JP3360165B2 - An efficient laser isotope separation and enrichment method for multiple isotopes using the same working substance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser isotope separation / concentration based on infrared multiphoton decomposition of a working material containing a plurality of isotopes, by sequentially changing the irradiation conditions of laser light.
The present invention relates to a laser isotope separation and concentration method for highly enriching a specific isotope in a product and a working material, respectively.

[0002]

2. Description of the Related Art A large amount of isotopes have been used mainly in nuclear power, but recently the use of stable isotopes without radioactivity has spread to various fields including medicine, and the importance of isotopes has been increasing. Sex is increasing more and more.

[0003] On the other hand, isotope separation / concentration has been achieved by repeating statistically huge number of times such as distillation, chemical exchange, diffusion, centrifugation, etc., focusing on the slight difference in the properties of isotopes. Inevitably, the equipment is large and cannot be easily implemented.

[0004] Recent advances in laser technology have made it possible to selectively separate and concentrate isotopes by optical means. One of the methods is infrared multiphoton decomposition of polyatomic molecules. Based on this method, separation and concentration of isotopes such as hydrogen, carbon, oxygen, silicon, and sulfur have been attempted. In particular, the separation and enrichment of carbon and silicon isotopes have attracted attention from a practical point of view. It is considered that laser isotope separation can be performed relatively easily with a small apparatus because the selectivity in one step is very high as compared with the isotope separation by the conventional method.

[0005] Infrared multiphoton decomposition refers to the decomposition of molecules observed near the focal point when low-pressure gas molecules are irradiated with pulsed light of a high-output infrared laser through a lens. Here, the gas molecules need to have infrared absorption near the wavelength of the laser light. Near the focal point, the fluence of the laser light, that is, the energy of the laser pulse per unit area is very high, so that the molecules absorb a large number of photons during the pulse and increase the internal energy to cause decomposition.

The atmospheric pressure lateral discharge excitation type carbon dioxide laser is a widely used high-output infrared pulse laser, and the pulse width is usually within several microseconds and the energy reaches several joules. The oscillation lines are numerous in the wavelength range of 9 to 11 μm, and each wavelength is unique, but it is manufactured so that each oscillation line oscillates independently. Will be.

In infrared multiphoton decomposition, it has been found that, at an appropriate wavelength, a molecule containing a specific isotope selectively absorbs light and decomposes, reflecting an isotope shift in infrared absorption. ing. As a result, specific isotopes are enriched in the decomposition products. This is the fundamental principle of isotope separation / concentration based on infrared multiphoton decomposition.

In the isotope effect on infrared absorption, heavier isotope absorption is observed at longer wavelengths. When investigating the relationship between infrared absorption, molecular vibration, chemical bond, isotope, etc. of a chemical substance, for example, absorption due to stretching vibration of CF bond is 1
At around 100 cm ⁻¹ , the absorption due to stretching vibration of Si—F is at around 1000 cm ⁻¹ , and the isotope shift between ¹² C and ¹³ C is about 25 cm ⁻¹ , between ²⁸ Si, ²⁹ Si and ³⁰ Si. The isotope shift is about 9 cm ^-1 . A normal infrared absorption spectrum corresponds to a case where a molecule absorbs one photon, and is different from a case where a molecule absorbs many photons so as to cause infrared multiphoton decomposition. However, multiphoton absorption is 1
Starting from photon absorption, it is believed that there is a strong relationship between selectivity in decomposition and isotope shifts in normal infrared absorption spectra.

[0009] From the practical point of view, when trying to separate and concentrate laser isotopes based on infrared multiphoton decomposition, it is most important to find a working material with high selectivity and good yield. Previous research and others (S. Arai, K. Sugit
a, P. Ma, Y .; Ishikawa, H .; Kaets
u, andchem. Phys. Lett. , 112,2
24 (1988); Arai, K .; Sugita,
P. Ma, Y .; tsu, and S.M. Isomura,
Appl. Phys. , B48, 427 (1989);
M. Kamioka, Y .; Ishikawa, H .; Ka
etsu, S .; Isomura, and S.M. Ara
i. Phys. Chem. , 90, 5727 (19
86); Patent Publication H3-31489, Patent Publication H2-5
6133), carbon isotopes ¹² C and ¹³ C
CHClF ₂ , CHBrF ₂ etc.
Silicon isotopes ²⁸ Si, ²⁹ Si and ³⁰ Si
It has been found that Si ₂ F ₆ is very promising and suitable as a working substance for the separation and concentration of.

