JPH05301029A - Separation of isotope - Google Patents

Abstract

PURPOSE:To effectively separate an even mass number isotope and an odd mass number isotope without being affected by the magnitude of the shift of the isotope and the size of a superfine structure. CONSTITUTION:This method for separating an isotope is constituted as follows. An atomic vapor flow is generated by heating a raw material incorporating the even mass number isotope and the odd mass number isotope of the same element. The atomic vapor flow is irradiated with plural pulse laser beams 15, 18 controlled in output. Thereby, level inversion based on an induced Raman adiabatic sweeping process is caused in the even mass number isotope to remove the even mass number isotope from a basic state. Successively, the odd mass number isotope component is ionized and recovered in an electrode by irradiating pulse laser beams consisting of a single wavelength or the combination of plural wavelengths, by which atoms being in a basic state are excited and ionized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an isotope separation method based on an atomic laser method, and in particular, it improves an isotope selective excitation step by a laser beam to obtain an odd mass number isotope and an even mass number isotope. The present invention relates to an isotope separation method capable of surely separating.

[0002]

2. Description of the Related Art For example, natural gadolinium, which is commonly used as a neutron absorber for controlling the reactivity of a nuclear reactor,
Gadolinium 154 (Gd-154), Gadolinium 1
55 (Gd-155), Gadolinium 156 (Gd-1
56), gadolinium 157 (Gd-157), gadolinium 158 (Gd-158), gadolinium 160
It contains a plurality of isotope components such as (Gd-160). Among them, the ones having a large neutron absorption effect are the odd mass number isotopes (Gd-155, Gd-157), and the reactivity control characteristics are improved by using gadolinium enriched with Gd-157 as the neutron absorber. Can be made

Further, natural zirconium which is generally used as a core structural material of a nuclear reactor includes zirconium 90 (Z
r-90), zirconium 91 (Zr-91), zirconium 92 (Zr-92), zirconium 94 (Zr-
94) and other isotopic components are included. Of these, the large neutron absorption effect is due to the odd mass number isotopes (Zr-9
Since it is 1), the characteristics as a nuclear reactor core structural material can be improved by using zirconium with depleted Zr-91 as the core structural material.

In addition to this, the neutron absorption effect is different between the odd mass number isotopes and the even mass number isotopes such as hafnium (Hf) and rhenium (Re), and the even mass number isotopes are concentrated or depleted. There are some examples in which can improve the quality as a reactor material.

Further, when uranium (U) is concentrated, U-23 is separated when U-238 and U-235 are separated.
If 4, U-236 can be separated at the same time, the quality of the product may be further improved.

As an isotope separation technique, development of a laser type isotope separation method, in particular, an isotope separation technique using an atomic laser method has been advanced in recent years.

In the isotope separation method based on the atomic laser method, a raw material is heated in a vacuum by an electron beam to generate an atomic vapor stream, and the atomic vapor stream is irradiated with a laser beam to obtain a specific isotope component. Is selectively excited to be ionized (ionized), and the ionized specific isotope component is collected in the electrode by, for example, an electrical method.

The isotope separation method by the atomic laser method utilizes the difference in the energy levels (isotope shift) between the isotope A and the isotopes B, C, D, ... Only A is selectively excited and ionized, and then collected on the electrode and concentrated.

[0009]

However, even if an attempt is made to perform separation by such an isotope separation method, there is a sufficiently large isotope shift enough to distinguish one particular isotope from the other isotopes. Not necessarily. In addition, the optical absorption resonance line of the odd mass number isotope has a spread called a hyperfine structure, and if the optical absorption resonance line of the even mass number isotope is included in this spread, the conventional isotope shift will occur. Based isotope separation methods may not be effective.

In the conventional isotope separation method, when the isotope shift is small and the specific isotope to be separated cannot be distinguished from others, or the light absorption resonance line of the even mass number isotope is the light absorption resonance line of the odd mass number isotope. It was difficult to separate isotopes when they were included in the hyperfine structure of the.

In view of the above, the present invention can effectively separate even-numbered and odd-numbered mass isotopes regardless of the magnitude of isotope shift and the size of hyperfine structure. It is an object of the present invention to provide a method for separating isotopes.

