Method for generating target nuclide

Abstract

To provide a method for producing a target nuclide that produces a radioactive target nuclide by radioactive nuclide decay, wherein it is possible to achieve stabilization in the proportion of the produced target nuclide and an elemental isotope of the target nuclide, namely, stabilization in specific radioactivity.SOLUTION: A method for producing a radioactive target nuclide by one or multiple rounds of radioactive decay of a parent nuclide includes a removal process to execute at least one of: a first step S202 for removing, from raw materials containing the parent nuclide, the target nuclide and an elemental isotope of the target nuclide; and a second step S204 for removing, from a reagent to produce the target nuclide, the target nuclide and the elemental isotope of the target nuclide.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for generating a target nuclide that generates a radioactive target nuclide by radioactive decay of a parent nuclide.

Background Art

[0002] Alpha-emitting nuclides are used in various fields such as the medical field, isotope batteries, and analytical instruments. For example, in the medical field, Targeted Alpha Therapy (TAT) using alpha-emitting nuclides is performed in cancer treatment.

[0003] Examples of such alpha-emitting nuclides include Bi-213. Bi-213 is known to be obtained by radioactive decay of Ra-225 or Ac-225. For example, Patent Document 1 describes a method for producing Bi-213 using Ra-225 and Ac-225 as parent nuclides.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, before generating the target nuclide Bi-213 from the parent nuclides Ra-225 or Ac-225, Bi-213 itself or isotopes of Bi may be mixed in the raw materials that are the parent nuclides or the reagents used for generation.

[0006] When generating the target nuclide using such raw materials or reagents, the target nuclide that was mixed in the raw materials or reagents and isotopes of the element of the target nuclide will also be mixed in the finally generated product. That is, the amount of the target nuclide and its isotopes mixed in the product varies for each generation operation.

[0007] Therefore, there is a risk that the ratio of the target nuclide contained in the product to the isotope of the element of the target nuclide will change every time the production operation is performed due to the target nuclide and the isotope of the element of the target nuclide mixed in the raw materials and reagents.

[0008] Here, for example, among the isotopes of Bi-213, there is a stable isotope having a very long half-life such as Bi-209. Therefore, if the ratio of the target nuclide to the isotope of the element of the target nuclide changes every time the production operation is performed, there is a risk that the specific radioactivity expected for the final product cannot be obtained.

[0009] For example, when there are many stable isotopes in the raw materials and reagents, the specific radioactivity of the final product will be lower than expected. On the other hand, when there are few stable isotopes, the specific radioactivity of the final product may be higher than expected.

[0010] That is, when using such raw materials and reagents, there is a risk that the specific radioactivity of the final product will become unstable due to the isotope of the element of the target nuclide. However, since the target nuclide and the isotope of the element of the target nuclide are the same element, it is difficult to remove only the isotope from the final product.

[0011] The present invention aims to provide a method for producing a target nuclide that can stabilize the ratio of the produced target nuclide and the isotope of the element of the target nuclide, that is, stabilize the specific radioactivity, in a method for producing a target nuclide that produces a radioactive target nuclide by radioactive decay of a parent nuclide.

Means for Solving the Problems

[0012] The method for generating a target nuclide of the present invention is a method for generating a radioactive target nuclide by one or a plurality of radioactive decays of a parent nuclide, and includes a removal step of performing at least one of a first step of removing the target nuclide and isotopes of the element of the target nuclide from a raw material containing the parent nuclide and a second step of removing the target nuclide and isotopes of the element of the target nuclide from a reagent used for generating the target nuclide.

[0013] According to the method for generating a target nuclide of the present invention, in the first step and the second step, by removing the target nuclide and isotopes of the element of the target nuclide, the purity of the nuclide at that stage can be improved.

[0014] As a result, it is possible to suppress the mixing of the target nuclide and isotopes of the element of the target nuclide that existed in the stage before generating the target nuclide (that is, mixed in the raw material and the reagent) in the finally generated product.

[0015] Therefore, according to the method for generating a target nuclide of the present invention, it is possible to suppress the mixing of the target nuclide and isotopes of the element of the target nuclide that were mixed in the raw material and the reagent into the product, so that the ratio of the target nuclide of the product to the isotopes of the element of the target nuclide can be stabilized. As a result, the specific activity of the finally generated target nuclide can be stabilized.

