JP7309268B2 - Self-shielding for RI manufacturing equipment - Google Patents

Description

The present invention relates to self-shielding for RI (radioisotope) production.

Positron Emission Tomography (PET) is available as an examination method for detailed examination of the brain, heart, cancer, and the like. In this PET examination, a test drug labeled with a radioisotope (positron-emitting nuclide) that emits positrons (positrons) is introduced into the subject's body by injection, inhalation, or the like. A test agent introduced into the body is metabolized or accumulated in a specific site (for example, a tumor or lesion site). Radiation (annihilation gamma rays) is emitted when the positron emitted from the radioisotope combines with the surrounding electrons and annihilates. images can be obtained.

As an apparatus for producing such a radioactive isotope (RI), for example, the apparatus disclosed in Patent Document 1 is known. In this device, a particle accelerator is arranged inside a self-shield, and a target is irradiated with a charged particle beam from the particle accelerator to produce radioactive isotopes.

JP-A-2000-105293

Here, the self-shield for RI manufacturing equipment as described above has a plurality of layers for shielding neutrons, gamma rays, and the like. A material having a large specific gravity may be used as a material for such shielding. Therefore, there is a problem that the weight of the self-shield becomes heavy. Since the self-shield is installed on the floor of the building, it has been required to reduce the weight of the self-shield from the viewpoint of the load capacity of the floor.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a self-shielding system for RI manufacturing equipment that can be light in weight.

The self-shield for the RI production apparatus of the present invention is an RI production apparatus in which an accelerator and an RI production apparatus are arranged inside, and radioactive isotopes are produced by irradiating a target with a charged particle beam from the accelerator inside the RI production apparatus. a first layer formed by a first gamma-ray shielding material for shielding gamma rays; A second layer formed of a neutron shielding material having a high neutron shielding property and a specific gravity smaller than that of the gamma ray shielding material of the first layer; and a third layer formed by a second gamma-ray shielding material having a higher gamma-ray shielding property than the neutron shielding material of the layer.

In this self-shielding for RI manufacturing equipment, the first layer shields primary gamma rays, the second layer shields neutrons, and the third layer, which is closer to the outer circumference than the second layer, shields trapped gamma rays. Specifically, since the second layer is arranged on the outer peripheral side of the first layer, the first layer is arranged at a position closer to the target than the second layer. In such an arrangement, compared to a structure in which the first layer is arranged on the outer peripheral side of the second layer, the thickness of the first layer is the same to obtain the same gamma ray shielding performance, The volume of gamma-ray shielding material can be reduced. Therefore, the weight of the first layer can be reduced. In addition, since neutrons pass through the first layer, a neutron moderation effect is obtained, and the second layer can shield neutrons more effectively. Therefore, the second layer can be made thinner and lighter in weight. On the other hand, since the trapped gamma rays do not pass through the first layer, the amount of trapped gamma rays to be shielded by the third layer increases. . As described above, the weight of the self-shield can be reduced.

The second gamma-ray shielding material of the third layer may have a lower specific gravity than the first gamma-ray shielding material of the first layer. This reduces the amount of heavy material in the self-shield.

The first layer may be positioned on the innermost side of the self-shield. This allows the volume of the gamma-ray shielding material of the first layer to be reduced.

The present invention provides self-shielding for RI manufacturing equipment that can be light in weight.

1 is a cross-sectional view along a horizontal plane of an RI manufacturing system with self-shielding according to an embodiment of the invention; FIG. 2 is a cross-sectional view along a vertical plane of the RI manufacturing system of FIG. 1; FIG. (a) is a cross-sectional view showing a layer structure of a self-shield according to an embodiment of the present invention, and (b) is a cross-sectional view showing a layer structure of a self-shield according to a comparative example.

Embodiments of self-shielding according to the present invention will be described in detail below with reference to the drawings. Also, the terms "top" and "bottom" are sometimes used in the description, which correspond to the upward and downward directions in the drawing.

FIG. 1 is a cross-sectional view of an RI manufacturing system 1. FIG. The RI manufacturing system 1 includes a target device 10 (RI manufacturing device). The RI manufacturing system 1 manufactures radioactive isotopes (RI). The RI manufacturing system 1 can be used, for example, as a cyclotron for PET, and the RI manufactured by the RI manufacturing system 1 is, for example, a radioisotope-labeled compound (RI compound). Used. Examples of radioisotope-labeled compounds used for PET examination (positron emission tomography) in hospitals include ¹⁸ F-FLT (fluorothymidine), ¹⁸ F-FMISO (fluorosonidazole), ¹¹ C-raclopride, and the like. .

