Patent Publication Number: US-9431207-B2

Title: Rotating-anode X-ray tube assembly and rotating-anode X-ray tube apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-191449, filed Sep. 17, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a rotating-anode X-ray tube assembly and a rotating-anode X-ray tube apparatus. 
     BACKGROUND 
     In X-ray photography which is conducted in a medical field, etc., a rotating-anode X-ray tube assembly is generally used. The X-ray photography is, for instance, Roentgen photography, CT photography, etc. The rotating-anode X-ray tube assembly includes a housing, and a rotating-anode X-ray tube which is stored in the housing and radiates X-rays. A lead plate, which shields X-rays, is stuck to the inner surface of the housing. An X-ray radiation window, which passes X-rays radiated from the X-ray tube, is provided on the outer wall of the housing. A coolant, such as an insulation oil, is sealed in a space between the housing and the rotating-anode X-ray tube. 
     The rotating-anode X-ray tube includes an anode target, a cathode, and an envelope which accommodates the anode target and the cathode and has its inside reduced in pressure. The anode target can rotate at high speed (e.g. 10000 rpm). The anode target includes a target layer (umbrella-shaped portion) formed of a tungsten alloy. The cathode is located with eccentricity from the rotational axis of the anode target and is opposed to the target layer. 
     A high voltage is applied between the cathode and the anode target. Thus, if the cathode emits electrons, the electrons are accelerated and converged, and collide upon the target layer. Thereby, the target layer radiates X-rays, and the X-rays are discharged from the X-ray transmission window to the outside of the housing. 
     For example, the shape of a light-load X-ray tube assembly is substantially rotation-symmetric with respect to the axis of the X-ray tube. The housing is cylindrical, and includes a projection portion having a side surface to which a high-voltage receptacle is attached, an X-ray radiation window, and side plates which close both opening end portions of the cylindrical housing. 
     In the meantime, in recent years, in an X-ray tube assembly for CT photography use, etc., a housing including a first divisional part and a second divisional part has begun to be used in accordance with an increase in complexity of the shape of the X-ray tube, an increase in weight of the X-ray tube, and an increase in rotational speed of a rotating frame on which the X-ray tube assembly is mounted. The coupling surface between the first divisional part and second divisional part is parallel to the axis of the X-ray tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view which illustrates a rotating-anode X-ray tube assembly according to a first embodiment,  FIG. 1  illustrating an X-ray tube in side view. 
         FIG. 2  is a cross-sectional view which illustrates a rotating-anode X-ray tube apparatus according to a second embodiment,  FIG. 2  illustrating an X-ray tube in side view and illustrating a cooler unit in block diagram. 
         FIG. 3  is a cross-sectional view which illustrates a modification of the rotating-anode X-ray tube apparatus according to the second embodiment,  FIG. 3  illustrating an X-ray tube in side view and illustrating a cooler unit in block diagram. 
         FIG. 4  is a cross-sectional view which illustrates another modification of the rotating-anode X-ray tube apparatus according to the second embodiment,  FIG. 4  illustrating an X-ray tube in side view and illustrating a cooler unit in block diagram. 
         FIG. 5  is a cross-sectional view which illustrates a rotating-anode X-ray tube assembly according to a third embodiment,  FIG. 5  illustrating an X-ray tube in side view. 
         FIG. 6  is a cross-sectional view which illustrates a rotating-anode X-ray tube assembly according to Comparative Example 1,  FIG. 6  illustrating an X-ray tube in side view. 