[0016] In addition, in this specification, the specific activity is defined as follows. Specific activity = (radioactive energy of the target nuclide to be targeted Bq) / [(mass of the target nuclide to be targeted g) + (mass of the isotope of the element of the target nuclide g)]

[0017] In the method for generating a target nuclide of the present invention, it preferably includes a daughter nuclide generation step of generating a daughter nuclide from the parent nuclide and a target nuclide generation step of generating the target nuclide from the daughter nuclide, and the first step includes a step of removing the target nuclide and isotopes of the element of the target nuclide from the raw material containing the parent nuclide in the daughter nuclide generation step.

[0018] According to such an aspect, in the daughter nuclide generation step, by removing the target nuclide and the isotopes of the element of the target nuclide from the raw material containing the parent nuclide, the purity of the raw material used in the target nuclide generation step, that is, the purity of the daughter nuclide is increased, so that the target nuclide contained in the raw material and the isotopes of the element of the target nuclide can be reduced. As a result, it becomes possible to stabilize the specific radioactivity of the finally obtained target nuclide.

[0019] In the method for generating a target nuclide of the present invention, it includes a daughter nuclide generation step of generating a daughter nuclide from the parent nuclide and a target nuclide generation step of generating the target nuclide from the daughter nuclide, and it is preferable that the first step includes a step of removing the target nuclide and the isotopes of the element of the target nuclide from the daughter nuclide before the target nuclide generation step.

[0020] According to such an aspect, by removing the target nuclide and the isotopes of the element of the target nuclide from the raw material containing the daughter nuclide before the target nuclide generation step, the purity of the raw material used in the target nuclide generation step, that is, the purity of the daughter nuclide is increased, so that the target nuclide contained in the raw material and the isotopes of the element of the target nuclide can be reduced. As a result, it becomes possible to stabilize the specific radioactivity of the finally obtained target nuclide.

[0021] In the method for generating a target nuclide of the present invention, it includes a daughter nuclide generation step of generating a daughter nuclide from the parent nuclide and a target nuclide generation step of generating the target nuclide from the daughter nuclide, the removal step includes the second step, and it is preferable that the target nuclide generation step includes an adsorption step of adsorbing the target nuclide generated from the daughter nuclide onto an adsorbent and an elution step of eluting the target nuclide from the adsorbent using the reagent.

[0022] According to such an aspect, the reagent used in the elution step may also be contaminated with isotopes of the element of the target nuclide present in the air. Therefore, by removing the target nuclide and the isotopes of the element of the target nuclide from such a reagent, the purity of the reagent can be increased and the elution in the elution step can be efficiently performed, so that the specific activity of the finally obtained target nuclide can be stabilized.

[0023] In the method for producing a target nuclide of the present invention, it is preferable that the first step is executed at a timing determined based on the half-life of at least one of the parent nuclide and the daughter nuclide.

[0024] According to such an aspect, by executing the removal step at a timing determined based on the half-life of at least one of the parent nuclide and the daughter nuclide, it is possible to stabilize the generation of the daughter nuclide generated by the radioactive decay of the parent nuclide, so that the generation of the target nuclide can be stabilized.

[0025] For example, by setting the timing determined based on the half-life of at least one of the parent nuclide and the daughter nuclide to the timing according to the amount of the daughter nuclide, the specific activity of the daughter nuclide generated by radioactive decay from the parent nuclide can be optimized.

[0026] In the method for producing a target nuclide of the present invention, it is preferable that the elution step is executed at a timing determined based on the half-life of at least one of the daughter nuclide and the target nuclide.

[0027] According to such an aspect, by executing the removal step at a timing determined based on the half-life of at least one of the daughter nuclide and the target nuclide, it is possible to stabilize the generation of the target nuclide generated by the radioactive decay of the daughter nuclide, so that the specific activity of the target nuclide can be stabilized.

[0028] For example, by setting the timing determined based on the half-life of the daughter nuclide to the timing according to the amount of the target nuclide, the specific activity of the target nuclide generated by radioactive decay from the daughter nuclide can be optimized.

[0029] Also, for example, by setting the timing determined based on the half-life of the target nuclide to the timing according to the amount of the target nuclide, the amount of the target nuclide that decreases due to radioactive decay can be made as small as possible.

