Isotope enrichment and separation method

Abstract

Provided is an isotope enrichment and separation method for concentrating and separating an isotopic element efficiently and at low cost even when the element has no gas compound. According to this isotope enrichment and separation method, with which a target isotope is concentrated and separated from an element in which different isotopes are present: an aqueous solution of an element compound in which different isotopes are present is prepared and then set in a centrifugal separator; a centrifugal force of the centrifugal separator is caused to act on the aqueous solution to cause the isotopes in the aqueous solution to migrate so as to change the concentration distribution of the isotopes in the aqueous solution in a gradual manner; and the aqueous solution located at the position of the desired isotope in the concentration distribution is separated out to perform concentration and separation of the target isotope.

Description

Isotope enrichment and separation method

[0001] The present invention relates to a method for enriching and separating isotopes, and more particularly to a method for enriching and separating isotopes by centrifugal separation from an aqueous solution of an element containing a mixture of the isotopes.

[0002] The majority of naturally occurring elements have multiple isotopes, and these isotopes can be separated and enriched to serve as tracers, medical testing reagents, and raw materials for nuclear fuel.

[0003] The effective methods for enriching and separating isotopes vary depending on the element, so research and development is being conducted individually to find enrichment and separation methods suitable for each element.

[0004] The most commonly used method for isotope enrichment and separation at present is the method using a centrifuge. For example, this method is used to enrich uranium for nuclear fuel, and because it is cost-effective, it is also used to separate isotopes of other elements.

[0005] This method of enrichment and separation by centrifugation is applied to gases, and can be said to be an effective method for elements that are gaseous in their simple form. On the other hand, for elements that are not gaseous in their simple form, gaseous compounds have been sought, and centrifugation has been applied to the discovered gaseous compounds. For example, the discovery of the gaseous compound uranium hexafluoride made it possible to enrich and separate uranium by centrifugation (see, for example, Patent Document 1). However, many of these gaseous compounds require careful handling, for example, due to their corrosive properties.

[0006] On the other hand, there are elements that do not exist as gaseous compounds. For such elements, mass spectrometry has traditionally been applied as a reliable method for enrichment and separation. This method accelerates ionized elements in a vacuum with an electric field, and utilizes the fact that the curvature of the magnetic field varies depending on the mass. This method can reliably enrich and separate elements, but because it requires a large amount of electricity, the separated isotopes are expensive and not cost-effective.

[0007] Therefore, a technique has been developed for concentrating and separating isotopes by applying centrifugation to a condensed phase consisting of a solid or liquid phase (see, for example, Patent Document 2).

[0008] JP 53-60495 A JP 2007-275725 A

[0009] However, in the case of the above-mentioned centrifugation targeting the condensed phase, although it is possible to increase the density compared to gas and increase the throughput, depending on the substance, a large acceleration field of 1 million g (g: gravitational acceleration) or more is required, and during separation, the rotor rotating at high speed and the isotopic material must be controlled to a temperature suitable for separation, for example, a temperature above the recrystallization temperature of the target material in the case of a solid phase, or a temperature above the melting point in the case of a liquid phase. Therefore, the concentration and separation device is unavoidably complex and expensive.

[0010] Therefore, an object of the present invention is to provide a method for enriching and separating isotopes that can enrich and separate isotopes of elements inexpensively and efficiently, even for elements that do not have gaseous compounds.

[0011] The present inventors have conducted extensive research into solving the above problems and have found that the above problems can be solved by the invention described below, thereby completing the present invention.

[0012] The invention described in claim 1 is a method for enriching and separating isotopes, which enriches and separates a target isotope from an element containing mixed isotopes, comprising the steps of: preparing an aqueous solution of an elemental compound containing mixed isotopes, setting the aqueous solution in a centrifuge; applying centrifugal force from the centrifuge to the aqueous solution to cause the isotopes in the aqueous solution to migrate, thereby gradually changing the concentration distribution of the isotopes in the aqueous solution; and collecting an aqueous solution at a point where the concentration distribution of the desired isotope is found, thereby enriching and separating the target isotope.

[0013] The invention described in claim 2 is the method for enriching and separating isotopes described in claim 1, characterized in that the elemental compound containing mixed isotopes is a compound that undergoes ion separation in an aqueous solution.

[0014] The invention described in claim 3 is the method for enriching and separating isotopes described in claim 2, characterized in that the compound that dissociates into ions in the aqueous solution is any one of a hydroxide, a halide, and a metal salt.

[0015] The invention described in claim 4 is the method for enriching and separating isotopes described in claim 1, characterized in that the centrifugal acceleration G that generates the centrifugal force is 200,000 times or more the acceleration of gravity g.

[0016] The invention described in claim 5 is the method for enriching and separating isotopes described in claim 1, characterized in that the product (Gr) of the centrifugal acceleration G [unit: g (acceleration of gravity)] that generates the centrifugal force and the radial distance r (unit: m) is 20,000 (unit: gm) or more.

[0017] The invention described in claim 6 is the method for enriching and separating isotopes described in any one of claims 1 to 5, characterized in that the centrifugal force is generated using a swing rotor of a centrifuge.

[0018] A seventh aspect of the present invention is the method for enriching and separating isotopes according to any one of the first to fifth aspects, characterized in that the centrifugal force is generated using an angle rotor of a centrifuge.

[0019] The invention described in claim 8 is the method for enriching and separating isotopes according to claim 7, characterized in that the angle of inclination of the angle rotor with respect to the centrifugal direction of the centrifuge tube is 20 to 40 degrees.

[0020] A ninth aspect of the present invention is the method for enriching and separating isotopes according to any one of the first to fifth aspects, characterized in that the centrifugal force is set in advance by simulation.

[0021] The invention described in claim 10 is the method for enriching and separating isotopes described in claim 9, characterized in that the simulation is a simulation in which the magnitude of acceleration, the time for applying the acceleration field, and the distance are used as parameters, and the centrifugal force is set based on the separation coefficients of each isotope calculated by the simulation.

[0022] An eleventh aspect of the present invention is the method for enriching and separating isotopes according to the ninth aspect, characterized in that the simulation is performed using a Monte Carlo (MC) method.

[0023] The invention described in claim 12 is the method for enriching and separating isotopes according to claim 9, characterized in that the simulation is performed using a finite element method.

[0024] The invention according to claim 13 is characterized in that the isotope is: ４８ 6. The method for enriching and separating an isotope according to claim 1, wherein the isotope is Ca.

[0025] According to the present invention, it is possible to provide a method for enriching and separating isotopes that can enrich and separate isotopes of elements inexpensively and efficiently, even for elements that do not have gaseous compounds.