         FIG. 7  is a cross-sectional view which illustrates a rotating-anode X-ray tube assembly according to Comparative Example 2,  FIG. 7  illustrating an X-ray tube in side view. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, there is provided a rotating-anode X-ray tube assembly comprising: an X-ray tube comprising an anode target including a target layer which emits X-rays, an anode target rotating mechanism configured to rotatably support the anode target, a cathode disposed opposite to the target layer in a direction along an axis of the anode target and configured to emit electrons, and an envelope accommodating the anode target, the anode target rotating mechanism and the cathode; a stator coil configured to generate a driving force for rotating the anode target rotating mechanism; a housing comprising an X-ray radiation port opening in a direction perpendicular to the axis, and storing and holding the X-ray tube and the stator coil; an X-ray radiation window configured to close the X-ray radiation port and to take out the X-rays to an outside of the housing; and a coolant filled in a space between the X-ray tube and the housing and absorbing at least part of heat produced by the X-ray tube. The housing includes a first divisional part which includes the X-ray radiation port and to which the X-ray tube is directly or indirectly fixed, and a second divisional part located on a side opposite to the anode target with respect to the anode target rotating mechanism and coupled to the first divisional part. A coupling surface between the first divisional part and the second divisional part is located on one plane, and is inclined to the axis, with exclusion of a direction perpendicular to the axis. 
     A rotating-anode X-tube assembly according to a first embodiment will be described hereinafter in detail with reference to the accompanying drawings. The rotating-anode X-ray tube assembly is used such that this assembly is fixed to, for example, a rotating frame of an X-ray CT scanner. 
     As illustrated in  FIG. 1 , a rotating-anode X-ray tube assembly  10  includes a housing  20 , an X-ray radiation window  20   w,  an X-ray tube  30  accommodated in the housing  20 , a coolant  7  filled in the space between the X-ray tube  30  and housing  20 , and a stator coil  90  functioning as a rotation drive module. In this case, the stator coil  90  generates a driving force for rotating an anode target rotating mechanism  14  (to be described later). 
     The housing  20  includes an X-ray radiation port  20   o   1  which is open in a direction perpendicular to an axis a of the X-ray tube  30 , and a through-hole  20   o   2  extending in a direction along the axis a. The housing  20  stores and holds the X-ray tube  30  and stator coil  90 . 
     The housing  20  includes a first divisional part  20   a  and a second divisional part  20   c,  which are divided. The housing  20  is formed of a metallic material or a resin material. In this embodiment, the first divisional part  20   a  and second divisional part  20   c  are formed of moldings using an aluminum alloy. Incidentally, the first divisional part  20   a  may be formed of an aluminum alloy molding (or resin material), and the second divisional part  20   c  may be formed of a resin material (or aluminum alloy molding). 
     The first divisional part  20   a  includes the X-ray radiation port  20   o   1  and through-hole  20   o   2 . The X-ray tube  30  is directly or indirectly fixed to the first divisional part  20   a.  In this embodiment, an insulation member  8  and an X-ray shielding member  60  are interposed between the X-ray tube  30  and the first divisional part  20   a,  and the X-ray tube  30  is indirectly fixed to the first divisional part  20   a.    
     The insulation member  8  is formed of a resin material or ceramics with high mechanical strength. The insulation member  8  prevents a positional displacement of the X-ray tube  30  in relation to the housing  20  in a direction perpendicular to the axis a. Furthermore, the insulation member  8  maintains electrical insulation between the X-ray tube  30  and the housing  20 . 
     In addition, the stator coil  90  is directly or indirectly fixed to the first divisional part  20   a.  In this embodiment, a connection member  9  is interposed between the stator coil  90  and the first divisional part  20   a,  and the stator coil  90  is indirectly fixed to the first divisional part  20   a  via the connection member  9 . Thus, the connection member  9  prevents a positional displacement of the stator coil  90  in relation to the housing  20  and X-ray tube  30 . In addition, the connection member  9  is formed of a metal. Since the first divisional part  20   a  is set at a ground potential, the connection member  9  can also ground the stator coil  90 . 
     The X-ray shielding member  60  is disposed along at least a part of the inner surface of the first divisional part  20   a.  In this embodiment, the X-ray shielding member  60  is stuck to at least a part of the inner surface of the first divisional part  20   a.  The X-ray shielding member  60  is formed of a material containing lead or a lead alloy as a main component. 
