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WO2019032223A2 - Enrichissement d'isotopes par condensation différentielle et réflexion d'isotopes pendant une diffusion de surface de gaz de faisceau supersonique - Google Patents

Enrichissement d'isotopes par condensation différentielle et réflexion d'isotopes pendant une diffusion de surface de gaz de faisceau supersonique Download PDF

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Publication number
WO2019032223A2
WO2019032223A2 PCT/US2018/040609 US2018040609W WO2019032223A2 WO 2019032223 A2 WO2019032223 A2 WO 2019032223A2 US 2018040609 W US2018040609 W US 2018040609W WO 2019032223 A2 WO2019032223 A2 WO 2019032223A2
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isotope
isotopologue
gas
supersonic beam
supersonic
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WO2019032223A3 (fr
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Steven J. SIBENER
Kevin J. NIHILL
Jacob D. GRAHAM
Alison A. MCMILLAN
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University of Chicago
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University of Chicago
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D59/00—Separation of different isotopes of the same chemical element

Definitions

  • Microelectronics may also begin to utilize isotopic enrichment, as highly enriched 28 Si wafers have markedly increased thermal conductivity and electron transport characteristics.
  • isotopic enrichment As highly enriched 28 Si wafers have markedly increased thermal conductivity and electron transport characteristics.
  • T. Ruf et al. Thermal conductivity of isotopically enriched silicon. Solid State Commun. State Commun. 115, 243-247 (2000); J.-Y. Li et al , Extremely high electron mobility in isotopically-enriched 28 Si two-dimensional electron gases grown by chemical vapor deposition. Appl. Phys. Lett . 103, 162105/1-4 (2013).
  • Gaseous diffusion, distillation, and gas centrifuges exhibit small isotopic separation effects which are overcome through large scale installations where many separation steps are performed in sequence.
  • AVLIS atomic vapor laser isotope separation
  • MAGIS magnetically activated and guided isotope separation
  • a supersonic beam of a gas that includes a first isotope of a first element (or a first isotopologue of a first compound) and a second isotope of the first element (or a second isotopologue of the first compound) is directed onto a surface, wherein the first isotope (or isotopologue) has a higher incident kinetic energy than the second isotope (or isotopologue).
  • the separation of the first and second isotopes can take place in one of two separation regimes.
  • the isotope (or isotopologue) having a higher incident kinetic energy is preferentially adsorbed onto the surface and the isotope (or isotopologue) having a lower incident kinetic energy is preferentially reflected from the surface.
  • the isotope (isotopologue) having a lower incident kinetic energy is preferentially adsorbed onto the surface and the isotope (or isotopologue) having a higher incident kinetic energy is preferentially reflected from the surface.
  • one embodiment of a method for enriching and/or separating isotopes includes the step of directing a supersonic beam comprising a gas comprising a first isotope of a first element and a second isotope of the first element onto a surface, the first isotope having a higher incident kinetic energy than the second isotope, wherein the first isotope is preferentially adsorbed onto the surface, relative to the second isotope.
  • the method further includes collecting either or both of the gas scattered from the surface and the adsorbate on the surface, wherein the gas scattered from the surface is enriched in the second isotope and the adsorbate is enriched in the first isotope, where enrichment in a given isotope is determined relative to the concentration of that isotope in the incident supersonic beam.
  • Another embodiment of a method for enriching and/or separating isotopes includes the step of directing a supersonic beam comprising a gas comprising a first isotope of a first element and a second isotope of the first element onto a surface, the first isotope having a higher incident kinetic energy than the second isotope, wherein the second isotope is preferentially adsorbed onto the surface, relative to the first isotope.
  • the method further includes collecting either or both of the gas scattered from the surface and the adsorbate on the surface, wherein the gas scattered from the surface is enriched in the first isotope and the adsorbate is enriched in the second isotope.