[0026] The rotation speed in a thermal equilibrium state when centrifugal force is applied to an aqueous solution of Ca by a swing rotor. ４０ Ca and ４８ 1 is a graph showing an example of the relationship between the isotope ratio IR of Ca and the rotation speed in a thermal equilibrium state when centrifugal force is applied to an aqueous solution of Ca by an angle rotor. ４０ Ca and ４８ 1 is a diagram showing an example of the relationship between the isotope ratio IR of Ca and the product (Gr) of the centrifugal acceleration and the radius in the centrifugal direction in a thermal equilibrium state when centrifugal force is applied to an aqueous solution of Ca by a swing rotor and an angle rotor. ４０ Ca and ４８ This is a diagram showing the relationship between the isotope ratio IR and Ca. When a centrifugal force from a swing rotor is applied to an aqueous solution of Ca for 25 hours, ４８ This is a diagram showing the concentration distribution of Ca when a centrifugal force from a swing rotor is applied to an aqueous solution of Ca for 25 hours. ４８ Ca and ４３ This is a diagram showing the distribution of Ca isotope ratio IR. When a Ca aqueous solution was subjected to centrifugal force by a swing rotor for 3 days, ４８ 1 is a diagram showing the concentration distribution of Ca when a centrifugal force from a swing rotor is applied to an aqueous solution of Ca for 3 days. ４８ Ca and ４３This is a diagram showing the distribution of the isotope ratio IR of Ca. The results are obtained by the Monte Carlo method and the finite element method when a Ca aqueous solution is subjected to centrifugal force using a swing rotor for 3 days. ４８ 10 is a diagram showing the simulation results of the Ca concentration distribution near the maximum radius of the centrifuge tube when the angle rotor 70Ti is used. ４８ 1 is a graph showing the change in Ca concentration over time when the angle rotor 70Ti is used. ４８ Ca / ４０ 1 shows the relationship between the number of repetitions and the isotope ratio IR when repeated enrichment is performed using the angle rotor S140AT. ４８ 1 shows the concentration distribution of Ca in a calcium nitrate aqueous solution with a concentration of 1N. ４０ 10 is a diagram showing the concentration distribution of Ca. FIG. 11 is a diagram illustrating the relationship between the change in the number of stages after optimization of the sample acquisition method and the change in the isotope ratio IR.

[0027] [1] How the present invention was accomplished In considering how to solve the above-mentioned problems, the present inventors noticed that many elements do not become gases but exist as ions in aqueous solutions, such as hydroxides, halides, and metal salts (e.g., nitrates). That is, if an aqueous solution of these compounds is prepared and isotopes are present in the aqueous solution as ions, the density can be made higher than that of gas at room temperature. Therefore, if this aqueous solution can be enriched and separated by centrifugation, it is believed that it will be possible to enrich and separate isotopes of elements inexpensively and efficiently, and that it will also be possible to enrich and separate many elements.

[0028] However, in the past, when it came to concentrating and separating isotopes, centrifugation has only been used for gases, and there have been few attempts to use it for aqueous solutions. The reason for this is unclear, but it is clear that there are several difficulties involved.

[0029] In other words, when isotope enrichment and separation is performed by centrifugation, it is necessary to evaluate whether the concentration distribution at equilibrium under centrifugal force is sufficiently non-uniform to achieve enrichment, and whether the initial uniform distribution can approach the equilibrium distribution in a realistic amount of time.

[0030] In the case of gases, by increasing the size of the device (increasing the radius) under a feasible centrifugal force, the concentration change can be made larger, while the large diffusion coefficient of gases also increases the migration speed of atoms, making it possible to achieve concentration changes in a realistic time, thereby making it possible to concentrate and separate gases by centrifugation.

[0031] In contrast, because the diffusion coefficient of atoms is small in aqueous solutions, it is generally difficult to enrich and separate isotopes by centrifugation. The inventors of the present invention have considered that it is possible to optimize this problem by evaluating the degree of enrichment and the time required to achieve it based on the centrifugal force and the size of the apparatus, and have thus achieved practical enrichment and separation by centrifugation of aqueous solutions. As a result of extensive research, they have completed the present invention.

[0032] [2] Specific Considerations The inventors considered it necessary to consider the following (1) to (4) as necessary conditions for concentrating and separating isotopes from an aqueous solution in which isotopes are ionized by centrifugation: (1) Large centrifugal force (acceleration) (2) Sufficient distance to create a difference in the concentration distribution of isotopes in a thermal equilibrium state (3) Achieving concentration in a realistic time (4) Controlling turbulence that stirs the distribution

[0033] The following will explain (1), (2), (3), and (4) in that order. Note that (1) and (2) are conditions that depend on the type and performance of the centrifuge, so they will be explained together.

[0034] 1. Large centrifugal force (acceleration) and sufficient distance to produce differences in isotope concentration distribution In recent years, high-performance centrifugal separators known as ultracentrifuges have been developed and have become important tools in molecular biology, biochemistry, and polymer science. The inventors have investigated the use of these ultracentrifuges.

[0035] As mentioned above, there have been no examples of isotope separation of ions in an aqueous solution using a centrifuge. To evaluate the possibility, it is necessary to consider whether the concentration distribution in the equilibrium state after centrifugation is larger than the desired concentration distribution.

[0036] It is known that the equilibrium concentration distribution of ions in a centrifuge as a function of their position (radius r: distance from the center of rotation of the rotor) in a centrifuge tube containing a solution is proportional to the Gibbs factor ρ(r) given by the following equation (1): In equation (1), k is the Boltzmann constant, T is the absolute temperature, and U(r) is the potential energy generated by centrifugal force.

[0037]

[0038] When the rotational angular velocity is ω and the mass of the ion is m, U(r) is given by the following formula:

[0039]

[0040] Therefore, the concentration distribution in the thermal equilibrium state inside the centrifuge tube can be expressed by the following equation, where N is a normalization constant.

[0041]

[0042] Here, the normalization constant N is the minimum radius of the centrifuge tube, r ｂ , the maximum value is r ｅ and the ratio of the centrifugal acceleration G to the gravitational acceleration g is α, the following equation can be used:

[0043]

[0044] The right-hand term of the above equation can be expressed as the following imaginary error function erfi(x):

[0045]

[0046] Because this imaginary error function erfi(x) cannot be expressed by elementary functions, numerical calculations are required for quantitative evaluation, but the tendency can be evaluated as follows. That is, in order for the concentration distribution under centrifugal force to produce the changes necessary for isotope enrichment, first, the centrifugal acceleration G produced by the centrifuge must be sufficiently large; specifically, a centrifugal acceleration G of 200,000 g (g: gravitational acceleration) or more is required. Furthermore, a sufficient distance (radial length) is required, and the product (Gr) of the centrifugal acceleration G (g) and the distance r (m) must be sufficiently large; specifically, a Gr of 20,000 gm or more is required.

