Isotope Separation Methods Research Articles

Separation of an isotope as a precursor of a gamma-raylaser medium

The nuclear isomer 178Hfm2, expected to be the most promising candidate for the gamma-ray medium, is rather difficult to produce in large quantities. There are a few ways to create this isomer, such as the irradiation of 179Hf with high-energy neutrons through the (n,2n) reaction, the irradiation of 176Yb with high-energy α particles through the (α,2n) reaction, the irradiation of 181Ta with protons through the (p,2p2n) reaction. In some of these reaction schemes the isotopically pure target works better than the natural one from the viewpoint of spectroscopic purity, handling of radioactive materials and productivity. However, isotope separation of heavy elements for producing a precursor as a target material is difficult in terms of cost/effectiveness. The atomic vapor laser isotope separation (AVLIS) method is expected as the most efficient way compared with the normal electromagnetic separation method.

Free expansion of a low-density laser plasma

Expansion of a laser plasma, formed by multistage selective ionisation of metal vapours in the atomic vapour laser isotope separation (AVLIS) method, is considered. The main feature of such a plasma is that the mean free path of particles in the plasma is much greater and the Debye radius is much smaller than the transverse dimensions of the ionisation region. A numerical solution of equations of two-fluid hydrodynamics is used to show that, when expansion becomes steady, the average-mass velocity is equal to about half the most probable velocity of the particles which have the temperature of electrons and the mass of ions. Plasma expansion becomes steady in a time approximately 1.5 times longer than the time of flight across the initial transverse size of the ionisation region at the steady expansion velocity. It is therefore reasonable to expect efficient ion extraction by free expansion in laser isotope separation by the AVLIS method.

Wave Packet Isotope Separation.

We introduce and demonstrate a general wave packet method for laser isotope separation. In this scheme, laser excited molecular (or atomic) wave packets of differing isotopes become spatially separated in the course of their long-time free evolution. In order to overcome the quantum spreading of wave packets, we make use of the phenomenon of revivals. We demonstrate experimentally, with mixed ${}^{79}$B${\mathrm{r}}_{2}$${\mathrm{/}}^{81}$B${\mathrm{r}}_{2}$ isotopes, that significant control over the isotope ratio can be achieved in a single shot.

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.

Chemical methods of stable isotope separation

The least expensive chemical methods of stable isotope separation are discussed. Between them are especially known chemical exchanges used for separation of boron, nitrogen and sulfur isotopes, low temperature rectification applied for enriching rare isotopes of carbon and oxygen and cryogenic adsorption served for obtaining very pure deuterium. The most important characteristics of installations, processes and working conditions are represented.

Centrifugal enrichment of chromium-50 for experiments on detecting solar neutrinos

The feasibility of enriched chromium-50 production by different methods of isotope separation are estimated. It is stated that about 800 g of highly-enriched (above 90%) 50Cr and 40 kg of 50Cr enriched to about 40% were produced using Russian centrifuge cascades for experiments on detecting solar neutrinos.

A New Concept of Isotope Separation Using Ion Cyclotron Resonance in a Magnetic Field Having a Radial Component

A new method of isotope separation is proposed. Isotopes are ionized in a magnetic field in a solenoid and are confined axially in an electrostatic potential well. Ions moving in a cyclotron orbit undergo a force which is perpendicular to both the radial magnetic field component and the velocity. Because axial oscillation takes place over the region where the component changes its direction, two isotopes can be separated in opposite directions by accelerating one of the isotopes at one extreme of the oscillation and the other at the other extreme. The axial motion of ions is assumed to be in phase (phase-locked). To experimentally confirm the effect of the radial component on ion motion, we moved the center of oscillation along the axis of the solenoid from its center to a position where both the axial and radial components vary with the coordinates, and we excited the cyclotron motion of ions. From the measured shift in the signal frequency of the accelerated ions, we could estimate the amount of displacement of the center of the cyclotron orbit as a function of the velocity of the accelerated ions. The condition for separation is studied by solving the equation for ion motion with two different magnetic field distributions. Computer simulation of the ion trajectory is carried out to demonstrate the feasibility of the method.

