Patent Publication Number: US-2020305268-A1

Title: Liquid target device

Description:
RELATED APPLICATIONS 
     The content of Japanese Patent Application No. 2019-054739, on the basis of which priority benefits are claimed in an accompanying application data sheet, is in its entirety incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     A certain embodiment of the present invention relates to a liquid target device. 
     Description of Related Art 
     As a technique in the related art, a liquid target device as described in the related art has been known. A target liquid is accommodated in the liquid target device and the target liquid is irradiated with a charged particle beam accelerated by a particle accelerator such that a radioisotope (RI) of the target liquid is generated. 
     SUMMARY 
     According to an aspect of the present invention, there is provided a liquid target device including a liquid accommodation portion in which a target liquid is accommodated, a beam passage through which a charged particle beam emitted from a particle accelerator passes to reach the liquid accommodation portion, a target foil that separates the beam passage and the liquid accommodation portion from each other, and a vacuum foil that separates a vacuum region provided upstream of the beam passage and the beam passage from each other. The beam passage is provided with a first gas chamber into which a cooling gas is supplied at a position on the vacuum foil side and a second gas chamber into which a cooling gas is supplied at a position closer to the target foil side than the first gas chamber and the first gas chamber and the second gas chamber are separated from each other by an intermediate foil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a liquid target device according to an embodiment. 
         FIG. 2  is a view for describing a cooling gas supply system of the liquid target device. 
     
    
    
     DETAILED DESCRIPTION 
     Ina liquid target device, a so-called target foil covers an opening upstream of an accommodation portion of a target. In the case of such a device configuration, a target foil may be damaged during irradiation with a charged particle beam. When the target foil is damaged, the target liquid may flow into a particle accelerator side. 
     It is desirable to provide a liquid target device in which a target liquid is prevented from flowing out toward a particle accelerator side even when a target foil is damaged. 
     According to the liquid target device, a vacuum foil and an intermediate foil that partition a beam passage are provided between the target foil of a liquid accommodation portion and a vacuum region. Therefore, even in a case where the target foil is damaged and a target liquid held in a liquid accommodation portion flows out toward a second gas chamber, the movement thereof is restricted by the intermediate foil and thus the target liquid is prevented from moving to the vacuum region via a first gas chamber. Therefore, even when the target foil is damaged, the target liquid can be prevented from flowing out toward the particle accelerator side. 
     Here, a flow system for the cooling gas relating to the first gas chamber and a flow system for the cooling gas relating to the second gas chamber may be independent of each other. 
     According to such a configuration, even when the target liquid flows out to the second gas chamber and the target liquid is discharged to the outside of a system along with movement of the cooling gas, the target liquid can be prevented from being erroneously supplied to the first gas chamber or the like since the flow system for the cooling gas relating to the second gas chamber and the flow system for the cooling gas relating to the first gas chamber are independent of each other. 
     The liquid target device may further include a pipe through which a fluid discharged from the second gas chamber flows and a recovery unit that is provided in the pipe and recovers a foreign substance contained in the fluid. 
     In a case where a configuration, in which the recovery unit that recovers the foreign substance contained in the fluid is provided in the pipe through which the fluid discharged from the second gas chamber flows, is adopted, even when the target liquid leaks into the second gas chamber and flows to the pipe along with movement of the cooling gas, the target liquid can be recovered in the recovery unit and thus the target liquid can be prevented from flowing out to a subsequent stage. 
     A flow system for the cooling gas relating to the first gas chamber maybe shared with another liquid target device that is different from the liquid target device. 
     In a case where one particle accelerator is provided with a plurality of liquid target devices, a flow system for a cooling gas may be shared with another liquid target device. In such a case, when a foreign substance such as the target liquid which is different from a cooling gas intrudes into the shared flow system, the influence thereof may become wide-ranging. However, when a configuration in which the flow system for the cooling gas relating to the first gas chamber that is on a side distant from the liquid accommodation portion in which the target liquid is accommodated is shared with the other liquid target device is adopted, the other liquid target device can be prevented from being influenced even in a case where the target foil is damaged. 