[0047] That is, the maximum radius r of the centrifuge tube is expressed by the following formula: ｅ and the minimum value r ｂ The concentration ratio (separation factor) between the two points must be sufficiently large. １ It is expressed as follows.

[0048]

[0049] From the above formula, the centrifugal acceleration G = αg (= rω ２ It is important that the mass is sufficiently large, for example, about 1 million g, but the product of the mass and the radius plays a more decisive role in isotope enrichment. The radial concentration difference also depends on the mass, which creates the concentration difference between isotopes and determines the enrichment (separation power).

[0050] That is, the enrichment (separation ability) can be characterized by the following formula: In the formula, the subscript 1 indicates an isotope other than the isotope to be separated, and the subscript 2 indicates the isotope to be separated.

[0051]

[0052] From the above, it can be seen that in order to ensure sufficient enrichment (separation ability) and know whether separation is possible, it is necessary to evaluate the normalization constant N. Furthermore, as the radial change in concentration distribution increases, it is the high-concentration areas that mainly affect N, and the effect of enrichment reaches a plateau. In other words, it can be seen that there is no need to increase the gravitational acceleration indefinitely.

[0053] Based on the above formulas, the radius of the centrifuge tube (solution tube) is determined to be within a certain range (r ｂ ~r ｅ The isotope ratio (ratio of isotope contents) IR between Isotope 1 and Isotope 2 when the solution is taken out from the N １ , N ２ are Error! Invalid link in isotope 1 and isotope 2, respectively.

[0054]

[0055] Below, including the above considerations, ω ２ r ｅ ２ The change in the isotope ratio IR that can be achieved using a centrifuge under the condition of =αgr was examined. Specifically, an Optima L-90 ultracentrifuge manufactured by Beckman Coulter was used to measure the change in the isotope ratio ( ４０ Ca and ４８ The separation of Ca) was evaluated using both a swing rotor with long centrifuge tubes and low centrifugal force, and an angle rotor with short centrifuge tubes arranged at an inclination angle of 20 to 40 degrees relative to the centrifugal direction, which has high centrifugal force.

[0056] The experiment was carried out using calcium isotopes ( ４０ Ca and ４８ The reason for separating Ca) is as follows: ４８ Although calcium is highly sought after in particle and nuclear physics and plays an essential role in the study of double beta decay and superheavy elements, its natural abundance is as follows: ４０ This is extremely small, at 0.187%, compared to 95% of Ca, and currently, it can only be determined by mass spectrometry. ４８ Because it is not possible to concentrate Ca, it is extremely expensive, costing several hundred million yen per 10g. For this reason, it is not suitable for beam physics, which requires a quantity of 0.1 to 10g, or for double beta decay observation, which requires a quantity of 1kg to 1t. ４８ For research that requires large amounts of Ca, alternatives to mass spectrometry are ４８ This is because there is a strong demand for a method for concentrating Ca.

[0057] (a) Swing rotor The swing rotor has a maximum radius r ｅ is 153 mm, minimum radius r ｂ Using a 67 mm swing rotor SW41Ti (manufactured by Beckman Coulter), the relationship between the rotation speed (rpm) and the isotope ratio IR at thermal equilibrium at a position 5% from the tip was determined. As shown in the upper right corner of Figure 1, this swing rotor generates a maximum centrifugal force corresponding to 288,000 g at a maximum rotation speed of 41,000 rpm.

[0058] In Figure 1, the horizontal axis represents the rotation speed (rpm). The vertical axis represents the isotope ratio IR, which indicates the change in the isotope ratio IR relative to the rotation speed, with the isotope ratio IR at the start of rotation set to 1. To observe the trend after the maximum rotation speed of 41,000 rpm, Figure 1 also includes calculation results for rotation speeds exceeding the device's capacity, to the right of the thick vertical solid line. Figure 1 shows that the isotope ratio IR reaches a near maximum at the maximum rotation speed of 41,000 rpm (288,000 g), and that the isotope ratio IR remains almost constant and saturates even at higher rotation speeds. This is because the isotope ratio IR returns to 1 when both species converge at the end, demonstrating that the ultracentrifuge achieves the performance required for enrichment.

[0059] (b) Angle rotor The angle rotor has a maximum radius r ｅ is 40 mm, minimum radius r ｂ The relationship between the rotation speed (rpm) and the isotope ratio IR was determined for a 20 mm angle rotor S140AT (manufactured by Eppendorf-Himack). The results are shown in Figure 2. As shown in the upper right corner of Figure 2, at a maximum rotation speed of 140,000 rpm, this angle rotor generates a maximum centrifugal force of 1,030,000 g, which is greater than the centrifugal force of 288,000 g generated by a swing rotor. Note that the angle rotor is tilted at an angle of 35 degrees with respect to the centrifugal direction of the centrifuge tubes.

[0060] In both Figure 1 (swing rotor) and Figure 2 (angle rotor), the same level of isotope ratio IR is obtained around the maximum centrifugal acceleration of the ultracentrifuge, and even if the centrifugal acceleration is increased beyond that, a tendency toward saturation is clearly evident. This shows that, while increasing the centrifugal acceleration during centrifugation of isotopes is effective in increasing the isotope ratio IR, it is not necessary to increase it indefinitely, and considerable performance can be achieved even with current ultracentrifuges. Note that in Figures 1 and 2, the unit of centrifugal acceleration is g (gravitational acceleration), and for example, "2.88 x 10 ５ g" means that the centrifugal acceleration G is 2.88 x 10 of the gravitational acceleration g. ５ This indicates that it is double.

[0061] Next, based on the results obtained in Figs. 1 and 2, the maximum radius r ｅ The isotope ratio IR in thermal equilibrium near the tip and the product Gr (= rω) of the centrifugal force G and the radius r (m) ２ ) (where the gravitational acceleration g is 1), the relationship between the isotope ratio IR and the horizontal axis is Gr. In FIG. 3, the thick vertical solid line indicates Gr at which the isotope ratio IR is maximum for the angle rotor (S140AT), and the thick vertical dashed line indicates Gr at which the isotope ratio IR is maximum for the swing rotor (SW41Ti).

[0062] As is clear from Figure 3, when an ultracentrifuge is used, even if different rotors are used, such as a swing rotor or an angle rotor, as long as Gr is the same, almost the same isotope ratio IR (about 17%) is obtained. This shows that Gr is the factor that determines the enrichment of isotopes, that isotope enrichment can be controlled by Gr, and that both swing rotors and angle rotors have the performance required for isotope separation.

[0063] That is, although the maximum centrifugal acceleration G of the swing rotor appears to be smaller than that of the angle rotor at first glance, it can be seen that it is possible to achieve the same isotope enrichment (isotope ratio IR) as the angle rotor.