  • One embodiment of a method for enriching and/or separating isotopologues includes the step of directing a supersonic beam comprising a gas comprising a first isotopologue of a compound and a second isotopologue of the compound onto a surface, the first isotopologue having a higher incident kinetic energy than the second isotopologue, wherein the first isotopologue is preferentially adsorbed onto the surface, relative to the second isotopologue.
  • the method further includes collecting either or both of the gas scattered from the surface and the adsorbate on the surface, wherein the gas scattered from the surface is enriched in the second isotopologue and the adsorbate is enriched in the first isotopologue, where enrichment in a given isotopologue is determined relative to the concentration of that isotopologue in the incident supersonic beam.
  • Another embodiment of a method for enriching and/or separating isotopologues includes the step of directing a supersonic beam comprising a gas comprising a first isotopologue of a compound and a second isotopologue of the compound onto a surface, the first isotopologue having a higher incident kinetic energy than the second isotopologue, wherein the second isotopologue is preferentially adsorbed onto the surface, relative to the first isotopologue
  • the method further includes collecting either or both of the gas scattered from the surface and the adsorbate on the surface, wherein the gas scattered from the surface is enriched in the first isotopologue and the adsorbate is enriched in the second isotopologue, where enrichment in a given isotopologue is determined relative to the concentration of that isotopologue in the incident supersonic beam.
  • One embodiment of an apparatus for enriching and/or separating isotopes includes: a pump configured to maintain a low pressure within a chamber; a first beam source configured to provide a supersonic beam comprising a gas comprising a first isotope of a first element and a second isotope of the first element, wherein the apparatus is configured to direct the supersonic beam onto a surface in the chamber, such that at least a portion of at least one of the first isotope and the second isotope adsorbs onto the surface and at least a portion of at least one of the first isotope and the second isotope scatters from the surface; a temperature control device in thermal communication with the surface; and a collector configured to collect the gas scattered from the surface.
  • an apparatus for enriching and/or separating isotopes includes: a pump configured to maintain a low pressure within a chamber; a beam source configured to provide a supersonic beam comprising a gas comprising a first isotope of a first element and a second isotope of the first element, wherein the apparatus is configured to direct the supersonic beam onto a surface in the chamber, such that at least a portion one of the first isotope and the second isotope preferentially adsorbs onto the surface and at least a portion of the other of the first isotope and the second isotope preferentially scatters from the surface; a temperature control device in thermal communication with the surface and configured to (a) maintain the surface within a first temperature range in which the first isotope or the second isotope is preferentially adsorbed onto the surface relative to the other isotope, and (b) maintain the surface within a second temperature range at which the adsorbate is desorbed
  • FIG. 1 shows a schematic of the ultra-high vacuum surface scattering instrument employed in an example of the methods described herein.
  • FIG. 2 displays the 6 Ar/ 40 Ar isotopic ratios measured to determine the enrichment factors of the methods described herein. Depicted are the ratios of the incident beam, the portion reflected from the argon condensate at 26 K, and the argon condensate itself at three incident velocities (1650 m/s, 1760 m/s, and 1027 m/s); error bars represent 1 ⁇ as determined from Poisson statistics.
  • the 6 Ar/ 40 Ar isotopic ratio of the incident beam was found to be 0.00264 +/- 0.00001, 0.00272 +/- 0.00001, and 0.00261 +/- 0.00001 for beam velocities 1650 m/s, 1760 m/s, and 1880 m/s, respectively.
  • the 6 Ar/ 40 Ar isotopic ratio of the reflected beam was found to be 0.0058 +/- 0.0003, 0.0040 +/- 0.0002, and 0.00305 +/- 0.00007 for beam velocities 1650 m/s, 1760 m/s, and 1880 m/s, respectively.
  • the 6 Ar/ 40 Ar isotopic ratio of the condensate was found to be 0.00242 +/- 0.00007, 0.00235 +/- 0.00006, and 0.00219 +/- 0.0003 for beam velocities 1650 m/s, 1760 m/s, and 1880 m/s, respectively.