     Hereinafter, an embodiment of the present invention will be described in detail with reference to attached drawings. Note that, the same reference numerals are assigned to the same constituent elements in description of the drawings and repetitive descriptions thereof will be omitted. 
       FIG. 1  is a schematic configuration view of a liquid target device used in a radioisotope manufacturing system. The radioisotope manufacturing system (hereinafter, “RI manufacturing system”) including a liquid target device  1  is an apparatus that manufactures a radioisotope (hereinafter, “RI”) by irradiating a target liquid T with a charged particle beam B. The RI manufactured by means of the system is used to manufacture a radiopharmaceutical (including radioisotope drug), which is a radioisotope-labeled compound, for example. The target liquid T is, for example,  18 O water, an acidic solution containing a metallic element such as  68 Zn,  65 Ni, and  nat Y, and the like. Examples of a radioisotope-labeled compound generated from the target liquid T as described above include  18 F-FDG (fluorodeoxyglucose),  68 Ga-PSMA,  64 Cu-DOTA-trastuzumab,  89 Zr-trastuzumab as compounds to be used in a PET inspection (positron emission tomography inspection) in a hospital or the like. 
     The RI manufacturing system includes a particle accelerator in addition to the liquid target device  1 . The particle accelerator is an accelerator that emits the charged particle beam B. Examples of charged particles include protons and heavy particles (heavy ions). Note that, as the particle accelerator, for example, a cyclotron, a linear accelerator (linac), or the like is used. As the charged particle beam, for example, a proton beam, a deuteron beam, an α-beam, or the like is used. In the following description, words such as “upstream side” and “downstream side” will be used corresponding to the upper stream and the lower stream of the charged particle beam emitted from a particle accelerator  3 . 
     The liquid target device  1  is mounted into a manifold  90  that is provided in a port for emission of the charged particle beam, the port being provided in the cyclotron. The cyclotron adjusts the trajectory of the charged particle beam in an acceleration space such that the charged particle beam is extracted from the port. The extracted charged particle beam is incident into the manifold  90  and reaches the liquid target device  1 . 
     The liquid target device  1  is configured to include a cooling unit  10  and a target holding unit  20 . Note that, although the cooling unit  10  and the target holding unit  20  will be described separately in the present embodiment, the way in which the units are classified can be appropriately changed. 
     The cooling unit  10  is provided in a state of protruding from the manifold  90  of the cyclotron. The cooling unit  10  includes a beam passage  11 , through which the charged particle beam B passes, at a position corresponding to an irradiation axis of the charged particle beam B. The beam passage  11  is formed to have a circular section with the irradiation axis of the charged particle beam B as a center line and is formed to extend along the irradiation axis. 
     The cooling unit  10  includes two sets of foils on the beam passage  11 . By a vacuum foil  31 , a region in the beam passage  11  that is upstream of the vacuum foil  31  is kept vacuum. In other words, a region upstream of the vacuum foil  31  is a vacuum region A 1 . In addition, an intermediate foil  32  is provided downstream of the vacuum foil  31  in the beam passage  11 . The vacuum foil  31  and the intermediate foil  32  are thin circular foils formed of metal such as titanium and chromium or an alloy thereof and the thickness thereof is approximately 10 μm to 100 μm. As a foil, for example, a Havar foil or the like containing iron, cobalt, nickel, chromium, molybdenum, manganese, tungsten, or the like can be used. However, the foil is not limited thereto. In addition, the intermediate foil  32  may be provided by stacking two foils as described above.  FIG. 1  shows a state where two foils  32   a  and  32   b  are stacked to form the intermediate foil  32 . In a case where the intermediate foil  32  is formed by stacking the two foils  32   a  and  32   b,  the mechanical strength of the intermediate foil  32  can be increased. 
     In addition, the cooling unit  10  includes two sets of cooling flow paths  12  and  13  through which a cooling gas such as helium is blown to the beam passage  11 . The cooling flow path  12  is configured to include a pair of cooling flow paths  12   a  and  12   b.  In addition, the cooling flow path  13  is configured to include a pair of cooling flow paths  13   a  and  13   b.    
