DE2404577A1 - ISOTOPE IONIZATION PROCESS AND SYSTEM FOR ITS IMPLEMENTATION - Google Patents

Description

DR. KARL TH. HEGEL DIPL-ING. KLAUS DICKEL

PATENT LAWYERS? Λ (Ί Λ R 7

20OO Hamburg 50

Große Bergstrasse 223 P.O. Box 5006 62 Telephone: (040) 396295 Telegram address: Doellnerpatent

Your reference: "Our reference: the date

H- 2222

Jersey Nuclear-Avco Isotopes, Inc. Bellevue, Washington, V. St. A.

Isotope ionization process and installation for its implementation

The invention relates to a method and a system for the selective ionization of an isotope in an environment containing several isotopes. It becomes this Process used primarily for the purpose of subsequent isotope separation or isotope enrichment.

Past all cleavage reactions that use the uranium isotope Upjr require a concentration of the Up ^ ₁ isotope which is greater than that occurring in the natural state. In the past, increasing the concentration of U ₀ -, _c to a desired level, starting from natural or already used uranium, is by means of

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been carried out many procedures that generally separate the Up35 ^of ^ ^{s on} its Uranium isotopes, primarily from the Up _33, because of its slightly different chemical properties or its mass difference. Enrichment methods based on these processes often require a step-by-step procedure, v / which repeatedly applies the same steps, each step bringing with it a small increase in the concentration of the desired isotope.

A promising technology for a more efficient separation of the U "~ Isotopes used selectively ionize this Isotopes in a uranium vapor without the U ₂₃₈ isotope of the vapor to ionize accordingly. The ionization gives the desired Up ₃₅ isotope electrical properties which allow this isotope to be separated from the other components of the uranium vapor. It may be the selective ionisation can be achieved by illuminating the uranium vapor by means of laser radiation, of which at least has a frequency and bandwidth which are chosen so that they ^recnen a specific energy gap of the desired U ₂ 35 ^Ent3 P i but not such a jump of the other Isotopes of uranium, ie mainly of U ₂₃₃ . The ionization of the

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Up ", - Isotopes is finally due to a jump in energy carried out from an excited intermediate state into the continuum of the ionized state through the application more laser beams to make this transition.

The usual theoretical model for the mutual effect of photons of the laser radiation and of particles, atoms or molecules, the UraniumSp ₃₅ isotope of the uranium vapor, is based on a probability calculation in which each particle of the Upoc isotope. is considered to be equipped with a specific radius. If a photon hits the cross section of a given particle, then the probability that the photon will cause an energy change in the particle is quite high. Typically, the effective cross-section is a function of the photon energy, or its frequency, both of which are linked in a known manner by Planck's constant. In general, the cross-section for excitation to an effective energy level will be negligibly small, except for those photoenergies that correspond to soft-determined transitions that are determined by a known absorption line of the atomic spectrum of the

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the element are highlighted. In general, the Cross-section for different energy jumps between different excited states may be different. Uranium has many hundreds of permitted transitions between discrete energy levels. In general are the cross sections for transitions into the continuum the ionized states are noticeably smaller than those for transitions between individual energy levels, which are below the ionization energy. This is contrary to the wish that all or almost all particles, which originally came from a ground state in an excited intermediate state were raised, then ionized. The limitation caused by this phenomenon the effectiveness of the enrichment or separation process can be overcome by using higher photon densities in the radiation used for ionization which, however, results in a corresponding increase in the complexity and costs of the system.

The present invention proposes a system and a method for the efficient ionization of the ^ ₂₃₅ isotope in a vapor of metallic uranium by means of a method which typically uses three energy transitions.

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Two discrete transitions are excited by radiation energy from lasers which have one or more frequencies in order to raise the Up ^ c isotope to a predetermined energy level just below the ionization value of this isotope. This predetermined energy level is chosen just below the ionization energy, so that a transition of the U ₂₃₅ isotope into the ionized state can be effected with a laser of relatively low energy, which effectively delivers a beam with a high photon density.

The predetermined energy level, which is just below the ionization potential of the U ₂₃₅ isotope, is preferably achieved by the radiation action of two lasers acting simultaneously on the uranium vapor. A first laser is precisely tuned to deliver a radiation whose frequency corresponds to a specific absorption line of the desired isotope, but without corresponding to an absorption line of the other isotopes occurring in the vapor. The excitation caused by the first laser radiation is therefore selective and results in a set of excited atoms in which the percentage of the U ₂₃ ^ isotope is well above its percentage.