     The X-ray shielding member  60  is not provided in a region opposed to the connection member  9  and in a region on the second divisional part  20   c  side of the region opposed to the connection member  9 . However, the X-ray shielding member  60  is provided with no gap in a region on the right side of the region opposed to the connection member  9  (i.e. the region opposed to the anode target  35 , cathode  36 , etc.). The X-ray shielding member  60  is also provided with no gap at a side edge of the X-ray radiation port  20   o   1  and at a side edge of the through-hole  20   o   2 . Incidentally, the X-ray shielding member  60  is provided so as not to hinder the radiation of X-rays, which are used, to the outside of the housing  20  in the X-ray radiation port  20   o   1 . 
     In addition, since the anode target  35  itself functions as an X-ray shielding member, the X-ray shielding member  60 , together with the anode target  35 , can prevent leakage of X-rays. Since the X-ray shielding member  60  (first divisional part  20   a ) extends in the direction along the axis a toward the second divisional part  20   c  side beyond an extension line of the surface of a target layer  35   a  (to be described later), the above-described advantageous effect can be obtained. 
     The second divisional part  20   c  is located on a side opposite to the anode target  35  with respect to the anode target rotating mechanism  14  (to be described later). The second divisional part  20   c  is coupled to the first divisional part  20   a.  In addition, the second divisional part  20   c  is formed so as not to affect the prevention of the above-described X-ray leakage. Specifically, the coupling surface between the first divisional part  20   a  and second divisional part  20   c  is located in a region where X-rays are shielded by the anode target  35 . 
     Besides, the coupling surface is located on one plane, and is inclined to the axis a, with the exclusion of a direction perpendicular to the axis a. Thus, at one end face of the coupling surface, an angle formed relative to the axis a on the one hand is an acute angle, and an angle formed relative to the axis a on the other hand is an obtuse angle. 
     In this embodiment, in an attitude in which the axis a is parallel to a horizontal line, the X-ray radiation window  20   w  is located on the upper side of the anode target  35  and the cathode  36  is located on the right side of the anode target  35 , the coupling surface is inclined in an upper-right direction. Thus, in this attitude, an upper-side one end face of the coupling surface forms an acute angle clockwise relative to the axis a, and forms an obtuse angle counterclockwise relative to the axis a. 
     By detaching the second divisional part  20   c  from the first divisional part  20   a,  the X-ray tube  30  and stator coil  90  can be exposed in a direction along the axis a and in a direction (upward) perpendicular to the axis a. Thus, the efficiency of manufacture of the rotating-anode X-ray tube assembly  10  can be enhanced. For example, after fixing the X-ray tube  30  to the first divisional part  20   a,  the stator  90  can be fixed to the first divisional part  20   a.    
     Further, since the through-hole  20   o   2  is formed in the first divisional part  20   a,  and not in the second divisional part  20   c,  the first divisional part  20   a  and the second divisional part  20   c  can be coupled without requiring skill. 
     Moreover, since it is possible to suppress an interference during working between the X-ray tube  30  and stator coil  90 , on the one hand, which are installed in the first divisional part  20   a,  and the second divisional part  20   c,  on the other hand, it becomes possible to suppress damage which is mutually suffered by at least one of the X-ray tube  30  and stator coil  90 , and the second divisional part  20   c.    
     Furthermore, after the X-ray tube  30  and stator coil  90  are installed in the first divisional part  20   a,  a gap between the X-ray tube  30  and stator coil  90  can be confirmed. Since the relative position between the X-ray tube  30  and stator coil  90  can be corrected where necessary, this can make it less likely that problems will arise with the rotational characteristics of the anode target rotating mechanism  14  of the X-ray tube  30  and the cooling capability of the X-ray tube  30 . 
     The first divisional part  20   a  includes a frame portion  20   b  on the outer edge side of the opening. The second divisional part  20   c  includes a frame portion  20   d  on the outer edge side of the opening. In the frame portion  20   b,  a frame-shaped groove portion, which is formed on the side opposed to the frame portion  20   d,  is formed. 