     The cooling flow path  12  is provided between the vacuum foil  31  and the intermediate foil  32  on the beam passage  11 . The cooling flow paths  12   a  and  12   b  are provided to face each other with the beam passage  11  interposed therebetween. In addition, each of the cooling flow paths  12   a  and  12   b  branches into a portion facing an upstream side and a portion facing a downstream side. A cooling gas is blown to the vacuum foil  31  on the upstream side through a portion of the cooling flow path  12   a  that faces the upstream side and the cooling gas is blown to the intermediate foil  32  through a portion of the cooling flow path  12   a  that faces the downstream side (refer to  FIG. 2  also). The cooling flow path  12   b  is provided as a flow path through which a cooling gas blown from the cooling flow path  12   a  is discharged from the beam passage  11 . 
     The cooling flow path  13  is provided downstream of the intermediate foil  32  on the beam passage  11 . The cooling flow paths  13   a  and  13   b  are provided to face each other with the beam passage  11  interposed therebetween. In addition, each of the cooling flow paths  13   a  and  13   b  branches into a portion facing an upstream side and a portion facing a downstream side. A cooling gas is blown to the intermediate foil  32  on the upstream side through a portion of the cooling flow path  13   a  that faces the upstream side and the cooling gas is blown to a target accommodation portion  23  (liquid accommodation portion) through a portion of the cooling flow path  13   a  that faces the downstream side (refer to  FIG. 2  also). The cooling flow path  13   b  is provided as a flow path through which a cooling gas blown from the cooling flow path  13   a  is discharged from the beam passage  11 . 
     The target holding unit  20  has an approximately columnar shape and includes a target foil  33 , a target container portion  21 , and a cooling mechanism  22 . The target holding unit  20  is connected to the cooling unit  10  at a position downstream of the cooling flow path  13 . 
     The target container portion  21  is disposed on an upstream side of the target holding unit  20 . The target foil  33  is interposed between the target container portion  21  and the cooling unit  10  on the upstream side. Note that, a configuration in which the target foil  33  is supported by being interposed between members constituting the target holding unit  20  may also be adopted and a configuration in which the target foil  33  is supported by being interposed between members constituting the cooling unit  10  as shown in  FIG. 1  may also be adopted. 
     In the case of a configuration as shown in  FIG. 1 , a portion of a front surface of the target foil  33  is exposed with respect to the beam passage  11 . The target foil  33  allows abeam to pass therethrough but blocks a fluid such as the target liquid T and a helium gas. The target foil  33  is a Havar foil or a thin circular foil formed of metal such as niobium or an alloy and the thickness thereof is approximately 10 μm to 50 μm. 
     The target container portion  21  includes the target accommodation portion  23  that is formed at a center portion as seen in front view and in which the target liquid T can be accommodated and a buffer portion  24  that is positioned above the target accommodation portion  23  and communicates with the target accommodation portion  23 . The target accommodation portion  23  and the buffer portion  24  are configured as a closed space formed when a front surface side of the target container portion  21  is closed by the target foil  33 . A portion of the closed space is the target accommodation portion  23  in which the target liquid T is stored and a portion of the closed space that is above the liquid surface of the target liquid T is the buffer portion  24 . In other words, the target foil  33  separates the beam passage  11  from the target accommodation portion  23  and the buffer portion  24 . The target liquid T is supplied to the target accommodation portion  23  through a pipe  41  such that the target accommodation portion  23  is filled with the target liquid T and the target liquid T after processing is recovered through the pipe  41  again. 
