GB1571209A

GB1571209A - Isotope separation process

Info

Publication number: GB1571209A
Application number: GB19896/78A
Authority: GB
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1978-01-01
Filing date: 1978-05-31
Publication date: 1980-07-09
Also published as: FR2413120A2; NL7805776A; AU3654878A; CH618956A5; BE867647A; AU526806B2; DE2826226A1; FR2413120B2

Description

(54) ISOTOPE SEPARATION PROCESS (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a process for the separation of the isotopes of an element, and preferably the isotopes of uranium, utilizing volatile uranyl compounds.

Especially suitable such compounds are certain hexafluoracetoacetonate complexes which together with processes for their preparation, are described and claimed in co-pending application 25023/77, (Serial No.

1,571208).

In order to appreciate the significance of the present invention it is first important to understand the background against which this invention was made. For years, those skilled in this art have tried to take advantage of the known fact that the absorption spectra of atoms or molecules of a given element exhibit an isotopic shift, and that it should therefore be possible to excite isotopes of those elements with light of a selected wavelength. The actual application of this principle has in certain cases, however, proven quite difficult, primarily for three reasons, namely the particular absorption lines involved are at wavelengths requiring the use of light sources which are not commercially available or economically feasible; or the particular atoms or molecules in question are not readily attainable in the vapor phase at reasonable operating temperatures: or the particular isotopic shift in question exhibits overlapping bands, thus rendering selective excitation considerably more difficult.

One example of the prior use of a commercially available laser light source for the isotopic separation of a gaseous compound at room temperature is disclosed in two recent references. Thus, Ambartzumian et al in an article in Soviet Physica JETP 21, 375, 1975, and Lyman et al in an article in Applied Physics Letters 27, 87 1975, report experiments in which gaseous SF6 at room temperature was irradiated by a CO2 laser. The wavelength of the CO2 laser corresponds to a fundamental absorption band of SF6 molecules containing one isotope of sulfur but not of SF6 molecules containing the other isotope.

Thus the CO2 laser provides an isotopically selective excitation of SF6. Furthermore, a CO2 laser is highly efficient, relatively inexpensive, and practical to build in the size needed for large scale industrial applications. If it can be used in an isotope separation process, the CO2 laser is clearly the laser of choice.

When it has been attempted to apply these teachings to the separation of uranium, great difficulties have been encountered. Uranium is a highly refractory metal, boiling only at extremely high temperatures. Thus, use of the abovedescribed process with uranium atoms involves obvious difficulties. U.S. Patent 3,772,519, for example, discloses the fact that uranium metal exhibits an isotopic shift and that its isotopes can be separated by employing uranium vapor. Extremely high temperatures, however, are necessary in such a process.

In addition, if one seeks to employ a CO2 laser to separate isotopes in a uraniumbearing molecule, additional difficulties are encountered. A great deal of attention has been paid to using UF6 for laser separation of uranium since it is a highly volatile compound. UF6, however, has two fundamental absorption bands which lie at 626 and 189 cm-', which have some isotope shift so that isotope separation can be effected. While it is within the skill of the art to build lasers which operate at either wavelength, such lasers at present are inferior to the CO2 laser both in terms of power and cost.

U.S. Patent No. 3,923,619 discusses the use of UO2F2 for the separation of the isotopes of oxygen. The patentees in this case state that this can be done in a liquid medium, and they employ ultraviolet radiation to induce photochemical reactions therein.

The UO2+2 ion has an absorption band in the infrared spectrum which absorbs light emitted by commercially available CO2 lasers. In addition, the uranium isotope shift of the asymmetric vibrational mode of the UO2+2 ion is 0.7 cm-1, while the width of this band is about 9 cm-', and thus the absorption bands of each isotope are not resolved (see Figure 2). It was believed that this absorption band was inhomogeneous, and that therefore in order to achieve isotope separation, narrow band irradiation at a precise band was necessary. In the case for certain oxygen isotope shifts (see Figure 1), the separation is about 19 cm-' and therefore fully resolved.