[0030] A method for generating a target nuclide is a method for generating a radioactive target nuclide by radioactive decay of a parent nuclide, including a first step of removing the target nuclide and isotopes of the element of the target nuclide from a raw material containing the parent nuclide, and a second step of removing the target nuclide and isotopes of the element of the target nuclide from a reagent used for generating the target nuclide. The method includes a removal step of performing at least one of the above steps, a daughter nuclide generation step of generating a daughter nuclide from the parent nuclide, and a target nuclide generation step of generating the target nuclide from the daughter nuclide. The parent nuclide is Th-228, the daughter nuclide is Ra-224, the target nuclide is Pb-212, and in the removal step, at least one of Pb-204, Pb-206, Pb-207, and Pb-208 is removed.

[0031] According to such an aspect, it is possible to increase the purity of Pb-212, which is the target nuclide to be generated. Therefore, it is possible to increase the specific activity per total Pb amount of the generated target nuclide.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0033] The method for generating the target nuclide of the present invention is a method for generating a radioactive target nuclide by one or a plurality of radioactive decays of a parent nuclide.

[0034] The method for generating the target nuclide includes, for example, a daughter nuclide generation step of generating a daughter nuclide from a parent nuclide, and a target nuclide generation step of generating a target nuclide from the daughter nuclide. Note that, in the method for generating the target nuclide of the present invention, only the target nuclide generation step of generating a target nuclide from a daughter nuclide may be executed.

[0035] The target nuclide can be appropriately set by the user who performs the operation. For example, it may be a daughter nuclide generated from a parent nuclide, or it may be a granddaughter nuclide generated from a daughter nuclide. In the present embodiment, an example in which a granddaughter nuclide generated from a daughter nuclide is used as the target nuclide will be described.

[0036] The target nuclide is not particularly limited as long as it is radioactive. Examples thereof include Bi-213, Pb-211, Pb-212, etc. In particular, Pb-211 and Pb-212 are preferable as target nuclides from the viewpoint of stabilizing the specific radioactivity because they have a plurality of natural (stable) isotopes (Pb-204, Pb-206, Pb-207, and Pb-208).

[0037] The daughter nuclide is not particularly limited as long as it is radioactive and can generate a target nuclide. For example, when the target nuclide is Pb-212, Ra-224 is preferable. When the target nuclide is Bi-213, Ac-225 is preferable. Further, when the target nuclide is Pb-211, Ra-223 is preferable.

[0038] The parent nuclide is not particularly limited as long as it is radioactive and can generate a daughter nuclide. For example, when the daughter nuclide is Ra-224, Th-228 is preferable. When the daughter nuclide is Ac-225, the parent nuclide is preferably Th-229. Further, when the daughter nuclide is Ra-223, the parent nuclide is preferably Th-227.

[0039] Hereinafter, as an embodiment of the present invention, a case where the parent nuclide is Th-228, the daughter nuclide is Ra-224, and the target nuclide Pb-212 is generated will be described.

[0040] FIG. 1 is a flowchart showing a daughter nuclide generation step of generating a daughter nuclide from a parent nuclide. As shown in FIG. 1, a first step, which is a removal step of removing the target nuclide (Pb-212) and isotopes of the element of the target nuclide from a raw material containing the above parent nuclide (Th-228), is performed (step S101). Incidentally, the target nuclide itself is also removed from the raw material in this step. The first step is preferably performed such that the amount of the isotope of the element of the target nuclide in the raw material containing the parent nuclide becomes, for example, 1 / 10 to 1 / 10000 of that before the first step is executed, more preferably 1 / 100 to 1 / 10000, and still more preferably 1 / 1000 to 1 / 10000.

[0041] The first step can be performed using an adsorbent that adsorbs isotopes of the element of the target nuclide. For example, it can be performed by a column separation method using a solid phase extractant. Incidentally, the removal of the isotope of the element of the target nuclide may be performed by an ion exchange resin column separation method, a chelate resin column separation method, a solvent extraction method, a precipitation method, or the like.

[0042] The removal of the isotope of the element of the target nuclide can be performed, for example, using di-t-butylcyclohexano 18-crown-6 (crown ether), which is classified as a highly selective solid phase extractant capable of adsorbing Pb when the element of the target nuclide is Pb. As such a highly selective solid phase extractant, for example, (trade name: Pb Resin (Pb resin), manufactured by Eichrom) can be used. Alternatively, it may be performed using a resin capable of adsorbing Pb. As such a resin, an ion exchange resin or a chelate resin can be used.

[0043] Incidentally, when the target nuclide is Pb-212, the isotopes of the element thereof include, for example, Pb-204, Pb-206, Pb-207, and Pb-208.

