Patent Publication Number: US-2022238293-A1

Title: X-ray module

Description:
TECHNICAL FIELD 
     One aspect of the present disclosure relates to an X-ray module. 
     BACKGROUND 
     An X-ray module has been known in which an electron gun that emits an electron beam and a target that generates an X-ray when the electron beam is incident on the target are disposed inside a housing and which outputs the X-ray from an output window that closes an opening portion of the housing (for example, refer to Japanese Patent No. 5179797). 
     In the above-described X-ray module, a decrease in focus to object distance (FOD) is required in some cases. For example, in a case where the X-ray module is used for a non-destructive inspection, when the FOD that is a distance from an X-ray focal point (irradiation point of the electron beam on the target) to an inspection object is small, observation at a high magnification ratio can be performed. Alternatively, when it is assumed that the magnification ratio remains equal, an X-ray imaging element can be disposed close to an X-ray source, so that a bright image can be acquired. 
     In addition, in the above-described X-ray module, an efficiency of conversion of the electron beam into the X-ray in the target is approximately 1%, and approximately 99% of the incident electron beam becomes heat. For this reason, in order to suppress a decrease in X-ray output caused by damage of the target due to heat, heat generated in the target needs to be satisfactorily radiated. 
     SUMMARY 
     Therefore, an object of one aspect of the present disclosure is to provide an X-ray module capable of satisfactorily radiating heat generated in a target while suppressing an increase in FOD. 
     According to one aspect of the present disclosure, there is provided an X-ray module including: a housing in which an opening portion is formed; an electron gun that emits an electron beam inside the housing; a target that includes an electron-incident surface and an X-ray-emitting surface opposite the electron-incident surface, and that transmits an X-ray generated when the electron beam is incident on the electron-incident surface and emits the X-ray from the X-ray-emitting surface; an X-ray-emitting window that seals the opening portion, and that transmits the X-ray emitted from the target and emits the X-ray to a first side in an axial direction; and a heat radiating unit disposed outside the housing. The housing includes a surface on which a protrusion protruding to the first side is formed, the opening portion is formed in the protrusion, and the target is disposed in the opening portion. The heat radiating unit includes a first portion extending along the surface and thermally connected to the surface, and a second portion extending from the first portion to a second side opposite the first side. 
     In the X-ray module, the target includes the electron-incident surface and the X-ray-emitting surface, transmits the X-ray generated when the electron beam is incident on the electron-incident surface, and emits the X-ray from the X-ray-emitting surface. In such a transmission type configuration, the target is more easily disposed close to the X-ray-emitting window and a FOD can be more reduced than in a reflection type configuration in which an electron-incident surface also serves as an X-ray-emitting surface. In addition, the protrusion protruding to the first side is formed on the surface of the housing, and the target is disposed in the opening portion formed in the protrusion. For this reason, the FOD can be further reduced. Then, the heat radiating unit includes the first portion extending along the surface and thermally connected to the surface. Accordingly, the heat radiating unit can be disposed using a space corresponding to a height of the protrusion, and heat generated in the target can be satisfactorily radiated while suppressing an increase in FOD. Further, the heat radiating unit includes the second portion extending from the first portion to the second side opposite the first side. Accordingly, heat radiation by the heat radiating unit can be improved while suppressing an increase in FOD. Therefore, the X-ray module is capable of satisfactorily radiating heat generated in the target while suppressing an increase in FOD. 
     The second portion may be located outside an outer edge of the surface when viewed in the axial direction, and may be located closer to the second side in the axial direction than the surface. In this case, heat radiation by the heat radiating unit can be improved while suppressing an increase in FOD. 
     The first portion may surround the protrusion when viewed in the axial direction. In this case, heat generated in the target can be more satisfactorily radiated. 
     The heat radiating unit may not protrude to the first side with respect to the protrusion. In this case, the FOD can be further reduced. 
     A surface of the heat radiating unit on the first side may be located on the same plane as a surface of the protrusion on the first side. In this case, the thickness of the first portion can be secured and heat radiation by the heat radiating unit can be improved while suppressing an increase in FOD. 
     A surface of the X-ray-emitting window on the first side may be located on the same plane as a surface of the heat radiating unit on the first side. In this case, the FOD can be further reduced. 
     The X-ray module according to one aspect of the present disclosure may further include a heat conducting member disposed between the first portion and the surface. In this case, heat generated in the target can be more satisfactorily radiated. 
     The second portion may include a plurality of fins. In this case, heat radiation by the heat radiating unit can be further improved. 