While these facts are thus known, no usable isotope separation process employing the uranyl radical in the vapor phase has been developed in the past. One of the principal reasons for this has been the fact that no one has previously discovered a volatile uranyl containing compound which can be useful in such a process and which meets all of the requisite parameters for such utility.

U.S. Patent, 3,951,768 discusses the use of a CO2 laser for the separation of isotopes.

One of the compounds mentioned with others as possibly usable for the separation of uranium compounds is UO2(NO3)2 . 6H2O. Therefore, this patent appears to suggest the use of uranyl compounds with a CO2 laser for isotope separation. Since this compound is listed with others which do not readily absorb the light from the CO2 laser it is not clear what was intended to be taught. Nevertheless, a uranyl compound is mentioned. The specific uranyl compound mentioned above which is contained in the Gurs patent, however, is known to be non-volatile in the sense that it decomposes and therefore cannot be employed in the vapor phase for isotope separation. In fact, most uranyl compounds decompose without vaporization when heated. The following discussion thus concerns the state of the art with respect to uranyl compounds in general, without regard to their use in isotope separation processes.

Some early reports on uranyl-containing compounds were made by Messrs.

Schlessinger and Brown in the late 1940's.

Thus, in U.S. Patent Application Serial No.

662,600 published in the Official Gazette on March 6, 1951, Chemical Abstract 46, 10192b, the authors disclose a class of uranyl-containing p-diketone compound which they investigated in connection with vapor phase processes for gas diffusion and uranium ore separation. They thus disclose compounds having the general formula:

where R may be a fluoro substituted alkyl group and R, a halogen substituted radical.

Subsequently, however, these same individuals, in the Journal of the America Chemical Society, 75, pages 2446-8 (1953) went on to report that "there is little likelihood of finding such compounds having vapor tensions above 0.1 mm. at 130"." In that article the only vapor pressure for a p-diketone, namely for UO2(thenoyl trifluoroacetone)2, is .0027 torr at 130"C.

These articles, in addition to several other articles, do discuss, however, the relationship between increased volatility and fluorination, Messrs. Schlessinger and Brown discussing the increase in volatility achieved by replacement of the methyl radicals of acetylacetone by the trifluoromethyl group They conclude, however, that based on their observations the search for a significantly more volatile uranium compound of the diketone type "held little promise of success". Similarly, in a comprehensive review of the properties of a number of uranyl compounds with various chelating ligands, Casellato et al, in Inorganica Chemica Acta, 18 77-112 (1976) review the behavior of the actinides in their various oxidation states combined with various organic chelating ligands such as the p-diketones. This article again indicates the contribution that fluorination plays in the volatility of these compounds, but in particular with regard to complexes of the type UO2(acetylacetonate)2L. It is indicated that the monodentate ligands (L) begin to come off between 83 and 170"C, followed by decomposition of the complex, even though ligands containing nitrogen donor atoms are said to result in decomposition temperatures that are much higher. Again, no direct discussion of volatility is contained in this portion of the Casellato et al article, which goes on to discuss the relationship between ligand selection and shifts in the absorption spectra of the molecule. It should again be noted that this article does not in any way discuss the use of any of these compounds for isotope separation.

Further general discussions of various uranyl p-diketone complexes in the prior art include that in Subramanian et al "Complexes of Uranyl A-Diketones with Aromatic Amine N-oxides", Journal of Inorganic Nuclear Chemistry, 33, 3001 (1971), which discusses a number of compounds of the class UO2(hexafluoroacetylacetonate)2L, where the ligands are various amine N-oxides, such as pyridine N-oxide. There is no discussion of the volatility of these compounds in the article, which further indicates that the amine N-oxides were selected by the authors over such materials as alcohols, ethers and amides because of the more polar nature of these compounds and the search for a stronger bond therewith. Also in Belford et al, "Influence of Fluorine Substitution on the Properties of Metal Chelate Compounds--III" Journal of Inorganic and Nuclear Chemistry, 14, 169178 (1960) the authors described their preparation of UO2(hexafluoroacetylacetonate)2 tetrahydrate, which they described as decomposing on heating above 58"C. This article, which shows the infrared absorption bands for various uranyl compounds, discusses the effect of ligand substitution on the visible spectra and the authors' conclusions that the more basic ligands attach more securely to the uranium atom decreasing its coordinating tendency.