The isotope abundance ratio in so-called natural carbon is ¹² C: ¹³ C = 98.9: 1.1. When gaseous CHClF ₂ and CHBrF ₂ are condensed and irradiated with pulsed light of a carbon dioxide gas laser having a wavenumber range of 1030 to 1060 cm ^{−1 so} that the fluence at the focal point is in a range of ² to 20 Jcm ⁻² , isotopes are obtained. Causing selective infrared multiphoton decomposition,

According to the formula, C ₂ F ₄ and HCl or HBr are produced. Here, X represents Cl or Br, and n represents the number of photons absorbed in one molecule.

For example, when CHClF ₂ of 50 Torr is irradiated with pulsed light of a carbon dioxide laser having a wave number of 1045.02 cm ⁻¹ and a fluence of 4.5 Jcm ⁻² at the focal point, ¹³ C is generated in C ₂ F ₄ generated. It is concentrated to close to 50%.

[0012] The presence ratio of the isotopes in the silicon of the so-called natural ^{28 Si: 29 Si: 30 Si} = 92.23:
4.67: 3.10. A carbon dioxide gas laser of 940 to 960 cm is applied to a gas of Si ₂ F ₆ of 10 Torr or less.
The pulse light in the wave number region of ^-1 has a fluence of 1 at the focal point.
When condensed and irradiated so as to be 0 Jcm ⁻² or less, isotope-selective infrared multiphoton decomposition occurs,

According to the formula, SiF ₂ and SiF ₄ are produced. Many SiF ₂ undergo a polymerization reaction to produce a white solid.

For example, 2.0 Torr Si ₂ F ₆
When a pulse number of a carbon dioxide gas laser having a wave number of 951.19 cm ^-1 and a fluence of 0.25 Jcm ^-2 at the focal point is irradiated, about 10% of ²⁹ Si is generated in generated SiF ₄ ,
It has been found that ³⁰ Si is enriched to about 50%.

[0014]

As described above, in the practical laser separation / concentration of carbon isotopes ¹² C and ¹³ C based on infrared multiphoton decomposition, the working material is CHCl.
For practical laser separation / concentration of fluorocarbon compounds such as F ₂ and CHBrF ₂ and silicon isotopes ²⁸ Si, ²⁹ Si and ³⁰ Si, Si ₂ F ₆ has been proposed as a working material. After separation and concentration of ¹³ C in the product C ₂ F ₄ based on infrared multiphoton decomposition of these working materials,
²⁹ Si and ³⁰ Si, especially ³⁰ Si, in SiF ₄
After separation and concentration of Si, these ¹³ C and ³⁰ Si
A large amount of undecomposed working material remains.

Previously, we enriched ¹³ C in the product CBr ₂ F ₂ with an isotope-selective infrared multiphoton decomposition of carbon in the CHClF ₂ plus Br ₂ system, followed by this CBr ₂ F ₂ It has been found that isotope-selective infrared multiphoton decomposition with respect to carbon in a system obtained by adding O ₂ to a solution can enrich ¹³ C in the product CF ₂ O to 90% or more. Also a large amount of undecomposed work material CH deficient in ^13C
ClF ₂ remains.

The simple disposal of undecomposed working substances often leads to environmental problems. For example, the disposal of CFC compounds may destroy the ozone layer, and the release of fluorinated silane generates harmful HF by reaction with moisture in the air. Therefore, it is desirable to effectively utilize undecomposed work materials as much as possible.

On the other hand, high-purity ¹² C is used as a solvent in NMR measurement and is a very high value-added substance. High-purity ²⁸ Si crystal is a substance that has been eagerly desired in the field of research on physical properties. is there. The present invention provides a method of effectively utilizing a decomposed work material in a work material containing a plurality of isotopes, that is, recovering an undecomposed work material, and irradiating a laser by changing irradiation conditions from the beginning, This is a method of enriching another isotope in the working material remaining without being decomposed.

[0018]

In the isotope-selective infrared multiphoton decomposition of a working material containing a plurality of isotopes, the optimum experimental conditions for the separation and concentration of each isotope are different. That is, isotope selectivity and yield are complex functions such as working material pressure, laser light wavelength and fluence, and the peak wavelength of infrared multiphoton absorption of molecules containing each isotope is determined by the isotope shift It is expected to be different to reflect this. Therefore, utilizing this difference, first, a specific isotope is irradiated with a laser under optimal conditions in consideration of selectivity and yield, and is separated and concentrated in a product. The product and undecomposed working material are then separated by chemical engineering means, for example, distillation, chromatography and the like. Thereafter, using undecomposed working material, laser irradiation is performed under different irradiation conditions from the first, for example, at a different wavelength, fluence, pressure, etc., and a specific isotope different from the first is highly concentrated in the remaining working material. I thought about the way.