     The first portion and the second portion may be formed in a pipe shape. In this case, for example, the first portion and the second portion can be used as a pipe for a cooling medium, a heat pipe, or the like, and heat radiation by the heat radiating unit can be further improved. 
     Each of the first portion and the second portion may define a flow path between the housing and the member for letting a cooling medium flowing. In this case, heat radiation by the heat radiating unit can be further improved. 
     The X-ray module according to one aspect of the present disclosure may further include a deflection unit that includes a permanent magnet, and that deflects the electron beam by means of a magnetic force of the permanent magnet. The second portion may be thermally connected to the deflection unit. In this case, the position of an X-ray focal point can be moved to a desired position by the deflection unit. In addition, the heating of the permanent magnet by heat generated in the target can be suppressed, and the X-ray can be stably output. 
     According to one aspect of the present disclosure, it is possible to provide the X-ray module capable of satisfactorily radiating heat generated in the target while suppressing an increase in FOD. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of an X-ray generation device according to an embodiment. 
         FIG. 2  is a cross-sectional view of an X-ray tube. 
         FIG. 3  is an exploded perspective view of the X-ray tube. 
         FIG. 4  is a cross-sectional view illustrating a periphery of a protrusion. 
         FIG. 5  is a cross-sectional view illustrating a periphery of a target. 
         FIG. 6  is a cross-sectional view of the X-ray tube. 
         FIG. 7  is a cross-sectional view illustrating a periphery of a deflection unit. 
         FIG. 8  is a cross-sectional view of an X-ray generation device according to a first modification example. 
         FIG. 9  is a cross-sectional view of an X-ray generation device according to a second modification example. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one embodiment of the present disclosure will be described in detail with reference to the drawings. In the following description, the same reference signs are used for the same or corresponding elements, and duplicated descriptions will be omitted. 
     [X-Ray Generation Device] 
     An X-ray generation device (X-ray module)  100  illustrated in  FIG. 1  is, for example, a microfocus X-ray source used for an X-ray non-destructive inspection in which an internal structure of an inspection object is observed. The X-ray generation device  100  includes an X-ray tube  1 , a heat radiating unit  7 , a case  110 , and a power source unit  120 . As illustrated in  FIG. 2 , the X-ray tube  1  is a transmission type X-ray tube that emits an X-ray XR from an X-ray-emitting window  5  in a direction along an incident direction of an electron beam B, the X-ray XR being generated when the electron beam B from an electron gun  3  is incident on a target  4  and transmitting through the target  4  itself. The X-ray tube  1  is a vacuum-sealed x-ray tube that includes a housing  2  having an internal space R in a vacuum state and does not require component replacement or the like. In the following description, it is assumed that a direction parallel to a tube axis AX of the X-ray tube  1  is an axial direction A, one side (upper side in the drawings) in the axial direction A is a first side S 1 , and the other side (side opposite the first side S 1 ) in the axial direction A is a second side S 2 . In the X-ray tube  1 , an optical axis of the electron beam B coincides with an optical axis the X-ray XR. 
     The housing  2  has a substantially columnar outer shape. The housing  2  includes a head portion  21  made of a metal material and an insulating valve  22  made of an insulating material such as glass. The target  4  and the X-ray-emitting window  5  are fixed to the head portion  21 . 
     The electron gun  3  is fixed to the insulating valve  22 . The electron gun  3  emits the electron beam B in the internal space R. For example, the electron gun  3  is configured such that a heater  31 , a cathode  32 , a first grid electrode  33 , and a second grid electrode  34  are disposed side by side in order from the second side S 2 . The heater  31  is formed of a filament that is energized to generate heat. The cathode  32  is heated by the heater  31  to emit electrons. The first grid electrode  33  and the second grid electrode  34  are formed in a cylindrical shape. The first grid electrode  33  is provided to control the amount of electrons emitted from the cathode  32 , and the second grid electrode  34  is provided to focus the electrons, which have passed through the first grid electrode  33 , toward the target  4 . The heater  31 , the cathode  32 , the first grid electrode  33 , and the second grid electrode  34  are electrically connected to a plurality of stein pins SP provided to penetrate through a bottom portion  22   a  of the insulating valve  22 . 
     The case  110  includes a cylindrical member  111  and a power source unit case  112 . The case  110  is made of a metal material. The cylindrical member  111  is formed in a substantially cylindrical shape, and includes an opening  111   a  and an opening  111   b  at both ends in the axial direction A. The X-ray tube  1  is inserted into the opening  111   a  such that the head portion  21  protrudes from the opening  111   a . An attachment flange  23   c  of the X-ray tube  1  is fixed to an end portion on the first side S 1  of the cylindrical member  111 . Accordingly, the X-ray tube  1  seals the opening  111   a . An insulating oil K that is a liquid insulating substance is sealed in the cylindrical member  111 . 