Additional discussion of such compounds of the type UO2(hexafluoro acetylacetonate)2. L where L is a sulfoxide or a phosphine oxide is contained in a number of articles, including one by Sieck entitled "Gas Chromatography of Mixed Ligand Complexes of the Lanthanides and Related Elements" submitted for his Ph.D.

thesis, Iowa State University, 1971, as well as two other articles by Mr. Sieck in Chemical Abstracts, 75, 147395Q and at Nuclear Science Abstracts, 25 (17), 39410 (1971). In these articles the author is discussing these mixed ligand complexes for the separation and detection of UO2+2 and detection of these complexes by gas chromatography at column temperatures of about 200 .

The effects of chelate and ligand substitution on the IR spectra is also discussed by Haigh and Thornton in "Ligand Substitution Effects in Uranyl ,B- ketoenolates", Chemical Abstracts, 75, 55935n and a further discussion of the effect of fluorine substitution for hydrogen on volatility is made by Swain et al in "Volatile Chelates of Quadrivalent Actinides", Inorganic Chemistry, 9, (7)1766-9 which relates to tetravalent uranium compounds, the most volatile of which is U(CF3COCHCOCF3)4, a compound which exhibits no useful absorption in the CO2 laser spectral output.

There is also an article by Bloor et al (Canadian Journal of Chemistry, 42, 2201- 2208) which teaches the existence of a compound described as uranyl phthalocyanine, which is sublimable under a vacuum "below 0.01 mm pressure at 400- 450"C." These conditions, however, would not have been considered preferable for use in gaseous isotope separation processes because very high temperatures are required to obtain low vapor pressures.

Very little additional work has been reported on uranyl hexafluoroacetylacetonate

or its complexes. The hfacac anion is a chelating anion, and is known to stabilize metal salts and allow for volatile species (Kutal, J. Chem. Ed. 52, 319 (1975)).

Furthermore, this anion has no bands in the infrared region of 9001000 cm-', the region where the UO2+2 group has a strong antisymmetric stretching mode, which is of interest for any isotope selective CO2-laser irradiation.

In general, uranyl compounds prefer to have five atoms coordinate to the central U ion (in addition to the oxygens of the uranyl), see e.g., U. Casellato et al, supra.

Since each hfacac group uses two coordination sites, this leaves an open site for a neutral ligand, which is necessary to produce a stable uranyl containing vapor. In the absence of an appropriate stabilizing neutral ligand it is impossible to generate the stable monomeric vapor of the uranyl (hfacac)2 which would be necessary for an isotope separation process. The various articles discussed above show that many of the various ligands previously attempted would not be suitable in a process such as that of the present invention since the compounds do not volatilize intact so as to form such a stable vapor phase species.

To be useful in accordance with the present invention, the uranyl compound must therefore form a stable vapor and have a significant vapor pressure, preferably at a relatively low temperature. The stable vapor species is a necessary part of any process which seeks to utilize selective excitation to produce a disequilibrium in an isotope specific manner and which seeks to destabilize only the selectively excited species. A second requirement which seeks to minimize the temperature at which the required high vapor pressure is achieved is invoked to minimize the hot band population which may lead to reduced selectivity in the process.

Use in a laser isotope separation also imposes other requirements upon the properties of the uranyl-containing molecule. These include spectral transparency of the ligands at the infrared and at the possible UV-visible excitation wavelengths.

