JP7515815B1 - Method for extracting technetium-99m from low specific activity molybdenum-99, method for producing physiological saline solution containing technetium-99m using said method, and system for recovering technetium-99m from natural molybdenum - Google Patents

Abstract

The present invention relates to a method for extracting technetium-99m from low specific activity molybdenum-99 in a short period of time, without being affected by the amount of molybdenum solution.
[Solution] A method for recovering technetium-99m from low specific activity molybdenum-99 is a method for recovering technetium-99m, a daughter nuclide produced by the decay of molybdenum-99 contained in a high-concentration molybdenum solution containing molybdenum-99 with low specific activity, by separating it with activated carbon, characterized in that the activated carbon is immersed in the molybdenum solution and selectively adsorbs trace amounts of technetium-99m even when the ratio of the number of molybdenum-99 atoms is ¹⁰¹⁶ or more.
[Selected Figure] Figure 1

Description

The present invention relates to a process and system for recovering, concentrating, purifying and separating radiopharmaceuticals made from low specific activity radioactive molybdenum-99 ( ⁹⁹ Mo) and radioactive technetium-99m ( ^99m Tc) as a raw material for labeling compounds thereof.

Tc (technetium) is a transition metal with atomic number 43, located in the 7th group and 5th period. Among the isotopes of Tc, ^99m Tc (technetium 99m) emits only gamma rays with a short half-life (6 hours) suitable for imaging diagnosis and a weak energy (140 keV) suitable for in-vitro measurement, and is generated by a generator ( ⁹⁹ Mo/ ^99m Tc generator) that utilizes radioactive equilibrium with ⁹⁹ Mo (molybdenum 99), and is widely used in nuclear medicine imaging diagnosis. Because of its short half-life, ^99m Tc is usually used in a method in which its parent nuclide ⁹⁹ Mo (half-life 66 hours) is obtained and ^99m Tc is obtained from ⁹⁹ Mo.

As a method for obtaining ⁹⁹ Mo, the fission method has been used worldwide as a practical technology, in which ⁹⁹ Mo with a very ^high specific radioactivity (the strength of radioactivity per unit mass of a substance containing a radioisotope) is produced by using the fission method by irradiating fissile uranium ( 235 U; uranium) with neutrons, and then separated from the fission products produced at the same time. In this case, since the specific radioactivity of ⁹⁹ Mo is high, the actual manufacturing technology used is to use aluminum oxide (alumina), which is generally used for medical purposes, as an adsorbent, to support Mo ( ⁹⁹ Mo) below the Mo saturation adsorption level, and to obtain ^99m Tc by eluting (milking) the daughter nuclide of ^{99 Mo} produced from Mo ( ⁹⁹ Mo) adsorbed on the alumina column with physiological saline.

On the other hand, there is a method for producing the desired ⁹⁹ Mo by using a molybdenum compound as a raw material, instead of uranium, as the raw material and utilizing the neutron activation (n, γ) reaction of ⁹⁸ Mo contained as one of its isotopes (a neutron capture reaction in which a substance irradiated with neutrons n undergoes a nuclear reaction and emits γ rays when it is changed into a radioactive substance). The specific radioactivity of ⁹⁹ Mo produced by this (n, ^γ ) method is extremely low, about 1/ ^10,000 , compared with that of the Fission method, and therefore, in order to put the (n, γ) method into practical use, it is necessary to separate and purify and recover a trace amount of ^99m Tc as a daughter nuclide produced from a trace amount of ⁹⁹ Mo contained in a large amount of non-radioactive Mo. So far, the sol-gel method, MEK method, and sublimation method have been known as methods that have been investigated or put into practical use as the (n, γ) method. The present inventors have separately developed and proposed a PZC (polyzirconium compound) method, which is a type of sol-gel method as an (n, γ) method.

Patent Document 1 describes a method and an apparatus for purifying a 99m Tc recovery liquid, which comprises the steps of: generating radioactive molybdenum ⁹⁹ Mo, which is the parent nuclide of technetium, by irradiating natural isotope Mo as a raw material with neutrons in a nuclear reactor through a ⁹⁸ Mo(n, γ) reaction; passing a Mo solution containing ⁹⁹ Mo through an activated carbon (AC) column to selectively adsorb and collect ^99m Tc, which is the daughter nuclide of ⁹⁹ Mo; washing away Mo (including ⁹⁹ Mo) remaining in the voids of the AC column and in the pores of the AC that is not adsorbed by the activated carbon with water; eluting ^{the 99m} Tc adsorbed on the AC from the AC using an alkali (caustic soda NaOH, etc.); and passing the solution through an AL column packed with aluminum oxide (alumina) located downstream of the AC column to remove Mo, ⁹⁹ Mo, radioactive impurities, and other impurities contained in the 99m Tc recovery liquid, thereby purifying the ^99m Tc recovery liquid.

