Torr of Si2F6 was irradiated at a fluence of 1.0 J/cm2 per pulse with the 10P(8) line of a TEA CO2 laser at 954.55 cm-1, the compound decomposed very efficiently with high isotope selectivity. The products SiF4 and white solids were enriched with 29Si and 30Si, while the residual Si2F6 was enriched with 28Si. The atomic fraction of 28Si in residual Si2F6 increased with increasing decomposition of Si2F6; 99.9% of 28Si was obtained at a consumption of 50% of initial Si2F6. The large-scale flow experiment yielded 99.7% 28Si at a production rate of 2.5 g/h, where a mixture of 3.3 Torr Si2F6 and 6.6 Torr argon was irradiated with 10P(8) laser pulses at a repetition rate of 5 Hz. Merits and demerits of the present laser separation are discussed in comparison to those of conventional separation methods. Laser enrichment of 28Si seems promising for economical production of large quantity of pure 28Si. Various applications of silicon isotopes are briefly reviewed.

Ion extraction from a laser-ionized plasma produced between parallel plate cathodes and an anode above them

We studied the behavior of a laser-photoionized plasma in atomic-vapor laser isotope separation under an external electric field with a two-dimensional one-fluid model, in which electrons are assumed to be in thermal equilibrium. Sheath-formation and ion-extraction processes are investigated in both a conventional parallel-electrode system and an M-type electrode system consisting of two parallel cathodes and one anode above them. The process of ion extraction in the M-type electrode was made clear and it is shown that ions are collected twice as fast as in the parallel-electrode system.

Selective photochemical isotope “burning” upon the interaction of resonant laser radiation with atoms

The method of laser isotope separation based on selective excited-atom “burning” in a flow with buffer and reagent gases was implemented experimentally for zinc and rubidium. Selective excitation of isotopes was accomplished by the one-photon method using weak absorption lines and at the edge of the Doppler contour of atomic absorption with small isotope shift.

Measurement of Oscillator Strengths in Uranium Using Laser Techniques

Laser Isotope Separation of Uranium (Atomic Vapor Laser Isotope Separation, «AVLIS») has stimulated, these last 20 past years, a number of studies on oscillator strength measurements. This interest for oscillator strength measurements is related to the importance of this parameter for scaling a future plant, since this parameter determines the laser fluences needed for effective atomic photoionization. This presentation will review several techniques (saturation, branching ratio + lifetime, Rabi oscillations, Autler-Townes) which have been used by CEA at Saclay. Examples of results for atomic uranium are given, advantages and disadvantages, accuracy and limitations of each method are discussed.

Gas-Flow Circulation Apparatus Coupled with TEA-CO2 Laser for Free Electron Laser Isotope Separation

A gas-flow circulation apparatus coupled with a TEA-CO2 laser has been developed for the purpose of the isotope separation experiments using a free electron laser (FEL). The working gaseous mixture filled in the reaction chamber was smoothly circulated by the ventilation fan. Using the reaction chamber with the large volume, the multi-photon dissociation of a SiF3I molecule was successfully demonstrated. The change of IR spectrum monitored on-line by a FT-IR spectrometer showed that the TEA-CO2 laser effectively assisted the multi-photon dissociation of the molecules by the FEL.

Researches on Laser Isotope Separation of Gadolinium and Boron.

Laser isotope separation experiments of Gd and B by atomic and molecular methods, respectively, have been performed. Gadolinium-157 was selectively photoionized by means of three linearly polarized dye lasers, the excitation process of which is based on the polarization selection rules. The effect of magnetic field on isotopic selectivity was discussed. 10BCl3 was selectively photodissociated through IR multiphoton dissociation by the irradiation of TEA CO2 laser or free electron laser (FEL). Selectivity was improved by two-color laser irradiation.

High Enrichment of 28Si by Infrared Multiple Photon Decomposition of Si2F6.