In accordance with the present invention, there is provided a process for the separation of isotopes of an element, said process comprising vaporizing a volatile uranyl compound, said compound having an isotopic ally shifted infrared absorption spectrum associated with said element, and irradiating said volatile uranyl compound with infrared radiation which is preferentially absorbed by a molecular vibration of molecules of said volatile uranyl compound containing a predetermined isotope of said element so as to provide excited molecules of said compound enriched in said molecules of said compound containing said predetermined isotope, and separating said excited molecules. By employing uranyl ioncontaining compounds which exhibit significant vapor pressures at relatively low temperatures, and which exhibit spectral transparency of the ligands at the excitation wavelengths of the uranyl ion, it is now possible to selectively excite the uranyl ion at commercially acceptable conditions. In addition, it is therefore also possible to employ a CO2 laser for such purposes, with all of the concommitant advantages of same as discussed above.

The process is especially suited to the separation of isotopes of uranium.

It has been found that when the large uranyl ion-containing molecules hereof are vaporized they occupy a surprisingly narrow distribution of states which are populated.

While it was previously believed that it was essential to utilize a compound which could exhibit as high a vapor pressure at as low a temperature as possible in order to minimize the hot band population for an efficient process, it has quite unexpectedly been discovered that in the present process this is not as serious a problem as one skilled in this art would have anticipated, due to the surprisingly narrow population distribution of these molecules, despite the large internal energy content.

It has also surprisingly been found that the infrared absorption characteristics of the UOvt2 ion asymmetric stretching mode is homogeneous-like rather than being inhomogeneous as was previously believed.

In one embodiment of the present invention separation of the excited molecules is achieved by irradiating the volatile uranyl compound under conditions such that the excited molecules dissociate.

Since the irradiation is essentially a means of heating the uranyl compound, when said irradiation is carried out, under the conditions of the instant invention, in an isotopically selective manner the selectively heated isotopes may be converted into a chemically different form by any means whose rate is sensitive to temperature. Thus the excitation step may be carried out to such an extent that the selectively heated molecules dissociate. In another embodiment, however, separation is achieved by irradiating the excited molecules employing a second infrared radiation in order to convert the excited molecules into a separable product.

In another embodiment of the present invention, separation is achieved by irradiating the excited molecules with visible or ultraviolet radiation in order to convert the excited molecules into a separable product. In yet another embodiment of the present invention, separation is achieved by chemically converting the excited molecules, preferably by reacting same with a gaseous reactant in order to produce a separable product, such as for example the reactant 112.

In a preferred embodiment of this invention the irradiation is carried out at a temperature of less than about 200 C., preferably less than about 1500C., more preferably less than about 1300C., and most preferably between about 50 and 130"C., under conditions whereby the uranyl compound exists in a gaseous or vapor phase. More particularly, the process is preferably carried out under conditions whereby the uranyl compound has a vapor pressure of at least about 0.02 torr, and most preferably at least about 0.1 torr, especially at these temperature conditions. In particular, the process is preferably carried out in an essentially collision less environment. This may be accomplished, for example, by adjusting the vapor pressure and excitation pulse width such that the product of this collision frequency and pulse duration is less than 1. On the other hand, this may also be accomplished by maintaining the vaporized uranyl compound in a beam under essentially collisionless conditions, as shown for example in Figure 3 hereof and discussed in Examples 4 and 5.

The isoptopes of uranium or oxygen may thus be separated in accordance herewith by selectively exciting a vaporized uranyl compound so as to either separate one of the uranium isotopes, that is either U235 or U238, or the uranyl ions which include either 016 and Ot8 atoms or a pair of 01B atoms.

In the accompanying drawings:- Figure 1 is a graph plotting the absorption spectrum of a UO2'6(hfacac)2 THF and UO'6O'8(hfacac)2 THF mixture; Figure 2 is a graph of Figure 1, showing absorption spectrum of a U23502(hfacac)2. THF and U23802(hfacac)2. THF mixture; and Figure 3 is a schematic representation of an apparatus for conducting the isotope separation process of the present invention.

