JPH0314491B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for concentrating carbon-13 using a laser, and more particularly to a method for concentrating carbon-13 by laser isotope separation using infrared multiphoton dissociation. In recent years, advances in laser technology have been remarkable.
Lasers that emit powerful light over a wide wavelength range have been developed. Research into using these lasers for photochemical reactions is also very active, and progress is literally being made every day. The first characteristic of laser light is that it exhibits excellent monochromaticity, and the second is that extremely high fluence of light can be obtained. Conventionally, various isotope separations have been attempted using these characteristics. For example, attempts have been made to utilize the first characteristic to separate isotopes of various elements ranging from hydrogen to uranium. That is, although some isotopic shifts are generally observed in the absorption spectra of isotopic compounds, when irradiated with laser light of an appropriate wavelength, specific isotopic compounds selectively absorb the light and are excited. Furthermore, by utilizing the second feature, which is the high fluence of laser light, it is possible to cause the same molecule to absorb many laser photons and induce decomposition. By the way, in isotope separation using infrared multiphoton dissociation, based on the characteristics of laser light, a specific isotopic compound is excited by multiple photons by irradiation with strong laser light in the infrared region where the isotope shift is large. It can be dissociated and its isotopes separated. An object of the present invention is to provide a method for concentrating carbon-13 in an isotope compound to a high concentration by laser isotope separation using infrared multiphoton dissociation. This object is achieved by the configuration of the present invention as set forth in the claims, which will be described in detail below. First, the first invention will be explained. ¹² CF ₃ ¹² CF ₃ or hexafluoroethane C ₂ F ₆ consisting of two carbon-12 isotopes is 1117 cm ^-1
It has strong absorption corresponding to the stretching vibration of CF bond,
The tail of this absorption extends to the oscillation region of carbon dioxide laser (900 to 1100 cm ^-1 ). The absorption of ¹³ CF ₃ ¹² CF ₃ exists on the lower wavenumber side than the absorption of ¹² CF ₃ ¹² CF ₃ , and is thought to selectively absorb the light of the carbon dioxide laser. Therefore, when the natural isotope concentration of C ₂ F ₆ (abundance ratio of carbon 13 is 1.1%) is irradiated with pulsed light from a carbon dioxide laser, ¹³ CF ₃ ¹² CF ₃ is selectively absorbed through so-called infrared multiphoton absorption. Excited and causes decomposition. ¹³ CF ₃ ¹² CF ₃ +nhν→ ¹³ CF ₃ + ¹² _CF If a halogen molecule such as Cl ₂ , Br ₂ or I ₂ is added to C ₂ F ₆ in advance, the following reaction results in CF ₃ Cl , CF ₃ Br or CF ₃ I is generated. ¹³ CF ₃ ¹² CF ₃ +X ₂ +nhν → ¹³ CF ₃ X+ ¹² CF ₃ X Here, X ₂ represents Cl ₂ , Br ₂ or I ₂ . ¹³ CF ₃ is concentrated in the product CF ₃ X, reflecting the selectivity in the multiphoton absorption process. For example, when a mixture of natural isotope-concentrated C ₂ F ₆ and Br ₂ is irradiated with pulsed light from a carbon dioxide laser, focused with a BaF ₂ lens, carbon-13 becomes concentrated.
CF ₃ Br is produced. Using the R(30) line of the 9.6 μm band of the carbon dioxide laser, the concentration factor β is
It reaches about 10. Here, the enrichment coefficient β is defined as follows. β = ratio of ¹³ C to ¹² C in the product CF ₃ Br / ratio of 13 ^C to ¹² C in the natural isotope concentration CF ₃ Br The concentration of ¹³ C in the natural isotope concentration CF ₃ Br is 1.1
%. We also conducted experiments with laser irradiation at low temperatures, and in this case β increased significantly, reaching 17. Next, the second invention will be explained as follows. CF ₃ Cl, CF ₃ Br, and CF ₃ I have long been attracting attention as working substances in the concentration and separation of carbon-13 by infrared multiphoton dissociation using a carbon dioxide laser. Infrared multiphoton dissociation of these compounds proceeds as follows, and carbon-13 is concentrated in _the product _C2F6 . _{CF 3 _ _} An example is -110℃
The concentration factor β reaches as high as 400. Here β is 400
means that the concentration of ¹³ C in C ₂ F ₆ is about 80%. It is desirable that the carbon-13 concentration in the carbon compound used as a tracer is high. If we were to concentrate it to 95%, a single laser irradiation would not be enough. Therefore, the following cycle using C ₂ F ₆ as a starting material is an effective and appropriate method for concentrating carbon-13 at a high concentration.