[0012]

In order to achieve the above object, the isotope separation method according to the present invention is a method of heating a raw material containing an even mass number isotope and an odd mass number isotope of the same element to heat the atomic vapor flow. Is generated and the vapor flow is irradiated with a plurality of pulsed laser beams whose output is controlled, the level inversion of the even mass number isotopes is caused by the stimulated Raman adiabatic sweep process, and the even mass number isotopes are ground state. And then the pulsed laser beam consisting of a combination of single or multiple wavelengths that causes the atom in the ground state to be ionized is excited to excite the odd mass number isotope component and ionized and collected at the electrode. It is a feature.

[0013]

According to the present invention configured as described above, since only the odd mass number isotopes are in the ground state and the even mass number isotopes are not in the ground state, the odd mass number isotopes in the ground state are The odd mass number isotopes and the even mass number isotopes can be separated by ionizing and recovering only the body.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

An isotope separation apparatus used in this isotope separation method will be schematically described with reference to FIG. A raw material (hereinafter, simply referred to as raw material) 1 composed of an odd mass number isotope and an even mass number isotope to be separated is housed in a crucible 2 for evaporation. Next, the electron beam 4 emitted from the electron gun 3 is deflected by an external magnetic field coil (not shown) to evaporate the crucible 2 for evaporation.
The raw material 1 inside is irradiated. Then, the raw material 1 which has been irradiated with the electron beam 4 is heated and evaporated to become the atomic vapor stream 5.

On the other hand, above the evaporation crucible 2, the positive electrodes 6 and the negative electrodes 7 of the strip-shaped plate are alternately arranged, and the photoreactive parts 8 are provided between the electrodes 6 and 7, respectively. First and second stage excitation pulsed laser light for inducing a Raman adiabatic process to a specific even mass number isotope from the laser light irradiation device 9 in the longitudinal direction of the photoreaction part 8, and subsequently the purpose. Of a pulsed laser beam for ionization consisting of a combination of single (in the case of one-step ionization) to plural (in the case of multi-step ionization) wavelengths for exciting the odd mass number isotopes of To do. Then, the odd mass number isotopes are selectively excited to increase their energy levels and ionized into ions.

Further, a voltage is applied between the positive electrode 6 and the negative electrode 7, and an electric field formed thereby adsorbs / recovers ions mainly consisting of odd mass number isotopes on the surface of the negative electrode 7.

The vapor flow mainly consisting of the even mass number isotopes that has passed through the photoreaction part 8 without being ionized is recovered by the vapor deposition plate 11 arranged on the outer edge side of the photoreaction part 8.

As shown in FIG. 2, the pulsed laser light output from the laser light irradiation device 9 is tuned to the optical transition 14 between the ground level 12 and the first excitation level 13 of the even mass number isotope atom. A first-stage excitation pulsed laser light 15 having no frequency spread, and a similar second-stage excitation pulsed laser light 18 tuned to an optical transition 17 between the first excitation level 13 and the second excitation level 16. Consists of.

When the pulse laser beams 15 and 18 are irradiated, the timing is adjusted as shown in FIG. 3, and the first stage excitation is performed at time t ₁ when the output of the second stage excitation pulse laser beam 18 becomes maximum. When the output of the second-stage excitation pulse laser light 18 is being attenuated and the output of the second-stage excitation pulse laser light 18 is being attenuated, the output of the first-stage excitation pulse laser light 15 increases and this process ends at time t _2. To do so.

Subsequent to this, a pulse laser composed of a combination of a single wavelength (in the case of one-step ionization) to a plurality of wavelengths (in the case of multi-step ionization) for exciting the odd mass number isotopes in the ground state to reach the ionization. The separation is completed by irradiating light to excite the target odd mass number isotopes to cause ionization, and electrically collecting the resulting ions of the odd mass number isotopes.

As shown in FIG. 2, the first-stage excitation pulse laser light 15 is activated at time t ₁ when the output of the second-stage excitation pulse laser light 18 is maximized. While the output of 18 is being attenuated, the output of the first-stage excitation pulsed laser light 15 is increased so that this process is completed at time t ₂ . Then, the induced Raman adiabatic sweep process (hereinafter abbreviated as Raman adiabatic process) between times t ₁ and t ₂ is: U. Gaubatz et a
l., J. Chem. Phys., Vol.92, (1990) 5365-5376) occurs between the ground level 12 and the second excitation level 16.