As noted above, volatile uranyl ioncontaining compounds including at least two isotopes of the element to be separated (e.g. uranium or oxygen) and having an isotopically shifted absorption spectrum associated with that element (see Figures 1 and 2) are employed in this invention. These compounds are employed in the vapor phase, preferably at a vapor pressure of at least about 0.1 torr. In accordance therewith, certain new compositions of matter, namely certain hexafluoroacetylacetonate compounds of UO2+2 which are complexed with a neutral ligand (L), have been found such that the products UO2(hfacac)2. L are stable and volatile and can be utilized in the processes of the present invention.

The most preferred volatile uranyl compounds for use in the present invention can be generally formulated as:

OR UO2(hfacac)2. L in which L is preferably isopropanol, ethanol, isobutanol, tert-butanol, ethylacetate, n-propanol, methanol, tetrahydrofuran, acetone or dimethylformamide.

The vapor pressures of such compounds are in the range of from about 0.1 to 10 torr when the temperature is in the range of from about 30 to 1500C. In addition, the compositions UO2(hfacac)2- L have no absorption in the infrared region 900975 cm-' interfering with the UO2 asymmetric stretch which could be isotope selectively excited with CO2 laser light.

All of these compositions vaporize intact at temperatures less than about 100"C and satisfy the infrared criterion discussed above.

After the composition is formed, it may be vaporized by heating from about 50"C to 1300C so as to form a vapor whose partial pressure is preferably greater than about 0.1 torr.

Irradiation of this uranyl-containing vapor is thus carried out in the manner discussed above. The particular uranyl compounds, as shown in Table I hereof, all have a UO2+2 infrared absorption within the range of from about 810 to 1116 cm-', i.e.

within the range of the CO2 laser, and more precisely the compounds shown therein are all within a very narrow range of between about 945-955 cm-', a particularly suitable range for that laser. It is also noted that these compounds do not otherwise absorb infrared radiation within that range.

It is noted that adjustments of the wavelengths of operation of the CO2 laser can be effected to some extent by variation of the carbon and/or oxygen isotope distribution of the CO2. Thus, while it is not absolutely prohibited to utilize compounds that absorb radiation in the region of operation, i.e. 810 to 1116 cm1, other than in the UO2 asymmetric stretching mode, it is important that absorption be avoided in the region in which the laser is being operated.

When the process of the instant invention is carried out by irradiation in the 810 to 1116 cm-' region alone, it is expected that the wavelength, bandwidth, energy, pulse width and pulse temporal character may have to be adjusted somewhat to provide maximum yield at optimal isotope separation. This may require the use of a second infrared laser, operating offresonance of the fundamental ground state absorption band or thermal populated hot band, or a combination thereof. For example, the first infrared radiation could be employed at a power level sufficiently high to heat molecules enriched in a selected isotope, but yet sufficiently low to insure that the heating was preferential in that the molecules were not overdriven as discussed in Example 5 hereof. The second infrared radiation would not be substantially absorbed by the fundamental molecular vibration of the molecule, but would be substantially absorbed by the selectively heated molecules. For example, the second infrared radiation could be shifted to the red of the first infrared radiation to provide radiation which is resonant with the selectively heated molecules but off resonance with respect to the unheated molecules. The intensity of the second infrared radiation would preferably be sufficient to further heat the selectively heated molecules to dissociation.

It is also considered possible that more than one frequency between the R(12) and P(6) vibrational-rotational transitions of the 10.6 ,um CO2 laser could be substituted for the first CO2 laser to preferentially excite the U235 species in the UO2(hfacac)2THF complex. It is further thought that a single CO2 laser device may possibly be utilized to generate radiation at all the required frequencies for both isotope selective resonance excitation, and for off-resonance dissociative excitation of the isotope selectively excited species if that is required.

It is also thought to be possible that radiation in the 6000 A+1000 A region may be used in place of the radiation provided by the second 10.6 ym CO2 laser described above, or possibly as another alternative, radiation in the 3700 Awl000 A region.

