JPS605330B2 - Isotope separation device - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention This invention relates to an isotope separation device, and more particularly to a new isotope separation device that can separate uranium isotopes with high efficiency using infrared laser light. .

'b} Technical Background Conventionally, centrifugation and diffusion methods have been used to separate uranium isotopes, but improvements are needed as they require a huge amount of equipment and have poor separation efficiency. It is rare.

On the other hand, in place of the well-known separation method that utilizes the difference in mass between isotopes, recently, isotope compounds in a gaseous state are irradiated with infrared laser light to selectively excite isotopes to be separated. However, methods have been proposed in which the excited isotopes are then chemically or physically separated. 'c} Conventional technology and problems In principle, the isotope separation method using Caesar light is as follows:
The strongest infrared absorption band of the UF6 (uranium hexafluoride) molecule is in the wavelength range of 16 Am, and the UF6 in parentheses is 60
When cooled to a temperature below K, due to isotope shift, pseudo-U
There is a slight difference in the absorption wavelength of F6 and 238UF6, resulting in pseudo-U
It is based on the theory that selective excitation of F6 becomes possible.

Therefore, in order to realize such a laser isotope separation method, it is necessary to cool the gaseous UF6 to a temperature sufficient to cause an isotope shift without liquefying it, and to obtain a wavelength that matches the absorption wavelength of the isotope to be separated. Obtaining a laser light source is an important issue. Here, as a method for cooling the gaseous isotope compound of UF6, it is common to utilize adiabatic expansion of UF6 gas as shown in, for example, West German Patent Application No. 2447762 and West German Patent Application No. 2458363. be.

However, at present, there is no practical infrared light source for excitation other than obtaining laser light in the 16-band range by wavelength conversion using a C02 laser or dye laser as a reference light source. This caused great inconvenience in the settings. '
d} Purpose of the Invention The present invention aims to improve the isotope separation efficiency by providing an infrared light source and its control system suitable for isotope separation using Caesar in view of the above-mentioned conventional situation. It is something to do.

'e} Structure of the Invention Briefly stated, the present invention provides that by using a lead chalcogen semiconductor diode laser, it is possible to easily achieve an oscillation wavelength of 16 wavelengths that matches the absorption wavelength of UF6, and to reduce the current or element temperature. This is based on the knowledge that the wavelength can be precisely adjusted through control.

Therefore, the first feature of the present invention is that the infrared light source for isotope separation is composed of a wavelength-tunable lead chalcogen-based semiconductor diode laser, and that the isotope is selectively excited by laser light irradiation from the light source. A means for monitoring the amount of separation is provided to control the oscillation wavelength of the diode laser so that the separation rate is maximized. The second feature of this invention is that a gas cell containing isotopes to be separated is provided, a portion of the laser light from the diode laser is introduced, the transmitted light is detected, and the laser light is absorbed within the gas cell. The oscillation wavelength of the diode laser is controlled so that the amount of light is maximized. In this case, although the output power of a single diode laser is insufficient for isotope excitation, the output power of multiple diode lasers may be combined or a CF4 TEA laser may be used to amplify the infrared light from the diode laser. In this way, sufficient power can be obtained for isotope excitation. M Embodiments of the Invention Preferred embodiments of the invention will now be described in more detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a first embodiment of an isotope separation apparatus according to the present invention.

In FIG. 1, the diode laser indicated by the reference numeral 10 is made of a lead chalcogen-based ternary semiconductor such as P-SnTe or PbSnSe, and is mounted on a refrigerator (not shown) and has an infrared wavelength of 16r. oscillates at a wavelength of Since the power of the laser light IR obtained from this diode laser 0 is currently about 1 W, a TEA filled with CF4 (carbon tetrafluoride) gas is used to amplify the laser light.
Required number of stages for laser 1 (only 1 stage is shown in the figure for convenience)
establish. The CF4 TEA laser 11 has a gain distribution G in the wavelength band of 16 wavelengths as shown in Fig. 2a, and this is shown in Fig. 2b, which corresponds to the absorption spectrum J of the isotope shown by the broken line. When excited with the laser light spectrum L from the diode laser 10 as shown, the laser light with the same wavelength is amplified with an amplification factor corresponding to the gain distribution G, and the second
It comes out with a spectrum as shown by - in Figure a.

Here, the amplification factor of the CF4TEA laser is generally determined by the length l
Since it is 5 to 10 times per meter, for example, the length of TE of one enemy is
By cascading three stages of A lasers, it is possible to obtain laser light of 200 W or more.