     The power source unit  120  supplies electric power to the X-ray tube  1 . The power source unit  120  is housed in the power source unit case  112 . The power source unit  120  seals the opening  111   b  of the cylindrical member  111 . The power source unit  120  includes a high-voltage power supply portion  121  including a connector  121   a  having a cylindrical shape. The high-voltage power supply portion  121  is electrically connected to the X-ray tube  1 . Specifically, a tip portion of the connector  121   a  is electrically connected to the stein pins SP protruding from the bottom portion  22   a  of the insulating valve  22 . In this example, with the target  4  (anode) having a ground potential, and a negative high voltage (for example, −10 kV to −500 kV) is supplied from the power source unit  120  to the electron gun  3  via the high-voltage power supply portion  121 . 
     [X-Ray Tube] 
     As illustrated in  FIGS. 1 to 7 , the X-ray tube  1  includes the housing  2 , the electron gun  3 , the target  4 , the X-ray-emitting window  5 , and a deflection unit  6 . As described above, the housing  2  includes the head portion  21  and the insulating valve  22 . The head portion  21  corresponds to an anode of the X-ray tube  1  in terms of electrical potential. The head portion  21  includes a body portion  23  and a lid portion  24 . The body portion  23  is made of, for example, stainless steel (for example, SUS304), copper, an iron alloy, a copper alloy, or the like in a substantially cylindrical shape coaxial with the tube axis AX, and includes openings  23   a  and  23   b  at both ends in the axial direction A. The opening  23   a  is closed by the lid portion  24 . The lid portion  24  is fixed to an edge portion of the opening  23   a . The body portion  23  communicates with the insulating valve  22  through the opening  23   b , the insulating valve  22  having a substantially cylindrical shape coaxial with the tube axis AX. An outer peripheral surface of the body portion  23  is provided with the attachment flange  23   c  that is formed in a substantially annular plate shape concentric with the body portion  23 . 
     The lid portion  24  is made of, for example, molybdenum in a substantially circular plate shape coaxial with the tube axis AX, and closes the opening  23   a  of the body portion  23 . A protrusion  26  protruding to the first side S 1  with respect to a surface  24   a  of the lid portion  24  on the first side S 1  is formed on the surface  24   a . The surface  24   a  has a circular shape, and the protrusion  26  is formed in a columnar shape concentric with the lid portion  24 . An opening portion  27  penetrating through the lid portion  24  along the axial direction A is formed in the protrusion  26 . 
     As illustrated in  FIGS. 4 to 6 , the opening portion  27  includes a first portion  27   a  that is open to a surface  26   a  of the protrusion  26  on the first side S 1 , and a second portion  27   b  that communicates with the first portion  27   a  and that is open to a surface  24   b  of the lid portion  24  on the second side S 2 . Each of the first portion  27   a  and the second portion  27   b  is formed in a circular shape in cross section which is concentric with the protrusion  26 . A diameter of the first portion  27   a  is larger than a diameter of the second portion  27   b , and a depth of the first portion  27   a  is shallower than a depth of the second portion  27   b . In other words, the first portion  27   a  is a recess formed in the surface  26   a  of the protrusion  26 , and the second portion  27   b  is a through-hole formed in a bottom surface of the first portion  27   a . The first portion  27   a  functions as a disposition portion in which the target  4  and the X-ray-emitting window  5  are disposed. The second portion  27   b  functions as an electron beam passage hole through which the electron beam B to be incident on the target  4  passes. An end portion of the second portion  27   b  on the second side S 2  is provided with a widening portion  27   ba  of which the diameter increases toward the second side S 2 , and is chamfered in a curved surface shape so as not to form a corner. 
     The target  4  and the X-ray-emitting window  5  are disposed in the first portion  27   a . The target  4  is made of, for example, tungsten, and includes an electron-incident surface  4   a  and an X-ray-emitting surface  4   b  on a side opposite the electron-incident surface  4   a . The target  4  transmits an X-ray generated when the electron beam B is incident on the electron-incident surface  4   a , and emits the X-ray from the X-ray-emitting surface  4   b . In this example, the target  4  is formed in a film shape on an entirety of a surface on the second side S 2  of the X-ray-emitting window  5 . Namely, the target  4  is integrally formed with the X-ray-emitting window  5 . The target  4  is disposed such that the electron-incident surface  4   a  faces the second side S 2  and the X-ray-emitting surface  4   b  faces the first side S 1 . A thickness of the target  4  is, for example, approximately several μm. 