The uranyl compositions described above, and processes for their preparation, are described in detail in our copending application No. 25023/77. (Serial No.

1,571,208).

Examples of Processes of the Invention EXAMPLE 1 The novel compound represented by the formula:

H I UO2(CF3-C-C-C-CF3)2 tetrahydrofuran II II 0 0 because of its combination of stability at the conditions at which the process of the instant invention is carried out, as well as its high volatility, is the most preferred compound for use in the process of the instant invention.

This compound may thus be vaporized to yield a pressure of greater than 0.02 torr at a temperature of less than about 130"C. This vapor may then be irradiated by a CO2 laser tunable over the 10.6 ,um transition at a power level between about 104 watts/cm2 and 106 watts/cm2 with a pulse width of between about 10-9 and 10-6 seconds. As a result of such irradiation the sample may be converted in an isotopically selective manner into a new species which is less volatile and/or less stable, but which may be separated from the unconverted molecules.

The wavelength, pulse width, energy, and operating temperature may be mutually adjusted to optimize enrichment or yield.

EXAMPLE 2 Referring to Figure 3, the oxygen isotopes of UO2(hfacac)2 THF (see Figure 1) were separated in accordance with the process of the present invention. The uranyl compound was placed in a heated oven, 1, constructed of stainless steel, and heated by heating means, 2. The oven had about a 0.005 inch diameter orifice, 3, and was heated to about 120"C. The uranyl compound thus melted, and the molten material had a vapor pressure of a few torr at this temperature, and a beam, 18, was thus produced at the orifice, 3. An estimated beam flux of about 1020 molecules/sec. cm2 was produced at the oven orifice, 3, and the molecular beam itself was maintained in an apparatus at about 1x10-7 torr pressure. The molecular beam, 8, was clearly defined by liquid nitrogen cooled collimator, 4, which permitted passage of only those molecules eminating from aperture, 3, with a predetermined spread of velocity vectors.

The beam, 8, was crossed at about 2 centimeters in front of the oven orifice, 3 beyond the liquid N2 cooled collimator, 4, by a pulsed CO2 TEA laser as shown by beam 5 in Figure 3. The beam, 5, passed through a pair of BaF2 windows, 6, utilized to couple the 10.6 ym radiation into the system maintained substantially under vacuum as discussed above. The laser had a pulse shape such that about 70% of the total pulse energy was contained in a 70 nanosecond (FWHM) initial pulse with about 30 /" of the pulse energy in a 500 nanosecond wide tail. The diameter of the laser beam, 5, at its intersection with the beam was about 1 centimeter. The irradiation by a resonant CO2 laser transition caused unimolecular decomposition to occur, producing fragments thereof. This dissociation process imparted sufficient random translational energy to the fragments to move the vast majority out of the beam. The beam itself continued on to a collector, 7, of the residual of the beam known as the tails, after passing through liquid N2 cooled aperture, 9, for collection of dissociated fragments, which was located about 50 centimeters downstream from the oven orifice, 3, and which subtended a solid angle of 10-4 steradians. The collector, 7, was also nitrogen cooled. In order to reduce the concentration of the UO2'6(hfacac)2-THF species in the tails by about 90%/pulse/pass the CO2 laser was tuned to the P(6) transition of the 10.6 m laser band and the molecular beam was irradiated at 140 mJ/pulse. In order to reduce the concentration of the UO'6O'8(hfacac)2 - THF species in the tails by about 90 X/pulse/pass the CO2 laser was turned to the P(26) transition of the 10.6 m band and ir comprising a liquid nitrogen cooled cylindrical collector therefor.

In order to increase the time integrated depletion in each of these cases the number of transits of the laser beam across the molecular beam could be increased, such as with angular reflecting walls. The most efficient photon utilization will occur if care is taken not to re-expose previously exposed portions of the molecular beam to the radiation in such a case. The pulse repetition rate can be adjusted so that when the multipass interaction volume is refilled by the beam, it is again in its entirety exposed to the laser radiation. The irradiation may be repeated as many times as it is desired. Alternatively, a CW laser could be employed. In such a case, the intensity can be adjusted in accordance with the transit time of the molecules through the laser beam width. This contact time is in many ways analogous to the laser pulse width in the pulsed mode.