High enrichment of 28Si has been carried out using the laser isotope separation technique based on the isotopically selective infrared multiple photon decomposition of Si2F6. When about 2 Torr of Si2F6 was irradiated at a fluence of 1.0 J/cm2 per pulse with the 10P(8) line of a TEA CO2 laser at 954.55 cm-1, the compound decomposed very efficiently with high isotope selectivity. The products SiF4 and white solids were enriched with 29Si and 30Si, while the residual Si2F6 was enriched with 28Si. The atomic fraction of 28Si in residual Si2F6 increased with increasing decomposition of Si2F6; 99.9% of 28Si was obtained at a consumption of 50% of initial Si2F6. The large-scale flow experiment yielded 99.7% 28Si at a production rate of 2.5 g/h, where a mixture of 3.3 Torr Si2F6 and 6.6 Torr argon was irradiated with 10P(8) laser pulses at a repetition rate of 5 Hz. Merits and demerits of the present laser separation are discussed in comparison to those of conventional separation methods. Laser enrichment of 28Si seems promising for economical production of large quantity of pure 28Si. Various applications of silicon isotopes are briefly reviewed.

Influence of charge exchange on the collection of the laser produced ions

We evaluated influences of charge exchange on ion collection of laser isotope separation of uranium. We made a two-dimensional code based on fluid dynamics taking the charge exchange term into consideration. Parametric study was performed in terms of electric amplitude, ion density, and electron temperature. In addition to parallel electrode arrangement, calculations were performed for Π- and M-type arrangements. The ratio of charge exchanged ions is found to largely depend on the collection time.

Optimisation of a multistage pulsed dye laser system

A multistage narrow-band dye laser amplifying system with an output power of up to several kilowatts is considered as a whole. Such systems became necessary due to the development of the method of laser isotope separation (the AVLIS method). The use of the simplified model of an amplifying cell allowed us to solve analytically the equations describing the laser system and to determine optimal parameters of each stage. The dye laser system with an output power of 1 kW is optimised based on the model proposed. The accuracy of the obtained estimates was verified by a direct numerical simulation of the system based on a rigorous solution of the equations describing the interaction of radiation with the dye solution.

New method for polarizing complicated atoms

In the optical pumping process, spontaneous emission plays a unique role in redistributing the population of the ground level among the magnetic sub-levels. It is clear that the branching ratio of the relevant transition in the optical pumping must be nearly equal to unity in order to avoid the loss of population involved. Unfortunately, most complicated atoms do not have a simple energy level structure and cannot be polarized using optical pumping. We propose here a new polarizing method of a purely laser-driven process that avoids spontaneous emission and can be used in many heavier atoms. For J = 0 ground-state atoms, a complete population transfer to the meta-stable state can be used as efficient laser isotope separation, whereas a coherently prepared superposition state of the non-magnetic ground state and one of the magnetic states of the meta-stable level can be used as a tool to study the decoherent process. For J of the ground level no less than unity, partly removing the population on one of its sub-magnetic states will enhance the magnetic resonance signal significantly.

The Livermore experience: Contributions of J H Eberly to laser excitation theory

This article summarizes the developing understanding of coherent atomic excitation, as gained through a collaboration of J. H. Eberly with the Laser Isotope Separation Program of the Lawrence Livermore National Laboratory, particularly aspects of coherence, population trapping, multilevel multiphoton excitation sequences, analytic solutions to multistate excitation chains, the quasicontinuum, pulse propagation, and noise. In addition to the discovery of several curious and unexpected properties of coherent excitation, mentioned here, the collaboration provided an excellent example of unexpected benefits from investment into basic research.

An efficient method for extracting plasma ions in laser isotope separation systems

The possibility of using a Hall-current accelerator to extract ions from a partially ionized plasma produced by selective laser isotope photoionization of atomic vapor is examined. A mechanism for ion acceleration is investigated using one-dimensional time-dependent equations of two-fluid magnetohydrodynamics. The current cutoff due to the ion space charge is prevented by electron emission. It is shown that, at an accelerating voltage of 25–50 V and emission current density of several mA/cm2, the ion component is accelerated throughout the entire plasma volume up to a velocity of ∼105 cm/s in a few microseconds. The influence of resonant charge exchange and secondary ionization by electrons on both the acceleration dynamics and selectivity degradation is taken into account. It is shown that the Hall-current extractor allows one to avoid selectivity degradation even when the plasma size exceeds the charge-exchange mean free path by one order of magnitude.