     The cooling mechanism  22  is provided rearward of a rear wall  43  constituting the target accommodation portion  23  and the buffer portion  24 . The cooling mechanism  22  cools the target accommodation portion  23  and the buffer portion  24  by supplying a cooling water that comes into contact with the rear wall  43 . The cooling mechanism  22  includes a rear water path  45  that is immediately rearward of the rear wall  43 , a water introduction path  47  through which the cooling water is introduced into the rear water path  45 , and a water discharge path  49  through which the cooling water is discharged from the rear water path  45 . The cooling water is supplied from the outside through a cooling water supply pipe connected to the water introduction path  47 . By the cooling mechanism  22  as described above, the target liquid T in the target accommodation portion  23  is cooled. In addition, when the buffer portion  24  is cooled by the cooling mechanism  22 , vapor evaporated from the target liquid T in the target accommodation portion  23  is condensed in the buffer portion  24  and returns to the target accommodation portion  23  due to the own weight thereof. Note that, the pressure in the target accommodation portion  23  and the buffer portion  24  is increased by an inert gas (for example, He) supplied through a pipe  51  and thus the boiling point of the target liquid T increases. 
     As described above, in the liquid target device  1 , the vacuum foil  31 , the intermediate foil  32 , and the target foil  33  form two gas chambers on the beam passage  11  through which a cooling gas passes. That is, a first gas chamber R 1  into which a cooling gas is supplied from the cooling flow path  12  ( 12   a  and  12   b ) and a second gas chamber R 2  into which a cooling gas is supplied from the cooling flow path  13  ( 13   a  and  13   b ) are formed on the beam passage  11 . The first gas chamber R 1  and the second gas chamber R 2  are separated from each other by the intermediate foil  32 . 
     Next, the flow of cooling gases supplied to the first gas chamber R 1  and the second gas chamber R 2  will be described with reference to  FIG. 2 . In the liquid target device  1 , a flow system for the cooling gas supplied to the first gas chamber R 1  and a flow system for the cooling gas supplied to the second gas chamber R 2  can be made independent of each other. Note that, a flow system for a cooling gas refers to a pipe system relating to supply of the cooling gas to a gas chamber and discharge of the cooling gas from the gas chamber. 
     In  FIG. 2 , three liquid target devices  1  ( 1 A,  1 B, and  1 C) are shown. Although one liquid target device  1  has been described in  FIG. 1 , a plurality of the liquid target devices  1  may be attached to one particle accelerator in an actual case. For example, in a case where a particle accelerator is a cyclotron, the cyclotron is provided with a plurality of ports and the liquid target device  1  may be attached to each port via a manifold. In this case, the plurality of liquid target devices  1  are installed in a state of being somewhat close to each other.  FIG. 2  schematically shows a state in which the three liquid target devices  1  ( 1 A,  1 B, and  1 C) are disposed in parallel. However, in an actual case, adjacent liquid target devices  1  maybe different from each other in installation angle depending on the configuration of the particle accelerator or the like. 
     In this case, a cooling gas supplied to the first gas chamber R 1  on the upstream side can be shared between the adjacent liquid target devices  1 . That is, a flow system S 1  for the cooling gas supplied to the first gas chamber R 1  is shared with another liquid target device. In the case of an example shown in  FIG. 2 , a cooling gas supplied to the liquid target device  1 A is supplied to the beam passage  11  (first gas chamber R 1 ) of the liquid target device  1 B from the cooling flow path  12   a  of the liquid target device  1 B via a pipe L 1  after being discharged from the cooling flow path  12   b.  Then, the cooling gas supplied to the first gas chamber R 1  of the liquid target device  1 B is supplied to the liquid target device  1 C from the cooling flow path  12   a  of the liquid target device  1 C via a pipe L 2  after being discharged from the cooling flow path  12   b.  As described above, regarding a flow system for a cooling gas with respect to the first gas chamber R 1 , a configuration in which cooling flow paths provided with respect to the first gas chambers R 1  of the liquid target devices  1  adjacent to each other from among the plurality of liquid target devices  1  are connected to each other via a pipe and a cooling gas is supplied via the pipe can also be adopted. 
     Meanwhile, a flow system S 2  for a cooling gas to the second gas chamber R 2  can be provided to be independent of an adjacent liquid target device  1 .  FIG. 2  shows the flow system S 2  for a cooling gas supplied to the liquid target device  1 B. In the case of such a supply system, a cooling gas (helium gas) cooled in a helium cooling and pressurizing device  61  is sent to the cooling flow path  13   a  via a pipe L 3  and is supplied to the second gas chamber R 2  from the cooling flow path  13   a.  As described above, a flow system for a cooling gas relating to the first gas chamber R 1  and a flow system for a cooling gas relating to the second gas chamber R 2  can be made independent of each other. 