[0044] By storing the raw material containing the parent nuclide for a predetermined period, a daughter nuclide is generated by radioactive decay of the parent nuclide (step S102). The predetermined period for storing the raw material containing the parent nuclide is preferably a period during which the daughter nuclide can be efficiently generated from the parent nuclide, and for example, it may be determined based on the half-life of the parent nuclide and the half-life of the daughter nuclide.

[0045] The period during which the daughter nuclide can be efficiently generated from the parent nuclide can be calculated using, for example, simulation software. Such simulation software is not particularly limited, but for example, ORIGEN (ORNL Isotope Generation and Depletion Code) (released by Oak Ridge National Laboratory (ORNL)) can be used. When the parent nuclide in the raw material is Th-228, the predetermined period for storing the raw material is preferably, for example, 1 to 100 days, more preferably 1 to 30 days, and even more preferably 10 to 20 days.

[0046] When the predetermined period exceeds 100 days, the amount of the target nuclide (Pb-212) in the raw material and the amount of the isotope of the element of the target nuclide tend to increase, and the effect of performing the first step, which is the removal step, tends to weaken. On the other hand, considering the amount of Ra-224, which is the generated daughter nuclide, the predetermined period is preferably within 30 days. Further, considering the amount of Ra-224, which is the generated daughter nuclide, and the radiation energy of Pb-212, which is the generated target nuclide, the predetermined period is preferably 10 to 20 days.

[0047] The predetermined period for storing the raw material containing the parent nuclide is preferably a period during which at least the required radiation energy of Ra-224 can be obtained. If the period is shortened, the radiation energy of Th-228 required to obtain the required radiation energy of Ra-224 increases, and simulation can be performed using simulation software (ORIGEN).

[0048] When a sufficient time (predetermined period) required for radioactive decay elapses, a separation operation is performed on the raw material containing the parent nuclide (step S103). The separation operation can be performed using an isotope generator (hereinafter also simply referred to as a generator).

[0049] FIG. 2 is a schematic configuration diagram showing an example of the configuration of the generator. As shown in FIG. 2, the generator 100 has an anion exchange resin column 10. In the ion exchange resin column 10, for example, an adsorbent that can adsorb the parent nuclide and cannot adsorb the daughter nuclide is provided inside the column.

[0050] The generator 100 has a first syringe pump 20. The first syringe pump 20 is filled with, for example, a raw material containing a parent nuclide.

[0051] The first syringe pump 20 and the second syringe pump 30 are connected via a three-way cock 40 so as to be able to supply a filling material to the anion exchange resin column 10.

[0052] The generator 100 has a recovery unit 50. The recovery unit 50 can recover the raw material containing the daughter nuclide separated from the raw material containing the parent nuclide by the ion exchange resin column 10.

[0053] The generator 100 has a second syringe pump 30. The second syringe pump 30 is filled with, for example, a reagent capable of eluting the raw material containing the parent nuclide adsorbed on the anion exchange resin column.

[0054] The separation operation includes an adsorption step of adsorbing a radionuclide onto an adsorbent, and an elution step of eluting the radionuclide from the adsorbent using a reagent. In the adsorption step, when a raw material containing a parent radionuclide is supplied from the first syringe pump 20 to the anion exchange resin column 10, the adsorbent in the anion exchange resin column 10 adsorbs the parent radionuclide. The daughter nuclide flows out of the anion exchange resin column 10 without being adsorbed by the adsorbent. The effluent containing the daughter nuclide that has flowed out of the anion exchange resin column 10 is collected in the collection unit 50. Thus, the daughter nuclide can be separated and recovered from the parent radionuclide.

[0055] In the elution step, when a reagent is supplied from the second syringe pump 30 to the anion exchange resin column 10, the parent radionuclide adsorbed by the adsorbent is eluted and flows out of the anion exchange resin column 10. The effluent containing the parent radionuclide is collected in the collection unit 50 that has been pre-exchanged. The effluent containing the recovered parent radionuclide may be reused as the parent radionuclide of the raw material as needed.

[0056] A first step, which is a removal step of removing a target nuclide and an isotope of the element of the target nuclide from the raw material containing the daughter nuclide obtained by the separation operation, is performed (step S104). This first step can be performed in the same manner as the first step of step S101. That is, in step S104, the raw material containing the parent radionuclide in step S101 is used as the raw material containing the daughter nuclide, and for example, the target nuclide can be removed by a solid phase extraction agent column separation method.