In Patent Document 2, similar to Patent Document 1, a method is compared and examined in which natural isotope Mo is used as a raw material, and ⁹⁹ Mo is irradiated with neutrons in a nuclear reactor to generate ⁹⁸ Mo (n, γ) reaction, and then ^99m Tc, the daughter nuclide of ⁹⁹ Mo, is recovered by using spherical activated carbon (BAC), and a method is compared and examined in which a Mo solution containing ⁹⁹ Mo is passed through an AC column by a pressurized flow in which it is pushed into the AC column by a pump, or a reduced pressure flow in which it is sucked in by a pump, and then a method is examined in which Mo (including ⁹⁹ Mo) that is not adsorbed to the activated carbon and remains in the voids in the AC column and in the pores of the AC is washed away with water, and then an alkali (caustic soda NaOH, etc.) solution is used to elute ^{the 99m} Tc adsorbed on the AC from the AC by heating to about 80° C. to promote elution, and then Mo, ⁹⁹ Mo, radioactive impurities, and other impurities contained in the ^99m Tc recovery solution are removed by a column packed with AL arranged after the AC column, thereby obtaining ^{99m Tc.} A method and apparatus for purifying Tc recovery fluid is described.

Patent Document 3, like Patent Documents 1 and 2, describes a method for recovering 99m Tc, a daughter nuclide, from ⁹⁹ Mo produced by the ⁹⁸ Mo(n,γ) reaction produced by irradiating natural isotope Mo as a raw material with neutrons in a nuclear reactor, by using AC. The method mainly involves piping a ^Mo solution tank containing ⁹⁹ Mo, which is installed inside a double-partitioned cell to shield radiation such as γ rays emitted from ⁹⁹ Mo and prevent leakage of radioactive materials, to an external cell in which an AC column with low radiation shielding ability is installed, piping the Mo solution to the AC column installed in the external cell, and then circulating the liquid back to the internal Mo solution tank, thereby selectively adsorbing and collecting ^99m Tc to prevent radiation leakage to the outside, and then washing out the non-adsorbed Mo (including ⁹⁹ Mo) remaining in the voids of the AC column and in the pores of the AC with water, and then eluting ^{the 99m} Tc adsorbed to the AC from the AC using an alkali (caustic soda NaOH, etc.) solution, and finally The present invention describes a method and an apparatus for purifying ^{a 99m} Tc recovery liquid by removing Mo, ⁹⁹ Mo, radioactive impurities and other impurities contained in the ^99m Tc recovery liquid by passing the liquid through a column filled with AL placed after the AC column.

Patent No. 5427483 Patent No. 5916082 Patent No. 6355462

In the prior art described in Patent Documents 1 to 3, in order to recover ^99m Tc produced in a Mo solution containing ⁹⁹ Mo, an AC capable of selectively adsorbing ^99m Tc is packed inside a metallic cylindrical container (column) connected to the inlet and outlet of the Mo solution, and the Mo solution is passed through the column.

In the conventional method, in order to completely adsorb and collect ^99m Tc contained in the Mo solution by passing it through an AC column, it is necessary to limit the flow rate when passing the Mo ( ⁹⁹ Mo) solution through a flow-through AC column. Specifically, since the ⁹⁹ Mo concentration is low in a low specific activity Mo solution, in order to recover the desired amount of ^99m Tc, it is necessary to pass a large amount of Mo ( ⁹⁹ Mo) solution through the AC column. For example, when the flow rate per unit time for passing through an AC column filled with 5 g of AC is a maximum of 50 to 100 mL/min, it takes 20 to 40 minutes or more to pass 2.0 L of Mo ( ⁹⁹ Mo) solution through the AC column, and the work efficiency is an issue in recovering ^99m Tc with a short half-life in a short time for diagnostic use.