The RI manufacturing system 1 is a so-called self-shielded particle accelerator system, and includes an accelerator 2 that accelerates charged particles, and a self-shield 6 that is a radiation shield (wall) surrounding the accelerator 2 to shield radiation. It has In the internal space S formed so as to be surrounded by the self-shield 6, in addition to the accelerator 2, there are a target device 10 used for manufacturing RI, a vacuum pump 4 for evacuating the inside of the accelerator 2, and the like. are placed. Furthermore, in the internal space S, accessories necessary for the operation of the accelerator 2, accessories used for cooling the target device 10, and the like are arranged.

The accelerator 2 is a so-called vertical cyclotron, and has a pair of magnetic poles, a vacuum box, and an annular yoke surrounding the pair of magnetic poles and the vacuum box. A pair of magnetic poles face each other at a predetermined interval in a vacuum chamber. Charged particles such as hydrogen ions are multiple-accelerated in the gap between the pair of magnetic poles. The vacuum pump 4 is used to maintain the vacuum environment within the accelerator 2 and is fixed to the side of the accelerator 2, for example. The accelerator 2 emits a charged particle beam B in the irradiation direction.

The target device 10 is for receiving the charged particle beam B emitted from the accelerator 2 to produce RI, and is formed with a storage section for storing raw materials (for example, target water; ¹⁸ O water). . A target device 10 is generally fixed to the side of the accelerator 2 as shown in FIGS. The RI manufacturing system 1 of this embodiment includes two target devices 10 arranged on both sides of the accelerator 2 . For example, the target device 10 arranged on the left side of the drawing is arranged on the upper side, and the target device 10 arranged on the right side of the drawing is arranged on the lower side (see FIG. 2). The target device 10 is covered with a target shield 7 provided on the accelerator 2 .

Self-shield 6 is composed of a plurality of parts and is formed to cover accelerator 2 and target device 10 . The self-shield 6 is a structure in which the accelerator 2 and the target device 10 are arranged, and RI is manufactured by irradiating the target with the charged particle beam B from the accelerator 2 inside the self-shield 6 . The self-shield 6 is a structure for shielding the radiation generated during the manufacturing of the RI and preventing it from leaking outside the self-shield 6 .

As shown in FIG. 2, the RI manufacturing system 1 completely shielded by the self-shielding 6 is placed in the RI manufacturing room 101 of the building 100 . The RI manufacturing system 1 is installed on the floor 102 of the RI manufacturing room 101 .

As shown in FIG. 1, the self-shield 6 has side walls 11 and 12 facing each other in the irradiation direction of the charged particle beam B, and the side walls 11 and 12 facing each other in the direction perpendicular to the irradiation direction of the charged particle beam B in the horizontal direction. Side wall portions 13 and 14 are provided. Side wall portion 11 and side wall portion 12 are arranged to be separated from each other, and side wall portion 13 and side wall portion 14 are arranged to be separated from each other. Side wall portions 13 and 14 have one end portion connected to both end portions of side wall portion 11 , and the other side end portion of side wall portions 13 and 14 connected to both end portions of side wall portion 12 . As a result, the internal space S of the self-shield 6 is surrounded by the side walls 11, 12, 13, and 14 without gaps.

As shown in FIG. 2, the upper end of self-shield 6 is closed by upper wall 15 . That is, the upper wall portion 15 is connected to the upper end portions of the side wall portions 11 , 12 , 13 and 14 . Lower ends of the side walls 11 , 12 , 13 , 14 are placed on the floor 102 of the RI production room 101 . As a result, the internal space S surrounded by the side walls 11, 12, 13, and 14 is closed vertically by the upper wall 15 and the floor 102 without gaps.

As described above, the side wall portions 11, 12, 13, and 14 of the self-shield 6 are arranged inside the side wall portion 103 of the RI production chamber 101 in which the self-shield 6 is arranged, and the target device is more likely than the side wall portion 103. It is arranged at a position closer to 10. In addition, the upper wall portion 15 of the self-shield 6 is arranged inside the upper wall portion 104 of the RI manufacturing chamber 101 in which the self-shield 6 is arranged, and is positioned closer to the target device 10 than the upper wall portion 104. placed in Although the side walls 11, 12, 13, and 14 are directly installed on the floor 102, a lower wall is provided to connect the lower ends of the side walls 11, 12, 13, and 14. A wall may be placed on the floor 102 .

The self-shield 6 has a configuration that can be divided in a direction perpendicular to the irradiation direction of the charged particle beam B (see FIG. 1). That is, the side walls 11 and 12 and the upper wall 15 are detachably divided near the central position. This divides the self-shielding 6 into a first structure 6A and a second structure 6B. Of these, the second structural body 6B reciprocates along a guide portion (not shown) provided on the floor 102 with respect to the first structural body 6A. As a result, the self-shield 6 can be opened and closed. The first structure 6A and the second structure 6B are connected without a gap so that radiation does not leak.

