Abstract
Isotope enrichment by laser activation wherein a multi-isotopic element Q, like Uranium, Silicon, Carbon is incorporated into gaseous QF.sub.n, QF.sub.6, QF.sub.4, QO.sub.mF.sub.n, etc and diluted in gas G like He, N.sub.2, Ar, Xe, SF.sub.6 or other inert gas; and wherein that mixture is cooled by adiabatic expansion or other means encouraging formation of dimers QF.sub.6:G in a supersonic super-cooled free jet; and wherein that jet is exposed to laser photons at wavelengths that selectively excite predetermined molecules .sup.iQF.sub.6 to .sup.iQF.sub.6*, thereby inducing rapid VT conversions and dissociations of .sup.iQF.sub.6*:G.fwdarw..sup.iQF.sub.6+G+kT, while leaving non-excited dimers .sup.jQF.sub.6:G intact; and wherein a skimmer separates the supersonic free-jet core stream containing heavier .sup.jQF.sub.6:G dimers from lighter core-escaped .sup.iQF.sub.6-enriched rim gases. Particularly an advanced technique is disclosed to enrich .sup.iUF.sub.6 by free jet expansion and isotope-selective dimerization suppression, utilizing a molecular CO laser and intra-cavity UF.sub.6 irradiation with laser lines overlapping predetermined .sup.iUF.sub.6 absorptions; and providing multiple free jet separator units irradiated by one laser beam, thereby enhancing process economics.
Claims
1. A process for enriching a selected isotope of uranium from a mixture of gaseous UF.sub.6 isotopomers in a supersonic low-pressure flow chamber, comprising the steps of: a. super-cooling multiple axisymmetric supersonic free jets comprising UF.sub.6 and carrier gases by adiabatic expansion of said gases from a common feed chamber into a common flow chamber through multiple inlet nozzles and in each of said supersonic free jets, thereby creating an axisymmetric supersonic jet core flow surrounded radially by a barrel shaped shock region and subsonic chamber-background rim gas; b. selectively exciting isotopomers of UF.sub.6 in a mixture of UF.sub.6 and carrier gases using photons and providing via said multiple jets acting together, an increased total peripheral escape surface area for said selectively excited UF6 isotopomers entering said chamber background rim gas; c. separating said supersonic jet core flows in each of said multiple jets from said subsonic chamber-background rim gas, by capturing said supersonic jet-core flows in said free jets with recovery skimmers, each said skimmer located opposite each inlet nozzle so as to intercept each supersonic core flow of each supersonic free jet; and d. wherein said multiple inlet nozzles producing said supersonic free jets are spaced apart in line internally on one side of said flow chamber, and wherein each of said skimmers is paired with one of said inlet nozzles and is located a distance away opposite said one of said gas inlet nozzles on the other internal side of said flow chamber.
2. The process of claim 1, wherein the supersonic free jets comprise a mixture of carrier gases G and UF.sub.6 in a predetermined UF.sub.6/G molecular ratio.
3. The process of claim 1, wherein the selected uranium isotope is one of U-232, U-233, U-234, U-235, U-236, U-237, or U-238.
4. The process of claim 1, wherein said supersonic free jets enter said flow chamber from a feed chamber having a gas pressure at least twice that of the flow chamber.
5. The process of claim 4 wherein said supersonic free jets enter said flow chamber via one of: a Laval nozzle and an open orifice connecting said feed chamber to said flow chamber.
6. The process of claim 1, wherein said skimmers separate said rim gas from said supersonic core flows of said supersonic free jets and said rim gas is pumped out separately from said supersonic core flows of said supersonic free jets.
7. The process of claim 2, wherein said carrier gas G comprises a heavy chemically inert gaseous molecule with a high gas coefficient =Cp/Cv.
8. The process of claim 2, wherein said carrier gas G is one of Xe, Rn, SF.sub.6, and SiBr.sub.4.
9. The process of claim 2, wherein said carrier gas G is a mixture of two gases Y and Z, wherein Y comprises one of He, Ar, and N.sub.2, and Z comprises one of Xe, SF.sub.6, and SiBr.sub.4.