[0057] The first step of step S104 is preferably executed at a timing determined based on the half-life of the daughter nuclide. For example, when Ra-224 is the daughter nuclide, the half-life of Ra-224 is 3.6319 days.

[0058] Therefore, since the radiation energy of Ra-224 decays over time after the separation operation in step S103, the first step of step S104 is preferably carried out continuously from the separation operation in step S103.

[0059] For example, if more than four days have elapsed since the separation operation in step S103, Ra-224 may decay to less than 50% of its radioactivity immediately after the completion of the step S103 process. Also, if more than 20 days have elapsed since the separation operation in step S103, Ra-224 may decay to less than 10% of its radioactivity immediately after the completion of the step S103 process. Therefore, it is preferable that the first step of step S104 be performed within four days after the completion of the separation operation in step S103.

[0060] The raw material containing Ra-224 obtained in this way serves as the raw material for the target nuclide generation step of generating the target nuclide from the daughter nuclide (step S105).

[0061] Figure 3 is a flowchart showing the target nuclide generation step of generating the target nuclide from the daughter nuclide. Pb-212 has a half-life of 10.64 hours. Therefore, it is difficult to store Pb-212 for a long time. Thus, Ra-224, whose half-life is sufficiently longer than that of Pb-212, is stored, and it is radioactively decayed to generate Pb-212 according to the timing when Pb-212 is used. As shown in Figure 3, the raw material containing Ra-224, which is the daughter nuclide, is stored for a predetermined period (step S201).

[0062] The first step, which is a removal step of removing the target nuclide and the isotope of the element of the target nuclide from the raw material containing the daughter nuclide, is performed (step S202). This first step can be performed in the same manner as step S104. Thus, the first step includes the step (step S202) of removing the target nuclide and the isotope of the element of the target nuclide from the daughter nuclide before the target nuclide generation step, that is, before the radioactive decay step (step S203) described later.

[0063] By storing the raw material containing the daughter nuclide for a predetermined period, the target nuclide is generated by the radioactive decay of the daughter nuclide (radioactive decay step: step S203). The predetermined period is preferably a period in which the amount of the target nuclide generated by the daughter nuclide is sufficiently large (the optimal amount) and such a target nuclide can be generated, and for example, it may be determined based on the half-life of the daughter nuclide or the like.

[0064] The predetermined period for storing the raw material containing the daughter nuclide can be calculated by simulation in the same manner as in step S102. When the daughter nuclide is Ra-224, the predetermined period is preferably, for example, 1 hour to 36 days, and more preferably 1 to 40 hours.

[0065] If the predetermined period exceeds 36 days, the radiation energy of Ra-224 may decrease to 1 / 1000 of that immediately after generation. Also, considering the radiation energy of the generated Pb-212, it is preferably 1 to 40 hours.

[0066] The predetermined period is the period during which the required specific activity of Pb-212 can be obtained. Shortening the period can obtain Pb-212 with a higher specific activity, but the radiation energy of Ra-224 required to obtain the required radiation energy of Pb-212 increases, and simulation can be performed using simulation software (ORIGEN).

[0067] As a removal step, the target nuclide contained in the reagent and the isotopes of the element of the target nuclide are removed (second step) (step S204). The removal of the isotopes of the element of the target nuclide, particularly stable isotopes, in the second step can be performed by a method similar to that in step S101 and step S104. The reagent is preferably one used in the elution step described later, and for example, hydrochloric acid, nitric acid, etc. can be used.

[0068] When a sufficient time (predetermined period) required for radioactive decay has elapsed, a separation operation is performed on the raw material containing the daughter nuclide (step S205). The separation operation can be performed by a method similar to that in step S103 using a generator.

[0069] In addition, the separation operation in step S205 can be performed using the generator 100 described during the separation operation in step S103. Also, for the generator 100 used in step S205, it is preferable to use a solid phase extraction material column 10 instead of the anion exchange resin column 10.

[0070] That is, in the adsorption step, when the raw material containing the daughter nuclide is supplied from the first syringe pump 20 to the solid phase extraction material column 10, the adsorbent of the solid phase extraction material column 10 adsorbs the target nuclide and the isotopes of the elements of the target nuclide. Nuclides other than the daughter nuclide and the target nuclide (for example, Bi-212, etc.) are eluted from the solid phase extraction material column 10 without being adsorbed by the adsorbent. Thereby, the target nuclide can be separated from nuclides other than the daughter nuclide and the target nuclide (for example, Bi-212). The eluent eluted from the solid phase extraction material column 10 containing nuclides other than the daughter nuclide and the target nuclide (for example, Bi-212) is recovered in the recovery unit 50. In addition, the daughter nuclide of the eluent may be reused as a raw material for generating the target nuclide as needed.