However, when the amount of Mo ( ⁹⁹ Mo) solution is, for example, 5 to 20 L, it takes 2 to 5 hours or more to pass the solution through the AC column to adsorb and collect ^99m Tc, reducing the efficiency of the work and causing the short half-life of the recovered ^99m Tc to change to ^99g Tc, which may make it unusable as a pharmaceutical raw material. ^99g Tc (technetium 99grand) is one of the radioisotopes of Tc with a half-life of 211,100 years that is produced from ^99m Tc, and is produced in proportion to the time that has elapsed since the extraction and separation of the pharmaceutical raw material ^99m Tc, and if there is too much, it becomes an impurity in the pharmaceutical raw material ^99m Tc.

In order to recover technetium-99m ( 99m Tc), which is a daughter nuclide of ⁹⁹ Mo produced by decay of ⁹⁹ Mo and contained in a high-concentration Mo solution containing radioactive molybdenum-99 ( ⁹⁹ Mo) as a radiopharmaceutical raw material, from the high-concentration Mo solution, an AC capable of selectively adsorbing and recovering a trace amount ^{of 99m Tc} even when the atomic ratio of Mo ( ⁹⁹ Mo) is 10 ¹⁶ or more may be used.

As a method for selectively separating and recovering the daughter nuclide ^99m Tc of ⁹⁹ Mo formed in a high-concentration Mo solution, if a metallic mesh cylindrical container containing an AC is immersed in the Mo solution and the surrounding Mo solution is stirred and flowed to adsorb and collect ^99m Tc in the Mo solution, it becomes unnecessary to pass the solution through an AC column which requires flow rate restriction. In other words, if ^{the 99m} Tc contained in the Mo solution is adsorbed and collected by the AC immersed in the Mo solution, it is not necessary to pass the solution through the AC column for a long time.

The present invention aims to provide a method for extracting technetium-99m from low specific activity molybdenum-99 in a short period of time, without being affected by the amount of molybdenum solution.

In order to solve the above problems, the method for recovering technetium-99m from low specific activity molybdenum-99 according to the present invention is a method for recovering technetium-99m, a daughter nuclide produced by the decay of molybdenum-99 contained in a high-concentration molybdenum solution containing molybdenum-99 with low specific activity, by separating it with activated carbon, characterized in that the activated carbon is immersed in the molybdenum solution and selectively adsorbs a trace amount of technetium-99m even when the ratio of the number of molybdenum atoms is ¹⁰ or more.

The method for recovering technetium-99m from low specific activity molybdenum-99 is characterized in that the molybdenum solution contains the radioactive nuclide molybdenum-99 produced by the neutron capture (n, gamma) reaction of the natural isotope of molybdenum.

The method for recovering technetium-99m from low specific activity molybdenum-99 is characterized in that the activated carbon is packed in a cylindrical metal mesh container that is not a column in which the flow rate is restricted, and is immersed in the molybdenum solution that is being stirred and flowing.

The method for producing a physiological saline solution containing technetium-99m according to the present invention is characterized in that the molybdenum remaining in the pores of the activated carbon to which technetium-99m recovered by the method for recovering technetium-99m from low specific activity molybdenum-99 is adsorbed is washed with water, the solution containing technetium-99m eluted from the activated carbon with an alkaline solution is passed through an IER column packed with a strongly acidic cation exchange resin to remove the alkaline components, and further passed through an AL column packed with alumina to capture technetium-99m, and the technetium-99m is eluted from the alumina column using physiological saline to purify the solution into a physiological saline solution containing technetium-99m from which impurities have been removed.

The method for producing a physiological saline solution containing technetium-99m is characterized in that the container containing the activated carbon, the IER column, and the AL column are made of materials that can be sterilized in an autoclave.

Furthermore, the system for recovering technetium-99m from natural molybdenum of the present invention comprises: a means for producing a high-concentration molybdenum solution containing molybdenum-99 with low specific activity produced by the neutron capture (n, gamma) reaction of the natural isotope of molybdenum; a means for producing the daughter nuclide technetium-99m in the molybdenum solution by the decay of molybdenum-99; and a means for filling a metallic mesh cylindrical container, which is not a column with a restricted flow rate, with activated carbon and immersing the activated carbon in the molybdenum solution which is being stirred and flowing. The apparatus is characterized by having a means for washing the remaining molybdenum-99 from the activated carbon on which technetium-99m has been adsorbed, a means for eluting technetium-99m from the washed activated carbon using an alkaline solution, passing the solution through a strong acid cation exchange resin column to remove the alkaline components, and passing the resulting solution through an alumina column to capture technetium-99m, and a means for eluting technetium-99m from the alumina column using physiological saline and recovering purified technetium-99m.

According to the present invention, a high-concentration Mo solution containing radioactive ^99Mo is produced and left for about 24 hours, whereby ^99mTc is produced from ^99Mo and mixed in a state of radioactive equilibrium (the ratio of the radioactivities of the parent and daughter nuclides is constantly balanced). Instead of passing the solution through an AC column as in the conventional method, an AC-filled metal mesh cylindrical container is immersed in the stirred and flowing Mo solution, whereby ^99mTc can be constantly adsorbed and captured by the AC.

Whether the amount of high-concentration Mo solution is as small as 0.1 L or as large as 5 to 20 L, the desired amount of ^99m Tc is selectively adsorbed and collected by AC during the time it takes for ^99m Tc to be produced from ⁹⁹ Mo and reach radioactive equilibrium or the time the desired amount of ^99m Tc is produced, and this method is particularly effective for recovering ^99m Tc with a short half-life (6 hours).

When ^99m Tc adsorbed and collected on AC in a cylindrical metal mesh container is desorbed, the Mo ( ⁹⁹ Mo) remaining unadsorbed on the AC is also leached out at the same time as ^99m Tc. However, by passing the ^99m Tc recovery solution through an alumina column, it is possible to purify and recover high-purity ^99m Tc for use as a pharmaceutical raw material without contamination with radioactive impurities such as Mo ( ⁹⁹ Mo).

FIG. 1 is a diagram showing an outline of a method for extracting technetium-99m from low specific activity molybdenum-99 according to the present invention, a method for producing a physiological saline solution containing technetium-99m using the method, and a system for recovering technetium-99m from natural molybdenum. FIG. 1 is a diagram showing a conventional method for passing a molybdenum solution through an activated carbon column. FIG. 1 is a diagram showing a method for extracting technetium-99m from low specific activity molybdenum-99 according to the present invention, a method for producing a physiological saline solution containing technetium-99m using the method, and the configuration of a system for recovering technetium-99m from natural molybdenum. FIG. 1 is a diagram comparing the process of the present invention for extracting technetium-99m from low specific activity molybdenum-99 with the process of a conventional method. FIG. 2 is a diagram showing the process conditions for short-time production of a physiological saline solution containing Technetium-99m according to the present invention.

Instead of passing a Mo solution containing ⁹⁹ Mo through an AC column to recover ^99m Tc, a cylindrical metal (e.g., stainless steel) mesh container filled with AC is constantly immersed in a ⁹⁹ Mo solution tank, and the Mo solution in which the AC container is immersed is stirred and kept flowing, so that the AC is always in a state where it can adsorb ^99m Tc.

At a predetermined or arbitrary timing, the AC container is removed from the Mo solution, and the non-AC-adsorbed ^99Mo remaining in the AC pores is washed away with water. The AC with adsorbed ^99mTc is then treated with an alkaline solution to elute the ^99mTc captured by the AC, and the solution is purified with a strongly acidic cation exchange resin (IER) and alumina (AL) to recover high-purity ^99mTc .

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. ^99m Tc is the radioactive nuclide technetium 99m, and ⁹⁹ Mo is the radioactive nuclide molybdenum 99. ⁹⁹ Mo is the parent nuclide, and ^99m Tc is the daughter nuclide. AC is activated carbon, IER is ion exchange resin, and AL is alumina (aluminum oxide).

1 and 3 show a method for extracting technetium-99m from low specific activity molybdenum-99, a method for producing a physiological saline solution containing technetium-99m using the method, and a system for recovering technetium-99m from natural molybdenum. Instead of passing a Mo solution containing ^99Mo through an AC column, ^99mTc in the Mo solution is adsorbed and collected in an AC-filled metal mesh cylindrical container, and ^99mTc is purified and recovered.

Figure 2 shows a conventional method of passing a molybdenum solution through an activated carbon column. Figure 4 shows a comparison between the method of extracting technetium-99m from low specific activity molybdenum-99 according to the present invention and the conventional process. Figure 5 shows the process conditions for short-time production of a physiological saline solution containing technetium-99m.

The method for extracting technetium-99m from low specific activity molybdenum-99 involves separating and recovering the daughter nuclide technetium-99m produced by the decay of molybdenum-99 contained in a high-concentration molybdenum solution containing molybdenum-99 with low specific activity using activated carbon.

The activated carbon is packed in a cylindrical metal mesh vessel that is not a column in which the flow rate is restricted, and is immersed in a molybdenum solution that is flowing by stirring, and selectively adsorbs minute amounts of technetium-99m in the solution even if the ratio of the number of molybdenum atoms is 10 ¹⁶ or more. The molybdenum solution contains the radioactive nuclide molybdenum-99 produced by the neutron capture (n, γ) reaction of the natural isotope molybdenum.

The method for producing a physiological saline solution containing technetium-99m involves washing with water the molybdenum remaining in the pores of the activated carbon to which technetium-99m recovered in the method for recovering technetium-99m from low specific activity molybdenum-99 has been adsorbed, passing the solution containing technetium-99m eluted from the activated carbon with an alkaline solution through an IER column packed with a strongly acidic cation exchange resin to remove the alkaline components, passing the solution through an AL column packed with alumina to capture technetium-99m, and eluting the technetium-99m from the alumina column using physiological saline to refine the solution into a physiological saline solution containing technetium-99m from which impurities have been removed.

The system for recovering technetium-99m from natural molybdenum includes a means for producing a high-concentration molybdenum solution containing molybdenum-99 with low specific activity produced by the neutron capture (n, gamma) reaction of the natural isotope molybdenum, a means for producing the daughter nuclide technetium-99m in the molybdenum solution by the decay of molybdenum-99, a means for filling a metal mesh cylindrical container that is not a column with a restricted flow rate with activated carbon and immersing the activated carbon in a molybdenum solution that is being stirred and flowing, a means for washing the remaining molybdenum-99 from the activated carbon to which technetium-99m has been adsorbed, a means for eluting technetium-99m from the washed activated carbon using an alkaline solution, passing the solution through a strong acid cation exchange resin column to remove the alkaline components, and passing the resulting solution through an alumina column to capture technetium-99m, and a means for eluting technetium-99m from the alumina column using physiological saline and recovering purified technetium-99m.

As shown in Fig. 1, a tank 100 storing Mo solution is placed in a hot cell that is shielded from radiation because ⁹⁹ Mo has a high radiation dose. A stirrer 110 is provided inside the Mo solution tank 100 to stir the solution, and a support 130 is also provided to hold a metal mesh cylindrical container 120 containing AC in the solution. A plurality of tanks 100 may be placed in the hot cell.

To produce the radiopharmaceutical raw material ^99mTc , a _Na299MoO4 solution is supplied to a tank 100 as a Mo solution containing the radioactive nuclide ^99Mo . _99Mo ^is produced by irradiating natural isotope _MoO3 with neutrons in a nuclear reactor ⁱⁿ advance. When _MoO3 containing ^99Mo is dissolved in _an alkaline (NaOH) solution, a pH- _neutral ^Na299MoO4 solution is produced.

The Mo solution containing radioactive ^99Mo is, for example, a high-concentration Mo solution containing 500g of Mo (750g as _MoO3 ) in 2L. To obtain about 500 Ci (curies) of ^99mTc at one time, a high-concentration Mo solution containing 500g of Mo in 2L is required, but a high-concentration Mo solution containing 50g of Mo (75g as _MoO3 ) in 200mL, which is one-tenth of that amount, or a high-concentration and large-volume Mo solution containing 5kg of Mo (7.5kg as _MoO3 ) in 20L, which is ten times the amount, may also be used.

A metal mesh cylindrical container 120 containing AC is placed in a tank 100 containing a Mo solution containing ⁹⁹ Mo, and the Mo solution is stirred using a stirrer 110 or a water flow from a circulating pump while the container is held in the Mo solution by a support 130. By maintaining this state, ^99m Tc generated in the Mo solution is adsorbed and collected by the AC.

Since ^99m Tc generated from ⁹⁹ Mo reaches a state of radiation equilibrium in about 24 hours, the metal mesh cylindrical container 120 may be pulled out of the Mo solution after waiting for that time to elapse, or may be pulled out at any time before reaching radiation equilibrium. ^99m Tc can be adsorbed by AC during the period from when the metal mesh cylindrical container 120 is immersed in the Mo solution until it is pulled out.

As shown in Fig. 2, the conventional TcMM (Technetium-99m Master Milker) is a method in which the entire amount of Mo solution is passed through an AC column in order to adsorb ^99m Tc in the Mo solution to AC. The AC column is a cylindrical container filled with AC, and the liquid comes into contact with the AC as it passes through the cylinder from the inlet to the outlet. In this method, the flow rate of the Mo solution passing through the AC column is limited, which limits the ability of the AC column to process the Mo solution, and this is problematic as a recovery technology for ^99m Tc, which has a short half-life (lifetime).

As shown in Fig. 3, the system for highly concentrating, purifying and recovering ^99m Tc from a low specific activity Mo solution is installed in a hot cell 140 isolated by a thick shielding wall to shield against high radiation. Activated ⁹⁹ _MoO3 is dissolved in alkali to generate a ⁹⁹ MoO3 solution in advance. The ⁹⁹ _MoO3 solution is supplied to a plurality of storage tanks 100 with a capacity of 1 to 20 L provided in the hot cell ₁₄₀ , and a high concentration Mo solution with a ⁹⁹ Mo radioactivity of 500 Ci is stored.

The metallic mesh cylindrical container 120 containing the AC is placed in the tank 100 using a hook, a carrier, or the like, and is held in the Mo solution containing ⁹⁹ Mo by a support 130. The radioactive ⁹⁹ Mo decays and changes to ^99m Tc, forming a Mo solution containing ^99m Tc.

Once the metal mesh cylindrical container 120 has been immersed in the Mo solution, it is advisable to stir the Mo solution with the stirrer 110 to bring the Mo solution into efficient contact with the AC. ^99m Tc produced in the Mo solution is adsorbed and collected by the AC. The metal mesh cylindrical container 120 is then lifted out of the tank 100, and the AC with ^99m Tc adsorbed thereon is collected. The AC is then placed in a column and washed with water to remove ⁹⁹ Mo and other elements remaining unadsorbed in the AC.

An alkaline (NaOH) solution is supplied to the AC-containing column while adjusting the flow rate and temperature, and passed through the column. By treating with the alkaline solution, ^99m Tc is eluted from the AC into the alkaline solution, and the discharged alkaline solution containing ^99m Tc is passed through the IER column 150. In the IER column 150, the alkaline component is captured by a strongly acidic cation exchange resin, and the discharged solution containing ^99m Tc is passed through the AL column 160.

In the AL column 160, ^99m Tc is captured by alumina, and impurities are discharged. Then, physiological saline with a NaCl concentration of about 0.9% is passed through the AL column 160, whereby ^99m Tc is eluted from the alumina into the physiological saline. This is discharged as a ^99m _TcO4 solution together with the physiological saline, and can be recovered as a physiological saline solution containing highly purified ^99m Tc to serve as a raw material for radiopharmaceuticals and labeled compounds.

Regarding the waste and waste liquid generated in the process of purifying and recovering high-purity ^99m Tc from the high-concentration Mo solution, the radioactivity attached thereto may be naturally attenuated to a low level, and then solidification treatment, etc. may be performed. A space for storing and accommodating various radioactive and non-radioactive wastes, etc., generated in the process may be provided in the hot cell 140, etc.

The container that contains the AC (metal mesh cylindrical container 120, AC containing column for washing the AC with water), the IER column 150, and the AL column 160 are preferably made of materials and have contents (AC, IER, AL) that can be sterilized in an autoclave (121°C, 2 atm).

As shown in Fig. 4, the conventional method and the process of the present invention are compared. The conventional method is a flow-type TcMM in which ^99m Tc contained in a Mo solution is adsorbed and collected by passing the solution through an AC column. The present invention is an improved batch-type TcMM in which, instead of passing the Mo solution through an AC column, a metallic mesh cylindrical container 120 containing an AC is immersed in a flowing high-concentration Mo solution, so that ^99m Tc generated in the Mo solution is adsorbed by the AC.

In the conventional method, in order to completely adsorb and collect ^99m Tc contained in the Mo solution by passing the Mo solution through the AC column, it was necessary to provide a flow rate restriction in the AC column to allow the Mo solution to flow. Specifically, since the concentration of ⁹⁹ Mo is low in the low specific activity Mo solution, in order to recover the desired amount of ^99m Tc, it is necessary to pass a large amount of Mo solution through the AC column. For example, when the flow rate per unit time for passing the solution through the AC column is set to a maximum of 50 to 100 mL/min, it takes 20 to 40 minutes or more to pass 2.0 L of Mo solution through the AC column, which is not efficient in terms of recovering ^99m Tc with a short half-life in a short time for diagnostic use.

Moreover, in the case of a low-concentration Mo solution, the concentration of ^99m Tc becomes even lower, so that when ^99m Tc is adsorbed and collected by the AC column, a larger amount of Mo solution must be passed through the AC column. For example, when the amount of Mo solution is 5 to 20 L, it takes 2 to 5 hours or more to pass the solution through the AC column, and the recovered ^99m Tc may be altered to ^{99 g} Tc, making it unusable as a pharmaceutical raw material.

In contrast, in the present invention, even if the AC contained in the metallic mesh cylindrical container 120 contains a high-concentration Mo solution containing radioactive ^99Mo and the ratio of the number of ^99Mo atoms to ^99mTc , which is a daughter nuclide produced by the decay of ^99Mo , is ¹⁰¹⁶ or more, it is possible to selectively separate and recover a trace amount of ^99mTc therein.

^{99m Tc in the Mo solution is easily adsorbed by the AC by immersing the metal mesh cylindrical container 120 containing the AC in the Mo solution and stirring the Mo solution to flow around the metal mesh cylindrical container 120. There is no need to adjust the flow rate of the Mo solution to pass it through the AC column, and 99m Tc} is always adsorbed by the AC from the entire Mo solution present around the metal mesh cylindrical container 120, making it possible to collect ^99m Tc in a short time.

As shown in Fig. 5, the time required for each step of immersing a metallic mesh cylindrical container 120 containing AC in a Mo solution and recovering purified ^99m Tc as a pharmaceutical raw material from the AC that has adsorbed and collected ^{99m Tc is significantly shorter than that of the conventional method. Since the AC always adsorbs and collects 99m Tc} , regardless of the amount of Mo solution or the radioactivity of ^99Mo , the process time required is zero. Thereafter, it takes about 10 minutes to purify and recover ^99m Tc from the AC, and since it is possible to operate in the same process at a constant time, this is an optimal method as a pharmaceutical raw material manufacturing technology that requires strict quality and shipping arrangements.

MoO ₃ (3,750 g) containing a very large amount of Mo (2,500 g) was dissolved in 6 M (molar concentration mol/L) NaOH (1.75-1.8 L), and then H ₂ O was added to prepare a Mo solution (10 L) with a pH of 8-9. The Mo solution was placed in a 15 L beaker, and 0.1 mg of Re (rhenium) was added as a substitute for ^99m Tc (500 Ci). A stainless steel metal mesh cylindrical container (diameter 1.6 cm, length 6 cm, capacity 12 cc) filled with AC (4.5 g) was immersed in the Mo solution, and the rotor blade of the stirrer was rotated (30 rpm) in the Mo solution for 6 hours to stir. After stirring, the metal mesh cylindrical container was removed from the Mo container and washed with water to remove the Mo remaining in the pores of the AC without adsorption, and the Re adsorbed on the AC was eluted from the AC with 1.3 M NaOH (30 mL). The solution was passed through an IER column packed with a strongly acidic cation exchange resin, and further passed through an AL column containing activated alumina (6 g), and Re was adsorbed and captured by the alumina. 20 mL of physiological saline (0.9% NaCl) was passed through the AL column to which Re was adsorbed, and a physiological saline solution (pH 4.8 to 5.2) containing Re was collected.

The half-life of ⁹⁹ Mo is 65.94 hours, and the half-life of ^99m Tc is 6.01 hours. The amount of ⁹⁹ Mo (500 Ci) was 1.04 mg, which is 1/500,000 relative to Mo (500 g), and the amount of ^99m Tc (500 Ci) was 0.095 mg, which is 1/5,000,000 relative to Mo (500 g). At the μCi test level, the activity of ⁹⁹ Mo was less than 5×10 ⁴ Bq (Becquerels), with a weight ratio to Mo (500 g) of less than 6e ^-15 , and the activity of ^99m Tc was less than 6×10 ⁴ Bq (Becquerels), with a weight ratio to Mo (500 g) of less than 6e ^-16 . As a result of radioactivity tests in the high range from μCi level to 80 Ci level and non-radioactivity tests equivalent to 500 Ci (Mo 500 g or more) TcMM tests, the separation factor of Mo and Tc by AC (selective adsorption of Tc) was ^10e16 or more.

The amount of Re recovered was 0.092-0.096 mg, and the recovery rate of Re was about 94%. Since this is equivalent to ^99m Tc (500 Ci), it is considered that similar results would be obtained when a cylindrical metal mesh container filled with AC is immersed in a Mo solution to adsorb and collect ^99m Tc with AC. This result shows that even if the ratio of the number of ⁹⁹ Mo atoms to the daughter nuclide ^99m Tc generated by the decay of ⁹⁹ Mo is 10 ¹⁶ or more in a high-concentration Mo solution, AC selectively adsorbs a small amount of ^99m Tc in the solution.

According to the present invention, a high-concentration Mo solution containing radioactive ^99Mo is produced and left for about 24 hours, whereby ^99mTc is produced from ^99Mo and mixed in a state of radioactive equilibrium (the ratio of the radioactivities of the parent and daughter nuclides is constantly balanced). Instead of passing the solution through an AC column as in the conventional method, an AC-filled metal mesh cylindrical container is immersed in the stirred and flowing Mo solution, whereby ^99mTc can be constantly adsorbed and captured by the AC.

Whether the amount of high-concentration Mo solution is as small as 0.1 L or as large as 5 to 20 L, the desired amount of ^99m Tc is selectively adsorbed and collected by AC during the time it takes for ^99m Tc to be produced from ⁹⁹ Mo and reach radioactive equilibrium or the time the desired amount of ^99m Tc is produced, and this method is particularly effective for recovering ^99m Tc with a short half-life (6 hours).

When ^99m Tc adsorbed and collected on AC in a cylindrical metal mesh container is desorbed, the Mo ( ⁹⁹ Mo) remaining unadsorbed on the AC is also leached out at the same time as ^99m Tc. However, by passing the ^99m Tc recovery solution through an alumina column, it is possible to purify and recover high-purity ^99m Tc for use as a pharmaceutical raw material without contamination with radioactive impurities such as Mo ( ⁹⁹ Mo).

The above describes examples of the present invention, but the invention is not limited to these.

100: Mo solution tank 110: Stirrer 120: Metal mesh cylindrical container 130: Support 140: Hot cell 150: IER column 160: AL column

Claims (5)

A method for recovering technetium-99m, a daughter nuclide produced by decay of molybdenum-99 contained in a high-concentration molybdenum solution containing molybdenum-99 with low specific activity, by separating the daughter nuclide with activated carbon, comprising:
The activated carbon is packed in a cylindrical metal mesh container that is not a column in which the flow rate is restricted, and is immersed in the molybdenum solution that is being stirred to flow, thereby selectively adsorbing trace amounts of technetium-99m in the solution.
A method for recovering technetium-99m from low specific activity molybdenum-99. The molybdenum solution contains the radionuclide molybdenum-99 produced by the neutron capture (n, gamma) reaction of the natural isotope of molybdenum;
2. The method for recovering technetium-99m from low specific activity molybdenum-99 according to claim 1. 3. The method for recovering technetium-99m from low specific activity molybdenum-99 according to claim 1 or 2, further comprising the step of washing with water the molybdenum remaining in the pores of the activated carbon to which the technetium-99m recovered has been adsorbed;
The solution containing technetium-99m eluted from the activated carbon with an alkaline solution is passed through an IER column packed with a strongly acidic cation exchange resin to remove the alkaline components;
The mixture is then passed through an AL column packed with alumina to capture technetium-99m.
eluting technetium-99m from the alumina column using physiological saline, thereby purifying the technetium-99m into a physiological saline solution containing technetium-99m from which impurities have been removed;
A method for producing a physiological saline solution containing technetium-99m, comprising the steps of: The container for accommodating the activated carbon, the IER column, and the AL column are made of materials that can be sterilized by autoclave.
4. The method for producing a physiological saline solution containing Technetium-99m according to claim 3 . A means for producing a high-concentration molybdenum solution containing molybdenum-99 having a low specific activity produced by a neutron capture (n, γ) reaction of the natural isotope of molybdenum;
means for generating a daughter nuclide, technetium-99m, in the molybdenum solution by decay of molybdenum-99;
a means for filling activated carbon in a cylindrical metal mesh vessel, which is not a column in which the flow rate is restricted, and immersing the activated carbon in the molybdenum solution which is being stirred and flowing;
a means for washing the remaining molybdenum-99 from the activated carbon on which the technetium-99m has been adsorbed;
a means for eluting technetium-99m from the water-washed activated carbon using an alkaline solution, passing the solution through a strongly acidic cation exchange resin column to remove the alkaline components, and then passing the resulting solution through an alumina column to capture technetium-99m;
and a means for eluting the technetium-99m from the alumina column with saline to recover purified technetium-99m.
A system for recovering technetium-99m from natural molybdenum.