[0064] Note that here, the mass difference is typically large. ４０ Ca and ４８ Although the example of Ca was shown, when considering mass dependence, the larger the mass difference, the higher the radial dependence of the concentration distribution for the same acceleration, so the acceleration requirement becomes lower. On the other hand, for light elements, a larger centrifugal acceleration is required to compensate for the small mass difference. In other words, it can be seen that isotope enrichment by centrifugation is a more appropriate method for enriching isotopes with a large mass difference.

[0065] 2. Feasibility of concentration in a realistic time frame To determine whether sufficient concentration can be achieved in a realistic time frame, it is necessary to determine the migration speed of ions under centrifugal force. Specifically, when a force F is applied to an ion, the migration speed ν of the ion in water can be evaluated using the Einstein-Stokes relation expressed as follows: In the following equation, D is the diffusion coefficient, a is the effective radius of the atom, and η is the viscosity of water.

[0066]

[0067] Here, the force F acting on the ion is the centrifugal force (= mrω ２ ) and, since the diffusion coefficient D is known for many elements, the migration velocity ν of ions in water can be related to the diffusion coefficient D and expressed as the following equation (3) from the above equation.

[0068]

[0069] The rate at which the ion concentration ρ approaches the equilibrium state distribution from a uniform distribution, that is, the change in ion concentration ρ with time, dρ / dt, is given by the conservation law shown in the following equation.

[0070]

[0071] Here, J is the flux and is given by the following equation (4).

[0072]

[0073] From the above, it can be seen that whether concentration can be achieved in a realistic time depends on whether the concentration distribution of ions changes over time due to this flow and whether it can reach the desired concentration distribution within a reasonable time.

[0074] Looking at equation (3), we can see that gas is advantageous for the centrifugal separation method. That is, the migration speed is proportional to the diffusion coefficient, and the diffusion coefficient of atoms in gas is about 10 －５ (m ２ / s), whereas the diffusion coefficient in aqueous solution is ∼10 －９ (m ２ / s), which is four orders of magnitude smaller than that of aqueous solutions, it is clear that gases are overwhelmingly advantageous. However, because the density of gases and aqueous solutions differs by three orders of magnitude, this difference narrows, and it is thought that there are conditions under which aqueous solutions can be concentrated depending on the shape of the device and the centrifugal force.

[0075] Furthermore, by rewriting the migration velocity ν as the following equation (5), we can understand another reason why centrifugation of isotopes in water has not been performed until now.

[0076]

[0077] That is, since it is known that the mass m of a molecule is roughly proportional to the cube of the radius a, from equation (5), the heavier the molecule, the larger a, the larger a ２ The migration speed ν increases in proportion to ν, and the particles eventually sink to the bottom and are removed. This is why a centrifuge separates macromolecules in a solution.

[0078] However, in the case of isotope enrichment and separation, which is determined by the movement of a single atom whose radius is not particularly large, high migration speeds cannot be achieved and it takes time, so the final result is a concentration distribution in the depth direction.To separate isotopes, it is necessary to fractionate them as a function of the radius of the centrifuge tube, unlike polymers, which are extracted by extracting the material that accumulates at the bottom.

[0079] Furthermore, looking at the relationship between the product Gr of the centrifugal acceleration G and the radius r, and the time required to achieve a predetermined concentration level, it is known that, for the same Gr, the time can be shortened by increasing G and decreasing r. Taking this into consideration, it can be seen that the use of an angle rotor, which provides a higher centrifugal force and has a shorter effective radius, is preferable from the perspective of shortening the time compared to a swing rotor. However, when an angle rotor is used, the direction of the centrifugal force differs from the direction of gravity, so that the concentration distribution (density distribution) of the solution generated in the radial direction by the operation of the centrifuge may move in the direction of gravitational acceleration when the centrifuge is stopped, causing agitation as described below.

[0080] 3. Control of turbulence that stirs the distribution Control of turbulence that stirs the distribution is a necessary condition to avoid the flow of atomic migration speed being stirred by other factors, which can cause the distribution to fall short of the distribution expected in equilibrium.

[0081] For example, if there is a temperature difference depending on the depth of the centrifuge tube, convection may occur, which may disrupt the distribution. Also, even if small vibrations are added to the rotation, stirring may occur, which may disrupt the distribution.

[0082] To prevent the occurrence of disturbances in the distribution in this equilibrium state, it is necessary that the dispersion due to turbulence is sufficiently small compared to the migration velocity given by equation (3), thereby enabling sufficient concentration.

[0083] In recent ultracentrifuges, measures have been taken to suppress the occurrence of convection. In the ultracentrifuge used above, the rotor rotates in a vacuum and sufficient temperature control is also performed. As described above, concentration was actually observed, and it was therefore confirmed that these conditions were fully met.

[0084] [3] Specific Embodiments 1. Experiment 1 The inventors conducted the following experiment to confirm the above-mentioned observations. The ultracentrifuges used were an ultracentrifuge (Optima L-90) manufactured by Beckman Coleman and a CS-FNX manufactured by Eppendorf-Himak, and as mentioned above, in combination with the rotor, a centrifugal force of more than 1,000,000 g can be achieved.

[0085] High centrifugal force can be obtained with an angle rotor in which the angle of inclination of the centrifuge tube relative to the centrifugal direction is constant; however, the concentration distribution in the r direction (radial direction of rotation) that occurs during rotation changes to a distribution in the direction of gravitational acceleration when stationary, which could cause stirring and lead to inconsistent results. Therefore, in this experiment, we initially decided to use a swing rotor (SW41Ti) in which the tip of the centrifuge tube always faces the direction of acceleration.

[0086] Although the swing-out rotor has a lower acceleration than the angle rotor, it is expected that concentration will proceed as calculated because a force is always applied downward to the centrifuge tube. In this experiment, as mentioned above, by combining it with the swing-out rotor SW41Ti, a maximum acceleration of 288,000 g can be obtained at the bottom of the centrifuge tube.

[0087] As a result, in centrifugal separation using an ultracentrifuge, the radial length is sufficient to satisfy the conditions for large centrifugal force (acceleration) and sufficient distance to create differences in the isotope distribution.Furthermore, by actually observing enrichment, it was confirmed that the conditions for the feasibility of enrichment in a realistic time frame and the conditions for the control of turbulence that stirs up the distribution are also satisfied.

[0088] Here, the ４８ The migration speed of Ca ions is calculated using equation (3) to be 3 mm per day. ４８ The dispersion (spread) of Ca ions is calculated as 12 mm per day using the following formula: where σ is the dispersion and D is the diffusion coefficient (7.9 × 10 for Ca). －１０ (m ２ / s), where t is time (s).

[0089]

[0090] and, ４８ The change in concentration of Ca ions over time is determined by the migration speed and diffusion calculated above.