[0071] In the elution step, when the reagent is supplied from the second syringe pump 30 to the solid phase extraction material column 10, the target nuclide adsorbed by the adsorbent and the isotopes of the elements of the target nuclide are eluted. The eluent containing the target nuclide and the isotopes of the elements of the target nuclide is recovered in the recovery unit 50 that has been exchanged in advance.

[0072] In the elution step of step S205, it is preferable to use the reagent purified in step S204. Further, the elution step may be executed at a timing determined based on the half-life of at least one of the daughter nuclide and the target nuclide.

[0073] For example, when Ra-224 is used as the daughter nuclide, the half-life of Ra-224 is 3.6319 days. When Pb-212 is used as the target nuclide, the half-life of Pb-212 is 10.64 hours.

[0074] Therefore, when eluting Pb-212, the timing of the elution step is preferably 1 hour to 36 days later, and more preferably 1 to 40 hours later.

[0075] The Pb-212 generated in this way can be used, for example, as a therapeutic agent for targeted therapy, etc. (step S206).

[0076] Thus, the method for generating the target nuclide of the present invention includes a removal step of performing at least one of a first step of removing the target nuclide and the isotope of the element of the target nuclide from the raw material containing the daughter nuclide, and a second step of removing the target nuclide and the isotope of the element of the target nuclide from the reagent used to generate the target nuclide. Note that in the removal step, either one of the first step and the second step may be performed even once, or each of the first step and the second step may be performed a plurality of times.

[0077] Note that in the above removal step, regardless of the isotope of the element of the target nuclide, the target nuclide and the isotope of the element of the target nuclide are adsorbed on the adsorbent. Therefore, from the raw material, the target nuclide is removed together with the isotope of the element of the target nuclide.

[0078] For example, when Pb-212 is the target nuclide, in the removal step, at least one of Pb-204, Pb-206, Pb-207, and Pb-208 is removed, and unless an adsorbent capable of selectively adsorbing isotopes is used, these are removed in the removal step without distinction.

Example

[0079] [Test Example 1] (Comparison of specific radioactivity) (Generation of Pb-212 by Comparative Example) The generation of Pb-212 by the comparative example was performed according to the following procedure.

[0080] A raw material of Th-228 (10 MBq) was obtained. The raw material of Th-228 (10 MBq) was used after 100 days had passed and it had been stored for an additional two weeks until use. Step (1-1) The above raw material containing the parent nuclide (Th-228) was separated into daughter nuclides over 30 minutes by an anion exchange resin column separation method. Step (1-2) The raw material containing the daughter nuclide (Ra-224) separated in step (1-1) was stored for 50 hours. Step (1-3) The raw material containing the daughter nuclide (Ra-224) was further stored for 40 hours to generate Pb-212 by radioactive decay. In Step (1-4), the raw materials produced in Step (1-3) were separated by a cation exchange resin column separation method over 2 hours to elute Pb-212 from Ra-224, Bi-212, etc.

[0081] When Steps (1-1) to (1-4) were completed, the radiation energy and mass of the parent nuclide Th-228, daughter nuclide Ra-224, target nuclide Pb-212, and the isotope Pb-208 of the element of the target nuclide contained in each solution were calculated using simulation software (ORIGEN). The results are shown in Table 1.

[0082] As shown in Table 1, when Th-228 (10 MBq) was used as the raw material, the production radiation energy of the target nuclide Pb-212 was 4.4 MBq (8.6 x 10 -11 g). This Pb-212 contains 3.2x10 -8 g of Pb-208.

[0083] If the specific activity of Pb-212 is defined as (radiation energy Bq of Pb-212) / [(mass g of Pb-212) + (mass g of Pb-208)], the specific activity of Pb-212 is 1.4 x 10 14 Bq / g. Here, when compared with the specific activity of carrier-free Pb-212, which is 5.14 x 10 16 Bq / g, the specific activity of Pb-212 is 0.3% of that. The results are shown in Table 3.

[0084]

Table 1

[0085] (Production of Pb-212 according to the example) The production of Pb-212 according to the example was carried out in the following procedure.