10. The process of claim 2, wherein the predetermined UF.sub.6/G molecular ratio is between 1/100 and 1/0.
11. The process of claim 1, wherein said photons are produced by selected emission lines from a 5-micron CO laser.
12. The process of claim 11, wherein said selected emission lines overlap the absorption lines of the 3v.sub.3 excited vibrations of UF.sub.6.
13. The process of claim 11, wherein said selected emission lines are the P.sub.8-15 line at 1876.30 cm.sup.1 and the P.sub.7-21 line at 1876.63 cm.sup.1 whose frequencies overlap the absorption lines of the 3v.sub.3 hot-band vibrations of .sup.235UF.sub.6 with hot co-vibrations v.sub.h=v.sub.6, v.sub.4, v.sub.5, and 2v.sub.6.
14. The process of claim 11, wherein said selected emission line is the P.sub.9-9 line at 1874.45 cm.sup.1 whose frequency overlaps the absorption line of the 3v.sub.3 hot-band vibration of .sup.238UF.sub.6 with hot co-vibration v.sub.h=2v.sub.6.
15. The process of claim 11, wherein said selected emission lines are produced by a resonator mirror set comprising a cooled suitably-angled ruled diffraction grating at a first end and a cooled retro mirror with substantially 100% reflectivities at a second end, between which said laser beam is generated traversing bidirectionally through a laser plasma gain section and through said supersonic free jets inside an intracavity flow chamber.
16. The process of claim 15, wherein said supersonic free jets have supersonic free jet axes and wherein said laser beam crosses said free jet axes cross-wise.
17. The process of claim 11, wherein said 5-micron CO laser is a high-power continuous (CW) running CO laser.
18. The process of claim 11, wherein said 5-micron CO laser is a high-peak-power pulsed CO laser and the flows of said supersonic jets are pulsed in synchronization with said CO laser pulses.
19. The process of claim 15, wherein said laser beam has an intra-cavity bi-directional intensity equaling or exceeding 3 kW per cm.sup.2 for a single grating-selected laser line.
20. The process of claim 11 wherein a selected emission line from said CO laser is ultra-fine frequency-shifted to coincide with one of the peak Q-branch absorptions of the selected UF.sub.6 isotopomer.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The foregoing aspects and many of the attendant advantages of the invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein.
(2) FIG. 1 shows the major hardware components of the simpler 5-micron CO-laser-driven advanced CRISLA process in comparison with those of a more complex pulsed 16-micron Raman-converted CO.sub.2 laser system;
(3) FIG. 2 shows the operation of a single UF.sub.6 laser enrichment separator unit employing a gaseous supersonic super-cooling free jet of a UF.sub.6/G gas mixture (G=carrier gas), which expands from a high-pressure feed tank through a nozzle into a constantly pumped-down low-pressure chamber, and whose gaseous jet core is axially or perpendicularly irradiated by a CO laser beam. Downstream, the core of the jet is separated from the chamber background gases by a skimmer, beyond which the core gas returns to subsonic flow and ambient condition;
(4) FIG. 3A shows the co-axial laser irradiation of a series of mini jets using one CO laser and a block of multiply adjoined nozzles, skimmers, and rim-gas pump-out plenums for UF.sub.6/G gas feed, tails, and product flows, producing isotopically depleted and enriched UF.sub.6 gas streams;
(5) FIG. 3B shows the cross-flow laser irradiation of a series of mini jets fed by a common UF.sub.6/G feed chamber and using a single CO laser beam inside a cell with many adjacent nozzles and skimmers, from which the rim-gas is pumped out to a common product chamber and the skimmer-captured gasses are collected by a common separate tails chamber, yielding tails, and product streams of separated isotopically depleted and enriched UF.sub.6;