     The first divisional portion  20   a  and second divisional portion  20   c  are touched such that the frame portions  20   b  and  20   d  are opposed, and the first divisional portion  20   a  and second divisional portion  20   c  are joined by a screw  20   f  serving as a fastening member. The gap between the frame portions  20   b  and  20   d  is liquid-tightly sealed by an O-ring which is provided in the above-described groove portion. The O-ring has a function of preventing leakage of the coolant  7  to the outside of the housing  20 . 
     The inner surface of the housing  20  and the surface of the X-ray shielding member  60  are in contact with the coolant  7 . 
     In this case, the rotating-anode X-ray tube assembly  10  includes a mounting portion  20   e.  The mounting portion  20   e  is formed so as to project from the outer surface of the first divisional part  20   a.  For example, the mounting portion  20   e  is directly or indirectly fixed to the rotating frame of an X-ray CT scanner. 
     The X-ray radiation window  20   w  is located in the outside of the housing  20 . The X-ray radiation window  20   w  can be formed by using a material with high mechanical strength. In this embodiment, the X-ray radiation window  20   w  is formed by using aluminum, but can also be formed by using other metallic material such as beryllium, or a resin. Thus, the X-ray radiation window  20   w  can take out X-rays to the outside of the housing  20 . The X-ray radiation window  20   w  has a concave shape, and is configured to reduce the distance between the X-ray tube  30  and the X-ray radiation window  20   w.    
     The X-ray radiation window  20   w  includes an attachment region which is directly attached to the first divisional part  20   a,  and an X-ray transmission region. An attachment surface is formed on an outer wall of the first divisional part  20   a,  which is opposed to the X-ray radiation window  20   w.  The attachment surface is flat. A frame-shaped groove portion is formed in the attachment surface of the first divisional part  20   a  in a manner to surround the X-ray radiation port  20   o   1 . An O-ring is disposed in the groove portion. 
     A screw  21  serving as a fastening member is passed through a through-hole formed in the attachment region of the X-ray radiation window  20   w,  and is fastened in a screw hole formed in the attachment surface of the first divisional part  20   a.  The screw hole formed in the first divisional part  20   a  forms, together with the screw  21 , a pushing mechanism. Thereby, the position of the X-ray radiation window  20   w  relative to the first divisional part  20   a  (housing  20 ) can be fixed. 
     The O-ring is interposed between the first divisional part  20   a  and the X-ray radiation window  20   w.  The O-ring has a function of preventing leakage of the coolant  7  to the outside of the housing  20 . Thus, the X-ray radiation window  20   w,  together with the O-ring, can liquid-tightly close the X-ray radiation port  20   o   1 . 
     The X-ray tube  30  includes an envelope  31 , an anode target  35 , an anode target rotating mechanism  14 , and a cathode  36 . The envelope  31  accommodates the anode target  35 , anode target rotating mechanism  14  and cathode  36 . 
     The envelope  31  includes a container  32 . The container  32  is formed of, for example, glass, or a metal such as copper, stainless steel or aluminum. An X-ray radiation window  33  is airtightly provided on the container  32 . In this case, the X-ray radiation window  33  is formed of beryllium. A part of the envelope  31  is formed of a high-voltage insulation member. 
     In this embodiment, the envelope  31  (X-ray tube  30 ) includes a high-voltage connection part  34  which extends in the direction along the axis a, passes through the through-hole  20   o   2 , and is exposed to the outside of the housing  20 . The high-voltage connection part  34  is formed of a high-voltage insulation member and a high-voltage supply terminal. The high-voltage insulation member is formed of ceramics. The high-voltage supply terminal is a metallic terminal. The high-voltage supply terminal is provided so as to penetrate the high-voltage insulation member, has one end exposed to the outside of the housing  20  from the surface of the high-voltage insulation member (the high-voltage connection part  34 ), and has the other end electrically connected to the cathode  36 . 