     The X-ray-emitting window  5  is made of, for example, a highly radiolucent material such as diamond or beryllium in a circular plate shape. The X-ray-emitting window  5  is disposed coaxially with the tube axis AX on the bottom surface of the first portion  27   a  of the opening portion  27 , is fixed to the bottom surface by a joining member such as a brazing material (not illustrated), and seals the opening portion  27 . The X-ray-emitting window  5  is in thermal contact with the bottom surface of the first portion  27   a  via the target  4 . In this example, a surface  5   a  of the X-ray-emitting window  5  on the first side S 1  is located on substantially the same plane as the surface  26   a  of the protrusion  26  on the first side S 1 . The X-ray-emitting window  5  faces the electron gun  3  in the axial direction A, transmits the X-ray XR emitted from the target  4 , and emits the X-ray XR to the first side S 1  in the axial direction A. As illustrated in  FIG. 5 , the X-ray XR is generated at an X-ray focal point F that is an irradiation point of the electron beam B on the target  4 , and is emitted while spreading around the X-ray focal point F. The target  4  may be provided in only a region exposed to the second portion  27   b  on the surface of the X-ray-emitting window  5 , or a part of the target  4  may also be provided on a wall surface of the second portion  27   b . In addition, the target  4  and the X-ray-emitting window  5  may be provided away from each other. 
     As illustrated in  FIGS. 2 and 7 , the deflection unit  6  includes a plurality of permanent magnets  61 , a holding member  62 , and a heat insulating member  63 . The deflection unit  6  includes a pair of the permanent magnets  61  facing each other in a radial direction. The pair of permanent magnets  61  are disposed such that different poles face each other in the radial direction. The permanent magnet  61  is formed of, for example, a ferrite magnet, a neodymium magnet, a samarium cobalt magnet, an alnico magnet, or the like. 
     The holding member  62  is made of, for example, a metal material such as aluminum in a flat cylindrical shape (annular shape) coaxial with the tube axis AX, and holds the permanent magnets  61 . The holding member  62  is disposed outside the housing  2 , and is fixed to the attachment flange  23   c  in a state where the holding member  62  is in contact with a surface of the attachment flange  23   c  of the body portion  23  on the first side S 1 . The holding member  62  overlaps a part of the body portion  23  in the radial direction, and is disposed close to the body portion  23  to cover a part of the outer peripheral surface of the body portion  23 . The holding member  62  is slightly separated from the body portion  23  in the radial direction, but may be in contact with the body portion  23 . In addition, the holding member  62  may be formed of a plurality of members instead of being a cylindrical (annular) integrated member. 
     The heat insulating member  63  is made of, for example, a resin material such as silicone resin, epoxy resin, acrylic resin, polyimide resin, polyphenylene sulfide (PPS) resin, polyetheretherketone resin (PEEK). In order to suppress a decrease in the magnetic force of the permanent magnets  61  caused by a heat treatment when the heat insulating member  63  is cured, silicone resin, epoxy resin, and acrylic resin that is curable at room temperature are preferably used as the material of the heat insulating member  63 . 
     The heat insulating member  63  houses the permanent magnet  61  inside. Namely, the permanent magnet  61  is disposed inside the heat insulating member  63  in a state where the permanent magnet  61  is surrounded by the heat insulating member  63 . For example, the heat insulating member  63  is fixed to the holding member  62 , and the holding member  62  holds the permanent magnet  61  via the heat insulating member  63 . The heat insulating member  63  isolates the permanent magnet  61  from the holding member  62 . A surface  63   a  of the heat insulating member  63  on the second side S 2  is in contact with the surface of the attachment flange  23   c  of the body portion  23  on the first side S 1 . An outer surface other than the surface  63   a  in the heat insulating member  63  is covered with the holding member  62 . Namely, the heat insulating member  63  is provided such that the heat insulating member  63  is embedded in the holding member  62  and only the surface  63   a  is exposed from the holding member  62 . In such a manner, the heat insulating member  63  includes a portion disposed between the permanent magnet  61  and the attachment flange  23   c  of the body portion  23 . The configuration of the heat insulating member  63  is not limited to the configuration in which the heat insulating member  63  houses the permanent magnet  61  inside. For example, a configuration may be adopted in which the holding member  62  directly holds the permanent magnet  61  and the heat insulating member  63  having a plate shape is interposed between the holding member  62  and the body portion  23  to partition between the holding member  62  and the surface of the attachment flange  23   c  of the body portion  23  on the first side S 1 . 