(6) FIG. 3C shows a cross-irradiated preferred arrangement of minijet nozzles and skimmers in a compact nested set of cylindrical chambers comprising a feed chamber, an irradiation chamber, and a skimmer chamber;
(7) FIG. 4 shows calculated curves of obtainable uranium isotope enrichment factors as a function of downstream jet temperature, pressure, UF.sub.6/G concentration, and the effect of the atomic mass of G;
(8) FIG. 5a shows a high-resolution spectrum of the overlap of several strong CO laser lines with a computer-calculated spectrum of the cold- and hot-band 3v.sub.3 vibrations of .sup.238UF.sub.6 and .sup.235UF.sub.6 at a super-cooled temperature of 200 K between 1874 and 1878 cm.sup.1;
(9) FIG. 5b shows a high-resolution spectrum of the overlap of several strong CO laser lines with a computer-calculated spectrum of the cold- and hot-band 3v.sub.3 vibrations of .sup.238UF.sub.6 and .sup.235UF.sub.6 at a super-cooled temperature of 150 K between 1874 and 1878 cm.sup.1;
(10) FIG. 5c shows a high-resolution spectrum of the overlap of several strong CO laser lines with a computer-calculated spectrum of the cold- and hot-band 3v.sub.3 vibrations of .sup.238UF.sub.6 and .sup.235UF.sub.6 at a super-cooled temperature of 100 K between 1874 and 1878 cm.sup.1;
(11) FIG. 6a shows an ultra-high-resolution laser-diode-measured absorption spectrum of the 3v.sub.3 vibration of natural UF.sub.6 at T=257 K in the hot-bands region between 1874.4 and 1874.9 cm.sup.1 where three strong CO laser lines reside; and
(12) FIG. 6b shows an ultra-high-resolution laser-diode-measured absorption spectrum of the v.sub.3 and 3v.sub.3 vibration of natural UF.sub.6 at T=257 K in the cold-band regions between 627.600 and 627.705 cm.sup.1 and between 1875.386 and 1875.600 cm.sup.1 respectively.
DETAILED DESCRIPTION OF THE INVENTION
(13) Turning first to FIG. 1, a 5-micron CW laser-driven CRISLA system 100 schematic is compared with that of a 16-micron pulsed laser uranium enrichment scheme 200. The complexity of providing pulsed 16-micron laser irradiation to the jet process chamber compared to continuous 5-micron laser delivery is immediately apparent. For simplicity, in FIG. 1 only a single irradiation process cell is shown, but in preferred embodiments of the advanced CRISLA system the system may comprise many (for example, one hundred) adjacent irradiated intra-cavity mini jets as shown in FIGS. 3a, 3b, and 3c. In the 16-micron case the incoming laser beam that enters the irradiation cell can be split and used to irradiate a number of production cells, but only uni-directionally; not as in the 5-micron CRISLA system, which can support a bi-directional intra-cavity recycling laser beam. Note that in FIG. 1 laser beam paths are shown with dashed lines.
(14) As may be seen in FIG. 1, the advanced CW 5-micron CRISLA system offers significant advantages in terms of simplicity and inexpensiveness relative to pulsed 16-micron systems. The advanced CRISLA system 100 comprises two primary hardware components: the continuous CO laser 101 and the intracavity process chamber 102, while a typical pulsed 16-micron system comprises five or more separate hardware components: as shown in 200, three lasers (a CW pilot CO.sub.2 laser 201, a pulsed TEA CO.sub.2 laser oscillator 202, and a pulsed TEA CO.sub.2 laser amplifier 203), one raman conversion cell 204, and one or more irradiation chambers 205. In addition, the 16-micron laser system requires (costly) liquid hydrogen (LH2 @ 20 K) coolant for its raman-cell, while the 5-micron CO laser requires (less expensive) liquid nitrogen (LN2 @ 77 K) cooling. Both systems comprise gas flow and mirror alignment control electronics, but the control electronics required for pulsed 16-micron systems are much more complicated than those for 5-micron systems.