Subsequently, the layer structure of the self-shield 6 will be described in more detail with reference to FIG. FIG. 3(a) is a schematic cross-sectional view showing the layer structure of the self-shield 6 according to this embodiment. FIG. 3(b) is a schematic cross-sectional view showing the layer structure of the self-shield 56 according to the comparative example. Although FIG. 3(a) shows only the layer structure of the side walls 12, 13 and 14, the other walls (not shown) also have the same layer structure.

As shown in FIG. 3( a ), the self-shield 6 has a first layer in order from the inner peripheral side to the outer peripheral side, that is, from the inner space S of the self-shield 6 to the outside of the self-shield 6 . 21 , a second layer 22 and a third layer 23 .

The first layer 21 is a layer formed of a first gamma-ray shielding material that shields gamma rays. The first layer 21 is arranged on the innermost side of the self-shield 6 . Here, "arranged on the innermost side" means that it is arranged on the innermost side as a layer having a function of shielding radiation. It shows a state in which no other layers, such as the first to third layers, that shield gamma rays and neutrons are formed. Therefore, even when the inner peripheral surface of the first layer 21 is covered with a coating layer formed by coating with paint or a protective material having no radiation shielding function, the first layer 21 can be protected by the self-shielding 6. It shall be arranged on the innermost peripheral side.

The first layer 21 is a layer that mainly shields the primary gamma rays L1 among the radiation from the target device 10 . As the first gamma-ray shielding material forming the first layer 21, a metal material composed of lead may be employed. The metal material composed of lead also has the function of moderating the neutron L2. Considering the shielding properties of the primary gamma rays L1 and the moderating effect of the neutrons L2, a metallic material composed of iron, a metallic material composed of tungsten, or the like may be employed as the first gamma-ray shielding material. . It should be noted that a metal material composed of a specific metal component (lead, iron, tungsten, etc.) having a gamma ray shielding property does not need to contain a small amount of the metal component, and shields the primary gamma ray L1. It must be contained at a content rate to the extent that it can demonstrate its function. Also, the specific metal component does not have to be contained 100%, and other components may be contained within a range that does not affect the shielding properties. That is, it is sufficient that the specific metal component is contained at a predetermined content rate. In addition, in the case where there are a plurality of metal components having shielding properties against the primary gamma rays L1, the total content of the plurality of metal components may satisfy a predetermined value.

The second layer 22 is a layer that mainly shields neutrons L2 among radiation that has passed through the first layer 21 . The second layer 22 is arranged on the outer peripheral side of the first layer 21 . Here, the second layer 22 is arranged so as to be adjacent to the first layer 21 on the outer peripheral side. The second layer 22 is made of a neutron shielding material having higher neutron shielding properties than the first layer 21 and having a lower specific gravity than the first gamma ray shielding material of the first layer 21 . In addition, "high neutron shielding property" means that when the first gamma ray shielding material of the first layer 21 and the neutron shielding material of the second layer 22 are compared at the same thickness, the thickness of the second layer 22 is This means that the neutron shielding material can shield more neutrons. A resin material made of polyethylene or the like may be employed as such a neutron shielding material. In addition, a resin material composed of paraffin or the like may be employed. In addition, the resin material composed of a specific resin component (polyethylene, paraffin, etc.) does not need to contain a small amount of the resin component, but the content rate is such that it can exhibit the function of shielding neutrons. Must be included. Also, the specific resin component may not be contained 100%, and other components may be contained within a range that does not affect the shielding properties. That is, it is sufficient that the specific resin component is contained at a predetermined content rate. In the case where a plurality of resin components having a shielding property against neutrons L2 are included, the total content of the plurality of resin components may satisfy a predetermined value.

The third layer 23 is a layer that mainly shields the trapped gamma rays L3 generated when the second layer 22 shields the neutrons L2. The third layer 23 is arranged on the outer peripheral side of the second layer 22 . Here, the third layer 23 is arranged so as to be adjacent to the second layer 22 on the outer peripheral side. The second gamma ray shielding material of the third layer 23 is more gamma ray shielding than the neutron shielding material of the second layer 22 . Also, the second gamma-ray shielding material of the third layer 23 has a smaller specific gravity than the gamma-ray shielding material of the first layer 21 . In addition, "high gamma ray shielding property" means that when the neutron shielding material of the second layer 22 and the second gamma ray shielding material of the third layer 23 are compared with the same thickness, the thickness of the third layer 23 is This means that the second gamma ray shielding material can shield more gamma rays. Heavy concrete may be employed as such a second gamma-ray shielding material.