     The deflection unit  6  deflects the electron beam B by means of the magnetic force of the permanent magnets  61  to change the position of the X-ray focal point F. When viewed in a direction (radial direction) perpendicular to a path P along which the electron beam B emitted from the electron gun  3  travels to the target  4 , the deflection unit  6  includes a portion overlapping the path P. Accordingly, the magnetic force of the permanent magnets  61  can be suitably applied to the electron beam B. In this example, an entirety of the deflection unit  6  overlaps the path P when viewed in the radial direction. The deflection unit  6  is attached to the attachment flange  23   c  such that an imaginary line connecting the pair of permanent magnets  61  facing each other is substantially orthogonal to the tube axis AX. The deflection unit  6  may be rotatable around the tube axis AX. In this case, the position of the X-ray focal point F can be moved by rotating the deflection unit  6 . 
     A thermal conductivity of the holding member  62  is higher than a thermal conductivity of the permanent magnet  61 . A thermal conductivity of the heat insulating member  63  is lower than a thermal conductivity of the body portion  23  of the housing  2  (portion of the housing  2  in contact with the deflection unit  6 ). Namely, heat insulation of the heat insulating member  63  is higher than heat insulation of the body portion  23 . In addition, the thermal conductivity of the heat insulating member  63  is lower than the thermal conductivity of each of the permanent magnet  61  and the holding member  62 . When the body portion  23  is made of SUS304, the thermal conductivity of the body portion  23  is, for example, 16.7 W/m·K. The thermal conductivity of the permanent magnet  61  is, for example, approximately 1 to 50 W/m·K, the thermal conductivity of the holding member  62  is, for example, approximately 100 to 400 W/m·K, and the thermal conductivity of the heat insulating member  63  is, for example, approximately 0.1 to 0.5 W/m·K. The thermal conductivity can be measured by general measurement methods such as a heat flow meter method, a laser flash method, and a hot wire method. 
     As illustrated in  FIGS. 1, 3, 4, and 6 , the heat radiating unit  7  includes a heat sink  70  that radiates heat generated in the target  4 , and a cooling unit  80  that cools the heat sink  70 , and is disposed outside the housing  2 . The heat sink  70  is made of, for example, a metal material such as aluminum. A thermal conductivity of the heat sink  70  is higher than the thermal conductivity of each of the body portion  23  and the permanent magnet  61 . The thermal conductivity of the heat sink  70  is, for example, approximately 100 to 400 W/m·K. The heat sink  70  includes a first portion  71  and a second portion  72 . 
     The first portion  71  is formed in a circular plate shape coaxial with the tube axis AX, and includes an opening  71   b  in a central portion thereof. The first portion  71  extends perpendicularly to the tube axis AX along the surface  24   a  of the lid portion  24 , and the protrusion  26  is disposed in the opening  71   b . The first portion  71  surrounds the protrusion  26  when viewed in the axial direction A. A surface of the first portion  71  on the second side S 2  is in contact with the surface  24   a  of the lid portion  24  via a heat conducting member  8  having a sheet shape. Accordingly, the first portion  71  is thermally connected to the surface  24   a  of the lid portion  24 . The heat conducting member  8  is, for example, a silicone sheet made of a silicone having a high thermal conductivity in a circular sheet shape, is disposed between an entirety of the surface  24   a  and the first portion  71 , and is in close contact with the surface  24   a  and the first portion  71 . Since the heat conducting member  8  intervenes between the first portion  71  and the lid portion  24 , heat conduction between the first portion  71  and the lid portion  24  can be more promoted than when the first portion  71  and the lid portion  24  that are made of a metal material are in direct contact with each other. 
     As illustrated in  FIG. 4 , the first portion  71  is slightly separated from the protrusion  26  in the radial direction. A distance L 1  between the first portion  71  and the protrusion  26  in the radial direction is smaller than a protrusion height L 2  of the protrusion  26  from the surface  24   a  of the lid portion  24  in the axial direction A, and is smaller than a diameter L 3  of the protrusion  26  (width of the protrusion  26  in the radial direction). The first portion  71  may be in contact with the protrusion  26 . The first portion  71  does not protrude to the first side S 1  with respect to the protrusion  26 . In other words, when a surface  71   a  of the first portion  71  on the first side S 1  and the surface  26   a  of the protrusion  26  on the first side S 1  are flat, the surface  71   a  is located on the same plane as the surface  26   a  or is located closer to the second side S 2  than the surface  26   a . In this example, the surface  71   a  is located on the same plane as the surface  26   a . In addition, the surface  71   a  is located on the same plane as the surface  5   a  of the X-ray-emitting window  5  on the first side S 1 . 