[0091] The experiment was carried out by pouring an aqueous calcium chloride solution and an aqueous calcium nitrate solution into a centrifuge tube for a swing rotor SW41Ti. Specifically, the concentration of each solution was adjusted so that the specific gravity was 1.1, and then the solution was poured into the centrifuge tube. The solution was then centrifuged continuously for about one day (25 hours) using a swing rotor SW41Ti (rotation speed: 41,000 rpm, centrifugal force: 288,000 g). After the operation was completed, the solution was taken from the centrifuge tube in 10 portions numbered 1 to 10, starting from the top. For each of the samples taken, ４３ Ca and ４８The concentration of Ca isotopes was measured using a mass spectrometer (Agilent 7900 ICP-MS) manufactured by Agilent Technologies, Inc. ４３ Ca and ４８ The Ca isotope ratio IR was determined. As a result, although the distributions were slightly different between the two compounds, no difference was observed in the change in the isotope ratio IR, so below, the results for the calcium chloride aqueous solution are shown.

[0092] Although ICP-MS is a preferred instrument for measuring isotopes, it uses argon as a carrier gas. ４０ Because Ca cannot be measured, ４０ Instead of Ca ４３ Measurements were performed using Ca. The error in ICP-MS, which measures the number of ions, is generally given as the reciprocal of the square root of the number of measurements, but in this experiment, a sufficient number was measured, so the error due to counting was small. On the other hand, the error due to the stability of the instrument was about 0.3%.

[0093] In parallel, the isotope ratio IR was similarly determined by simulating the actual ion movement (MC simulation) using the Monte Carlo (MC) method. Specifically, the migration velocity of a single ion in the r direction, determined by the ion's position (r), and the random movement due to diffusion were varied in minute time increments, and the time changes were tracked for a large number of ions, and the time change in concentration was derived as a function of radius r. Note that the accuracy of the results depends on the square root of the number of ions simulated.

[0094] A comparison of the experimental results and the MC simulation results is shown in Figures 4 and 5. ４８ This is a graph showing the change in Ca concentration, and the vertical axis is normalized with the initial value set to 1. ４８ The horizontal axis represents the concentration of Ca, and the horizontal axis represents the position of the centrifuge tube from which the sample was taken. ４８ Ca / ４３ The vertical axis shows the change in the Ca ratio, normalized with the initial value set to 1 ( ４８ Ca / ４３ The horizontal axis indicates the position of the centrifuge tube into which the sample was taken.

[0095] 4 and 5, it can be seen that the results of the MC simulation reproduce the experimental results with a high degree of accuracy. Furthermore, as shown in FIG. 4, as the end of the centrifuge tube (position 10) is approached, ４８ It can be seen that the Ca concentration tends to increase, and at the end, the concentration has increased by several tens of percent. Similarly, from Figure 5, it can be seen that the change from the initial value (natural abundance ratio) of the isotope ratio IR also increases towards the end, with heavier isotopes increasing and becoming enriched by about 2%. From these results, it can be seen that centrifugation ４８ It can be seen that Ca is being concentrated.

[0096] In addition, in the measurement of isotope ratio IR by ICP-MS, the concentration change comes only from the effect of mass, but ( ４８ Ca / ４３ The Ca) isotope ratio IR was 0.12 times the concentration change, which was consistent with the experimental results, and the concentration and isotope ratio IR, as well as their respective radius dependencies, confirmed enrichment by centrifugation. ４０ For Ca ４８ The concentration of Ca is important, and this is ４８ Ca and ４３ The ratio is 1.6 times that of Ca.

[0097] 2. Experiment 2 For further confirmation, the inventors performed three days of continuous operation in the same manner as above. The results are shown in Figures 6 and 7 together with the results of MC simulation. In Figures 6 and 7, the horizontal axis is normalized with the end of the centrifuge tube as 1.

[0098] As shown in Figures 6 and 7, at both ends of the centrifuge tube, ４８ The Ca concentration is ±40%, and the IR is ±4% ( ４０ There is a 5% change in the ratio of Ca to Cr, which indicates that the material is definitely enriched. The results are also consistent with the MC. This agreement justifies the use of calculated values, and shows that the enrichment conditions can be evaluated by calculation.

[0099] 4 and 6, and 5 and 7, it can be seen that the change in concentration is larger in the three-day continuous operation than in the one-day continuous operation, and the isotope ratio IR also changes accordingly. Furthermore, the amount of change is almost the same as the MC simulation.

[0100] As described above, in Experiments 1 and 2, the time changes in both concentration and isotope ratio IR were almost as calculated. This confirmed that the evaluation of the time it takes for concentration and isotopes to change was performed correctly, and the conditions for achieving sufficient concentration in future centrifugal enrichment were clarified.

[0101] 3. Experiment 3 In order to confirm the results of the MC simulation, the inventors also used the finite element method, which divides the inside of a centrifuge tube into small cells and calculates the changes between the cells. ４３ Change in Ca concentration, and ( ４８ Ca / ４３ The change in the Ca) ratio was determined.

[0102] Specifically, calculations were performed based on cells (single cell length: 0.86 mm) obtained by dividing a centrifuge tube (length: 86 mm) of an SW41 rotor into 100 cells in the depth direction. As a result, it was found that the results obtained using the finite element method were almost the same as those obtained using MC simulation, and it was confirmed that calculations based on the finite element method, which can obtain highly accurate results in a short time, are preferable to MC simulations based on the Monte Carlo method. For example, ４８ As shown in FIG. 8, the results of the change in Ca concentration obtained by the MC simulation (Monte Carlo method) and the results obtained by the finite element method show good agreement.

[0103] 4. Experiment 4 (Study on time constant) When centrifugal separation is carried out for a long period of time, the concentration distribution eventually reaches a thermal equilibrium state. The inventor evaluated how this thermal equilibrium state is approached using the finite element method. As a result, it was found that the change in concentration over time can be approximately expressed by the following formula. In the following formula, t is time, ρ ｅｑ is the concentration distribution at thermal equilibrium, ρ ０is the concentration distribution at the start of operation (t=0), and τ is the time constant (a measure of the time it takes to reach equilibrium).

[0104]

[0105] The above equation indicates that the concentration distribution approaches the equilibrium distribution exponentially with a time constant τ.

[0106] FIG. 9 shows the results of the centrifuge tube near the maximum radius when using the angle rotor 70Ti. ４８ This is a graph showing the change in Ca concentration over time (change every 0.5 days), where ○ indicates the result of numerical calculation (finite element method) and ● indicates the result of fitting using the function above. From Figure 9, it can be seen that the two calculation results are almost identical.

[0107] Here, the time constant τ was set to 3.25 days. In this case, the time constant τ can be simply expressed by the following formula, which is obtained by dividing the migration distance by the average migration speed.