[0086] Raw materials of Th-228 (10 MBq) were obtained and stored for 100 days until use. Immediately before using the raw material in Step (2-1), the target nuclides (such as Pb-212 and Pb-208) contained in the Th-228 solution were removed using Pb Resin so that their amount became 1 / 1000 (Removal Step, First Step). In Step (2-2), the daughter nuclides and target nuclides were removed so that the amount of daughter nuclides in the Th-228 solution became 1 / 100. The removal of the daughter nuclides and target nuclides was carried out for 30 minutes by the anion exchange resin column separation method. In Step (2-3), the Th-228 after the implementation of Step (2-3) was stored for a predetermined period (two weeks) to generate Ra-224 by radioactive decay. In Step (2-4), the daughter nuclides were separated from the raw material containing the parent nuclides after storage over 30 minutes. In Step (2-5), the target nuclides (Pb-212 and Pb-208) contained in the Ra-224 solution were removed using Pb Resin so that their amount became 1 / 100 (Removal Step, First Step). In Step (2-6), the raw material containing the daughter nuclide Ra-224 after Step (2-6) was stored for 50 hours. In Step (2-7), the target nuclides (Pb-212 and Pb-208) contained in the Ra-224 solution were removed using Pb Resin so that their amount became 1 / 100 (Removal Step, First Step). In Step (2-8), the raw material containing Ra-224 was stored for 10 hours to generate Pb-212 by radioactive decay. In Step (2-9), the isotopes (such as Pb-204, Pb-206, Pb-207, and Pb-208) of the element of the target nuclide contained in the reagent used in the elution step were removed using Pb Resin so that their concentration became 1×10 -12 g / mL (1 ppt) or less (Removal Step, Second Step). In Step (2-10), the Ra-224 raw material containing Pb-212 etc. generated in Step (2-9) was separated over 1 hour by the solid phase extraction agent column separation method (Pb Resin column method) to separate Pb-212 from Ra-224, Bi-212, etc.

[0087] When the above steps (2-1) to (2-10) were completed, the radiation energy and mass of the parent nuclide Th-228, daughter nuclide Ra-224, target nuclide Pb-212, and the isotope Pb-208 of the element of the target nuclide contained in each solution were calculated using simulation software (ORIGEN). The results are shown in Table 2.

[0088] According to the results, when Th-228 (10 MBq) was used as the raw material using the method for producing the target nuclide of the present invention, the radiation energy of Pb-212, which is the target nuclide, was 2.4 MBq (4.7 × 10 -11 g). This Pb-212 contained 1.8 × 10 -11 g of Pb-208.

[0089] In the same manner as the description of the comparative example, the specific activity of Pb-212 was defined and calculated. As a result, the specific activity of Pb-212 obtained in the example was 3.7 × 10 16 Bq / g. This specific activity is 72% of the specific activity of carrier-free Pb-212.

[0090] [Table 2]

[0091] [Table 3]

[0092] As described above, the specific activity of the Pb-212 product of the example obtained by the method for producing the target nuclide of the present invention is approximately 240 times higher than that of Pb-212 of the comparative example produced by the conventional method.

[0093] [Test Example 2] (Comparison of production time of target nuclide) Table 4 shows the amount and specific activity of Pb-212 when the storage time of step (1-6) of the comparative example was 10 hours and when the storage time of step (2-9) of the example was 10 hours, as described in Test Example 1. However, the separation operation time was not included in order to align the conditions.

[0094]

Table 4

[0095] When the storage time of the steps (1-6) of the comparative example described in Test Example 1 is 40 hours and the storage time of the steps (2-9) of the example is 40 hours, the amount and specific activity of Pb-212 in each case are shown in Table 5. However, the separation operation time was not included in order to align the conditions.

[0096]

Table 5

[0097] As shown in Tables 4 and 5, it was found that the specific activity of Pb-212 generated in the examples was higher than that in the comparative examples. Also, it was found that the specific activity of Pb-212 generated in the comparative examples and the examples was higher at a storage time of 10 hours than at a storage time of 40 hours. Moreover, this was remarkable in the examples.

[0098] [Test Example 3] (Measurement of Adsorption Distribution Coefficient with Respect to Acid Concentration) A Pb adsorption test was performed using solutions with different acid concentrations, and the distribution coefficient was calculated. That is, the adsorption behavior of Th(IV), Ra(II), Pb(II), and Bi(III) on Pb Resin (manufactured by Eichrom), which is an adsorbent, was tested.

[0099] (Calculation of Distribution Coefficient) The distribution coefficient (K d ) was determined by the following formula (1).