(15) Turning to FIG. 2, a schematic overview of the advanced CRISLA process is shown. FIG. 2 illustrates the basic process steps involved in a single laser-irradiated CRISLA isotope separator unit. Starting at the upper left of FIG. 2, UF.sub.6 103 and the carrier gas G 104 are introduced into a mixing tank 105, and thence pass as a UF.sub.6/G mixture 106 to a feed tank 107. Upon exiting the feed tank the UF.sub.6/G mixture expands after passing through a supersonic nozzle 108 into an evacuated low-pressure process chamber 109 where the gas flow develops into a supersonic super-cooling jet 110 (note that the jet is shown here by dotted lines). This jet generates UF.sub.6:G dimers downstream from the nozzle, after the jet reaches a temperature below about 100 K. The jet is irradiated either with co-axial laser beam 118 or cross-axially by laser beam 120 with isotope-selective photons from a 5-micron laser, in this case CO laser 101 (note that the coaxial laser beam is shown here by a dashed line 118). Upstream absorption of these isotope-selective photons by UF.sub.6 isotopomers prevents laser-excited isotopic .sup.iUF.sub.6* monomer molecules from forming dimers downstream where the gas temperature drops below 100 K. The excited non-dimerizable .sup.iUF.sub.6* monomer molecules tend to escape from the core of the jet after they experience a vibration-to-translation energy conversion in an encounter and a brief sub-nanosecond association with a potential dimer partner G. At the same time, the non-excited isotopomers of UF.sub.6 form much heavier UF.sub.6:G dimers that tend to remain in the jet core. In preferred cross-wise irradiations, most .sup.iUF.sub.6 molecules are laser-excited in the laser beam just after they leave the nozzle exit in the 100<T<170K temperature zone, before they enter the down-stream (T<100K) dimerization zone. The particular embodiment of the advanced CRISLA process shown in FIG. 2 also includes a CaF.sub.2 Brewster windows 114, a laser end mirror 115 and a laser line grating 116.
(16) A jet skimmer 111 separates the core of the supersonic gaseous jet from the chamber background or rim gases. This chamber 109, which processes these rim gases will be referred to as the irradiation or product chamber. The skimmer's inlet diameter is usually somewhat larger than the nozzle or orifice outlet diameter and collects the majority of non-excited dimerized .sup.iUF.sub.6:G species in the jet core in the tails chamber 117. Because the flow is supersonic, there are no back-propagation effects from the skimmer onto the jet. As the jet's core gas enters the skimmer mouth, it will go through a standing shock wave in the mouth of the skimmer beyond which the flow returns to subsonic flow and ambient conditions. Following their sub-millisecond supersonic flight as .sup.jUF.sub.6:G dimers in the jet chamber, the .sup.jUF.sub.6:G dimers in the gas mix will dissociate again to .sup.jUF.sub.6 and G monomers, after passing the skimmer entrance. Both rim gases 112 and core gases 113 are continuously pumped out separately to product and tails reservoirs (respectively) for further stage processing or final retrieval. In the retrieval compartments, enriched or depleted UF.sub.6 is separated from carrier gas G via well-known standard cold-trapping methods.
(17) Turning to FIGS. 3a, 3b, and 3c, multi jet embodiments of the advanced CRISLA system are shown. As may be seen these embodiments comprise sets of adjacent multiple mini-jets traversed co-axially or cross-wise by one laser beam shown as a dotted line 118 in FIGS. 3a, 3b, and 3c. In the coaxial arrangement shown in FIG. 3a, the laser beam crosses all portions of the process gas, including the low-pressure low-temperature dimerization region of the jet as well as the stagnant feed chamber regions, which are at higher pressures and temperatures. Since non-dimerizable laser-excited .sup.iUF.sub.6* monomers diffuse radially out of the jet core during their supersonic jet flight (promoting enrichment), and because they are radially distributed in the jet, a maximum number of them can be laser-energized with a co-axial irradiation arrangement FIG. 3a. In this arrangement, most of the total population of laser-excited .sup.iUF.sub.6* will loose their energy by VT relaxations in the higher-pressure feed-tank and nozzle before they escape from the jet core in the low-pressure process chamber. However because of the low UF.sub.6 laser photon absorption cross-section at 5 microns, this loss is tolerable since less than 0.1% of the laser photons are lost per pass through each mini-separator unit. However, unless means can be found to avoid excessive diffraction losses as the intracavity beam passes through the small nozzle throats, the coaxial arrangement shown in FIG. 3a may be impractical and the cross flow arrangements of FIGS. 3b and 3c are preferred.