Furthermore, multiple TEA lasers can be used in parallel or in series as required. The thus amplified high power laser beam 12 is irradiated onto the cooled gas 13 of the UF6.

Figure 3 a and b are phantom 5UF6 and 238UF, respectively.
At a temperature of 295K, the absorption peaks of the two isotopes overlap and selective excitation is impossible, but at temperatures below 6pK, the absorption wavelength changes due to an isotope shift. It can be seen that there is a difference in
As a means of cooling UF6 as an isotopic compound while it is in a gaseous state, the principle of adiabatic expansion as described above is used, and as shown schematically in Figure 1, UF6 in a gaseous state is
6 is ejected from the ejection nozzle 14 into the excitation space together with a carrier gas (for example, an inert gas such as Ne) for preventing liquefaction. As a result, the above-mentioned isotope shift occurs in the gas molecules of UF6, so by matching the wavelength of the laser light to the absorption wavelength of the young 5UF6 to be separated, it is possible to selectively excite only the isotope in question. Become. As described above, pseudo-UF6
After selectively exciting the UF 5 UF and the female UF 6 can be dissociated by irradiating them with ultraviolet rays from the ultra violet light source 15.

In this invention, a mass spectrometer 16 is provided to monitor the amount of pseudo UF5 after the dissociation.

The output signal of this mass spectrometer constitutes a control loop for wavelength control that controls the driving power supply 17 for the semiconductor diode laser 01. That is, lead chalcogen-based infrared semiconductor lasers are tunable, as is well known, and the oscillation wavelength can be changed continuously and accurately by controlling the drive current or element temperature. Therefore, the diode current adjustment circuit 18 is connected to the laser drive source 17.
If the diode current is controlled by the output of the mass spectrometer 16 so that the pseudo UF6 separation rate is always the highest, highly efficient isotope separation can be achieved without the need for wavelength adjustment. Become. The above is an example of monitoring the separation rate of isotopes using the mass spectrometer 16 and stably maintaining the wavelength of the diode laser 10 with its output. by 2 mirror UF
It is also possible to ionize 60, selectively deflect it under the action of an electric or magnetic field, detect it as an ion current, and control the diode current based on the output.

Furthermore, instead of the above-mentioned dissociation method using ultraviolet irradiation in combination, a desired isotope can also be dissociated by multistage excitation with infrared laser light. Next, a second basic embodiment of the invention will be described.

FIG. 4 is a schematic configuration diagram of such an isotope separation device, and is different from the embodiment shown in FIG. 1 in that the wavelength control loop for the diode laser is provided independently of the isotope separation system. is attracting attention. That is, the ternary semiconductor diode laser 10 made of PbSnTe or PbSnSe
is used as an infrared light source, and the laser light is used as a T of CF4 gas.
The configuration of irradiating the cooling gas 13 of the UF6 ejected from the nozzle 14 through the amplification system in which the required number of EA lasers 11 are connected in cascade is the same as in the embodiment shown in FIG. 1, but a gas cell is newly installed behind the diode laser 10. 20 and a photodetecting element 21 for detecting the transmitted light thereof, the laser beam IR' of the same wavelength emitted behind the laser element 10 is transmitted to the gas cell 20.
I am trying to detect it through.

In the gas cell 20, there is a speck 5U as an isotope to be separated.
F6 is flowing in a gaseous state, and therefore, when the oscillation wavelength of the diode laser coincides with the absorption peak wavelength of 5UF6, the output signal of the photodetecting element 21 becomes minimum. The photodetecting element 21 has a configuration of a cooled infrared detector made of a ternary semiconductor such as HgCdTe, and its output signal is processed by an absorption amount calculation/holding circuit 22 and sent to a laser driving power source 17. is applied to the current adjustment circuit 18. If the diode current is automatically adjusted so that the absorption of laser light in the gas cell 20 is always maximized, the most efficient wavelength tuning for isotope selective excitation of UF6 can be obtained. Specifically, the laser current is adjusted to sweep the wavelength, and the absorption characteristic K is calculated from the output of the sensing element at that time to maintain the current at the maximum absorption value. In addition, in the embodiment shown in FIG.
The gas of UF6 is the same gas as the isotope compound to be separated, but in order to control the oscillation wavelength of the laser beam, it is necessary to cool it and give an isotope shift in the same manner as in the separation system.