     Note that, a cooling gas discharged from the second gas chamber R 2  via the cooling flow path  13   b  is returned to the helium cooling and pressurizing device  61  via a pipe L 4 . Note that, on the pipe L 4 , a gas-water separation device  62  and a filter  63  are provided. The gas-water separation device  62  and the filter  63  function as a recovery unit that recovers a foreign substance including the target liquid T in a case where the target foil  33  is damaged and the target liquid T flows into the pipe L 4 . Here, the “foreign substance” refers to all substances different from a cooling gas which is a fluid supposed to flow through the flow systems S 1  and S 2 . The only fluid supposed to flow through the pipe L 4  is a helium gas. 
     The gas-water separation device  62  is provided to prevent the target liquid T from flowing to the subsequent stage in a case where a fluid (helium gas) flowing through the pipe L 4  contains the target liquid T with the target foil  33  being damaged. Although the configuration of a device for gas-water separation is not particularly limited, a configuration in which gas-water separation can be performed by changing the shape of a tank as shown in  FIG. 2  maybe adopted. In addition, a function of performing a neutralization process with respect to a liquid or a gas recovered in the gas-water separation device  62  may be provided. 
     The filter  63  is provided to remove water vapor and the like contained in a gas flowing through the pipe L 4 . In addition, in a case where a gas of which a component is different from the helium gas is contained in the gas, a filter that can adsorb the component may be used. 
     A gas flowing from the second gas chamber R 2  is returned to the helium cooling and pressurizing device  61  via the gas-water separation device  62  and the filter  63  on the pipe L 4 . Since the gas passes through the gas-water separation device  62  and the filter  63 , the target liquid T flowing in can be removed even in a case where the target foil  33  is damaged. Therefore, the helium cooling and pressurizing device  61  can be prevented from being damaged. 
     As described above, in the liquid target device  1  according to the present embodiment, the vacuum foil  31  and the intermediate foil  32  that partition the beam passage  11  are provided between the target foil  33  defining the target accommodation portion  23  (liquid accommodation portion) and the vacuum region A 1  on the upstream side. Therefore, even in a case where the target foil  33  is damaged and a target liquid held in the target accommodation portion  23  flows out toward the second gas chamber R 2 , the movement thereof is restricted by the intermediate foil  32 . Therefore, the target liquid is prevented from moving to the vacuum region on the upstream side via the first gas chamber R 1 . Therefore, even when the target foil  33  is damaged, the target liquid can be prevented from flowing out toward the particle accelerator side. 
     In a configuration in the related art, no intermediate foil  32  is provided and a gas chamber through which a cooling gas passes is configured as one chamber. Therefore, in a case where the target foil  33  is damaged and the target liquid T leaks into the gas chamber, the target liquid T may flow to a position downstream of the vacuum foil  31 . In this case, the target liquid T may flow to the vacuum region A 1  on the upstream side when the vacuum foil  31  is damaged. When the target liquid T flows to the vacuum region A 1 , the particle accelerator on the upstream side maybe influenced. Particularly, in a case where an acidic target liquid T is used, the vacuum region A 1  may be corroded by an acid, which results in a serious influence. With regard to this, in the liquid target device  1  according to the present embodiment, the beam passage  11  is provided with the two gas chambers separated from each other by the intermediate foil  32  such that the leakage of the target liquid T is prevented from reaching the vacuum foil  31 . Therefore, even when the target foil  33  is damaged, the target liquid T moving toward the particle accelerator can be suppressed. 