     The second portion  72  is formed in a substantially cylindrical shape concentric with the first portion  71 , and extends from an outer edge of the first portion  71  to the second side S 2 . The second portion  72  is located outside an outer edge of the surface  24   a  of the lid portion  24  when viewed in the axial direction A, and is located closer to the second side S 2  in the axial direction A than the surface  24   a . In this example, an entirety of the second portion  72  is located closer to the second side S 2  than the surface  24   a , but only a part of the second portion  72  may be located closer to the second side S 2  than the surface  24   a . The second portion  72  overlaps a part of the body portion  23  in the radial direction, and covers a part of the outer peripheral surface of the body portion  23 . The second portion  72  is slightly separated from the body portion  23  in the radial direction, but may be in contact with the body portion  23 . A surface  72   b  of the second portion  72  on the second side S 2  is in contact with a surface on the first side S 1  of the holding member  62  of the deflection unit  6 , and is thermally connected to the deflection unit  6 . 
     A plurality of fins  72   a  are formed in an outer peripheral surface of the second portion  72 . Each of the fins  72   a  is formed in a substantially circular plate shape concentric with the second portion  72 . The plurality of fins  72   a  are disposed parallel to each other and side by side at equal intervals along the axial direction A. Air from a cooling fan  84  to be described later is supplied to the fins  72   a.    
     The cooling unit  80  includes an air blowing unit  81  and a surrounding portion  82  formed in a substantially cylindrical shape to surround the heat sink  70 . The air blowing unit  81  includes a hood portion  83  and the cooling fan  84 . The hood portion  83  covers one side of the cylindrical member  111  in the direction perpendicular to the axial direction A, and forms a space  83   a . The cooling fan  84  is disposed in the space  83   a . A plurality of through-holes are formed as a ventilation portion  83   b  in the hood portion  83 . The cooling fan  84  sends outside air to the surrounding portion  82  as cooling air, the outside air being suctioned from the ventilation portion  83   b.    
     The surrounding portion  82  includes an upper wall portion  82   a  and a side wall portion  82   b . The upper wall portion  82   a  is formed in an annular shape, and defines an opening  82   c  on the first side S 1  of the surrounding portion  82 . The surrounding portion  82  is disposed such that the surface  71   a  of the first portion  71  on the first side S 1  is exposed from the opening  82   c . The side wall portion  82   b  is formed in a cylindrical shape, and surrounds the plurality of fins  72   a , together with the upper wall portion  82   a . The surrounding portion  82  forms a flow path through which the cooling air sent from a communication portion between the air blowing unit  81  and the surrounding portion  82  circulates so as to flow through spaces between the plurality of fins  72   a  in a circumferential direction. Accordingly, a heat radiation efficiency of the heat sink  70  can be improved. Incidentally, the cooling air is exhausted from a ventilation portion (not illustrated) provided in the side wall portion  82   b . Accordingly, it is possible to make it difficult for the exhausted cooling air to flow to an inspection object side, and an influence of exhausting during imaging can be suppressed. In addition, the cooling fan  84  may operate to suction outside air from the ventilation portion provided in the side wall portion  82   b  and to exhaust the outside air from the ventilation portion  83   b  provided in the hood portion  83 . 
     [Function and Effects] 
     In the X-ray generation device  100 , the target  4  includes the electron-incident surface  4   a  and the X-ray-emitting surface  4   b , transmits the X-ray XR generated when the electron beam B is incident on the electron-incident surface  4   a , and emits the X-ray XR from the X-ray-emitting surface  4   b . In such a transmission type configuration, the target  4  is more easily disposed close to the X-ray-emitting window  5  and the FOD can be more reduced than in a reflection type configuration in which an electron-incident surface also serves as an X-ray-emitting surface. In addition, the protrusion  26  protruding to the first side S 1  is formed on the surface  24   a  of the housing  2 , and the target  4  is disposed in the opening portion  27  formed in the protrusion  26 . For this reason, the FOD can be further reduced. Then, the heat sink  70  includes the first portion  71  extending along the surface  24   a  and being thermally connected to the surface  24   a . Accordingly, the heat sink  70  can be disposed using a space corresponding to the height of the protrusion  26 , and heat generated in the target  4  can be satisfactorily radiated while suppressing an increase in FOD. Further, the heat sink  70  includes the second portion  72  extending from the first portion  71  to the second side S 2  opposite the first side S 1 . Accordingly, heat radiation by the heat sink  70  can be improved while suppressing an increase in FOD. Therefore, the X-ray generation device  100  is capable of satisfactorily radiating heat generated in the target  4  while suppressing an increase in FOD. 