(18) The preferred cross-beam laser irradiation arrangements depicted in FIGS. 3b and 3c have the advantage that adjacent mini jets may be put much closer to each other (e.g. drilled out of one block as shown in FIG. 3b) than is possible for the axial irradiation case of FIG. 3a. For large-scale commercial enrichments, the arrangement shown in FIGS. 3b and 3c are much preferred. While FIG. 3b shows a general cross-sectional view of the cross-beam arrangement, FIG. 3c shows a concentric arrangement of a cylindrical feed chamber, irradiation chamber, and tails chamber that allows multiple gas mini jets to expand from the denser inner feed chamber 107 through an annular irradiation chamber 109 towards the more voluminous low-pressure outer cylindrical annular tails chamber 117. Various components are labeled as described earlier with respect to FIG. 2.
(19) FIG. 4 shows a plot of enrichment factors as a function of downstream jet temperature, and atomic weight of the carrier gas G, the major dimer partner in the UF.sub.6/G mix. This plot was calculated from analytical relations as described in the CRISLA public literature. The plot clearly shows that the heavier the dimer partner G, the higher the isotope separation. While jet-cooling of pure UF.sub.6 gas with atomic mass M=352 amu might appear attractive, VV transfers, premature UF.sub.6 freeze-outs, and slow adiabatic jet expansions with =1.06, make the co-mixed carrier gas G preferable. A UF.sub.6/G mix with excess carrier gas G also prevents excessive VV exchange losses between .sup.235UF.sub.6 and .sup.238UF.sub.6, and favors adequate jet-cooling of UF.sub.6 for optimum selective spectral absorptions and avoidance of premature cluster formation of UF.sub.6 (snowing). The inert carrier gas G should have a high gas constant (=Cp/Cv) to provide sufficient supersonic cooling. The heavy monatomic gas Xe with =1.66 and the fairly inert heavy gas SF.sub.6 with =1.30 are suitable. These carrier gases, G, yield high peak enrichment factors according to FIG. 4 for 1/50 mixtures of UF.sub.6/G. Experimental testing may be used to determine optimum values for UF.sub.6/G ratios and selection of the best carrier gas G. Additionally, some embodiments of the advanced CRISLA system may employ a three-component UF.sub.6/Y/Z gas mixture generating heavier UF.sub.6:Z dimers (e.g. Z=SiBr.sub.4).