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sentence is in the basic state. The second transition is caused by the beam of a second laser, which preferably to a second discrete and selected energy transition from the first energy level to the yor determined just below the ionization energy Energy level is matched.

The ionization step is carried out by simultaneous irradiation from a low-frequency laser, such as an infrared CO _? Laser, which can easily deliver a much higher photon density. This higher photon density makes up for the relatively small cross-section for the ionization step emanating from the excited atom.

It · provides the described combination of a first and a second tuned laser for selective, discrete excitation, uit the use of one High power laser for effective ionization, the desired ionization of the Upoc isotope. Thereafter this isotope is separated from the non-icnised isotopes, for example by using an MHD cross-field accelerator, so that the desired isotope is available for use.

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In the following, the invention will be based on aiiaes Ausfiihrungsbeispiels and the drawing are explained in more detail. Show it:

1 shows an energy level representation of previously used ones Energy transitions to achieve a selective Ionization;

Fig. 2 is an energy level representation of the proposed Method with three energy transitionsiii;

3 shows a schematic representation of an example of a system for selective lomdsatioai nand separation of an isotope J

3A shows a modification of FIG. 3; and

Fig. 4 shows an inner cross section through the fold of the Fig. 3.

It works the proposed ¥ erfaiaren in an isotopic enrichment plant by selective excitation, up to the ionization of particles welclae zaaraämlest atoms or molecules of a Isotopes in a fegetarag which both this isotope as well as one or MEKR & re more isotopes contains include. The ionized isotope is collected separately in order to bring about an enrichment of this isotope. Although many uses order,

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it is particularly desirable to enrich the Uq ^ b I ^soto P of uranium in natural uranium or in a depleted mixture of the U ₂₃₅ isotope and the much more common Up3 «^ ^soto P ^es .

• In a typical, illustrated in Fig. 1, known A first energy transition 12 from the ground state 14 of the isotope mixture is a method for selective ionization based on the use of precisely matched laser radiation with a narrow bandwidth. The laser is on an absorption line of the desired Up ^ c isotope matched which transition 12 leads from the basic state 14 to an excited intermediate state 16. The vote of the laser is sufficiently accurate to excite the desired Up ", - Isotopes without corresponding stimulation of others Ensure uranium isotopes. After the transition 12, the energy state 16 becomes a noticeably higher concentration of the desired Upr isotope than that in the Basic state 14 ensemble.

Simultaneous irradiation of radiation from a second laser, which does not have to be tuned as precisely as the first, causes a second transition 18, the excited atoms of the isotope that are in the intermediate state 16. The Sanitary Energy of Transitions 12 409839/0618

and 18 is at least equal to the ionization potential of the U ₂₃₅ isotope represented by level 20 in FIG. 1, but preferably greater than this. The transition 18 thus raises the energy level of the desired isotope from the intermediate state 16 into the ionization region 22. Then the ionized particle or the atom of the desired Up35 isotope has a positive charge, in contrast to the generally electrically neutral state of the other uranium particles. Accordingly, as described below, the ionized atoms are separated using an MHD cross-field accelerator.

It is known from theory and from experiment that the cross section for photon absorption to generate a discrete transition, as shown under 12, is much larger than the effective cross-section for an ionization transition shown under 18. Typical effective cross-sections for the transition 12 are about three Orders of magnitude larger than those for the transition 18. The larger the cross-section of a transition is, the greater the probability that a certain atom of the desired Up__ isotope with a Photon of the radiated radiation interacts, and that an energy transition takes place. In other words, ever

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the larger the cross section, the smaller the radiation intensity, which is needed to bring about the desired transitions. Accordingly, many like it Uranium atoms are raised from the ground state to the intermediate state 16 due to the precisely coordinated first laser radiation are ionized, however, a noticeably smaller number of them are ionized from state 16 to region 22, provided that that both laser beams have the same photon density. In view of this lower ionization probability, starting from the excited state, a considerable number of uranium atoms excited to the 16 state are not ionized.

In order to circumvent this limitation and to increase the ionization yield, the photon density in the for the transition 18 used laser radiation can be increased. However, it is the ionization energy of the transition 18, as can be seen from the illustration in FIG. 1, is approximately equal to half the ionization energy of uranium. There the ionization potential of uranium is about 6.2 electron volts, you normally have to make transition 18 a photon energy of about 3.0 electron volts is available or, in a widely used notation, a wave number of 25 * 000. In this energy area

are not effective sources of high-intensity laser radiation 409839/0613

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known. The currently available laser sources high intensity to emit a stream of photons higher Density work in or near the infrared region of the spectrum, with the photon having energy by more than one Is an order of magnitude smaller than the energy typically used for the transition 18.