     A heat transfer path will be described with reference to  FIGS. 4 to 6 . As described above, a large amount of heat can be generated in the target  4 . In the X-ray generation device  100 , as indicated by arrows in  FIGS. 4 to 6 , heat generated in the target  4  is transferred from the protrusion  26  of the housing  2  to the lid portion  24 . The heat transferred to the lid portion  24  is transferred to the first portion  71  of the heat sink  70  via the heat conducting member  8 . The heat transferred to the first portion  71  is transferred to the second portion  72 . Accordingly, the heat generated in the target  4  can be effectively radiated by the heat sink  70 . In addition, since the thickness is increased by the protrusion  26 , the heat capacity of a region thermally connected to the target  4  can be increased. 
     Here, when the protrusion  26  is not provided, the target  4  is disposed closer to the second side S 2 , and the FOD is increased by an amount corresponding to a thickness of the first portion  71  of the heat sink  70 , so that the advantages of the transmission type X-ray tube are impaired. In this case, when the first portion  71  of the heat sink  70  is omitted, an increase in FOD can be suppressed, but heat generated in the target  4  cannot be effectively radiated. Therefore, the protrusion  26  is provided, so that the position of the target  4  is brought close to the inspection object and the heat sink  70  is disposed using the space corresponding to the height of the protrusion  26 , which is very effective in satisfactorily radiating heat generated in the target  4  while suppressing an increase in FOD. 
     In addition, when the heat sink  70  protrudes farther to the first side S 1  than the surface  26   a  on the first side S 1  of the protrusion  26 , the FOD is increased, and the advantages of the transmission type X-ray tube are impaired. The reason for the concern is that the inspection object comes into contact with the heat sink  70  and the inspection object cannot be brought close to the X-ray focal point F. On the other hand, in the X-ray generation device  100 , the heat sink  70  does not protrude to the first side S 1  with respect to the protrusion  26 . Accordingly, the FOD can be further reduced. In addition, the surface  71   a  of the first portion  71  of the heat sink  70  on the first side S 1  is located on the same plane as the surface  26   a  of the protrusion  26  on the first side S 1 . Accordingly, the thickness of the first portion  71  can be secured and heat radiation by the heat radiating unit  7  can be improved while suppressing an increase in FOD. In addition, heat radiation by the heat sink  70  can also be improved by shortening a distance from a heat generation portion (X-ray focal point F) to the first portion  71 . 
     The second portion  72  is located outside the outer edge of the surface  24   a  of the housing  2  when viewed in the axial direction A, and is located closer to the second side S 2  in the axial direction A than the surface  24   a . Accordingly, heat radiation by the heat sink  70  can be improved while suppressing an increase in FOD. 
     The first portion  71  surrounds the protrusion  26  when viewed in the axial direction A. Accordingly, heat generated in the target  4  can be more satisfactorily radiated. 
     The surface  5   a  of the X-ray-emitting window  5  on the first side S 1  is located on the same plane as the surface  71   a  of the first portion  71  on the first side S 1 . Accordingly, the FOD can be further reduced. 
     The heat conducting member  8  is disposed between the first portion  71  and the surface  24   a  of the housing  2 . Accordingly, heat generated in the target  4  can be more satisfactorily radiated. 
     The second portion  72  includes the plurality of fins  72   a . Accordingly, heat radiation by the heat radiating unit  7  can be further improved. 
     The deflection unit  6  is provided which deflects the electron beam B by means of the magnetic force of the permanent magnets  61 , and the second portion  72  is thermally connected to the deflection unit  6 . Accordingly, the position of the X-ray focal point F can be moved to a desired position by the deflection unit  6 . In addition, when heat generated in the target  4  is transferred to the permanent magnet  61 , the permanent magnet  61  is heated and the magnetic force decreases. In this case, the amount of deflection of the electron beam B is changed, and the position of the X-ray focal point is changed. For example, when the position of the X-ray focal point is changed during continuous imaging by computed tomography (CT) or the like, an acquired image is blurred. In contrast, in the X-ray generation device  100 , even when heat generated in the target  4  is transferred to the deflection unit  6 , the heat can be released to the heat radiating unit  7 . As a result, the heating of the permanent magnets  61  by the heat generated in the target  4  can be suppressed, and the X-ray can be stably output. 