[0108]

[0109] In the above formula, r ０ is the initial average radius at the start of operation (t = 0), r ｅｑ is the mean radius of the equilibrium concentration distribution, ν ａｖ is the average migration velocity, (r ｅｑ -r ０ ) corresponds to the migration distance. Note that the average radius r ｅｑ is given by the following formula:

[0110]

[0111] Using the two equations above, the time constant τ for the angle rotor 70Ti is found to be 2.2 days, which is roughly reproducible, although there is a deviation of about 2 / 3. This deviation is thought to be due to the fact that the correlation between the speed at a position with a large radius in the centrifuge tube and the distance that can be moved is small, and conversely, the speed at a position with a small radius is small but the distance that can be moved is large, is not captured by the average value alone. However, the tendency for the deviation from the equilibrium point value to change exponentially over time is reproducible. Furthermore, a numerical calculation method has been established for accurate evaluation. Note that since Gr is nearly constant, τ is proportional to 1 / ω2.

[0112] 5. Experiment 5 (Enrichment and Amount) Experiments 1 to 4 above confirmed that enrichment using a swing rotor is possible, but it was also found that it takes several times longer than the realistically desired timescale (approximately one year). In actual enrichment, it is important to obtain a sufficient amount of solution with the desired concentration within the desired timescale.

[0113] Therefore, the inventors attempted to use an angle rotor to shorten the time constant τ and optimize the operating conditions. As mentioned above, the angle rotor can obtain a higher centrifugal force and has a short effective radius, so it can reach an equilibrium state in a short time and achieve a predetermined enrichment level.

[0114] That is, with a swing rotor, the force direction is always toward the end of the centrifuge tube, resulting in the accumulation of heavy isotopes at the tip. On the other hand, with an angle rotor, the high g and short r force result in a small time constant τ, making it suitable for shortening the time. However, the acceleration direction changes from horizontal during rotation to downward after stopping, so the biggest concern is whether the concentration distribution will be maintained even after stopping. Regarding this point, the inventors felt that preliminary tests would be sufficient, but ultimately confirmed that a high enrichment level could be achieved in a realistic time when using an angle rotor 70Ti (70,000 rpm, 500,000 g). The optimization of operating conditions was addressed by repeatedly proceeding to the next step when the enrichment level was just under half of the equilibrium value.

[0115] In this case, the parameters can be appropriately set based on the desired isotope enrichment and amount, with the final amount extracted and the time required for one enrichment. Note that the inventors have established calculation methods such as the Monte Carlo method and the finite element method as tools for calculating these.

[0116] As an example of actual concentration, for example, if the top 1 / 3 of the concentrate obtained in one centrifugation is used for the next centrifugation, and this is repeated twice a day for 12 consecutive days (approximately 25 times), a concentration of approximately 5.2% can be obtained.

[0117] 6. Experiment 6 (Study on the practicality of concentration using an angle rotor) As mentioned above, an angle rotor is preferable to a swing rotor in terms of reducing the time required. However, when an angle rotor that rotates at a fixed angle stops, the lateral acceleration changes downward, which may cause agitation.

[0118] Therefore, the present inventors have investigated the practicality of concentration using an angle rotor and have confirmed that results that are sufficient for practical use can be obtained.

[0119] Specifically, the entire length of the tube (89 mm) was divided into 10 equal parts using an angle rotor 70Ti (angle: 23 degrees), and the numbers 0 (innermost end) to 10 (outermost end) were assigned from the inside to the outside. ４８ Ca / ４０ The Ca isotope ratio IR was calculated and compared with the calculated value. The results are shown in Figure 10. In Figure 10, the horizontal axis represents the tube position and the vertical axis represents ４８ Ca / ４０ This is the Ca isotope ratio IR, where ○ indicates the experimental value and ● indicates the calculated value.

[0120] 10, it can be seen that the calculated values ​​and experimental values ​​are relatively consistent near the tip of the tube. This result is not inconsistent with the idea that the change in concentration of ion particles due to the acceleration field generated in the horizontal direction by the centrifugal force described above creates a change in concentration in the vertical direction in the bulk (overall) due to the density of the aqueous solution, and shows that concentration that is practically feasible can be achieved even with an angle rotor. It can be seen that when an angle rotor that generates a large centrifugal force is used, the effect of shortening the concentration time is significant and the effect of stirring is also sufficiently practical.

[0121] however, ４８ Repeated experiments were required to increase the Ca abundance from the natural abundance of 0.187% to nearly 50%. Therefore, a multi-stage concentration experiment was conducted using a HIMAC ultracentrifuge (CS150FNX) and an angle rotor S140AT with the highest centrifugal force (1,030,000 g at 14,000 rpm).

[0122] As mentioned above, the angle rotor S140AT (maximum radius: 4.79 cm, angle: 35 degrees) can generate a maximum centrifugal force of 1.03 million g at 140,000 rpm. Furthermore, since the tube was positioned at a short distance of 20 to 40 mm and the time constant was short at approximately 0.4 days, the concentration was repeated 25 times (13 days) over a period of 0.5 days, with a time change that is close to linear. When repeating the concentration cycle, the aqueous solution in the centrifuge tube was divided into three parts, with the deepest concentrated part added to the next sample, the middle part (unchanged) added to the same part, and the shallowest part (reduced concentration) added to the previous part.

[0123] The relationship between the number of repetitions and the isotope ratio IR is shown in Figure 11. In Figure 11, the horizontal axis represents the number of repetitions, the vertical axis represents the isotope ratio IR, and the points marked with ■ represent the values ​​obtained in the experiment. ４８ Ca / ４０ Ca isotope ratio IR (▲ indicates ４８ Ca / ４３ Ca). In Figure 11, the concentration per cycle is set to 5.3%. ４８ Ca / ４０ The Ca isotope ratio IR was calculated using an exponential function. ４８ Ca / ４０The calculated values ​​for the Ca isotope ratio IR are shown as curves.

[0124] As shown in Figure 11, the number of times ４８ Ca / ４０ Ca isotope ratio IR, ４８ Ca / ４３ It was found that both the Ca isotope ratio IR increased, and it was confirmed that more effective enrichment can be achieved by performing multi-stage enrichment.

[0125] Specifically, the isotope ratio IR at the 10th stage is 1.67, which is about 20 mg, a realistic amount. ４８ Ca was successfully obtained. Concentration to 5.3% was achieved in 0.5 days per stage, but the 2.5 times longer process (25 times) was required for 10 stages because the amount was reduced by one-third with each stage. This number of stages increases as the concentration level increases, and concentration beyond 50% requires five times the number of stages (approximately one year). Concentration by centrifugation requires samples from all stages, so production speeds up after reaching 50%, making it possible to achieve 1 g / year, and further improvement is expected by adjusting the conditions.