FIG. 4 shows an example of calculation of level inversion by the Raman adiabatic process. In this example, t ₁ = 20 nanoseconds and t ₂ =
40 nanoseconds, ground level 12, first excitation level 13,
The total angular momentum of the second excitation level 16 is 6, 6, 7 respectively.
Was calculated as

In FIG. 4, the second excitation level occupation rate 19 increases and the ground level occupation rate 20 decreases between the times t ₁ and t ₂ . Reference numeral 21 is the first excitation level occupation rate.

The Raman adiabatic process is a resonance process,
In addition, pulsed laser light for inducing the Raman adiabatic process 1
Since Nos. 5 and 18 have no frequency spread, as shown in FIG. 5, the optical resonance absorption line 22 of even mass number isotopes is included in the hyperfine structure of the optical absorption resonance line 23 of odd mass number isotopes. As shown in FIG. 6, even when the optical resonance absorption lines 22 and 23 of each isotope are close to each other, the Raman adiabatic process has a small effect on the isotopes of odd mass numbers, and the population inversion is almost even masses. It will occur only in several isotopes.

In the second stage of isotope separation, the odd-numbered mass isotopes in the ground state are excited, and pulsed laser light composed of a combination of a single wavelength or a plurality of wavelengths is used for ionization. The optical absorption resonance line 23 of several isotopes has the hyperfine structure broadening shown in FIGS. 5 and 6, and since it is necessary to excite or ionize all of them, these pulsed laser lights have frequency components in a wide band. However, the light absorption resonance frequency component of the even mass number isotope which is not desired to be ionized is also mixed. However, most of the even-mass-number isotopes have an inverted distribution and are not already in the ground level. Therefore, most of the even-mass-number isotopes do not react (resonate) with the laser light and reach ionization.

In this way, only the desired odd mass number isotopes are selectively ionized, and the resulting isotope ions are electrically recovered to complete the separation.

When gadnium is used as the raw material 1 and used for separating Gd-157, a gadolinium material having excellent reactivity control characteristics and suitable for a neutron absorbing material can be obtained. Also applied to the separation of Zr-91,
By producing zirconium in which is depleted, it becomes suitable for a core structure material, and the characteristics as a reactor core structure material can be improved.

Further, this isotope separation method is incorporated into the uranium enrichment process by the atomic laser method to prevent adiabatic reversal of U-234 to U-236 prior to the ionization of U-235 to prevent their incorporation into these products. By doing
It is possible to produce high-quality enriched uranium.

[0030]

Since the present invention has the above-mentioned structure,
Even if the isotope shift is small, it is possible to reliably separate even mass number isotopes and odd mass number isotopes.
In principle, separation can be performed using any combination of a large number of optical absorption resonance lines unique to the element. Moreover,
It is easy to use a wavelength band in which the laser device used has a high oscillation efficiency, which can improve the efficiency of separation.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an isotope separation device used in the isotope separation method of the present invention.

FIG. 2 is a diagram showing a relationship between each level of even-numbered mass isotopes and first and second pulsed laser beams when causing level inversion due to Raman adiabatic process.

FIG. 3 is a timing diagram of the output times of the first and second excitation pulsed laser lights.

FIG. 4 is a graph showing a calculation example of a Raman adiabatic process.

FIG. 5 is a graph showing an example of each optical absorption resonance line of an even mass number isotope and an odd mass number isotope.

FIG. 6 is a graph showing another example of the same.

[Explanation of symbols]

 1 Raw Material 3 Electron Gun 4 Electron Beam 5 Atomic Vapor Flow 6,7 Electrode 8 Photoreactive Part 10 Laser Beam 12 Ground Level 13 First Excitation Level 15,18 Laser Beam Light 16 Second Excitation Level 19 Second Excitation Level 19 Occupancy rate 20 Ground level occupation rate 21 First excitation level occupation rate 22 Optical absorption resonance line of even mass number isotopes 23 Optical absorption resonance line of odd mass number isotopes

Claims (1)

[Claims] 1. A raw material containing an even mass number isotope and an odd mass number isotope of the same element is heated to generate an atomic vapor stream,
By irradiating the vapor stream with a plurality of pulse-controlled laser beams whose output is controlled, the even mass number isotopes are caused to undergo level inversion by the stimulated Raman adiabatic sweep process to remove the even mass number isotopes from the ground state, Subsequent isotope characterized by irradiating a pulsed laser beam consisting of a combination of one or more wavelengths that excites atoms in the ground state to cause ionization and ionizes odd mass number isotope components and collects them at electrodes. Body separation method.