  • FIG. 3 depicts a single thermal desorption spectrum showing desorbed 40 Ar and 6Ar as a function of increasing surface temperature (T s ) after the condensation of a helium seeded Ar beam with velocity of 1650 m/s onto a 26 K amorphous argon condensate.
  • the background-subtracted and integrated waveforms for 6 Ar and 40 Ar provided an isotopic ratio of 6 Ar/ 40 Ar of 0.00242 +/- 0.00007 in the condensate.
  • FIG. 4A shows the scattering enrichment factors for 6 Ar derived from measured isotopic ratios.
  • FIG. 4B shows the condensation enrichment factors for 40 Ar derived from measured isotopic ratios. The scattered fraction is enriched in 6 Ar while the condensed fraction is enriched in 40 Ar.
  • FIG. 5 depicts the isotopic ratio of 6 Ar/ 40 Ar, incident and reflected, from an argon condensate at 29 K at two incident velocities (563 m/s and 1027 m/s); error bars represent 1 ⁇ as determined from Poisson statistics.
  • the 6 Ar/ 40 Ar isotopic ratio of the incident beam at both velocities was 0.00308 +/- 0.00002. Enrichment of 40 Ar and depletion of 6 Ar in the reflected beam were observed at both incident beam velocities.
  • the isotopic ratio of 6 Ar/ 40 Ar after reflection was found to be 0.00245 +/- 0.00033 for the lower velocity beam and 0.00261 +/- 0.00033 for the higher velocity beam.
  • FIG. 6 depicts a single thermal desorption spectrum showing desorbed 40 Ar and 6Ar as a function of increasing surface temperature (T s ) after the condensation of a helium seeded Ar beam with velocity of 1027 m/s onto a 29 K amorphous argon condensate.
  • the background-subtracted and integrated waveforms for 6 Ar and 40 Ar provided an isotopic ratio of 6 Ar/ 40 Ar of 0.00327 in the condensate.
  • FIG. 7 depicts the 6 Ar/ 40 Ar isotopic ratio incident on, and as condensed on, a 29 K amorphous argon surface at two incident velocities (563 m/s and 1027 m/s); error bars represent 1 ⁇ as determined from the standard deviation of eight experimental runs.
  • the 6Ar/ 40 Ar isotopic ratio of the incident beam at both velocities was 0.00308 +/- 0.00002. Enrichment of 6 Ar and depletion of 40 Ar in the condensate were observed at both incident beam velocities.
  • the isotopic ratio of 6 Ar/ 40 Ar after condensation was found to be 0.00313 +/- 0.00004 for the lower velocity beam, and 0.00328 +/- 0.00001 for the higher velocity beam.
  • the apparatus and methods are based on using the narrow velocity distribution of a high Mach number supersonic beam where, essentially, all components entrained in the supersonic flow travel with the same velocity.
  • Different isotopes (or isotopologues) therefore collide with the surface with differing impact energies due to their differing atomic masses. Given that the probability of gaseous condensation depends on the incident gas-surface collision energy, these conditions result in differential condensation (reflectivity) of varying isotopes (or isotopologues) due to changes in the energy exchanged between the surface and the components entrained within the incident and nearly
  • the apparatus and methods may be used to enrich or separate isotopes (or isotopologues) via differential condensation or reflection of various isotopes (or isotopologues) involving such a supersonic beam.
  • a method for enriching or separating isotopes comprises directing a monovelocity supersonic beam containing a first isotope of an element and a second isotope of the element onto a surface, wherein the heavier of the two isotopes has a higher incident kinetic energy and momentum than the lighter of the two isotopes.
  • the method can be carried out under conditions (e.g., incident supersonic beam velocities, incident supersonic beam angles, and surface temperatures) that allow for either the heavier isotope or the lighter isotope to be preferentially condensed onto the surface, relative to the other isotope.
  • the methods further include the step of collecting and isolating the heavier isotope, the lighter isotope, or both, from the gas scattered from the surface or the condensate on the surface.
  • the larger incident energy of the heavier isotope relative to the lighter isotope results in the portion of the supersonic beam that is not condensed on the surface (the scattered portion) being enriched in the lighter isotope, as illustrated in Example 1.