(20) FIGS. 5a, 5b and 5c show low-temperature (T=200K in FIG. 5a, 150K in FIG. 5b, 100K in FIG. 5c) computer-calculated plots of the 3v.sub.3 absorption spectra of .sup.238UF.sub.6 and .sup.235UF.sub.6 between 1874 and 1878 cm.sup.1 and the strong CO laser lines at 1874.45 (P.sub.9-9), 1876.30 (P.sub.8-15), and 1876.63 (P.sub.7-21) cm.sup.1. The plots show that because of the isotope shift of 1.8 cm.sup.1, the cold and hot-band-shifted 3v.sub.3 spectra of .sup.238UF.sub.6 and .sup.235UF.sub.6 at super-cooled temperatures below 200 K are well separated. Besides showing the cold Q peaks of 3v.sub.3 near 1875.6 and 1877.4 cm.sup.1 for .sup.238UF.sub.6 and .sup.235UF.sub.6 respectively, FIGS. 5a, 5b and 5c clearly show the well-separated Q-branch peaks of the first four anharmonically shifted hot-bands of .sup.238UF.sub.6 and .sup.235UF.sub.6 due to the low-energy co-vibrations v.sub.6, v.sub.4, v.sub.5, 2v.sub.6. The cold vibration involves a 3v.sub.3 excitation of a UF.sub.6 molecule with no other active side vibrations on-going while the transition occurs; UF.sub.6 has six normal vibrations of which the low-energy vibrations v.sub.4, v.sub.5, v.sub.6 are easily once- or twice-excited in thermal collisions. The plots of FIGS. 5a, 5b and 5c show that the CO laser line at 1876.63 strikes the partially overlapping Q-branches of v.sub.4 and v.sub.5 co-vibrating hot-bands of .sup.235UF.sub.6(3v.sub.3) while the line at 1876.30 cm.sup.1 strikes the 2v.sub.6 hot-band of .sup.235UF.sub.6(3v.sub.3). The CO laser line at 1874.45 cm.sup.1, on the other hand, strikes the 2v.sub.6 hot band of the other isotope .sup.238UF.sub.6(3v.sub.3).
(21) The CO laser line frequencies have been measured quite accurately, while the computer-calculated absorption bands of .sup.238UF.sub.6 and .sup.235UF.sub.6 are based on measured molecular vibrational constants. They were obtained with a high-resolution computer program (COMISH) that simulates octahedral QF.sub.6 spectra, requiring more than thirty molecular input parameters including six (measured) anharmonic constants to calculate hot-band shifts. The calculated spectra were compared/calibrated with measured ones.
(22) FIG. 6a shows ultra-high-resolution measurements with a laser diode of the .sup.238UF.sub.6(3v.sub.3) absorption band in the hot-band region of interest at T=257 K and p=3.5 Torr. Because UF.sub.6 condenses at low temperatures and its vapor pressure is only 0.006 Torr at 200 K and around 10.sup.20 Torr at T=100 K, very long absorption lengths through the gas are required to measure low-temperature absorption spectra of the weakly absorbing 3v.sub.3 vibration of gaseous .sup.238UF.sub.6(3v.sub.3). Even at T=257 K, the vapor pressure of UF.sub.6 is only 3.5 Torr (=0.046 atmospheres) and to obtain sufficient spectral detail at high resolution, an absorption length of 1000 meters had to be used with a 3-meter long absorption cell and multi-path-folding minors. For this reason it is nearly impossible to measure gaseous UF.sub.6(3v.sub.3) spectra at carrier-gas-produced super-cooled temperatures below T=250 K of millisecond durations. Thus the COMISH computer program was developed yielding the plots shown in FIGS. 5a, 5b and 5c. The 2v.sub.6 hot-band spectrum of .sup.238UF.sub.6(3v.sub.3) shown in FIG. 6a shows the expected typical A, B, C, D, E, F, G sub-peaks of a Q-branch as observed also for the cold .sup.238UF.sub.6(3v.sub.3) and .sup.238UF.sub.6(v.sub.3) absorption bands shown in FIG. 6b.