The present invention is generally applicable to isotope separation / concentration based on isotope-selective infrared multiphoton decomposition of a working material containing a plurality of isotopes, such as boron, carbon, nitrogen, and the like. It can also be applied to the separation and concentration of isotopes such as oxygen, silicon, sulfur and chlorine.

[0020]

DETAILED DESCRIPTION OF THE INVENTION The present invention is capable widely applied to the laser separation and concentration of isotopes, carbon isotopes ^{12 C} and
It is demonstrated using ¹³ C and separation and concentration of silicon isotopes ²⁸ Si, ²⁹ Si and ³⁰ Si.

For the separation and concentration of carbon isotopes, CHBrF
₂ was used as a working material, and Si ₂ F ₆ was used as a working material for separation and concentration of silicon isotopes. An outline of the experimental apparatus used in the present invention is shown in the figure. First, the working substance was collected from the sample supply device into the reaction vessel at a predetermined pressure, and then pulsed light of a predetermined wavelength of a carbon dioxide laser was condensed by a lens and irradiated to the working substance in the irradiation vessel. The pulse energy was adjusted using a filter or the like as needed. As a result, the fluence at the focal point can be set to a predetermined value. After irradiation with a predetermined number of pulses, the entire irradiation sample was transferred to an irradiation sample separation device, and separated into a product and an undecomposed work material mainly by low-temperature distillation. Here, the undecomposed work material was returned to the sample supply device and stored, and used for subsequent experiments. In addition, a certain percentage of the product and the end decomposition work material was analyzed by a gas chromatograph mass spectrometer, and the composition of the isotope therein was measured.

[0022]

Example 1 According to the natural isotope abundance ratio, ¹² C and
CHBrF ₂ containing ¹³ C, 20.5 Torr, wave number 1
A pulsed light of a carbon dioxide gas laser of 045.02 cm ^-1 was condensed such that the fluence at the focal point was 4 Jcm ^-2, and irradiation was carried out for 1000 pulses. In the product C ₂ F ₄
¹³ C was highly concentrated from 1.1% before irradiation to 31%. On the other hand, the concentration of ¹³ C in a large amount of undecomposed CHBrF ₂ was reduced to 0.9%. The production amount of C ₂ F ₄ is 1.03
μmol, the amount of undegraded CHBrF ₂ is 240 μmol
Met. The same experiment was repeated until the concentration of ¹³ C was 0.1.
A large amount of the 9% reduced CHBrF ₂ was recovered and used in subsequent examples.

10 Torr of the above undecomposed CHBrF ₂
Then, a pulsed light of a carbon dioxide gas laser having a wave number of 1045.02 cm ^-1 was condensed so that the fluence at the focal point became 11 Jcm ^-2 , and 500 pulses were irradiated. Here, about 73% of CHBrF ₂ remains without being decomposed as compared to before irradiation,
The concentration of ¹² C was highly concentrated to 99.8%. on the other hand,
The concentration of ¹³ C dropped to 0.2%.

[0024]

Example 2 10 Torr of the above undecomposed CHBrF ₂
Then, pulse light of a carbon dioxide gas laser having a wave number of 1052.50 cm ^-1 was condensed so that the fluence at the focal point was 5.7 Jcm ^-2 , and 1500 pulses were irradiated. Here, compared to before irradiation, about 76% of CHBrF ₂ remained without decomposition, and the concentration of ¹² C was highly concentrated to 99.9%. On the other hand, the concentration of ¹³ C decreased to 0.1%.

[0025]

Example 3 10 Torr of the above undecomposed CHBrF ₂
Then, a pulsed light of a carbon dioxide gas laser having a wave number of 1074.65 cm ^-1 was condensed so that the fluence at the focal point became 6.2 Jcm ^-2, and irradiated with 200 pulses. Although the decomposition proceeded vigorously, about 54% of CH was compared with that before irradiation.
BrF ₂ remained without decomposition. The concentration of ¹² C therein was almost 100%, and ¹³ C was not detected.