[Table] In other words, a gas mixture of C ₂ F ₆ and X ₂ is irradiated with laser under appropriate _conditions to produce CF ₃ After separation using a separation method such as gas chromatography or low-temperature distillation, laser irradiation is performed to produce C ₂ F ₆ in which ¹³ C is highly concentrated.
If a very high concentration of carbon-13 is required, laser irradiation and product separation may be performed again according to this cycle. Note that ¹³ C in the product is
When concentrated by 50% or more, it is also advantageous to selectively dissociate carbon-12-containing CF ₃ X by appropriately changing the wave number of the laser pulse. Infrared multiphoton dissociation of a gas mixture of C ₂ F ₆ and Br ₂ produces CF ₃ Br enriched in carbon-13 with β=10. If this CF ₃ Br is subjected to infrared multiphoton dissociation at an even lower temperature, if β = 200, carbon 13
When is concentrated, the carbon in the product C ₂ F ₆
The concentration of 13 reaches 95%. EXAMPLE FIG. 1 shows an outline of the apparatus used in the present invention.
Pulse light 2 of carbon dioxide laser 1 with appropriate wave number
The light is focused by a BaF ₂ lens 3 and irradiated onto a sample gas 6 which is a mixed gas of C ₂ F ₆ and Br ₂ in a reaction vessel 5 placed in a constant temperature bath 4 . The temperature of the constant temperature bath is −
Can be varied up to about 150℃. In the figure, 7 is a temperature sensor, 8 is an aperture, and 9 is a KBr window plate. After irradiation, the reaction product was separated by gas chromatography and immediately introduced into a mass spectrometer to determine the abundance ratio of carbon-13. C ₂ F ₆ with a natural isotope concentration of 2.0 Torr and 5.0 Torr
The infrared absorption spectrum of the gas mixture with Br ₂ is shown in Part 2a.
As shown in the figure. The absorption that shows a maximum at 1117 cm ^-1 is mainly due to
¹² CF ₃ Caused by ¹² CF ₃ . The carbon dioxide laser's R(30) in the 9.6 μm band, that is, 1085 cm, is applied to this gas mixture.
The infrared absorption spectrum measured after irradiation with ^-1 pulsed light is shown in Figure 2b. The pulse energy is
0.1J/pulse, focal length of lens 3 used is 20
cm. The absorptions at 1080 and 1200 cm ^-1 in the spectrum corresponded to CF ₃ Br, which was confirmed to be the product. On the other hand, the production of CF ₃ Br was also confirmed by gas chromatography analysis. Concentration factor β of carbon-13 for the product CF ₃ Br observed when a gas mixture of 2.0 Torr C ₂ F ₆ and 5.0 Torr Br ₂ is irradiated with pulsed light from a carbon dioxide laser
Figure 3 shows the relationship between the wave number of the laser beam and the wave number of the laser beam. The energy of the laser pulse at each wavenumber is approximately 0.1J/
I adjusted it to pulse and used a lens with a focal length of 20cm. The irradiation temperature was room temperature, but some results at lower temperatures were also included. β increases as the wavenumber increases. From the above results, it is clear that CF ₃ Br enriched in carbon-13 is generated by infrared multiphoton dissociation of a mixed gas of C ₂ F ₆ and Br ₂ . Next, FIG. 4 shows the relationship between β for the product C ₂ F ₆ in infrared multiphoton dissociation of CF ₃ Br, the pressure of CF ₃ Br, and the irradiation temperature. The wave number of the laser pulse was adjusted to 1045 ^-1 cm ^-1 and the pulse energy was adjusted to 0.3 J/pulse. Infrared multiphoton dissociation of CF ₃ Br significantly enriches carbon-13, resulting in C ₂ F ₆ and Br ₂
It is understood that C ₂ F ₆ containing a high concentration of carbon-13 can be produced by combining it with infrared multiphoton dissociation of a gas mixture of It is also understood that the higher the infrared multiphoton dissociation is at a lower temperature, the higher the concentration coefficient β becomes, and the higher the concentration of carbon-13 is concentrated.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the concentrator used in the example of the present invention, and Figures 2a and 2b show the infrared rays of the C ₂ F ₆ -Br ₂ system obtained in the example of the present invention before and after laser irradiation. The absorption spectrum is shown. FIG. 3 is a graph showing the wave number dependence of the enrichment coefficient β in the C ₂ F ₆ -Br ₂ system obtained in the example of the present invention, and _FIG . Graph showing the relationship between concentration coefficient β, pressure, and irradiation temperature. Codes in the diagram: 1... Carbon dioxide laser, 2...
Laser light, 4... Constant temperature bath, 5... Reaction container, 6
...Sample gas.

Claims (1)

[Claims] 1 Hexafluoroethane C ₂ F ₆ and halogen molecule
A method for concentrating carbon-13, which comprises concentrating carbon-13 by irradiating a gas mixture with _X2 with a carbon dioxide laser. 2. The method for concentrating carbon-13 according to claim 1, wherein the halogen molecule X ₂ is Cl ₂ , Br ₂ , or I ₂ . 3 Hexafluoroethane C ₂ F ₆ and halogen molecules
A gas mixture with X ₂ is irradiated with a carbon dioxide laser to produce halogenated methane CF ₃ A method for cyclic enrichment of carbon-13, characterized in that it produces hexafluoroethane enriched in 4. The method for concentrating carbon-13 according to claim 3, wherein the halogen molecule X ₂ is Cl ₂ , Br ₂ or I ₂ .