     The anode target  35  is provided within the envelope  31 . The anode target  35  is formed in a disc shape. The anode target  35  includes a target layer  35   a  which is provided on a part of the outer surface of the anode target. Electrons radiated from the cathode  36  collide upon the target layer  35   a,  and thereby the target layer  35   a  emits X-rays. The anode target  35  is formed of a metal such as molybdenum or a molybdenum alloy. The target layer  35   a  is formed of a metal such as a tungsten alloy. The anode target  35  is rotatable. 
     The cathode  36  is provided within the envelope  31 . The cathode  36  is disposed opposite to the target layer  35   a  in a direction along the axis a. The cathode  36  emits electrons which are radiated on the anode target  35 . A relatively negative voltage is applied to the cathode  36  via the high-voltage supply terminal of the high-voltage connection part  34 , and a filament current is supplied to a filament (electron emission source), not shown, of the cathode  36 . 
     The anode target rotating mechanism  14  rotatably supports the anode target  35 . The anode target rotating mechanism  14  includes a rotor, a bearing, a fixed body and a rotary body. The fixed body is formed in a columnar shape, and is fixed to the envelope  31 . The fixed body rotatably supports the rotary body. The rotary body is formed in a cylindrical shape and is provided coaxial with the fixed body. The rotor is fixed to the outer surface of the rotary body. Incidentally, the rotor receives a driving force which is generated by the stator coil  90 . The anode target  35  is fixed to the rotary body. The bearing is formed between the fixed body and the rotary body. The rotary body is provided so as to be rotatable together with the anode target  35 . 
     In the meantime, the anode target  35  is grounded. For example, the anode target  35  is connected to a ground terminal (not shown) which is electrically insulatively provided on the housing  20 , via the anode target rotating mechanism  14 , a conductor line (not shown), etc. 
     The rotating-anode X-ray tube assembly  10  further includes a seal ring  26 . The seal ring  26  is configured to liquid-tightly seal the coolant  7  coming through a gap between the through-hole  20   o   2  and the high-voltage connection part  34 , and to prevent leakage of the coolant  7  to the outside of the housing  20 . 
     The seal ring  26  is formed in a frame shape. The shape of the seal ring  26  is associated with the shape of the through-hole  20   o   2  and high-voltage connection part  34 . In this case, the seal ring  26  is formed in an annular shape. 
     An annular groove portion is formed in an inner peripheral edge of the seal ring  26 , which is opposed to the high-voltage connection part  34 . A gap between the seal ring  26  and the high-voltage connection part  34  is sealed by an annular O-ring which is provided in the annular groove portion. The O-ring has a function of preventing leakage of the coolant  7  to the outside from the gap between the seal ring  26  and the high-voltage connection part  34 . 
     A frame-shaped groove portion is formed in the outer surface of the first divisional part  20   a,  which surrounds the through-hole  20   o   2  and is opposed to the seal ring  26 . An O-ring is disposed in the frame-shaped groove portion. 
     A screw  27  serving as a fastening member is passed through a through-hole formed in the seal ring  26 , and is fastened in a screw hole formed in the first divisional part  20   a.  The screw hole formed in the first divisional part  20   a  forms, together with the screw  27 , a pushing mechanism. Thereby, the position of the seal ring  26  relative to the first divisional part  20   a  (housing  20 ) can be fixed. 
     The O-ring is interposed between the first divisional part  20   a  and the seal ring  26 . The O-ring has a function of preventing leakage of the coolant  7  to the outside from the gap between the first divisional part  20   a  and the seal ring  26 . 
     From the above, the seal ring  26 , together with the O-ring and high-voltage connection part  34 , can liquid-tightly close the through-hole  20   o   2 . 
     The coolant  7  is filled in the space between the X-ray tube  30  and housing  20 . The coolant  7  absorbs at least part of the heat produced by the X-ray tube  30 . Incidentally, the coolant  7  also absorbs heat produced by the stator col  90 , etc., other than the X-ray tube  30 . As the coolant  7 , an insulation oil or a water-based coolant can be used. In this embodiment, a water-based coolant is used as the coolant  7 . 