[0126] 7. Experiment 7 (Study on Optimization of Concentration Conditions) In Experiment 6 above, it was confirmed that when concentrating ions in an aqueous solution by centrifugation, repeated centrifugation is necessary to concentrate the ions to the target isotope ratio IR. Therefore, the optimization of the concentration conditions was studied as follows.

[0127] (a) Selection of Ca Salt When changing the isotope ratio IR of Ca ions by centrifugation, it is preferable to use a Ca salt with high solubility. When the present inventors tested calcium chloride and calcium nitrate, they found that there was little difference in the radius dependence of the isotope ratio, but that calcium nitrate showed a larger concentration change. This means that a larger amount of concentrated Ca was obtained, and therefore it was found that calcium nitrate is preferable as the salt to be actually used. It should be noted that calcium thiosulfate is also considered as a Ca salt with high solubility, but considering the complexity of subsequent chemical treatment, calcium nitrate is preferable.

[0128] We then investigated the concentration dependence using calcium nitrate aqueous solutions with concentrations ranging from 0.1N to 2N. We found that while there was little effect on the radius dependence of the isotope ratio IR, the more dilute the solution, the greater the concentration change. While a highly concentrated solution is desirable for extracting large amounts, if the solution becomes too concentrated, the concentration change decreases, and the amount actually obtained decreases. Therefore, we decided to operate the reactor at a concentration of 1N, and in some cases allowed it to be slightly diluted.

[0129] (b) Operating time The degree of concentration possible in a single centrifugation (separation factor: the ratio of the concentration ratio after separation to the concentration ratio before separation) is about 10%, and in order to achieve a high degree of concentration, repeated concentration is necessary. In order to optimize this procedure, it is necessary to improve the concentration and yield per run and to optimize the realistic procedure for obtaining samples when repeated concentration is performed.

[0130] In the case of concentration using the angle rotor S140AT, when operating at the maximum centrifugal force of 1.03 million g, the equilibrium value is approached with a time constant of approximately 7 hours. Note that, while the change is proportional to time over a short period of time, the change slows down as the equilibrium point is approached. Since the work involved in the repetition requires approximately half an hour, repetition over a short period of time is not considered an effective method. In the case of repetition every 12 hours, which allows concentration to approximately 80% of the equilibrium value, the optimal time is set, and replacement is performed twice a day at the same time, making this a practically effective method. Therefore, the replacement time was set at 0.5 hours, resulting in an operating time of 11.5 hours.

[0131] (c) Operational behavior In order to obtain the maximum concentration within the above-mentioned 11.5-hour operating time, we investigated the change in temperature over time and found that the change in isotope ratio caused by the equilibrium concentration distribution is greater at low temperatures, but the time required to achieve that isotope ratio is shorter at high temperatures where the diffusion coefficient and mobility are greater.

[0132] Next, the optimum temperature change over an 11.5-hour operation was evaluated by simulation. Specifically, because an ultracentrifuge can raise the temperature up to 40° C., the majority of the operation time (10.25 hours) was set at 40° C., the next 1.0 hour at 20° C., and the final 0.25 hour at 10° C. The simulation evaluated whether this time allocation provided the maximum value.

[0133] When the ultracentrifuge stops after a certain operating time, the centrifugal force that was directed outward ceases to act, and instead a force acts in the downward direction of gravity. The concentration distribution created by the centrifugal force is naturally replaced by a change in the specific gravity of the solution, which is then replaced by a change in the direction of gravity. This has been confirmed by experimental observations of concentration. However, once the centrifugal force ceases to act, the distribution changes and becomes more uniform due to diffusion.

[0134] In this experiment, the ultracentrifuge and angle rotor were combined to shorten the radial distance and concentrate the sample in a short time. The time for diffusion after stopping was also short, which has a significant impact, especially when there is a large concentration gradient. Therefore, the rotor was stopped as quickly as possible (not at maximum speed, but early), ensuring that the sample removal time was within 10 minutes. Furthermore, the final temperature was set to 10°C to reduce the speed at which the concentration distribution becomes uniform after stopping.

[0135] (d) Centrifuge tubes Centrifuge tubes are used to put the aqueous solution into the rotor. In particular, with angle rotors, the aqueous solution surface faces up and down when centrifugal force is applied, so centrifuge tubes of a type that are completely sealed are sometimes used. However, the present inventors have confirmed that if a method is adopted in which the aqueous solution is directly injected into the holes in the rotor without using centrifuge tubes, it is possible to increase the amount of solution that can be handled and reduce the time required for removal.

[0136] Specifically, we were able to increase the amount of aqueous solution that could be added per well from 1 cc to 2.2 cc, and confirmed that sample extraction could be achieved in 10 minutes at most, and in 5 minutes at best. We also confirmed that the expected change in isotope ratio IR could be obtained even when samples were extracted directly without using a centrifuge tube.

[0137] (e) Repetition In the above (a) to (d), the conditions for maximizing the change in isotope ratio per cycle have been described. Next, optimization of the conditions for repeated enrichment will be described.

[0138] Each isotope ( ４８ Ca, ４０ The concentration distribution of Ca) was measured using ICP-MS. ４８ The Ca concentration distribution is shown in Figure 13. ４０ 12 and 13, the constants are subtracted from the measured values ​​of each data, and the portion that fits the exponential function (the exponential function portion of the approximation curve composed of the exponential function and the constants) is also shown. In both cases, the R-squared value is close to 1, indicating a sufficient correlation, and it was confirmed that these functions are valid as functions representing the concentration distribution in a thermal equilibrium state under a centrifugal potential.

[0139] Next, the optimal conditions for repeating the concentration by centrifugation were determined using the function (exponential function + constant) obtained above. With the function system determined, the optimal conditions for repeating the concentration by centrifugation were determined as a function of the amount of aqueous solution extracted from the tip. ４８ Ca and ４０ The amount of Ca and its isotope ratio IR are determined, and by continuously concentrating, it is possible to track changes in the amount and isotope ratio IR. Once the target isotope ratio IR is determined, it becomes possible to concentrate as a function of the number of ultracentrifuges and time.

[0140] If only the tip is removed, a high concentration can be obtained, but the amount is small, and each time it is repeated, the procedure to recover the lost amount increases. Considering that the amount to be put into the rotor hole is fixed, and that amount must be collected before proceeding to the next step, dividing it into certain amounts increases overall efficiency.

[0141] In other words, assuming that approximately 35% of the aqueous solution is extracted from the concentrated tip under actual optimized experimental conditions, the amount of ions extracted will be approximately 50% due to the increased concentration, but simply repeating this process will only halve the amount each time, and after 10 concentration cycles the amount will be approximately 1 / 1000, so it will be necessary to concentrate the remaining portion, which has become less concentrated, and add half of that amount. The number of times this is repeated will be determined by the concentration and amount.