The method described here, which allows the use of a high-intensity radiation source of high efficiency for the ionization transition, can best be understood with reference to the energy diagram of FIG. A first transition 26 lifts the desired Up, - isotope from a ground state into a first excited energy state 28, which is far below the ionization level 30. The laser radiation used for the transition 26 is provided by a precisely tuned laser, as described below, for example, a tunable dye laser. The laser radiation, which is precisely matched to the transition 26, excites a direct transition of the U ^ ₃₅ isotope without causing a corresponding excitation of a transition of the Up "" or other isotopes.

A second transition 32, starting from the energy level 28, is made, for example, by lighting with a second one

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Laser excited. The frequency of the second radiation will preferably be tuned to correspond to a further discrete energy transition of the upon isotope from level to a second level 34. The energy level 34 just lies. slightly below the ionization level 30. The amount of energy which is necessary to generate an ionization starting from level 34 corresponds to the energy of photons in the infrared part of the spectrum, an area for which effective lasers of high intensity are available can generate a high density of photons. Typical examples of such lasers include the well-known C0 _? Lasers, but other lasers with frequencies from less than a thousand to a few thousand can also be used. This low frequency radiation causes the ionization transition 35.

From this it can be seen that the method of FIG. 2 permits an effective, selective ionization of a desired isotope, in particular uranium U ₃₃₅ , with a three-stage excitation typically being carried out.

3 and 4 show a system for carrying out the ionization in three stages, which system is an adaptation of the system described in French patent no. 71.14007 published under 409839/06 1 8

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No. 2,094,967. Reference is made here to this patent. Referring to Figure 3, a first Laser device 36 has a stimulable medium 38, which is generated by the stimulation system 40 for a predetermined beam duration, usually a fraction of a microsecond, is excited, specifically in response to a signal from the clock generator 42 there. A tuning device 44 controls the frequency and the bandwidth of the beam emerging from the medium 3S ~ 46 in order to obtain a precisely defined, narrow band for the selective excitation, as indicated above.

The laser device 36 may include, for example, one of the commercially available dial-a-line lasers from Avco Everett Research Laboratory Lasers, as described in US Pat. No. 3,684,979. The frequency and bandwidth of the laser beam 46 is adjusted _{to correspond to one of the absorption lines of the U 235} isotope and the frequency spread of the beam 46 is kept narrow in order to avoid that it noticeably overlaps with an adjacent absorption line of the undesired isotope. If necessary or desired, a calibration filter can be used to narrow the bandwidth of the frequency of the beam 46, and it can

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2A04577

one or two jet intensification levels can be used. A typical frequency for generating transition 26 can be found in the literature such as LA-4501, "Current State of Analysis of the First and Second Spectrum of uranium (UI and Uli), derived from measurements of optical Spectra "published by the Los Alamos Scientific Laboratory of the University of California.

The beam 46 passes through a dichroic mirror 48, where a beam 50 coming from a second laser system 52 is superimposed on it. This second laser system will usually be similar to the laser system 36 and be matched to the second transition 32 shown in FIG. The beam 54 consists of the superposition of the beams 46 and 50. The exact frequency of the second transition 32 can be determined experimentally by _{changing the frequency of the laser beam 50 directed at the excited U 2} ^ ₅ isotope until an absorption line is determined spectroscopically . It should be noted that a transition of sufficient energy is desired to reach a level 34 which is only slightly below the ionization level.

A laser system 60 delivers a bundle 58, which with the dichroic mirror 56 with the bundle 54

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is stored to form a composite bundle 62 which simultaneously has radiant energy of three separate radiations. The laser system 60 will usually be a CO ₂ laser which has intense radiation in the energy region of photons with a wave number of less than a thousand up to a few thousand. Such lasers are well known to those skilled in the art.

For certain applications it may be more advantageous to reach the bundles 58 and 54 by gradual convergence, instead of using a dichroic Mirror 56. Figure 3A shows a corresponding embodiment. By placing a mirror on the path of the bundle 58 56a, but not in the way of the bundle 54, the bundle 58 becomes in a direction almost parallel to the bundle 54 deflected, but still so that it easily converges with this, so that after a certain path the composite bundle 62a arises.