(23) The measurements shown in FIG. 6a were made using natural UF.sub.6 with 99.3% .sup.238UF.sub.6, and thus they cannot show any spectral peaks of the small 0.7% .sup.235UF.sub.6 fraction directly. However to assess the 2v.sub.6 hot-band absorption region for the .sup.235UF.sub.6(3v.sub.3) isotopomer, the wave-number scale was shifted by the measured isotope shift of 1.82 cm.sup.1 between .sup.238UF.sub.6(3v.sub.3) and .sup.235UF.sub.6(3v.sub.3) as shown in the upper part of FIG. 6a, assuming Q-branches of both are the same (actually there is a different hyperfine-effect which may change the sub-peak structures slightly). The strong CO laser line at 1876.30 in the upper portion of FIG. 6a shows that it should strike a sub-peak of the 2v.sub.6 hot-band of .sup.235UF.sub.6(3v.sub.3), while the CO laser line at 1876.63 cm.sup.1 should strike close to a sub-Q-peak of the overlapping v.sub.4 and v.sub.5 hot-bands of .sup.235UF.sub.6(3v.sub.3), in agreement with the spectral predictions shown in FIGS. 5a, 5b and 5c. The CO laser line at 1874.45 cm.sup.1 shown in the lower part of FIG. 6a indicates it overlaps the 2v.sub.6 hot-band of .sup.238UF.sub.6(3v.sub.3), also in agreement with the calculated plots shown in FIGS. 5a, 5b and 5c. Laser excitations of UF.sub.6(3v.sub.3) are best optimized experimentally. Incomplete explorations in 1986 unequivocally showed repeated moderate .sup.235UF.sub.6 enrichments with CO-laser-induced 3v.sub.3 excitations of natural UF.sub.6 (supercooled to far-from-optimum temperatures and pressures). These experiments confirm that the above-mentioned CO laser lines do strike .sup.235UF.sub.6(3v.sub.3) hot-bands at reasonably strong absorptive regions of the UF.sub.6 hot-band spectrum shown in FIGS. 5a, 5b, 5c and FIG. 6a or such enrichments would not have been observed.
(24) In a preferred embodiment of the advanced CRISLA system, for optimum CRISLA enrichment of UF.sub.6, the system comprises a combination of a high-power 5-micron CO laser and a train of a hundred or more mini jet separators irradiated intra-cavity in a cross-wise fashion as shown in FIGS. 3b and 3c. The CO laser typically has a beam diameter between 1 and 15 mm and a long-path intra-cavity bi-directional circulating laser beam of 10 KW/cm.sup.2 (single line) or higher. The laser must be operated on the P.sub.8-15 laser line at 1876.30 cm.sup.1 and/or the P.sub.7-21 laser line at 1876.63 cm.sup.1 which overlap the first four spectrally shifted low-energy hot bands of the 3v.sub.3 vibration with side vibrations v.sub.h=v.sub.6, v.sub.4, v.sub.5, or 2v.sub.6 of .sup.235UF.sub.6(3v.sub.3). Also the CO laser line at 1874.45 cm.sup.1 (P.sub.9-9) may be used which overlaps the 2v.sub.6-hot-band-shifted .sup.238UF.sub.6(3v.sub.3) resonance.
(25) In applications with coaxial irradiation of a series of mini-jets, the nozzle throat diameters of the mini jets must be larger (3-16 mm) to allow low-loss passage of the laser-beam. In this case of co-axial irradiation, alignment of the nozzle throats of a hundred or so adjacent mini-separators fabricated in series must be accurate to within 0.1 mm to allow clear passage of a straight 5 micron laser beam through all of the nozzles (see FIG. 3a). While a greater number of UF.sub.6 molecules in the process stream may be laser-excited in a co-axial irradiation embodiment, a drawback of this intra-cavity approach besides the throat diffraction losses, is that the length of a hundred or so adjacent mini jets (see FIG. 3a) will be longer than in a cross-wise embodiment in which intra-cavity laser irradiation of a hundred jets is utilized (see FIGS. 3b and 3c). Because of excessive throat diffraction losses and longer traversing lengths as the intracavity laser beam passes through the multiple nozzle or orifice throats shown in FIG. 3a, the cross-irradiated scheme illustrated in FIGS. 3b and 3c is preferred for large-scale commercial enrichment applications.
(26) Note that the nozzles, skimmers, chambers, pumps, traps, and all other components of the advanced CRISLA system may comprise metal, plastic, composite, ceramic, or other materials as known in the art and may be manufactured by any technique known in the art including but not limited to machining, casting, and printing.