The Separation Study of Hydrogen Isotopes with ‘Cryogenic-Wall’ Thermal Diffusion Column

The thermal diffusion is one of the useful methods of the hydrogen isotope separation. This paper reports on the experiments using Cryogenic-Wall thermal diffusion column cooled by liquid nitrogen which have been performed in the total reflux and the withdraw modes. As using the same inner diameter column, Cryogenic-Wall thermal diffusion column has the higher separation factor, but the lower optimum pressure than Ordinary-Wall thermal diffusion column cooled by water. It is obtained that Cryogenic-Wall column with a smaller inner diameter has the remarkable high separation factor and the higher optimum pressure. In the withdraw mode, the characteristics of the separation factor as a function of the feed rates is obtained about the several inner diameter columns.

The rate of an exchange reaction of hydrogen and deuterium in a Mg 2Ni bed

Hydrides of intermetallic compounds of Mg 2Ni have a comparatively large isotopic effect in the equilibrium isotherm between hydrogen and deuterium or tritium. An experimental and analytical study is made on the isotopic exchange reaction of hydrogen and deuterium in a Mg 2Ni bed for isotope separation. Values of the first moment, the second moment and a height equivalent to a theoretical plate (HETP) are obtained on the basis of a pulse or a step change of an influent deuterium concentration. It is found that the HETP values have the least at an optimum temperature and linear velocity, and the value is about 3 cm. The activation energy of the isotopic exchange reaction of Mg 2Ni is 18.5 kJ mol −1. Thus the Mg 2Ni bed serves as an effective method for the isotopic separation of hydrogen isotopes.

Plasma isotope separation methods

Six major types of isotope separation methods which involve plasma phenomena are discussed. These methods are: plasma centrifuge, AVLIS (atomic vapor laser isotope separation), ion wave, ICR (ion cyclotron resonance), calutron, and gas discharge. The plasma phenomena in these major categories are described. An attempt is made to include enough references so that a more detailed study or evaluation of a particular method could readily be pursued. A brief discussion of isotope separation using mass balance concepts is also included. >

Practical Sulfur Isotope Separation by Distillation

Abstract Sulfur isotopes were separated in 1.07 and 1.50-m experimental packed distillation columns at cryogenic temperatures under total reflux. The 32S/34S ratio at column top was as much as 19% different from the bottom ratio. The 32S/33S separations were the square root of 32S/34S separations. Typical relative volatilities of 32S/34S are 1.0023 for H2S, 0.9978 for SF4, 0.9985 for SF6, 1.0006 for COS, and 1.0011 for CH3SH. A 12C/13C volatility of 0.9982 was also seen in COS. Sulfur separations in SF4 and SF6 and the carbon separation in COS are reverse isotope effects. Distillation is a feasible method for sulfur isotope separation. Hydrogen sulfide is the best candidate compound for a practical sulfur isotope separation. Existing distillation columns could economically produce as much as 50 kg/yr of contained 34S at 15% enrichment. Smaller amounts of more highly enriched isotopes could also be produced.

A concept for isotope separation in a sheet plasma by using ion cyclotron resonance heating

The concept of a novel method for separation of isotopes, the sheet plasma method, is described. A unique feature of this method is to perform isotope separation in a special kind of magnetized plasma: a sheet plasma: ions of a desired isotopic species in this plasma are selectively energized by ion cyclotron resonance heating. Owing to the unique characteristics of sheet plasmas — (i) the guiding centers of all gyrating ions he in the vicinity of the midplane of a plasma and (ii) the plasma thickness is as thin as twice the mean ion Larmor radius — extremely efficient separation of isotopes is possible.

Pulsed single-mode laser ionization of hyperfine levels of zirconium-91

We identify a considerable improvement in proposed schemes for isotopic depletion of zirconium-91 on the basis of the atomic vapor laser isotope separation (AVLIS) method. The improvement lies in applying a single-longitudinal-mode dye laser for selective excitation of all hyperfine split levels of the ground state of zirconium-91. High-resolution laser-induced fluorescence spectroscopy of atomic beams of zirconium produced through laser vaporization–supersonic expansion has been used to identify transitions of zirconium with suitable hyperfine structure. Casimir magnetic-dipole and electric-quadrupole coupling constants and isotope shifts have been derived and are reported for five excited configurations. Suitable intermediate levels in a multistep resonance ionization pathway have been identified by two-color resonance ionization spectroscopy. Isotope depletion has been demonstrated on one ground-state-transition ( z F33∘←a F32at 593.7 nm) by using a specially constructed pulsed, single-longitudinal-mode dye-laser oscillator. Prospects and future directions in zirconium AVLIS are discussed.