     [Modification Examples] 
     In a first modification example illustrated in  FIG. 8 , a first portion  71 A and a second portion  72 A of the heat radiating unit  7  are formed in a pipe shape. The first portion  71 A linearly extends perpendicularly to the tube axis AX along the surface  24   a  of the lid portion  24 , and is thermally connected to the surface  24   a . The first portion  71 A may be disposed in an annular shape (spiral shape) or in such a manner that a linear portion is folded, on the surface  24   a  of the lid portion  24 . In this case, the thermal connection area can be further increased. The second portion  72 A extends from the first portion  71 A to the second side S 2 . In this example, the first portion  71 A and the second portion  72 A form a heat pipe, and a hydraulic fluid is sealed thereinside. 
     In the first modification example, the cooling fan  84  is disposed in the power source unit case  112 . The second portion  72 A extends to the vicinity of the cooling fan  84  to include a facing portion  72 Aa facing the cooling fan  84 . The cooling fan  84  is also used to cool a control substrate  130  disposed in the power source unit case  112 . Namely, in the first modification example, one cooling fan serves as both a cooling fan that radiates heat generated in the target  4  and a cooling fan that cools the control substrate  130 . Accordingly, low cost can be achieved. In addition, since the cooling fan  84  is disposed at a position away from the target  4  (X-ray tube  1 ), a failure of the cooling fan  84  caused by X-ray exposure can be suppressed. For example, the control substrate  130  controls operation of the power source unit  120 . The control substrate  130  faces the facing portion  72 Aa. 
     Also in the first modification example, similarly to the above embodiment, heat generated in the target  4  can be satisfactorily radiated while suppressing an increase in FOD. In addition, since the first portion  71 A and the second portion  72 A are formed in a pipe shape, the first portion  71 A and the second portion  72 A can be used as a heat pipe or the like, and heat radiation by the heat radiating unit  7  can be improved. In addition, since heat can be transported over a long distance, as described above, the cooling fan  84  can be disposed at a position away from the target  4 . 
     The heat radiating unit  7  may be configured as in a second modification example illustrated in  FIG. 9 . In the second modification example, a first portion  71 B and a second portion  72 B of the heat radiating unit  7  include members  71 Ba and  72 Ba that define flow paths  73  and  74  between the housing  2  and the first and second portions  71 B and  72 B, respectively, a cooling medium C flowing through the flow paths  73  and  74 . The member  71 Ba is formed in an annular plate shape coaxial with the tube axis AX, and defines the flow path  73  having an annular shape coaxial with the tube axis AX on the surface  24   a  of the lid portion  24 . The first portion  71 B is formed of the member  71 Ba and the flow path  73 . The first portion  71 B extends along the surface  24   a  of the lid portion  24 , and is thermally connected to the surface  24   a . The second portion  72 B is formed in a cylindrical shape concentric with the first portion  71 B, and defines the flow path  74  having a cylindrical shape concentric with the first portion  71 B on the outer peripheral surface of the body portion  23 . The second portion  72 B is formed of the member  72 Ba and the flow path  74 . The second portion  72 B extends from the first portion  71 B to the second side S 2  along the axial direction A. 
     Also in the second modification example, similarly to the above embodiment, heat generated in the target  4  can be satisfactorily radiated while suppressing an increase in FOD. In addition, since the first portion  71 B and the second portion  72 B define the flow paths  73  and  74  between the housing  2  and the first and second portions  71 B and  72 B, respectively, for letting the cooling medium C flowing, heat radiation by the heat radiating unit  7  can be further improved. 
     The present disclosure is not limited to the above embodiment. The materials and the shapes of the configurations are not limited to the materials and the shapes described above, and various materials and shapes can be adopted. The first portion  71  may not surround the protrusion  26  when viewed in the axial direction A, and may be formed in a shape other than an annular shape. The heat sink  70  may protrude farther to the first side S 1  than the surface  26   a  of the protrusion  26  on the first side S 1 . The deflection unit  6  may be omitted. The heat conducting member  8  may be omitted. In the above embodiment, forced air cooling is performed using the cooling fan  84 , but the cooling fan  84  may be omitted and natural air cooling may be performed. The cooling fan  84  may be provided adjacent to the fins  72   a . The heat radiating unit  7  may be a cooling mechanism other than the above-described example. In the first modification example, the first portion  71 A and the second portion  72 A may form a cooling water pipe for letting cooling water flowing. Even in this case, similarly to the first modification example, heat radiation by the heat radiating unit  7  can be improved. In addition, at least a part of the deflection unit  6  or the heat radiating unit  7  may be integrated with the X-ray tube  1 . In the above embodiment, the X-ray module forms the X-ray generation device  100 ; however, the X-ray module may not necessarily form the X-ray generation device, and may include, for example, only the X-ray tube  1  and the heat radiating unit  7  (heat sink  70 ).