(27) The high-power 5-micron CO laser may be any appropriate CO laser known in the art. In particular, the high-power CO laser may comprise a liquid-nitrogen-cooled LCL-516 model made by LISCHEM which can deliver 3 to 10 kW/cm.sup.2 (single line) of intracavity circulating power when run continuous (CW), or a peak pulse of 30 to 50 kW/cm.sup.2 (single line) if Q-switched. For higher intensities one may construct a CO laser powered by an e-beam-assisted gas-discharge as was developed in previous high-power laser programs known to those skilled in the laser art, potentially delivering 100 kW/cm.sup.2 of intra-cavity bi-directional laser power. Spectral fine-tuning of the CO laser emission lines to shift them to the Q-peaks of the afore-mentioned resonant absorptions of .sup.235UF.sub.6(3v.sub.3) and .sup.238UF.sub.6(3v.sub.3) may be profitable if enrichment factors can thereby be enhanced. A number of spectral-line fine-tuning techniques have been developed known to those familiar with the laser art, which may be suitable for use in CRISLA. In applying fine-tuning, care must be taken not to lower bi-directional intra-cavity laser power levels. Possible schemes developed for spectral fine-tuning or chirping include but are not limited to piezo-driven micro-vibrations of the CO laser end-mirror and/or laser grating; imposition of electric and/or magnetic fields intra-cavity across laser-irradiated process gas flows or across the CO lasing plasma; micro-wave mixing; orbital-spin manipulations of laser photons, and laser beam transmission through a non-linear optical medium in any combination.
(28) The carrier gas G may be chosen from known inert gas molecules with a high gas constant =Cp/Cv. Monatomic gases have the highest values (=1.66), and the heaviest stable member of this class is Xe with atomic mass M=133 amu. Another heavy gaseous molecule that is reasonably inert with a usable is SF.sub.6 with M=146 amu and =1.30. Still heavier carrier gases such as SiBr.sub.4 with M=348 amu and =1.1 might be considered but they are usually more chemically reactive. The optimum dilution ratio UF.sub.6/G to obtain highest enrichments is best determined experimentally. The optimum dilution ratio depends on many pressure-dependent and temperature-dependent parameters such as VV transfer rates and dimer formation rates that vary dramatically as the process gas expands and is laser-irradiated. From prior research, it appears that a UF.sub.6/G ratio between 1/50 and is reasonable but only experimental tests can pinpoint the optimum for a particular selection of carrier gas G and a particular process chamber design. The optimum downstream super-cooling temperature and pressure for maximum enrichment, which can be controlled by the nozzle-to-skimmer separation distance and by the process gas pumping speeds of separated rim and core gases, are also best determined experimentally in conjunction with the selection of carrier gas G.
(29) Process gas pumping speeds used in CRISLA for both the rim and core gas fractions are typically between 1000 and 10,000 liters/minute, and pumps with these capacities are commercially available from Hereaus (Leybold Hereaus/Balzers; with headquarters in Cologne and Hanau, Germany, and in Liechtenstein), the Edwards corporation (headquartered in Crawley, W. Sussex, Great Britain), and other vacuum equipment companies. Cryo-trapping cells to collect and separate depleted or enriched UF.sub.6 from carrier gases G like Xe or SF.sub.6, can use liquid nitrogen or other suitable cryogen. These are also commercially available and their use is well-known to those skilled in the art. The advanced CRISLA system may employ any appropriate pump or trap as known in the art.
(30) While plausible operating parameters for various embodiments of the advanced CRISLA system have been herein identified, variations of these parameters from those quoted may of course be utilized without diminishing the value or utility of the presently disclosed system and method.
(31) Note also that while this disclosure focuses on the separation and enrichment of UF.sub.6, in alternative embodiments the advanced CRISLA system may be employed to separate and enrich isotopes of other materials and elements as known in the art.
(32) With respect to the above description then, it is to be realized that material disclosed in the applicant's drawings and description may be modified in certain ways while still producing the same result claimed by the applicant. Such variations are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and equations and described in the specification are intended to be encompassed by the present invention.
(33) Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact disclosure shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