Cross Sections of Charge Transfer between Uranium Atoms and Ions Produced by Autoionization

A technique to reduce charge transfer has been studied to cut enrichment loss during atomic vapor laser isotope separation. The charge transfer cross sections of uranium were experimentally examined. The cross sections of charge transfer for case A (between ground-state ions and atoms) and, cases B and C (between ions populated in some excited states and atoms) were relatively measured in the energy range of 100–2,000 eV by the cross-beam method. The charge transfer cross sections for cases A, B and C do not depend on impact energy, and the cross sections for case A are smaller than those for cases B and C. These results are in fairly good agreement agreed with theoretical predictions. It is confirmed experimentally and theoretically that the uranium charge transfer cross section depends on its initial ionic state, therefore ion loss by charge transfer will be reduced by controlling the initial state of the ions.

High-efficiency Zn isotope separation in a photochemical reaction induced by two-photon excitation

High-efficiency laser isotope separation was accomplished for zinc atoms in the situation when isotope shifts are much smaller than the Doppler width. The atoms were excited via two-photon absorption of two counter-propagating waves slightly detuned from the intermediate state, so that all “0requisite” atoms were excited. The isotope separation results from a photochemical reaction between the selectively excited zinc isotope and the CO2 molecules. The reaction rate is 3–5 orders of magnitude higher than for the unexcited atoms. The mechanisms of two-photon resonance line broadening are considered both theoretically and experimentally, and the possibilities of the method for obtaining isotopes in quantitative yields are estimated.

Enhancement of ion extraction from a cold plasma with radio-frequency plasma heating

Ion extraction from a cold plasma produced by laser multiphoton ionization has been enhanced by using radio-frequency (140 MHz) dielectric plasma heating. When 10 W in heating power is applied to a plasma of ion density around 3×1010 cm−3, it is observed that the peak ion flux extracted with an electrostatic voltage of 20 V increases by a factor of more than 2. The time for extracting all the ions becomes short by a factor of 3 without any production of radio-frequency discharged plasma. It is considered that these results are due to the increase in the electron temperature of the plasma. This method will be very useful for the process of ion extraction in atomic vapor laser isotope separation.

Enhancement of electron temperature in a laser-induced plasma using a radio-frequency electric field

An experimental study of the enhancement of the electron temperature of a laser-induced plasma by use of radio-frequency dielectric heating has been carried out. A radio-frequency electric field of 140 MHz is used to heat the plasma produced by multistep resonant photoinization. It is clearly observed that the electron temperature increases from 0.3 to 1.0 eV when a radio-frequency input power of 1.0 W is applied. Also, applying heating induces a plasma oscillation. This is due to the generation of ion waves in the plasma, and therefore, means that the enhanced electron temperature is higher than the ion temperature. It is expected that this method will improve the efficiency for extracting ions rapidly from a laser-induced plasma in atomic vapor laser isotope separation.

Synthesis of a classical atom: Wavepacket analogues of the Trojan asteroids

The reason why atomic physicists are interested in celestial mechanics is simple: the gravitational and Coulombic potentials are mathematically identical and a one-electron atom is, therefore, governed by the same Hamiltonian as is the Kepler problem. However, once one goes beyond the two-body Kepler problem the connections between atomic physics and celestial mechanics become less direct. For example, the three-body problem, arguably the raison d'etre of celestial mechanics for several centuries, has received relatively little attention from atomic physicists because it does not have a direct quantum counterpart: three quantum particles cannot mutually attract one another and at the same time interact through a purely Coulombic force law. Nevertheless, in the last five years several research groups have discovered that quantum analogues of a particular limit of the three-body problem, the restricted three-body problem, not only exist but contain dramatically new physics. This article will describe this work and in particular will demonstrate the possibility of producing localized electronic states in atoms that are direct analogs of the coherent states of the harmonic oscillator. These coherent wavepackets behave in a similar way to the coherent states of the harmonic oscillator and the resulting atom mimics a 'classical' or Bohr atom although external fields must be used to maintain their integrity. Such wavepacket states are of as much fundamental interest in laser chemistry as they are in atomic, molecular, optical, and solid state physics. The potential applications of time-evolving quantum wavepackets seem limitless; some examples of their uses include: the exploration of the boundary between classical and quantum mechanics, the investigation of the interpretation of quantum mechanics by creating experimental realizations of such classic experiments as Schrodinger's Cat, the control of chemical reaction dynamics to achieve laser isotope separation, the storage of coherence for quantum computational or communications purposes, and the construction of optical switches and modulators.