  • the condensed portion which may be amorphous or crystalline
  • Opposite enrichment trends can be achieved using a lower energy supersonic beam, as illustrated in Example 2.
  • the relative enrichment effect observed between the scattered portion and condensed portion is influenced by the absolute sticking coefficients of the isotopes.
  • the absolute sticking coefficients of the isotopes By way of illustration, if 100% of the supersonic beam condensed on the surface, no enrichment effect would be observed in the condensed portion. Likewise, if 0% of the supersonic beam condensed on the surface, no enrichment effect would be observed in the scattered portion. When sticking coefficients are near, but not at, these limits, the maximum enrichment is observed for each condition.
  • Ri RF(1-S2) + RcS2
  • Ri the ratio of the first isotope to the second isotope that is present in the incident supersonic beam before it strikes the surface
  • RF the ratio of the first isotope to the second isotope that is present in the scattered portion of the supersonic beam
  • Rc the ratio of the first isotope to the second isotope that is present in the condensed portion of the supersonic beam
  • S2 is the absolute sticking coefficient of the second isotope.
  • the absolute sticking coefficient can be manipulated by adjusting the incident kinetic energy of the supersonic beam, the incident angle of the supersonic beam, and/or the temperature of the surface.
  • Heating the nozzle and/or seeding the isotopes in a low molecular weight carrier gas such as helium or hydrogen
  • a high molecular weight carrier gas such as xenon
  • the sticking coefficient can be modified by the angle of incidence; a more glancing angle of incidence will produce a lower sticking coefficient than an angle of incidence more perpendicular to the plane of the surface.
  • a precise sticking coefficient as a function of gas temperature, angle of incidence, and surface temperature may be determined experimentally.
  • the velocity of the seeded beam is not highly dependent on the concentration of the carrier gas, (e.g., helium). If one wants to tune the velocity precisely, then a variable temperature nozzle is preferably used to heat or cool a given seed gas/carrier gas
  • thermodynamics Mixing in a low percentage of the substance to be enriched with the helium results in a beam with a velocity close to that of pure helium. More precisely, one can calculate using a weighted average of the heat capacity of the carrier gas plus that of the seed gas. Therefore, it is preferable to tune the energy of the beam by nozzle temperature for a given composition rather than by composition. This allows one to broadly tune the incident kinetic energy. For different regions, one might use H2, He, or Ne, for example, as the seed gas with temperature tuning used for overall energy control. See equation 8 of "Development of a Supersonic 0( Py), Nozzle Beam Source," S.J. Sibener, R.J. Buss, C.Y. Ng, and Y.T. Lee, Rev. Sci. Instrum. 51, 167-182 (1980).
  • any given isotope or isotopologue once a vacuum condensation temperature is obtained, one can optimize the conditions by, for example, decreasing the beam velocity from a high velocity (i.e., higher nozzle temperature), while keeping the substrate at a fixed temperature below the vacuum condensation temperature and observing the beam velocity at which the material first condenses. One can then adjust the beam velocity to find a point of maximum enrichment of the condensate and/or scattered material, depending on the desired product.
  • the substrate temperature may also be varied, but the effect on the amount of enrichment is expected to be smaller.
  • the supersonic beam may be generated by a variety of atomic beam sources configured to supersonically expand a gas through a variable temperature nozzle.
  • the gas comprises the first and second isotope.
  • first and second isotope it is meant two forms of the same element that contain equal numbers of protons but different numbers of neutrons.
  • the gas may comprise additional isotopes, each of which may be enriched or separated using the method.
  • the gas may comprise molecules that are isotopologues, e.g., hydrogen, which may be comprised of two or more of H2, HD, HT, D2, DT and T 2 .
  • the invention can be used to enrich or deplete a sample of one or more of the isotopes (or isotopologues).
  • the composition of the gas and the type of isotopes are not particularly limited.