However, momme 5UF6 has a high condensation temperature, and if simply cooled, it liquefies and cannot maintain its gas state at temperatures below 6K. Therefore, on the side of the monitoring gas cell 20 as well, it is desirable to adopt a configuration in which the gas of 5UF6 is ejected from the ejection nozzle to obtain a cooling state through adiabatic expansion.
In this case, a cell 20 is prepared by further mixing pseudo UF6 with an inert gas such as Ne, and inserting the mixture into the optical path of the laser beam through a compressor.
It is preferable to have a configuration in which the parts are circulated. FIG. 5 is a schematic diagram showing a third embodiment of the isotope separation apparatus according to the present invention, which conceptually belongs to the second embodiment shown in FIG.

In this embodiment of FIG. 5, the diode laser 0
A beam splitter 23 is inserted into the laser light path to split a portion of the laser light, and a monitoring gas cell 20 similar to that shown in FIG. 4 is placed in the branched light path. The light transmitted through the gas cell 20 is detected by the photodetector element 21, and the detection signal is given to the laser drive power source 17 through the absorption curve differential processing circuit 24. In other words, when the current adjustment circuit 18 of the drive power source 17 is controlled to sweep the wavelength of the diode laser 10, the detection output of the photodetector element 21 is
Corresponding to the absorption spectrum of pseudo-UF6 inserted in , it exhibits absorption characteristics as indicated by K in the figure. Then, if this absorption characteristic curve K during wavelength scanning is differentiated with respect to the swept wavelength using the following absorption curve differential processing circuit, a differential curve with a differential output of zero at the maximum absorption value, as shown by K' in the figure, is obtained. can get. Therefore, by adjusting the laser current so as to maintain the wavelength of the laser light at the point where the output of this differential processing circuit becomes zero, it is possible to achieve the most efficient wavelength tuning for selective excitation of the scales 5UF6 to be separated. . In this case as well, gas cell 2
This is the same machine as in the case of Fig. 4, in which the gas in 0 is placed in a near-temperature state equivalent to that of the gas to be separated. (g) Effects of the Invention As is clear from the above description, the present invention uses a wavelength-tunable lead chalcogen semiconductor diode laser as an infrared light source in isotope separation using infrared laser light, and has a high separation efficiency. The key point is to provide an automatic wavelength control loop that maximizes the wavelength.

Thus, according to the present invention, the excitation light source is extremely easy to handle and adjust, and the oscillation wavelength can be precisely and stably matched to the absorption line of the isotope to be separated, thereby significantly improving the separation efficiency. be able to.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a first embodiment of an isotope separation device according to the present invention, and Figs. 2 a and b show the relationship between the gain characteristics of a TEA laser using CF4 gas and the oscillation spectrum of a diode laser. Figures 3a and 3b are diagrams illustrating the isotope shift relationship between SatoshiUF6 and 2$UF6 as uranium isotope compounds, and Figures 4 and 5 are diagrams showing the isotope separation device according to the present invention, respectively. It is a figure showing a schematic structure showing a 2nd and a 3rd example. 10: Semiconductor diode laser, 11: CF4T for amplification
EA laser, 1 2: Excitation laser beam, 13: Isotope compound gas (CF6), 14: Adiabatic expansion nozzle, 15:
Ultraviolet light source, 16: Mass spectrometer, 17: Laser drive power source,
18: current adjustment circuit, 20: gas cell, 21: photodetection element, 22 absorption amount calculation and holding circuit, 23: beam splitter, 24: absorption characteristic differential processing circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. After selectively exciting the isotope by irradiating the gaseous uranium isotope compound with infrared light in the 16 μm band that matches the absorption wavelength of the uranium isotope to be separated, the excited isotope is In the configuration in which the infrared light is separated, the light source of the infrared light is composed of a lead chalcogen-based wavelength tunable semiconductor diode laser, and the infrared light in the 16 μm band is extracted from the semiconductor diode laser into two optical paths, one of which is separated. The infrared light in the optical path is transferred to a T
While irradiating the above uranium isotope compound via an EA laser, a gas cell containing the isotope to be separated is installed in a part of the other infrared optical path, and the amount of laser light absorbed through the gas cell is detected. and means for controlling the emission wavelength of the semiconductor diode laser based on the output of the detection means, and controlling the oscillation wavelength of the diode laser so that the amount of laser light absorbed in the gas cell is maximized. This isotope separation device is characterized by: