JP4410716B2 - Radioisotope production equipment - Google Patents

Description

  The present invention relates to a radioisotope production apparatus that produces nuclides composed of radioisotopes, and more particularly to a technique related to a target irradiated with an ion beam (proton beam) to generate a radioisotope.

  In recent years, PET (Positron Emission CT) has attracted attention as a screening method for cancer screening, brain disease, and heart disease. In PET examination, a radiopharmaceutical using a nuclide that emits positron (positron) as a label is administered to the body of the examinee, and γ-rays released outside the body from the radiopharmaceutical accumulated in the affected area of the cancer are detected. This is an examination to identify the position of the affected area.

Thus, the nuclide contained in the radiopharmaceutical used for PET inspection has a very short half-life of the radioisotope constituting the nuclide. Therefore, when carrying out a PET inspection, the nuclide after production needs to be subjected to inspection promptly in consideration of the time required for transport of the radiopharmaceutical and the half-life (for example, see Non-Patent Document 1). ).
For this reason, nuclides cannot be stored. Therefore, in order to ensure a sufficient amount immediately before carrying out the PET examination, it is necessary to produce a large amount in a short period of time.

By the way, in the method for producing such a nuclide, a substance (raw material) that is a source of the nuclide is accommodated in a target, and a high-energy ion beam of several MeV to several tens MeV accelerated by using an accelerator. Is irradiated. For this reason, since the temperature of a raw material rises by irradiation, the voids, such as a bubble, produce | generate inside it, the frequency | count of a nuclear reaction will reduce, and the situation where the yield of a nuclide will fall will generate | occur | produce.
In order to avoid such a situation, the raw material heated by ion beam irradiation is pressurized and cooled so that voids such as bubbles are not generated.
“PET Communication 1998 WINTER No. 25”, pp. 15-17, Institute of Advanced Medical Technology

  By the way, since the inside of the accelerator through which the ion beam passes (accelerated) is a vacuum region, and the source material of the nuclide irradiated with the ion beam is a liquid, the boundary between the vacuum region and the source material The presence of a member for partitioning is essential. As this member, for example, a titanium thin film having a thickness of several tens of microns is used, and a stopper for supporting the thin film in contact with the pressurized raw material is used.

  Until now, aluminum, copper, and titanium (Ti) having high thermal conductivity have been used for the stopper. However, these metals have a problem that their mechanical strength deteriorates at high temperatures, and when they are used repeatedly, the deformation becomes large and they cannot be used. In order to overcome this, if a strong iron-based metal is used, the thermal conductivity deteriorates, the temperature of the raw material rises, and voids such as bubbles are formed inside the raw material. There was a problem that the yield decreased.

  Also, a method of combining a material with good thermal conductivity and a material having high mechanical strength at high temperature (bonding, plywood, etc.), or cooling by flowing a coolant between the two thin films However, there is a problem that the structure becomes complicated and the energy loss of the ion beam in the thin film increases.

  An object of the present invention is to solve such a problem, and by adopting a target having a stopper having excellent cooling performance and high mechanical strength, a radioisotope can be obtained in a high yield. An element manufacturing apparatus is provided.

  In order to solve the above-described problems, the present invention accelerates an ion source that emits an ion beam and an accelerator having a vacuum region that accelerates the ion beam emitted from the ion source, in a radioisotope manufacturing apparatus. A target that contains a raw material that generates a radioisotope when irradiated with the ion beam; a transmission film that forms a boundary between the vacuum region and the raw material and transmits the ion beam; And a first stopper provided with a plurality of passages through which the ion beam passes, the first stopper being formed of alumina dispersion strengthened copper, To do.

With this configuration, the stopper is formed of alumina dispersion-strengthened copper that has both excellent heat conduction characteristics and mechanical characteristics. For this reason, even if the temperature of the raw material rises due to the irradiation of the ion beam, the heat is easily diffused to the outside due to the high thermal conductivity of the stopper. Therefore, the temperature rise of the adjacent raw material is suppressed, and even if the intensity of the ion beam to be irradiated is increased, a part of the raw material is hardly vaporized, and voids such as bubbles are not generated, so that the nuclide yield can be increased.
Further, even when a high pressure is applied to the raw material, this stopper is less likely to be deformed due to its high mechanical strength (Young's modulus, yield stress) at high temperatures. For this reason, it is possible to increase the pressure applied to the raw material accommodated in the target, and even if the raw material becomes high temperature, it is possible to suppress the generation of voids and the like inside, and to increase the yield of nuclide. Can do.

  According to the present invention, by adopting alumina dispersion-strengthened copper having high thermal conductivity and excellent mechanical strength at high temperature as the material of the stopper, bubbles are generated in the raw material even when irradiated with an ion beam. Therefore, a radioisotope production apparatus capable of obtaining nuclides with high yield is provided.

(First embodiment)
Next, the radioisotope manufacturing apparatus according to the first embodiment of the present invention will be described in detail with reference to the drawings as appropriate.
As shown in FIG. 1, a radioisotope production apparatus 10 of this embodiment includes an ion source 11, a radio frequency quadrupole linear accelerator (hereinafter referred to as RFQ) 12a, a drift tube linear accelerator (Drift). Tube Linac (hereinafter referred to as DTL) 12b and target 20. The accelerator 12 in the present invention is formed by a combination of the RFQ 12a and the DTL 12b.

The ion source 11 serves to ionize a source material (in this case, hydrogen) to be an ion and extract it as a positive ion beam R, and a magnet (not shown) that selectively extracts only desired ions by mass is provided around the ion source 11. And an electrostatic lens (not shown) for shaping the ion beam R, an ion beam generator, and the like are provided.
As the ion source 11, a hot cathode type duoplasmatron type ion source or a PIG type ion source can be used. A microwave discharge ion source that can generate a large current with a long lifetime can also be used.

The RFQ 12a is provided at the subsequent stage of the ion source 11, and accelerates the ion beam R emitted from the ion source 11 to a predetermined energy. A vacuum chamber having a wavy quadrupole electrode is provided inside the RFQ 12a. The quadrupole electrode forms a quadrupole electric field in a direction perpendicular to the traveling direction of the ion beam R, and the ion beam R is accelerated while being focused.
In place of the RFQ 12a used here, a multi-electrode type high-frequency accelerator having an even number of magnetic poles of six or more poles may be used, and other high-frequency accelerators may be used.

The DTL 12b receives the ion beam R accelerated by the RFQ 12a and further accelerates it. A plurality of drift tubes 17 are arranged in the axial direction at the center inside the DTL 12b. A quadrupole electromagnet (not shown) is incorporated in the drift tube 17, and the ion beam R is converged when passing through the drift tube 17. The ion beam R is accelerated between the drift tubes 17 and 17.
Such RFQ 12a and DTL 12b are combined to function as a linear accelerator (accelerator) 12 that finally generates an ion beam R having a high energy of about 10 MeV. In addition, the accelerator used by this invention is not limited to such a linear accelerator, A cyclotron may be used.

The target 20 exists in the target shielding body 13 fixed to the floor.
As shown in FIG. 2A, the target 20 includes a first stopper 21a (21), a thin permeable membrane 22, a base 24, and a cooling path 25 provided in the base 24. The container 26 that holds the nuclide raw material 23, the holder 28 that holds the first stopper, and the cooling passage 29 that cools the holder 28 and the first stopper 21a. The container 26 and the base 24 may be integrally formed. As shown in FIG. 2 (b), the first stopper 21a is provided with a plurality of passage openings 27a, 27a.

The raw material 23 is an aqueous solution (concentrated water) containing ¹⁸ O (oxygen 18) after being concentrated, and is accommodated in a space of the target 20 surrounded by the permeable membrane 22, the container 26, and the base 24. When the target 20 is irradiated with the ion beam R, the ion beam R is, passage holes 27a of the stopper 21a, 27a ..., passes through the permeable membrane 22, and impinges on the material 23, ¹⁸ O ( Oxygen 18) undergoes a nuclear reaction, and ¹⁸ F (fluorine 18), which is a radioisotope, is generated as a nuclide. Further, the raw material 23 accommodated in the target 20 is pressurized with argon gas (Ar) introduced from the inlet 26a so as not to boil due to temperature rise and generate bubbles, and the cooling paths 25, 29 The refrigerant circulates to cool the entire target 20. And the produced | generated water containing ¹⁸ F is discharged | emitted by the pressurization of argon gas to the exterior of the target 20 through piping which is not shown in figure.

Here, the optimum material to be used for the first stopper 21a (21) is examined. As a material for the stopper (including a second stopper 21d described later), it is selected that it has excellent thermal conductivity and excellent mechanical properties at high temperatures.
First, referring to FIG. 3A, the physical property values of copper (Cu) and stainless steel (SUS) that have been conventionally used as the material of the target 20 will be compared. Then, Cu shows that the mechanical properties indicated by the yield stress and Young's modulus are inferior to those of SUS, but the thermal conductivity is excellent. Therefore, Cu and SUS are both excellent in heat transfer characteristics and mechanical characteristics, but the other is greatly inferior, so the selection criteria are not sufficiently satisfied. I can't say that.

Next, FIG. 3B showing thermal conductivity, FIG. 4A showing yield stress, and FIG. 4B showing Young's modulus will be referred to. [References: ITER BLANKET, SHIELD AND MATERIAL DATA BASE, IAEA / ITER / DS / 1991, IAEA, VIENNA, 1991.].
According to these databases, DS Copper (alumina dispersion strengthened copper) has a thermal conductivity of about 350 W / mK, a yield stress of 260-320 MPa (200-300 ° C.), and a Young's modulus of 110-120 GPa (200- 300 ° C.).
TZM (Titanium / Zirconium-added molybdenum alloy) has a thermal conductivity of about 100 W / mK, a yield stress of 680-700 MPa (200-300 ° C.), and a Young's modulus of 280-295 GPa (200 −300 ° C.).
Mo-5% Re (Rhenium-added molybdenum alloy) has a thermal conductivity of about 110 W / mK and a yield stress of 450-500 MPa (200-300 ° C.).

Next, consider the rigidity of the stopper. Here, the rigidity is proportional to the product of the Young's modulus E and the cross-sectional secondary moment M. Note the second moment M is the cube of the thickness of the material ^{(M = bh 3/2,} b is the width of the material, h is the thickness of the material) is proportional to.
Here, the rigidity of the conventionally used composite material in which Cu and SUS are bonded together is represented by the following equation (1), where the thickness of Cu and SUS is 1.
On the other hand, the case where DS Copper (alumina dispersion strengthened copper) is used as a representative of the above-mentioned materials will be examined as a representative. The total thickness of Cu and SUS is 2, and the thickness becomes 2, as shown in the following formula (2): Shown in From formulas (1) and (2), it is shown that DS Copper (alumina dispersion-strengthened copper) has a rigidity about 3 times greater than that of Cu / SUS.

E _SUS × M _SUS + E _Cu × M _Cu = 210 × 1 ³ + 80 × 1 ³ = 290 (1)
E _DSCu × M _DSCu = 110 × 2 ³ = 880 (2)

Conventionally, DS Copper, titanium / zirconium-added molybdenum alloy, rhenium-added molybdenum alloy, and lanthanum-added molybdenum alloy are targets 20 that generate nuclides for use in radiopharmaceuticals, as compared with Cu and SUS, which have been used as target materials. The requirements for the material of the stopper 21 are satisfied. TEM (Lanthanum-added molybdenum alloy) can also be preferably used.
Among them, DS Copper (alumina dispersion strengthened copper) showing high values in a good balance of heat conduction, yield stress and Young's modulus is excellent as a material for the first stopper 21 of the target 20 that generates a radionuclide used for a radiopharmaceutical. I can say that.

  Thus, if alumina dispersion-strengthened copper is used for the first stopper 21 (including the second stopper 21d described later), a stopper having high mechanical strength and high cooling performance can be provided. The temperature of 23 can be effectively cooled, and thereby the volume of voids such as bubbles grown in the raw material 23 can be reduced, so that a high yield of the nuclide to be generated is achieved.

Next, the operation of the radioisotope manufacturing apparatus 10 configured as described above will be described with reference to FIGS. In operating the radioisotope production apparatus 10, the target 20 is accommodated in the target shield 13 in advance.
When an operation switch (not shown) is operated, predetermined high-frequency power is supplied to the RFQ 12a and DTL 12b, and an electric field is formed in each RFQ 12a and DTL 12b. Thereafter, predetermined power is supplied to the ion source 11. As a result, the ion beam R emitted from the ion beam generator (not shown) of the ion source 11 is accelerated to a predetermined energy by the RFQ 12a. The accelerated ion beam R is emitted from the RFQ 12a, is incident on the subsequent DTL 12b, and is further accelerated by the DTL 12b.
The ion beam R accelerated to high energy in this way is irradiated to the raw material 23 in the target 20, that is, ¹⁸ O concentrated water. When the ion beam R is irradiated onto ¹⁸ O, ¹⁸ F is generated by a nuclear reaction.

At this time, the raw material 23 is heated by the irradiation of the ion beam R, but the first stopper 21 that is in wide contact with the raw material 23 has high heat conduction characteristics, so that the temperature rise can be suppressed. . For this reason, a part of the raw material 23 is hardly vaporized, and voids such as bubbles are not generated.
Even if there is concern about the generation of voids such as bubbles, the generation can be suppressed by increasing the pressure of the argon gas (Ar) introduced from the inlet 26a and further pressurizing the raw material 23. As described above, even if the pressure applied to the raw material 23 is increased, the first stopper 21 has high mechanical characteristics, so that it is less likely to be deformed even when used repeatedly.

In this way, when the nuclide composed of ¹⁸ F radioisotope is generated, the concentrated water containing ¹⁸ F is sent from the pipe (not shown) connected to the target 20 to the radiopharmaceutical synthesizer (not shown). It is ¹⁸ F from the concentrated water containing ¹⁸ F are extracted. Note that the remaining ¹⁸ O concentrated water that did not undergo nuclear reaction to ¹⁸ F is very expensive and is collected and reused in the target 20.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, since the configuration other than the first stopper 21b (21) is the same as that in the first embodiment, the description thereof is omitted. As shown in FIG. 5 (b), the first stopper 21b is provided with a passage opening 27b in a portion having the maximum beam intensity among the plurality of passage openings 27b provided on the surface irradiated with the ion beam R. It is not.
Here, the maximum portion of the beam intensity usually indicates that the current distribution of the ion beam R shows a Gaussian distribution as shown in FIG. . For this reason, since the power injected into the raw material 23 increases as the distance from the center of the stopper 21 increases, the temperature of the raw material 23 also increases and the central portion reaches the maximum temperature.

  In the first stopper 21b shown in FIG. 5, since the passage opening 27b does not exist in the portion where the beam intensity is high, the intensity of the ion beam R that reaches the center portion of the raw material 23 is greatly attenuated. The temperature of 23 does not rise locally. Therefore, since the temperature distribution of the raw material 23 is flattened as a whole and the maximum temperature is lowered, the bubble volume is also reduced. FIG. 5 shows an example in which the hole of the passage opening 27b at the center of the first stopper 21b is closed. However, the stopper 21b of the present embodiment is not limited to this. According to the position of the maximum intensity of R, the hole of the passage opening 27b at the corresponding position is closed.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG. In the present embodiment, the configuration other than the first stopper 21c is the same as that in the first embodiment, and a description thereof will be omitted. As shown in FIG. 6, in the first stopper 21c (21), the plurality of passage openings 27c provided on the surface irradiated with the ion beam R have a uniform number density, but the beam intensity is high. Accordingly, the hole diameter is changed. In this way, the opening area of the passage opening 27c located at the site where the intensity of the ion beam R is high is formed relatively small with respect to the passage opening 27c located at the site where the intensity is low.

Thus, even when the passage opening 27c is arranged in the first stopper 21c, the ion beam R having a strong distribution in the center as shown in FIG. 6C does not reach the raw material 23. Since it is restricted, an increase in the temperature of the raw material 23 is suppressed. And as it goes to the periphery of the first stopper 21c, the hole diameter of the passage port 27c increases, and the amount of the ion beam R reaching the raw material 23 increases, but the beam intensity decreases. The rise of is suppressed. As a whole, the temperature distribution of the raw material 23 is flattened. As a result, the maximum temperature of the raw material 23 is lowered, and the bubble volume is also reduced.
FIG. 6 shows an example in which the hole diameter of the passage opening 27c at the center of the first stopper 21c is the smallest. However, the present invention is not limited to this, and the stopper 21c of the present embodiment is an ion beam. According to the position of the maximum intensity of R, the hole diameter of the corresponding passage opening 27b is minimized.

  Therefore, in the first stopper 21c used in the third embodiment, alumina dispersion strengthened copper (DSCopper) is used, and the hole diameter is changed and distributed according to the magnitude of the beam intensity. Thus, the effect of increasing the yield of the nuclide to be generated by reducing the bubble volume can be obtained. In addition, in the 1st stopper 21c used for 3rd Embodiment, since the passage opening 27c exists also in the site | part with the largest beam intensity compared with the 1st stopper 21b used for 2nd Embodiment, it is an ion beam. The energy of R can be used effectively.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, the configuration other than the target 20 ′ is the same as that in the first embodiment, and a description thereof will be omitted.
Compared with the target 20 of the first embodiment, the target 20 ′ used in the fourth embodiment is opposed to the cooling path 35 through which the refrigerant that absorbs heat generated by irradiation of the ion beam R circulates and the permeable membrane 22. In addition, a heat dissipation film 31 provided in contact with the raw material 23, and a second stopper 21d (21 provided with a plurality of cooling ports 37 provided so that a refrigerant that supports and circulates the heat dissipation film 31 is in contact with the heat dissipation film 31. ) And the point provided with.

  Thus, the circulating refrigerant contacts the heat radiating film 31 that separates the raw material 23 by a thin film through the cooling ports 37, 37. By adopting such a configuration, further improvement in the cooling performance of the target 20 'is achieved.

In the first to fourth embodiments, an example in which only the stopper 21 is made of an alumina dispersion-strengthened copper material has been shown, but other members (the permeable membrane 22, the base 24) other than the stopper 21 are shown. It is also possible to apply the alumina dispersion strengthened copper to the container 26, the retainer 28, etc. to produce the targets 20, 20 '.
By constructing the invention as described above, it is possible to achieve both improvement in thermal conductivity and improvement in mechanical properties at high temperatures in the targets 20 and 20 ′, and reduce the bubble volume to generate. The effect of increasing the yield of nuclide is obtained. Further, the same effect can be obtained by replacing the material to be applied with alumina dispersion strengthened copper and applying at least one substance selected from the group consisting of a titanium / zirconium-added molybdenum alloy, a rhenium-added molybdenum alloy, and a lanthanum-added molybdenum alloy. .

It is sectional drawing which shows the side surface cross section of the radioisotope manufacturing apparatus which concerns on 1st Embodiment of this invention. (A) is side surface sectional drawing of the target used by 1st Embodiment of this invention, (b) is a front view which shows the front of the target which an ion beam irradiates. (A) is a table | surface which shows the heat transfer characteristic of Cu and SUS, and a mechanical characteristic. (B) is an arithmetic expression for deriving the thermal conductivity of each material with respect to each temperature. (A) is a graph which shows the yield effect with respect to the temperature of the material used for this invention, (b) is a graph which shows a Young's modulus similarly. (A) is side surface sectional drawing of the target used by 2nd Embodiment of this invention, (b) is a front view which shows the front of the target which an ion beam irradiates, (c) is an ion beam in an XX cross section. It is a figure which shows current distribution. (A) is side surface sectional drawing of the target used by 3rd Embodiment of this invention, (b) is a front view which shows the front of the target which an ion beam irradiates, (c) is an ion beam in an XX cross section. It is a figure which shows current distribution. It is a target side sectional view used in a 4th embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radioisotope production apparatus 11 Ion source 12 Accelerator 20, 20 'Target 21 (21a, 21b, 21c) 1st stopper 21 (21d) 2nd stopper 22 Permeation membrane 23 Raw material 25, 35 Cooling path 27 (27a, 27b, 27c) Passage port 31 Heat radiation film R Ion beam

Claims (6)

An ion source that emits an ion beam;
An accelerator having a vacuum region in which the ion beam emitted from the ion source is accelerated;
A target containing a raw material that generates a radioisotope when irradiated with the accelerated ion beam;
In the target, a permeable film that forms a boundary between the vacuum region and the raw material and transmits the ion beam;
A first stopper that supports the permeable membrane and is provided with a plurality of passage ports through which the ion beam passes,
The radioisotope manufacturing apparatus according to claim 1, wherein the first stopper is made of alumina dispersion strengthened copper.   The radioisotope manufacturing apparatus according to claim 1, wherein the passage opening is not provided in a portion where the intensity of the ion beam irradiated to the first stopper is maximum. The number density of the passage openings provided in the first stopper is uniform,
The opening area of the passage opening located at a portion where the intensity of the ion beam is high is formed relatively small with respect to the passage opening located at a portion where the intensity is low. Radioisotope production equipment. A cooling path through which a refrigerant that absorbs heat generated by irradiation of the ion beam circulates;
A heat dissipating film provided in contact with the raw material in opposition to the permeable film,
The second stopper having a plurality of cooling ports that support the heat dissipation film and that are provided so that the circulating refrigerant contacts the heat dissipation film. The radioisotope manufacturing apparatus of any one of Claims.   The radioisotope manufacturing apparatus according to any one of claims 1 to 4, wherein the member constituting the target is made of a material of alumina dispersion-strengthened copper. An ion source that emits an ion beam;
An accelerator having a vacuum region in which the ion beam emitted from the ion source is accelerated;
A target containing a raw material that generates a radioisotope when irradiated with the accelerated ion beam;
In the target, a permeable film that forms a boundary between the vacuum region and the raw material and transmits the ion beam;
A first stopper that supports the permeable membrane and is provided with a plurality of passage ports through which the ion beam passes,
The radioisotope manufacturing apparatus according to claim 1, wherein the first stopper is made of at least one material selected from the group consisting of a titanium / zirconium-added molybdenum alloy, a rhenium-added molybdenum alloy, and a lanthanum-added molybdenum alloy.

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