  • the supersonic beam may be continuous or pulsed, or modulated, for example, via mechanical chopping.
  • the supersonic expansion may be free or may be passed through an aperture, such as a skimmer or collimator, before it strikes the surface.
  • This skimming effect will cause a slight enrichment of the heavier isotope (or isotopologue) present in the beam before it strikes the surface, as the heavier isotope (or isotopologue) is preferentially concentrated toward the centerline of the supersonic beam during the expansion.
  • This skimming effect which may influence the composition of the incident beam under favorable expansion conditions, can therefore be used advantageously to further increase the desired enrichment.
  • the wide range of incident beam conditions can be used to dial in a desired sticking coefficient for both weakly interacting, physisorption systems and strongly interacting, chemisorption systems.
  • Illustrative examples of isotopes that can be enriched or separated by these methods include but are not limited to 6 Ar and 40 Ar; 6 Li and 7 Li; 22 Ne and 20 Ne; 24 Mg and 26 Mg; 124 Xe, 129 Xe, 131 Xe, 1 2 Xe, and 1 4 Xe; and 78 Kr, 82 Kr, and 86 Kr. This method also is applicable to elements extending across the periodic table.
  • any isotopologues that can be co-expanded in a supersonic molecular beam can be enriched or separated by the methods. Isotopologues with fewer normal modes will be particularly amenable to these methods. It will be apparent to one of skill in the art how to vaporize these isotopologues to enable co-expansion in a supersonic beam.
  • Illustrative examples of isotopologues that can be enriched or separated by these methods include but are not limited to 12 CH 4 and 1 CH 4 ; 28 SiH 4 and 29 SiH 4 ; 28 SiF and 29 SiF ; Hi, HD, HT, D 2 , DT, and T 2 ; 1 H 2 16 0, 3 ⁇ 4 2 ⁇ 16 0, 2 H 2 16 0, 3 ⁇ 4 2 16 0, and 3 ⁇ 4 2 18 0; 16 0 2 and 18 0 2 ; 14 N 2 and 15 N 2 ; HBr and DBr; HC1 and DC1; HI and DI; H 2 S and D 2 S; CH 3 F, CD 3 F, 1 CH 3 F, and 1 CD 3 F; CH 3 C1, CD 3 C1, 1 CH 3 C1, and 1 CD 3 C1; 1 C 16 0 2 , 12 C 16 0 2 , 1 C 18 0 2 , and 12 C 18 0 2 ; 12 C 18 0, 1 C 18 0, 1 C 16 0, and 1 C 18 0; NH 3
  • any surface can be used, provided the temperature of the surface can be maintained at a temperature that is below the condensation temperature of the material (isotope or isotopologue) to be enriched or separated; as noted above, incident beam velocity and incident beam angle can modify these values and differ substantially from equilibrium conditions where the incident gas and surface are at the same thermal temperature.
  • the surface may be placed in thermal contact with a cooler, such as a cryogenic cooler.
  • a cooler such as a cryogenic cooler.
  • the surface should be cooled to a temperature below 31 K.
  • the surface in order to separate 3 ⁇ 4 2 16 0 and 2 H 2 16 0, the surface should be cooled to a temperature below 140 K, the temperature at which water condenses in a vacuum.
  • the vacuum condensation temperatures of other common materials may be found in the published literature (see, M. P. Collings, M. A.
  • This enrichment or separation method results from the preferential adsorption of a given heavier (or lighter) isotope (or isotopologue) on a substrate and the preferential scattering (reflection) of a lighter (or heavier) isotope (or isotopologue).
  • a lighter or heavier isotope (or isotopologue).
  • the scattered angle distribution is typically lobular, leading to negligible angular separation of the isotopes (or isotopologues).
  • the condensate may be crystalline or amorphous, depending on the condensation conditions.
  • the enrichment or separation process occurs at the surface, and straightforward collection techniques used for molecular beam apparatus can be employed.
  • the scattered gas can pass through an aperture which leads to a separate vacuum chamber that is pumped by a high vacuum pump, where the exhaust of the high vacuum pump contains the reflected portion enriched in the lighter isotope.