[0026]

Example 4 According to the natural isotope abundance ratio, ²⁸ Si, ²⁹
Si ₂ F ₆ 2.5 Torr containing Si and ³⁰ Si
Then, pulsed light of a carbon dioxide gas laser of 951.20 cm ^-1 was condensed so that the fluence at the focal point was about 2.0 Jcm ^-2 , and 3000 pulses were irradiated. Product SiF ₄
Isotopic ratio in the ^{28 Si: 29 Si: 30 Si} = 58:
At 9:33, ³⁰ Si was highly concentrated. On the other hand, the isotope ratio in undecomposed Si ₂ F ₆ is ²⁸ Si: ²⁹ Si:
³⁰ Si = 93: 5: 2. The same experiment was repeated, and a large amount of Si ₂ F ₆ containing 93% of ²⁸ Si was recovered and used in the following examples.

2.0 Torr of the undecomposed Si ₂ F ₆
Then, a pulsed light of a carbon dioxide gas laser having a wave number of 954.56 cm ^-1 was condensed so that the fluence at the focal point was 2.5 Jcm ^-2 , and 4,000 pulses were irradiated. Here, about 64% of Si ₂ F ₆ remains without being decomposed as compared with before irradiation,
The concentration of ²⁸ Si was concentrated to 99.2%.

[0028]

Example 5 2.0 Torr of the above undecomposed Si ₂ F ₆
A pulsed light of a carbon dioxide gas laser having a wave number of 954.56 cm ^-1 was condensed so that the fluence at the focal point became 2.6 Jcm ^-2 , and 6,000 pulses were irradiated. Here, about 40% of Si ₂ F ₆ remains without being decomposed as compared to before irradiation,
The concentration of ²⁸ Si was concentrated to approximately 100%.

[0029]

Although the laser isotope separation has a very high selectivity in one operation step, it is still not easy to economically separate and concentrate the isotopes. The present invention proposes and demonstrates a method for highly enriching at least two types of isotopes from the same working material.Each isotope is effectively used in various fields, and not only generates value but also improves efficiency. It plays a major role in lowering the cost of isotopes through the utilization of working materials.

Further, even when working materials that may cause a problem in the working environment or the natural environment when they are released or discarded into the environment, the working materials are completely utilized, so that there is no need to release or discard them in the first place.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an experimental apparatus used to carry out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Carbon dioxide laser 2 Lens 3 Irradiation container 4 Power meter 5 Sample supply device 6 Irradiation sample separation device 7 Gas chromatograph mass spectrometer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-56-91828 (JP, A) JP-A-6-296828 (JP, A) JP-A-9-131515 (JP, A) JP-A 60-91828 132629 (JP, A) JP-A-4-300633 (JP, A) JP-A-63-97217 (JP, A) JP-A-62-45327 (JP, A) JP-A-63-289224 (JP, A) JP-A-63-242326 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 59/00-59/50

Claims (3)

(57) [Claims] Claims: 1. In the separation and enrichment of isotopes based on infrared multiphoton decomposition in a suitable working material containing two or more isotopes, with or without additives, first the appropriate conditions Irradiates the working material with a laser light to form a product enriched in a specific isotope and separates it from the working material, and then irradiates the working material with laser light of different appropriate conditions to identify Of multiple isotopes using the same working material, further forming a product enriched with the same isotope and enriching another isotope in the remaining working material by separating it from the working material Laser isotope separation and concentration method. 2. The method according to claim 1, wherein the working material is ¹² C and ¹³
CHClF ₂ or CH containing C in the natural isotopic abundance
BrF ₂ , which is first irradiated with laser light of appropriate conditions to the working material to form a ¹³ C-enriched product and to separate it from the working material, which is then different to the working material ^{13 C} is irradiated with laser light conditions are concentrated ^{respectively 12 C} working substance in which this was left by the separation from the working substance with further forming a product enriched, laser according to claim 1 Isotope separation and enrichment method. 3. The method according to claim 1, wherein the working material is ²⁸ Si, ²⁹ S
Si ₂ F containing i and ³⁰ Si in a natural isotope abundance ratio
₆ , first irradiating the working material with a laser beam of appropriate conditions to form a product enriched in ²⁹ Si and ³⁰ Si and to separate it from the working material, Irradiation of laser light under appropriate conditions further forms a product enriched in ²⁹ Si and ³⁰ Si, and enriches ²⁸ Si in the remaining working material by separating it from the working material. 2. The method for separating and concentrating a laser isotope according to item 1.