Bas bundle 62 {or 62a), which · from the combination the bundle 54 and 58 is created by the dichroic mirror 56, occurs through a for the frequencies of the bundle 62 a permeable window 66 into a vacuum chamber 64. The window 66 can be made of quartz crystal exist. To keep uranium pollution 66 small,

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The ray 62 passes through an Eohr 67. Thereafter it passes through the bundle 62 an area of action 68, which above a uranium vapor source 70 in a uranion collector 72 lies. Usually the bundle 62 becomes the vacuum chamber 64 via another Eohr 73 and through a window 74 in order to then enter another Eohr 76, to which a further, similar vacuum chamber is attached, so that the laser beam 62 has a considerable length of Einiriirkungs areas how the area .68 crosses in order to use as many photons of the bundle as possible. Sine vacuum pump 78 is connected to chamber 64 via line 80 to maintain a low pressure therein to maintain the desired process not by burning uranium fumes or deflecting the Particle flow is impaired.

FIG. 4 shows a section of the chamber 64 along the line 4-4 in FIG. 3. The natural steam source 70 supplies a radially expanding steam stream 82 in Towards the ion trap 72, to produce this Steam 82 can the source 70, as described in the above-mentioned French patent 71.14007, performed be, and will usually be lütte! have to have a To heat uranium crucibles to its evaporation temperature,

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and collimator slots for directing vapor 82 toward ion trap 72.

The uranium vapor 82 enters the area of action 68 of the ion trap 72, onto which the laser beam is directed in order to effect _{a selective ionization of the U 235 isotope. The U 00} ^ ions in the resulting plasma are placed on a plate of ions d.00

trap 72 accumulated, using MHD cross-field acceleration, as described, for example, in above-mentioned French Patent No. 71.14007. To the generation this crossed field is provided by a magnetic field source 84 having, for example, coils and a current source a magnetic field in area 68, while an electric field source, not shown, has electrodes 86 in the ion trap 72 for short periods of time, usually not exceeding two milliseconds creates an electric field. This time interval corresponds approximately to the charge exchange time under the present conditions. A timer 88 is with the timers 42 in the laser systems 36, 52 and 60 are connected to the electric field and the corresponding lateral acceleration · forces immediately after the action of the compound Laser beam 62 to deliver. It can be the accelerated

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Ions are collected on a plate 92 located in their V » ^T ege, for the purpose of periodic removal of the enriched uranium. A plate 90 collects the remaining components of the steam jet. In a preferred mode of use, the laser beam 62 and the subsequent crossed fields are triggered periodically by the timer 88 to allow ionization and the collection of all possible particles of the U ₂₃₅ isotope.

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Claims (29)