  • the condensed portion can be collected by periodically warming the condensate above its condensation temperature. As the condensed portion desorbs and enters the gas phase, the exhaust of the chamber's high vacuum pump will be enriched in the heavier isotope (or isotopologue).
  • the isotopes (or isotopologue) collected from both the condensed portion and the reflected portion can separately be recompressed with a mechanical compressor. Once recompressed, each portion can be further enriched through subsequent passes (e.g., 2, 10, 100, 1000, or more passes) through this isotopic (or isotopologue) enrichment technique until a desired level of enrichment is obtained.
  • subsequent passes e.g., 2, 10, 100, 1000, or more passes
  • subsequent passes e.g., 2, 10, 100, 1000, or more passes
  • the same surface or different surfaces can be used in the subsequent passes.
  • the beam-surface interaction parameters could be adjusted by changing the incidence angle (6>j), azimuth ( ⁇ ), and tilt ( ⁇ ) of the surface manipulator, as well as the temperature of the surface, which is controlled by a button heater and closed-cycle helium refrigerator to maintain temperatures between 24 and 500 K as measured by a silicon diode.
  • the 6 Ar/ 40 Ar isotopic ratio of the scattered beam was determined by square-wave chopping the incident beam while the mass filter setting of the QMS was switched
  • Desorption measurements were carried out by dosing the argon beam on the surface below the condensation temperature for 5-10 minutes (with 100% duty cycle), blocking the incident beam, and then raising the surface temperature at a rate of 1 K/min while the mass filter setting of the QMS was switched (modulated) between mass 40 and mass 36 at 10 Hz.
  • Adsorption is governed by the energy transfer between an impinging gas particle and a surface, with physisorption or chemisorption occurring when the kinetic energy of the particle is lower than its binding energy to the surface. This inelastic process is mediated via energy loss to multiphonon excitations. Particles that transfer proportionally more energy to the surface by inelastic processes are more likely to be condensed.
  • a mixture of gases in a supersonic molecular beam exhibit seeding, whereby species with different masses will exit the source with the same velocity; this phenomenon does not occur in effusive sources.
  • the velocity of the helium seeded beam was 1650 m/s, while the velocities of the 580 K and 650 K hydrogen seeded beams were 1760 m/s and 1880 m/s, respectively.
  • the 6 Ar/ 40 Ar ratios of the incident beams for the three velocities were 0.00264 +/- 0.00001, 0.00272 +/- 0.00001, and 0.00261 +/- 0.00001 for beam velocities 1650 m/s, 1760 m/s, and 1880 m/s, respectively.
  • the reflected beam was enriched in 6 Ar and has an 6 Ar/ 40 Ar isotopic ratio of 0.0058 +/- 0.0003.
  • the reflected beam was less enriched in 6 Ar and has an 6 Ar/ 40 Ar isotopic ratio of 0.0040 +/- 0.0002.
  • the reflected beam was even less enriched in 6 Ar and has an 6 Ar/ 40 Ar isotopic ratio of 0.00305 +/- 0.00007.
  • the 6 Ar enrichment factors, shown in FIG. 4A, for the lowest, intermediate, and highest velocity incident beams were found to be 2.2 +/- 0.1, 1.46 +/- 0.06, and 1.17 +/- 0.03, respectively.
  • the 6 Ar enrichment factor is defined as the scattered 6Ar/ 40 Ar isotopic ratio divided by the incident 6 Ar/ 40 Ar isotopic ratio.
  • 6Ar/ 40 Ar ratio of natural abundance Ar (0.00335); this is due to an effect of seeding whereby the heavier species in a beam (here, 40 Ar) is focused into the center of the beam, whereas the lighter mass is pushed to the edge of the beam, leading to a slight enrichment in the higher mass as the incident beam passes through the skimmer and collimating apertures.
  • the condensate should exhibit enrichment of the heavier isotope: 40 Ar.