     In the rotating-anode X-ray tube assembly  10  with the above-described structure, a predetermined current is applied to the stator coil  90 , and thereby the rotor of the anode target rotating mechanism  14  rotates and the anode target  35  rotates. Next, a predetermined high voltage is applied between the anode target  35  and the cathode  36 . In this case, the anode target  35  is grounded, and a negative high voltage and filament current are supplied to the cathode  36 . 
     Thereby, an electron beam is radiated from the cathode  36  to the target layer  35   a  of the anode target  35 , X-rays are radiated from the anode target  35 , and the X-rays are radiated to the outside through the X-ray radiation window  33  and X-ray radiation window  20   w.    
     According to the rotating-anode X-ray tube assembly  10  of the first embodiment with the above-described structure, the rotating-anode X-ray tube assembly  10  includes the rotating-anode X-ray tube  30 , stator coil  90 , housing  20 , X-ray radiation window  20   w,  and coolant  7 . 
     The housing  20  includes the first divisional part  20   a  and second divisional part  20   c.  The first divisional part  20   a  includes the X-ray radiation port  20   o   1 , and the X-ray tube  30  is directly or indirectly fixed to the first divisional part  20   a.  The second divisional part  20   c  is located on the side opposite to the anode target  35  with respect to the anode target rotating mechanism  14 , and is coupled to the first divisional part  20   a.  The coupling surface between the first divisional part  20   a  and second divisional part  20   c  is located on one plane, and is inclined to the axis a, with the exclusion of the direction perpendicular to the axis a. 
     After disposing only the X-ray tube  30  in the first divisional part  20   a,  the stator coil  90  can be disposed in the first divisional part  20   a.  The workability can be enhanced since there is no need to dispose the X-ray tube  30  and stator coil  90  as one body in the first divisional part  20   a  in the state in which the stator coil  90  is inserted over the X-ray tube  30 . For example, a simple work can be made. Then, the stator coil  90  can be disposed with high precision. 
     The gap between the X-ray tube  30  and the stator coil  90  can be confirmed. Since the relative position between the X-ray tube  30  and stator coil  90  can be corrected where necessary, it becomes possible to avoid such a situation that problems will arise with the rotational characteristics of the anode target rotating mechanism  14  of the X-ray tube  30  and the cooling capability of the X-ray tube  30 . 
     In addition, since there is no need to set a wide gap between the X-ray tube  30  and stator coil  90 , it is possible to prevent degradation in the efficiency of rotary drive by a produced magnetic field of the stator coil  90 , and to prevent an increase in power consumption of the stator coil  90 . 
     The X-ray shielding member  60  (first divisional part  20   a ) extends in the direction along the axis a toward the second divisional part  20   c  side beyond the extension line of the surface of the target layer  35   a.  Specifically, the coupling surface between the first divisional part  20   a  and second divisional part  20   c  is located in a region where there is no fear of X-ray leakage. Thus, the X-ray shielding member  60 , together with the anode target  35 , can prevent leakage of X-rays. 
     In addition, since there is no need to adopt a special structure by providing an X-ray shielding member in the second divisional part  20   c  in a manner to overlap the X-ray shielding member  60 , an increase in processing cost of the housing  20  can be suppressed. 
     Further, the first divisional part  20   a  includes the through-hole  20   o   2  extending in the direction along the axis a. The high-voltage connection part  34  extends in the direction along the axis a, passes through the through-hole  20   o   2 , and is exposed to the outside of the housing  20 . Since the through-hole  20   o   2  is formed in the first divisional part  20   a,  and not in the second divisional part  20   c,  the first divisional part  20   a  and the second divisional part  20   c  can be coupled without requiring skill. 
     Moreover, since it is possible to suppress an interference during working between the X-ray tube  30  and stator coil  90 , on the one hand, which are installed in the first divisional part  20   a,  and the second divisional part  20   c,  on the other hand, this can make it less likely that damage is mutually suffered by at least one of the X-ray tube  30  and stator coil  90 , and the second divisional part  20   c.    