[0142] When extracting a sample, the enriched portion (the portion with increased enrichment) and the depleted portion (the portion with decreased enrichment) are separated and extracted, and the enriched portion is sent to the next step for further enrichment, but because the enrichment level differs depending on the radius, it may seem at first glance that dividing it into smaller portions would be more efficient. However, dividing it into smaller portions makes the procedure more complicated, which takes more time and actually leads to a decrease in efficiency.

[0143] The inventors actually performed calculations and found that even a three-stage division could provide efficiency comparable to that of a finer division. Furthermore, considering the need to shorten the extraction procedure, if the sample is divided into three sections—a concentrated section (L1: one-stage concentrated), a depleted section 1 (L-1: one-stage depletion), and a depleted section 2 (L-2: two-stage depletion)—both L-1 and L-2 are more concentrated than their natural abundance ratios in the more concentrated sample, so it is necessary to increase their amounts by concentrating them as well. Ultimately, the raw solution (L0) can be divided into L1 (0.35), L-1 (0.55), and L-2 (0.1), which are the first stage forward, L-1 (0.55), and L-2 (0.1), which are the second stage backward. In this case, calculations using a function revealed that the concentration improves by about 8% for each stage forward.

[0144] After optimizing the enrichment method described above, enrichment was actually carried out, and currently, enrichment has been achieved up to the 16th stage (number of repetitions: 16). Figure 14 shows a diagram illustrating the relationship between the change in the number of stages after optimizing this sample acquisition method and the change in isotope ratio IR. As shown by the approximation curve in Figure 14, although there is some variation, the results obtained are almost exponential. This indicates that enrichment is being achieved stepwise through multi-stage enrichment, and that if we continue in this manner, we will be able to achieve higher enrichment.

[0145] In Figure 14, the concentration per plate (separation factor) is 8.2%, which is a significant improvement over the 5.3% in the first experiment (Figure 11) due to the optimization of the concentration method. It can also be seen that the concentration per plate is close to the calculated value, and is an almost ideal value. Furthermore, as shown in Figure 14, a concentration of about 3.5 times was achieved at the 16th plate, and it can be seen that a 10-fold concentration is possible by proceeding to the 30th plate.

[0146] [4] Usefulness of the Present Invention Next, the usefulness of the present invention will be explained.

[0147] The technology demonstrated in this invention, "applying a centrifuge to an aqueous solution to concentrate and separate isotopes," is unprecedented.

[0148] As described above, the centrifugal separation method increases both concentration and enrichment, and therefore an improvement in yield can be expected with a separation factor of 5 to 10%. In the currently used methods of isotope enrichment and separation, it is rare to achieve a separation factor of 5 to 10% accompanied by an increase in yield, and high performance can be expected with the centrifugal separation method using an aqueous solution.

[0149] by centrifugation ４８ In the case of calcium concentration, a maximum difference (separation factor) of about 17% can be expected at equilibrium using various rotors. However, considering the time it takes to approach equilibrium and the efficiency of separation, a cascade-style operation in which the next step is proceeded to after about half the amount, or 8%, is more effective. The angle rotor S140AT, which reaches a centrifugal force of 1 million g, has a time constant of about 0.4 days, making it possible to proceed to the next step in half a day, making it efficient.

[0150] Recent developments in ultracentrifuges have been remarkable. The present invention has made it possible to separate and concentrate isotopes from aqueous solutions by centrifugation. This was made possible not only by increasing the magnitude of centrifugal force, but also by clarifying the conditions that the centrifuge tube and rotor must meet, and by suppressing the agitation of water within the centrifuge tube.

[0151] If it becomes possible to separate isotopes in aqueous solution by centrifugation, it will be possible to make the equipment more compact, replacing the huge centrifuges used in uranium enrichment, and this is expected to have many applications.

[0152] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-described embodiments. It should be noted that various modifications can be made to the above-described embodiments within the scope of the same or equivalent to the present invention.

Claims

1. An isotope enrichment and separation method for enriching and separating a target isotope from an element containing a mixture of isotopes, After preparing an aqueous solution of the elemental compound containing the aforementioned isotopes, it is placed in a centrifuge having an angle rotor. By applying the centrifugal force of the centrifuge to the aqueous solution, the isotopes in the aqueous solution are made to move, thereby changing the concentration distribution of the isotopes in the aqueous solution in a gradient manner. A method for concentrating and separating isotopes, characterized by taking an aqueous solution from a location in the concentration distribution of a desired isotope and concentrating or separating the target isotope.

2. The method for concentrating and separating isotopes according to claim 1, characterized in that the elemental compound containing the aforementioned isotopes is a compound that undergoes ion separation in an aqueous solution.

3. The method for isotope concentration and separation according to claim 2, characterized in that the compound separated into ions in the aqueous solution is one of a hydroxide, a halide, or a metal salt.

4. The method for isotope enrichment and separation according to claim 1, characterized in that the centrifugal acceleration G that generates the centrifugal force is 200,000 times or more the gravitational acceleration g.

5. The method for isotope enrichment and separation according to claim 1, characterized in that the product (Gr) of the centrifugal acceleration G [unit: g (gravitational acceleration)] that generates the centrifugal force and the radial distance r (unit: m) is 20,000 (unit: gm) or more.

6. The method for enriching and separating isotopes according to claim 4, characterized in that the centrifugal acceleration G that generates the centrifugal force exceeds 1 million times the gravitational acceleration g.

7. The method for isotope enrichment and separation according to claim 1, characterized in that the inclination angle of the angle rotor with respect to the centrifugal direction of the centrifuge tube is 20 to 40 degrees.

8. The method for enriching and separating isotopes according to any one of claims 1 to 7, characterized in that the centrifugal force is set in advance by simulation.

9. The aforementioned simulation is a simulation that calculates using the magnitude of acceleration, the time and distance over which the acceleration field is applied as parameters. The isotope enrichment and separation method according to claim 8, characterized in that the centrifugal force is set based on the separation coefficient of each isotope calculated by the simulation.

10. The method for isotope enrichment and separation according to claim 8, characterized in that the simulation is performed using the Monte Carlo (MC) method.

11. The method for isotope enrichment and separation according to claim 8, characterized in that the simulation is performed using the finite element method.

12. The aforementioned isotope, ４８ A method for enriching and separating isotopes according to any one of claims 1 to 7, characterized in that the isotope is Ca.

13. The method for enriching and separating isotopes according to any one of claims 1 to 7, characterized in that the enrichment and separation of the target isotopes are performed while shortening the enrichment time.

14. The method for concentrating and separating isotopes according to any one of claims 1 to 6, characterized in that an aqueous solution of an element compound containing the isotopes is prepared and then directly injected into a hole formed in the angle rotor before being set in the centrifuge.