  • Experimental determination of the condensate composition is possible through temperature- programmed desorption (TPD), in which the surface is dosed with the supersonic Ar beam below the sticking temperature and subsequently heated at a rate of 1 K/min while switching between the two masses of interest on the mass spectrometer.
  • FIG. 3 illustrates a single experimental TPD spectrum. Again, the incident beams had 6 Ar/ 40 Ar isotopic ratios of 0.00264 +/- 0.00001, 0.00272 +/- 0.00001, and 0.00261 +/- 0.00001 for beam velocities 1650 m/s, 1760 m/s, and 1880 m/s, respectively.
  • the condensate was enriched in 40 Ar and had an 6 Ar/ 40 Ar isotopic ratio of 0.00242 +/- 0.00007.
  • the condensate was further enriched in 40 Ar and has an 6 Ar/ 40 Ar isotopic ratio of 0.00235 +/- 0.00006.
  • the condensate was even further enriched in 40 Ar and has an 6 Ar/ 40 Ar isotopic ratio of 0.00219 +/- 0.0003.
  • the 40 Ar enrichment factors, shown in FIG. 4B, for the lowest, intermediate, and highest velocity incident beams were found to bel.09 +/- 0.03, 1.16 +/- 0.03, and 1.19 +/- 0.02, respectively.
  • the 40 Ar enrichment factor is defined as the incident 6 Ar/ 40 Ar isotopic ratio divided by the condensed 6 Ar/ 40 Ar isotopic ratio.
  • Isotopic ratios of scattered and desorbed argon were measured using an ultra-high vacuum (UHV) scattering apparatus.
  • UHV ultra-high vacuum
  • the instrument has been thoroughly described elsewhere.
  • UHV ultra-high vacuum
  • it is composed of three sections: a differentially pumped supersonic beam source, a chamber that houses the surface, and a rotatable differentially pumped quadrupole mass spectrometer (QMS).
  • the beam-surface interaction parameters could be adjusted by changing the incidence angle (6>j), azimuth ( ⁇ ), and tilt ( ⁇ ) of the surface manipulator, as well as the temperature of the surface, which is controlled by a button heater and closed-cycle helium refrigerator to maintain temperatures between 26 and 500 K as measured by a silicon diode.
  • the 6 Ar/ 40 Ar isotopic ratio of the scattered beam was determined by square-wave chopping the incident beam while the mass filter setting of the QMS was switched
  • Desorption measurements were carried out by dosing the argon beam on the surface below the condensation temperature for 20 minutes (with 100% duty cycle), blocking the incident beam, and then raising the surface temperature at a rate of 1 K/min while the mass filter setting of the QMS was switched (modulated) between mass 40 and mass 36 at 10 Hz.
  • Adsorption is governed by the energy transfer between an impinging gas particle and a surface, with physisorption occurring when the kinetic energy of the particle is lower than its binding energy to the surface.
  • This inelastic process is mediated by multiphonon excitations; a straightforward consequence of this is that a surface with more phonon modes available to excite (i.e., colder) has a greater ability to condense an impinging gas particle.
  • particles with less incident energy to be removed by inelastic processes are more likely to be condensed.
  • a mixture of gases in a supersonic molecular beam exhibit seeding, whereby species with different masses will exit the source with the same velocity; this phenomenon does not occur in effusive sources (See, G. Scoles, Atomic and Molecular Beam Methods Volume I (Oxford University Press, New York, 1988).)
  • the velocity of the pure and helium seeded beams are 563 m/s and 1027 m/s, respectively.
  • a direct outcome of this energy difference between the 6 Ar and 40 Ar isotope is that a supersonic beam of argon impinging upon an amorphous argon condensate grown on a surface below the sticking (i.e., condensation) temperature (measured to be -32 K) will exhibit a preferential sticking of the lighter 6 Ar isotope.
  • FIG. 5 shows the background-subtracted reflected ratio of 6 Ar/ 40 Ar at two incident beam velocities.