EXAMPLE 3 In order to separate the isotopes of uranium (See Figure 2) a similar example to that described in Example 4 was again conducted using the apparatus of Figure 3.

In this case in order to reduce the concentration of U23802(hfacac)2 THF in the tails and to achieve an enrichment of U235 in the tails (a=1.22)*, the 10.6 ym CO2 laser was operated on the P(10) transition at a laser energy of 120 mJ/cm2 with a pulse width of 400 nanoseconds (FWHM) using an enriched sample, (i.e.

47% U238/U238=-), 53% and about 60 ,' depletion of the sample was attained.

[U235/U238]after irradiation *(Y= [U235/U238]before irradiation In order to reverse the process and to thus reduce the concentration of the U235 species in the tail and to achieve an enrichment of 1.12 of the U236 species in the tails radiation of 87 mJ/cm2 of the P(4) transition of 10.6 ssm CO2 laser band was utilized and about SOon depletion was observed.

It was interesting to note that if the energy fluence of the CO2 laser on the P(4) transition was raised to 150 mJ/cm2 from 87 mJ/cm2 as described above, no such enrichment was observed (about 69 Mn depletion was observed). An expected characteristic of homogeous-like line shaped absorbers which have overlapping isotope absorptions (see Figure 2) is that it is rather easy to overdrive the system and thus lose isotopic selectivity therewith. The implications of this are that every molecule of each isotope component has the characteristic exhibited by the line shape.

The line shape is thus not a statistical representation as in may instances, but is an actual representation of the absorption characteristics of each molecule. Thus, the emission line of the laser can either be narrow or as broad as practical for CO2 laser devices, while not being broader than onehalf the width at one-half the maximum of the absorption band. Thus in accordance with the present process, contrary to prior processes, one can use a plurality of lasers having adjusted frequencies and broad widths to provide a highly efficient isotope separation process.

WHAT WE CLAIM IS: 1. A process for the separation of isotopes of an element, said process comprising vaporizing a volatile uranyl compound, said compound having an isotopically shifted infrared absorption spectrum associated with said element, and irradiating said volatile uranyl compound with infrared radiation which is preferentially absorbed by a molecular vibration of molecules of said volatile uranyl compound containing a predetermined isotope of said element so as to provide excited molecules of said compound enriched in said molecules of said compound containing said predetermined isotope, and separating said excited molecules.

2. A process as claimed in claim 1, wherein said isotopes comprise the isotopes of uranium.

3. A process as claimed in claim 1 or claim 2, wherein said uranyl compound is in the vapor phase at a temperature of less than 200"C.

4. A process as claimed in claim 3, wherein said uranyl compound is in the vapor phase at a temperature of less than 130"C.

5. A process as claimed in any preceding claim, wherein said uranyl compound is in the vapor phase at a vapor pressure of at least 0.1 torr.

6. A process as claimed in any preceding claim, wherein said volatile uranyl compound is irradiated at a wavelength of from 810 to 1116 cm-'.