Isotope Separation with Drift Tube, (I)

A new method of isotope detection and separation based on transport phenomena of ions in gases, which consist of a drift tube, is proposed and the analytical expression of resolution power of the method has been derived from a diffusion equation. The expression shows that the resolution power increases with the square root of the voltage supplied to the tube. A simple drift tube was constructed and natural Li was isotopically separated in Ne 100 Torr with the maximum resolution power, about 2. The variations of the resolution power with the applied voltage were measured by using the ion source of 6Li and 7Li separately and compared with calculations.

Isotope separation with drift tube. (I). Basic analysis and experiment.

A new method of isotope detection and separation based on transport phenomena of ions in gases, which consist of a drift tube, is proposed and the analytical expression of resolution power of the method has been derived from a diffusion equation. The expression shows that the resolution power increases with the square root of the voltage supplied to the tube. A simple drift tube was constructed and natural Li was isotopically separated in Ne 100 Torr with the maximum resolution power, about 2. The variations of the resolution power with the applied voltage were measured by using the ion source of 6Li and 7Li separately and compared with calculations.

Ion guide method for on-line isotope separation

A new ISOL technique, the ion guide method for isotope separation, has been developed. The method is based on thermalization of primary recoil ions from nuclear reactions in helium and on their transfer by helium flow through a differential pumping system into the accelerating stage of an isotope separator. With this approach, separation times in the submillisecond region are achievable for all elements. The ion guide has no ionizer but instead exploits charge exchange mechanisms related to nuclear reactions and recoil thermalization processes. Operation takes place at room temperature and the simple construction involves no components that can wear out. These properties ensure smooth and stable operating conditions. The overall separation efficiencies measured for heavy nuclides produced by light-ion reactions are up to 10%. The shortest-lived activity identified in an on-line separation is the 182-μs isomeric state of 207Bi. The production rate of the mass separated 440-μs isomeric state of 43Sc is ≈ 2 × 10 3 ions/μC.

A new method of isotope separation by means of laser deflection of an atomic beam

The radiation pressure produced by two-laser fields on a two-level atom is obtained. These results show that the radiation pressure produced by two-laser fields with appropriate detunings with atom is much greater than that produced by a single-laser field. This great radiation pressure is possible to be applied to isotope separation by laser deflection of an atomic beam.

Statistics of photodeflection

Abstract We consider random fluctuations in the velocity of a molecule which is subjeclted to laser radiation. Three cases are treated, each applicable to a proposed method of isotope separation. In the first case, an exact solution is found for the velocity distribution using combinatorial methods. In the second and third cases. approximate solutions are obtained.

Lithium Isotope Separation: A Review of Possible Techniques

Abstract Published methods for 6Li-7Li lithium isotope separation have been reviewed. Future demand for 6Li, whose main use will be as a tritium breeder in blankets surrounding the core of DT fusion power reactors, is likely to exceed 5 Mg/a in the next century. The applicability of the various available methods to such a large-scale production rate has been assessed. Research on improving the effectiveness of current lithium isotope separation processes has been carried out worldwide in several major areas during the past decade; these include two-phase chemical exchange systems, ion-exchange resin chromatography, and highly isotope-selective techniques like laser photoactivation and radiofrequency spectroscopy. Chemical exchange systems appear to offer good potential in the near term for 6Li enrichment, but efficient, laser-based methods could probably be developed for large-scale production by early in the next century.

The isotopic composition of helium in the cosmic radiation above 11 gigavolts

The He-3/He-4 abundance ratio above 11 GV has been measured with a balloon-borne experiment that employs the geomagnetic method of isotope separation near earth's equator. Above a kinetic energy of approximately 6 GeV per nucleon, the He-3/He-4 ratio is measured to be 0.24 + or - 0.05 under the assumption that the helium spectrum at earth is a power law in rigidity of the form R to the -2.65th. The implied interstellar mean escape pathlength of about 15 g per sq cm, with this assumption, is considerably greater than values determined from observations of heavier elements. Propagation models more complex than the standard simple leaky box would be required to simultaneously understand the propagation of both the lighter and heavier components of cosmic rays.