Patent claims 1. Isotope enrichment method by selective Ionizing an isotope in an environment containing multiple isotopes characterized by the following Steps: - irradiating a first radiation in those environmental surroundings to the particles that stimulate a Isotopes to a predetermined, lying below the lonisierungsanregung to bring energy level corresponding to the particles without said other isotope; - Setting that predetermined excitation level to a value from which a transition to the ionized state by means of an effective, intense radiation source can be achieved; - Radiation into said environment of a second Radiation, which is much more intense than the first, to ionize the selectively excited and particles brought to the predetermined energy level of that one isotope reach. 240-577 2. The method according to claim 1, characterized in that the irradiation of the first radiation includes the following steps: - The irradiation of a first and a second laser radiation into the environment and the setting of the frequency of the first laser radiation to a value which is selective Energy absorption by one isotope without corresponding absorption by the other Isotopes guaranteed. 3. The method according to claim 2, characterized in that the frequency of the second laser radiation is selected is that it is selectively absorbed by said one excited isotope without being absorbed by the other isotopes to be absorbed accordingly. 4. The method according to claim 1, characterized in that the photon energy of the second radiation in the is essentially in the infrared region. 5. The method according to claim 1, characterized in that the isotopes contain those from the group formed by uranium and uranium compounds and that one isotope is U ₂₃₅ . - 20 409839/0618 6. The method according to claim 1, characterized in that there is the further step of separating the ionized particles that comprise an isotope of the environment. 7. The method according to claim 1, characterized in that the second radiation by a substantially is generated in the infrared working, low-frequency laser. 8. The method according to claim 1, characterized in that the first and the second radiation simultaneously be radiated. 9. The method according to claim 1, characterized in that the first and the second radiation are combined to irradiate the same area. 10. The method according to claim 9, characterized in that combining the use of converging The bundle of the first and the second radiation includes itself. 11. The method according to claim 1, characterized in that a steam to form the environment said isotope is generated. 12. The method according to claim 1, characterized - 21 409839/0618 shows that the photon flux in the second radiation is greater than that in the first radiation, inversely proportional to the ratio of the cross sections for ionizing and exciting that one isotope. 13. Isotope enrichment process by selectively ionizing an isotope in an environment which also contains other isotopes and where one isotope is to be separated from the other, 'indicated by the following steps: - Radiation into that environment of a first radiation with a frequency and bandwidth that are suitable to bring that first isotope selectively into a first excited state without corresponding excitation of the other isotopes, - Radiation in that environment of a second radiation of a frequency which is suitable to that one Bringing the isotope into a second excited state below its ionization energy, and - Radiation of further radiation energy into the environment in order to ionize the one isotope in the second excited state. - 22 409839/0618 14. The method according to claim 13, characterized in that the irradiation of further radiation energy into the environment by means of radiation of substantially
higher photon density than those of the first and
second radiations is carried out. 15. The method according to claim 13, characterized in that the energy difference between the second excited state and the ionization energy essentially corresponds to the energy of a photon located in the infrared region of the spectrum « 16. The method according to claim 13, characterized in that the irradiation of the first radiation is carried out over a narrow bandwidth and at a frequency that corresponds to a discrete energy jump
one isotope, but no jump in energy from the other
Isotopes. 17. The method according to claim 16, characterized in that the irradiation of the second radiation causes a selective excitation of the one isotope from said first to said second excited state
will. 18. System for the selective ionization of an isotope in an environment of several other isotopes for the purpose of isotope 4 0 9 8 3 97 S% T 8 enrichment, characterized by: - First means to radiate the radiant energy of one or more radiations into the environment, - Means to keep the photon energy of that first radiation in a range which the excitation of one isotope causes a predetermined excited state, which below by a predetermined amount of energy of the ionization level of one isotope is, this amount being much smaller than is the mean energy of the photons of the first radiation, - second means for irradiating in order to radiate a second radiant energy into the environment, whose photon energy corresponds to the energy that is necessary around the one isotope, starting out from that predetermined excited state to ionize. 19. Plant according to claim 18, characterized in that that the first funds have the following parts: - A device for generating a first radiation with a frequency profile that the selective 409839 / Q61 ~ 8 240A577 Excitation that causes an isotope to a first excited state, and - A device for generating a second radiation in order to excite the one isotope from the first excited state to the predetermined excited state. 20. Plant according to claim 19, characterized in that said devices comprise lasers. 21. Plant according to claim 18, characterized in that that the second means comprise a laser with a high photon output density. 22. Plant according to claim 18, characterized in that the second means comprise a laser, its Radiation is essentially in the infrared. 23. Plant according to claim 18, characterized in that it comprises means for producing a steam has the isotopes to create the environment. 24. Plant according to claim 18, characterized by separating means to that one isotope after its ionization to separate from the environment. 25. Plant according to claim 24, characterized in that - 25 409839/0618 2Α0Λ577 net that the release agent is an MHD cross-field accelerator exhibit. 26. Plant according to claim 18, characterized by means for the simultaneous application of the first and second Radiation. '. 27. Plant according to claim 18, characterized by means to converge the first and the second radiation so that both are present at the same time in the area of their application to the environment. 28. System for the selective ionization of an isotope in at least one other isotope ent- ■ holding environment, for the purpose of isotope enrichment, characterized by: - Means to radiate a first radiation into the environment, the frequency band of which is selective Excitation that causes an isotope to a first excited state, - Means to radiate a second radiation into the environment and that one isotope into one to raise the second excited state, whose energy is below the ionization energy lies, and - Means to get more radiant energy into the - 26 - 409839/0618 To radiate environment and that in the second excited state to an isotope ionize. 29. A method for the selective ionization of an isotope in an environment containing several isotopes, for isotope enrichment, characterized by the following steps: - Generation of the environment using a vapor from the isotopesJ - Einstrahisn in this environment of a first laser radiation with a frequency and bandwidth that would raise that one isotope into a first cause excited state without corresponding excitation of the other isotopes; - Radiation into this environment of a second laser radiation of one frequency, polygamy lifting the one causing an isotope from the first to a second excited state, the latter is an amount of energy below the ionization energy of that one isotope, that of the photon energy of effective laser radiation sources corresponds to high intensity; Radiation into the vicinity of a third laser radiation with a relatively high photon density and lower frequency, which is essentially in the infrared region, starting from second excited state, ionizing that one isotope, with all three radiations are irradiated at the same time; Acceleration of that one ionized isotope to effect its separation from the environment. - 28 - 409839/0618