The thickness of the first layer 21 is thinner than the thickness of the second layer 22 and the thickness of the third layer 23 . For example, the thickness of the first layer 21 may be set to be thinner than the thickness of the second layer 22 and the thickness of the third layer 23 by a predetermined ratio.

Next, the action and effect of the self-shield 6 according to this embodiment will be described.

First, the layer structure of the self-shield 56 according to the comparative example will be described with reference to FIG. 3(b). As shown in FIG. 3(b), the self-shield 56 comprises a second layer 22, a first layer 21 and a third layer 23 in order from the inner periphery. At this time, the neutrons L 2 from the target device 10 are shielded by the second layer 22 . At this time, in the second layer 22, a trapped gamma ray L3 is generated when the neutron L2 is shielded. In contrast, the first layer 21 shields the primary gamma rays L1 and the trapped gamma rays L3. However, since radiation (gamma rays L1, L3 and neutrons L2) that cannot be shielded by the first layer 21 leaks, the third layer 23 on the outermost side shields those radiations.

In contrast, in the self-shield 6 according to this embodiment shown in FIG. 3A, the first layer 21 shields the primary gamma rays L1, the second layer 22 shields the neutrons L2, and the second layer A third layer 23 on the outer peripheral side of 22 shields the trapped gamma rays L3. Here, since the second layer 22 is arranged on the outer peripheral side of the first layer 21 , the first layer 21 is arranged at a position closer to the target T than the second layer 22 . In such an arrangement, compared with the structure according to the comparative example shown in FIG. volume can be reduced. Therefore, the weight of the first layer 21 can be reduced. Also, since the neutrons L2 pass through the first layer 21, a moderating effect of the neutrons L2 is obtained, and the second layer 22 can shield the neutrons L2 more effectively. Therefore, the second layer 22 can be made thinner and lighter than the comparative example. On the other hand, since the trapped gamma rays L3 do not pass through the first layer 21, the amount of the trapped gamma rays L3 to be shielded by the third layer 23 increases. no significant impact on As described above, the weight of the self-shield 6 can be reduced.

For example, when lead is used as the material of the first layer 21, the first layer occupies a large proportion of the total weight of the self-shield 6 because of its high specific gravity of 11.3 g/cm ³ . Therefore, by reducing the volume of the first layer 21, the weight of the self-shield 6 can be reduced. By reducing the weight of the self-shield 6 in this way, the floor 102 of the building 100 can bear a sufficient load, and the transportation work and the like at the time of installation can be facilitated. Further, since the unit weight of lead is expensive, the material cost of the entire self-shield 6 can be reduced by reducing the volume of lead.

The second gamma-ray shielding material of the third layer 23 has a smaller specific gravity than the first gamma-ray shielding material of the first layer 21 . This reduces the amount of heavy material in the self-shield 6 .

The first layer 21 is arranged on the innermost side of the self-shield 6 . Thereby, the volume of the gamma-ray shielding material of the first layer 21 can be reduced.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and may be modified without changing the gist of each claim.

For example, in the embodiment described above, the third layer 23 was made of a material having a lower specific gravity than the first layer 21 . Alternatively, the third layer 23 may employ the same gamma-ray shielding material as the first layer 21 .

In the above-described embodiments, the layers are directly bonded to each other, but a member that does not shield radiation may be interposed between the layers.

2 -- accelerator, 6 -- self-shield, 10 -- target device (RI manufacturing device), 21 -- first layer, 22 -- second layer, 23 -- third layer.

Claims (3)

A self-shield for an RI production apparatus in which an accelerator and an RI production apparatus are arranged inside, and radioisotopes are produced by irradiating a target with a charged particle beam from the accelerator inside the RI production apparatus,
a first layer formed by a first gamma-ray shielding material that shields gamma rays;
It is arranged on the outer peripheral side than the first layer, has a higher neutron shielding property than the gamma ray shielding material of the first layer, and has a smaller specific gravity than the gamma ray shielding material of the first layer. a second layer formed by a shielding material;
A third layer formed of a second gamma-ray shielding material that is arranged on the outer peripheral side of the second layer and has a higher gamma-ray shielding property than the neutron shielding material of the second layer,
the first gamma-ray shielding material of the first layer is at least one material selected from lead, iron, and tungsten;
said second gamma-ray shielding material of said third layer is heavy concrete;
said first layer surrounds said target, said second layer surrounds said first layer, and said third layer surrounds said second layer;
Self-shielding for RI manufacturing equipment. 2. The self-shield for RI manufacturing equipment of claim 1, wherein said second gamma-ray shielding material of said third layer has a lower specific gravity than said first gamma-ray shielding material of said first layer. 3. The self-shield for RI manufacturing equipment according to claim 1 or 2, wherein said first layer is arranged on the innermost side of said self-shield.

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