  • the 6 Ar/ 40 Ar ratio of the incident beam for both velocities was constant at 0.00308 +/- 0.00002.
  • the reflected beam was enriched in 40 Ar and has a 6 Ar/ 40 Ar isotopic ratio of 0.00245 +/- 0.00033.
  • the reflected beam was less enriched in 40 Ar and has a 6 Ar/ 40 Ar isotopic ratio of 0.00261 +/- 0.00033.
  • the isotopic ratio above the sticking temperature was below the 6Ar/ 40 Ar ratio of natural abundance Ar (0.00335); this is due to an effect of seeding whereby the heavier species in a beam (here, 40 Ar) is focused into the center of the beam, whereas the lighter mass is pushed to the edge of the beam, leading to a slight enrichment in the higher mass as the incident beam passes through the skimmer and collimating apertures.
  • the condensate should exhibit enrichment of the lighter isotope: 6 Ar.
  • thermo- programmed desorption in which the surface is dosed with the supersonic Ar beam below the sticking temperature and subsequently heated at a rate of 1 K/min while switching between the two masses of interest on the mass spectrometer.
  • FIG. 6 illustrates a single experimental TPD spectrum.
  • FIG. 7 illustrates this 6 Ar enrichment in the condensate at the two incident beam velocities. Again, the incident beam had a 6 Ar/ 40 Ar isotopic ratio of 0.00308 +/- 0.00002. For the lower velocity beam, the condensate was enriched in 6 Ar and had a 6 Ar/ 40 Ar isotopic ratio of 0.00313 +/- 0.00004.
  • the condensate was further enriched in 6 Ar and has a 6 Ar/ 40 Ar isotopic ratio of 0.00328 +/- 0.00001.

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Abstract

L'invention concerne un appareil et des procédés pour enrichir et séparer des isotopes ou des isotopologues. L'appareil et les procédés enrichissent et/ou séparent des isotopes ou des isotopologues présents dans un faisceau supersonique incident sur une surface par l'intermédiaire de la condensation ou de la réflexion différentielle de différents isotopes ou isotopologues sur la surface.
PCT/US2018/040609 2017-07-07 2018-07-02 Enrichissement d'isotopes par condensation différentielle et réflexion d'isotopes pendant une diffusion de surface de gaz de faisceau supersonique Ceased WO2019032223A2 (fr)

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US11413579B2 (en) 2017-05-19 2022-08-16 The University Of Chicago Separation of isotopes in space and time by gas-surface atomic diffraction
US12109535B2 (en) * 2020-11-06 2024-10-08 The University Of Chicago Enrichment and separation of isotopes, isotopologues, or other chemical species, via differential embedding in a capture matrix
US12296299B2 (en) 2021-04-30 2025-05-13 The University Of Chicago Isotopologue or isotope enrichment via preferential condensation of isotopologues or isotopes under non-equilibrium gas-surface collision conditions

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DE2458563A1 (de) * 1974-12-11 1976-06-16 Uranit Gmbh Verfahren zur isotopentrennung mittels laser
IL48553A (en) * 1975-11-27 1978-07-31 Aviv Ami Rav Method and apparatus for the separation of isotopes
US4119509A (en) * 1976-06-11 1978-10-10 Massachusetts Institute Of Technology Method and apparatus for isotope separation from a gas stream
FR2975920A1 (fr) * 2011-06-01 2012-12-07 Univ Rennes Procede et dispositif pour la separation d'isotopes a partir d'un ecoulement gazeux

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11413579B2 (en) 2017-05-19 2022-08-16 The University Of Chicago Separation of isotopes in space and time by gas-surface atomic diffraction
US12109535B2 (en) * 2020-11-06 2024-10-08 The University Of Chicago Enrichment and separation of isotopes, isotopologues, or other chemical species, via differential embedding in a capture matrix
US12296299B2 (en) 2021-04-30 2025-05-13 The University Of Chicago Isotopologue or isotope enrichment via preferential condensation of isotopologues or isotopes under non-equilibrium gas-surface collision conditions

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