7. A process as claimed in any preceding claim wherein said uranyl compound is irradiated by means of a CO2 laser.

8. A process as claimed in any preceding claim, wherein said separation of said excited molecules is achieved by irradiating said volatile uranyl compound under conditions whereby said excited molecules dissociate.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. comprising a liquid nitrogen cooled cylindrical collector therefor. In order to increase the time integrated depletion in each of these cases the number of transits of the laser beam across the molecular beam could be increased, such as with angular reflecting walls. The most efficient photon utilization will occur if care is taken not to re-expose previously exposed portions of the molecular beam to the radiation in such a case. The pulse repetition rate can be adjusted so that when the multipass interaction volume is refilled by the beam, it is again in its entirety exposed to the laser radiation. The irradiation may be repeated as many times as it is desired. Alternatively, a CW laser could be employed. In such a case, the intensity can be adjusted in accordance with the transit time of the molecules through the laser beam width. This contact time is in many ways analogous to the laser pulse width in the pulsed mode. EXAMPLE 3 In order to separate the isotopes of uranium (See Figure 2) a similar example to that described in Example 4 was again conducted using the apparatus of Figure 3. In this case in order to reduce the concentration of U23802(hfacac)2 THF in the tails and to achieve an enrichment of U235 in the tails (a=1.22)*, the 10.6 ym CO2 laser was operated on the P(10) transition at a laser energy of 120 mJ/cm2 with a pulse width of 400 nanoseconds (FWHM) using an enriched sample, (i.e. 47% U238/U238=-), 53% and about 60 ,' depletion of the sample was attained. [U235/U238]after irradiation *(Y= [U235/U238]before irradiation In order to reverse the process and to thus reduce the concentration of the U235 species in the tail and to achieve an enrichment of 1.12 of the U236 species in the tails radiation of 87 mJ/cm2 of the P(4) transition of 10.6 ssm CO2 laser band was utilized and about SOon depletion was observed. It was interesting to note that if the energy fluence of the CO2 laser on the P(4) transition was raised to 150 mJ/cm2 from 87 mJ/cm2 as described above, no such enrichment was observed (about 69 Mn depletion was observed). An expected characteristic of homogeous-like line shaped absorbers which have overlapping isotope absorptions (see Figure 2) is that it is rather easy to overdrive the system and thus lose isotopic selectivity therewith. The implications of this are that every molecule of each isotope component has the characteristic exhibited by the line shape. The line shape is thus not a statistical representation as in may instances, but is an actual representation of the absorption characteristics of each molecule. Thus, the emission line of the laser can either be narrow or as broad as practical for CO2 laser devices, while not being broader than onehalf the width at one-half the maximum of the absorption band. Thus in accordance with the present process, contrary to prior processes, one can use a plurality of lasers having adjusted frequencies and broad widths to provide a highly efficient isotope separation process. WHAT WE CLAIM IS:

1. A process for the separation of isotopes of an element, said process comprising vaporizing a volatile uranyl compound, said compound having an isotopically shifted infrared absorption spectrum associated with said element, and irradiating said volatile uranyl compound with infrared radiation which is preferentially absorbed by a molecular vibration of molecules of said volatile uranyl compound containing a predetermined isotope of said element so as to provide excited molecules of said compound enriched in said molecules of said compound containing said predetermined isotope, and separating said excited molecules.

9. A process as claimed in any one of

claims 1 to 7, wherein said excited molecules are separated by irradiating said excited molecules by means of a visible or U.V. laser so as to convert said excited molecules into a separable product.

10. A process as claimed in any one of claims 1 to 7, wherein the separation of said excited molecules is achieved by irradiating said excited molecules with a second infrared radiation so as to convert said excited molecules into a separable product.

11. A process as claimed in any one of claims 1 to 7, wherein said excited molecules are separated by chemically converting said excited molecules into a separable product.

12. A process as claimed in claim 11, wherein said chemical conversion of said excited molecules comprises reacting said excited molecules with a gaseous reactant so as to produce a separable product.

13. A process as claimed in any preceding claim, wherein said uranyl compound comprises ~~~~~~~~~~~~~~~~~~~~~

wherein L is a ligand.

14. A process as claimed in claim 13, wherein said ligand (L) is selected from isopropanol, ethanol, isobutanol, tertbutanol, methanol, tetrahydrofuran, acetone, dimethylformamide, n-propanol and ethyl acetate.

15. An isotope separation process as claimed in claim 1 and substantially as herein described.

16. An isotope separation process as claimed in claim 1 and substantially as herein described with reference to any one of Examples 1 to 3.

17. An isotope of an element whenever obtained by a process claimed in any preceding claim.