Equation

[0100] (Measurement of Element Concentration and Radioactivity Concentration) The measurement of the elemental concentrations of Th, Pb, Bi, etc. was performed by inductively coupled plasma mass spectrometry (ICP-MS), and the measurement of the radioactivity concentration was performed by gamma-ray spectrometry using a Ge detector.

[0101] (Measurement of acid concentration) As the acid, a nitric acid solution was used. The acid concentration of the nitric acid solution was determined by neutralization titration using phenolphthalein as an indicator.

[0102] Figure 4 shows the measurement results of the adsorption distribution coefficient with respect to the acid concentration. Specifically, Figure 4 shows the results of examining the adsorption behavior of Ra(II) and Pb(II) on Pb Resin. As shown in Figure 4, it was found that Pb(II) is adsorbed on Pb Resin with high efficiency even from a high-concentration nitric acid solution (for example, 8M HNO3) (KD = 600 - 700 mL / g), and Th(IV) is not adsorbed on Pb Resin from 8 M HNO3 (KD = <10 mL / g).

[0103] Based on this, by flowing an 8 M HNO3 solution mainly containing Th-228, Pb-212, and Pb-208 through a Pb Resin column, the lead isotopes contained in the Th-228 solution, namely Pb-212 and Pb-208, etc., can be reduced to 1 / 1000 or less of their original contained amounts.

[0104] Also, it was found that Pb(II) is adsorbed on Pb Resin with high efficiency from nitric acid solutions over a wide range of concentrations, and Ra(II) is not adsorbed on Pb Resin. For example, the distribution coefficient from a 1M HNO3 solution to Pb Resin was KD = 2,000 - 3,000 mL / g for Pb(II) and KD = 10 mL / g for Ra(II). Based on this, using Pb Resin, the total amount of lead isotopes contained in the Ra-224 solution can be reduced to 1 / 100 or less of its initial amount.

Explanation of symbols

[0105] 100 Generator 10 Ion exchange resin column 20 First syringe pump 30 Second syringe pump

Claims

1. A method for generating a radioactive target nuclide by one or multiple radioactive decays of a parent nuclide, comprising: A removal step of performing a first step of removing the target nuclide and isotopes of the element of the target nuclide from a raw material containing the parent nuclide; A daughter nuclide generation step of generating a daughter nuclide from the parent nuclide; A target nuclide generation step of generating the target nuclide from the daughter nuclide, wherein the first step includes a step of removing the target nuclide and isotopes of the element of the target nuclide from the raw material containing the parent nuclide in the daughter nuclide generation step by a column separation method, a solvent extraction method, or a precipitation method. A method for generating a target nuclide, characterized in that.

2. The target nuclide generation step includes an adsorption step of adsorbing the target nuclide generated from the daughter nuclide onto an adsorbent provided in an anion exchange resin column, and an elution step of eluting the target nuclide from the adsorbent using a reagent. The removal step performs a second step of removing the target nuclide and isotopes of the element of the target nuclide from the reagent used in the elution step. The method for generating a target nuclide according to claim 1, characterized in that.

3. The first step includes a step of removing the target nuclide and isotopes of the element of the target nuclide from the daughter nuclide before the target nuclide generation step. The method for generating a target nuclide according to claim 1 or 2, characterized in that.

4. The method for generating a target nuclide according to any one of claims 1 to 3, characterized in that the first step is performed at a timing determined based on the half-life of at least one of the parent nuclide and the daughter nuclide.

5. The method for generating a target nuclide according to claim 2, characterized in that the elution step is performed at a timing determined based on the half-life of at least one of the daughter nuclide and the target nuclide.

6. A method for generating a radioactive target nuclide by radioactive decay of a parent nuclide, comprising: a removal step of performing a first step of removing the target nuclide and isotopes of the element of the target nuclide from a raw material containing the parent nuclide; a daughter nuclide generation step of generating a daughter nuclide from the parent nuclide; a target nuclide generation step of generating the target nuclide from the daughter nuclide, wherein the first step includes a step of removing the target nuclide and isotopes of the element of the target nuclide from the raw material containing the parent nuclide in the daughter nuclide generation step by a column separation method, a solvent extraction method, or a precipitation method; the parent nuclide is Th-228, the daughter nuclide is Ra-224, and the target nuclide is Pb-212; A method for generating a target nuclide, characterized in that at least one of Pb-204, Pb-206, Pb-207, and Pb-208 is removed in the removal step.

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