     In addition, the flow system S 1  for a cooling gas relating to the first gas chamber R 1  and the flow system S 2  for a cooling gas relating to the second gas chamber R 2  can be made independent of each other. According to such a configuration, even when the target liquid T flows out to the second gas chamber R 2  and the target liquid T is discharged to the outside of a system via the flow system S 2  along with movement of a cooling gas, the target liquid T can be prevented from being erroneously supplied to the first gas chamber R 1  or the like since the flow system S 2  for the cooling gas relating to the second gas chamber R 2  and the flow system S 1  for the cooling gas relating to the first gas chamber R 1  are independent of each other. That is, only the second gas chamber R 2  comes into contact with the target liquid T and the first gas chamber R 1  can be prevented from coming into contact with the target liquid T and thus the target liquid T can be prevented from moving toward the particle accelerator. 
     In addition, the pipe L 4  through which a fluid discharged from the second gas chamber R 2  flows and the gas-water separation device  62  and the filter  63  as the recovery unit that is provided in the pipe L 4  and recovers a foreign substance contained in the fluid may further be provided. According to such a configuration, even when the target liquid T leaks into the second gas chamber R 2  and flows to the pipe L 4  along with movement of the cooling gas, a foreign substance relating to the target liquid T can be recovered in the recovery unit and thus the target liquid T can be prevented from flowing out to a subsequent stage. That is, the foreign substance relating to the target liquid T can be prevented from being discharged out of the system and a pump, a pipe, and the like for supply of a cooling gas to the second gas chamber R 2  like the helium cooling and pressurizing device  61  can be prevented from coming into contact with a substance relating to the target liquid T. 
     In addition, as described above, the flow system S 1  for the cooling gas supplied to the first gas chamber R 1  is shared with another liquid target device different from the liquid target device. In a case where one particle accelerator is provided with a plurality of liquid target devices, a flow system for a cooling gas may be shared with another liquid target device. In such a case, when a foreign substance such as the target liquid T which is different from a cooling gas intrudes into the shared flow system, the influence thereof may become wide-ranging. However, when a configuration in which the flow system for the cooling gas relating to the first gas chamber R 1  that is on a side distant from the target accommodation portion  23  is shared with another liquid target device is adopted as in the case of the liquid target device  1  described above, the other liquid target device can be prevented from being influenced even in a case where the target foil  33  is damaged. 
     Starting with the above-described embodiment, the present invention can be carried out in various modes that are variously modified and improved on the basis of the knowledge of those skilled in the art. In addition, modification examples can also be configured using technical features described in the above-described embodiment. The configurations of each embodiment may be appropriately combined with each other. 
     For example, the shape or the like of each part constituting the liquid target device  1  can be appropriately changed. For example, although the second gas chamber R 2  has been described as a portion of the cooling unit  10 , a configuration relating to the second gas chamber R 2  may be configured as a portion of the target holding unit  20 . 
     In addition, a structure or the like supporting the foils is not limited to that described in the above-described embodiment. In addition, the intermediate foil  32  does not need to be formed by stacking two foils and may be configured by using one foil. 
     In addition, the number of gas chambers provided in the beam passage  11  may be three or more. However, since the number of members separating gas chambers from each other (members corresponding to intermediate foil  32 ) increases as the number of gas chambers increases, the efficiency of irradiation of the target liquid T with a charged particle beam may be lowered. 
     In addition, a configuration in which the flow system S 1  for the cooling gas relating to the first gas chamber R 1  and the flow system S 2  for the cooling gas related to the second gas chamber R 2  are not independent from each other may also be adopted. However, for example, when a configuration in which a cooling gas discharged from the second gas chamber R 2  is prevented from being directly supplied to the first gas chamber R 1  is adopted, a foreign substance relating to the target liquid T can be prevented from flowing to the first gas chamber R 1  in a case where the target liquid T leaks into the second gas chamber R 2  as described above. In addition, a configuration in which the flow system S 1  for the cooling gas relating to the first gas chamber R 1  is not shared with another liquid target device  1  may also be adopted. 
     In addition, the gas-water separation device  62  and the filter  63  as the recovery unit maybe in a state of not exhibiting a function as the recovery unit when there is no abnormality in the liquid target device  1 , that is, the target foil  33  is not damaged. In this case, when a configuration in which control is performed such that the function as the recovery unit is exhibited when some abnormality is detected is adopted, the function as the recovery unit described in the above-described embodiment can be realized. 
     It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.