     From the above, the rotating-anode X-ray tube assembly  10  can be obtained which can prevent leakage of X-rays, has high product reliability, has a good manufacturing yield, and can suppress an increase in manufacturing cost and power consumption. 
     Next, a rotating-anode X-ray tube apparatus  1  according to a second embodiment will be described. In this embodiment, the same functional parts as in the above-described first embodiment are denoted by like reference numerals, and a detailed description thereof is omitted. The rotating-anode X-ray tube apparatus  1  is used such that this apparatus  1  is fixed to, for example, a rotating frame of an X-ray CT scanner. 
     As illustrated in  FIG. 2 , the rotating-anode X-ray tube apparatus  1  includes the rotating-anode X-ray tube assembly  10  according to the first embodiment. The rotating-anode X-ray tube apparatus  1  further includes a conduit  11  and a cooler unit  100 . The conduit  11  is made to communicate with the housing  20 , and forms, together with the housing  20 , a passage of the coolant  7 . The cooler unit  100  includes a casing  110 , a circulating pump  120  which is accommodated in the casing  110 , a radiator  130 , and a fan unit  140  serving as an air feed module. The circulating pump  120  is attached to the conduit  11 , and circulates the coolant  7 . The radiator  130  is attached to the conduit  11 , and radiates heat of the coolant  7 . The fan unit  140  produces a flow of air in the vicinity of the radiator  130 . The radiator  130  and fan unit  140  constitute a heart exchanger. 
     The conduit  11  includes a first conduit  11   a,  a second conduit  11   b  and a third conduit  11   c.  The first conduit  11   a  has one end portion connected liquid-tightly to an opening of the first divisional part  20   a,  and has the other end portion connected liquid-tightly to an intake port of the circulating pump  120 . The second conduit  11   b  has one end portion connected liquid-tightly to a discharge port of the circulating pump  120 , and has the other end connected liquid-tightly to the radiator  130 . The third conduit  11   c  has one end portion connected liquid-tightly to the radiator  130 , and has the other end connected liquid-tightly to the other opening of the first divisional part  20   a.    
     According to the rotating-anode X-ray tube apparatus  1  of the second embodiment with the above-described structure, the rotating-anode X-ray tube apparatus  1  includes the rotating-anode X-ray tube assembly  10 . The rotating-anode X-ray tube assembly  10  includes the rotating-anode X-ray tube  30 , stator coil  90 , housing  20 , X-ray radiation window  20   w,  and coolant  7 . Thus, the same advantageous effects as in the above-described first embodiment can be obtained. 
     The rotating-anode X-ray tube apparatus  1  includes the circulating pump  120 . Since forced convection can be caused to occur in the coolant  7  in the housing  20 , the temperature distribution of the coolant  7  in the housing  20  can be made uniform. 
     The rotating-anode X-ray tube apparatus  1  includes the radiator  130  and fan unit  140 . Thus, the radiation to the outside of the heat produced by the X-ray tube  30 , etc. can be further promoted. 
     From the above, the rotating-anode X-ray tube assembly  10  and rotating-anode X-ray tube apparatus  1  can be obtained which can prevent leakage of X-rays, has high product reliability, has a good manufacturing yield, and can suppress an increase in manufacturing cost and power consumption. 
     Next, a modification of the rotating-anode X-ray tube apparatus  1  according to the second embodiment will be described. Incidentally, in this modification, too, the same advantageous effects as in the second embodiment can be obtained. 
     As illustrated in  FIG. 3 , the X-ray tube  30  may include a cooling passage  30   a  which radiates at least part of the heat which is produced by the X-ray tube  30  itself. The cooling passage  30   a  includes an intake port for taking in the coolant  7 , and a discharge port for discharging the coolant  7 . In this case, the conduit  11  can be directly attached to the intake port of the cooling passage  30   a.  Since forced convection can be caused to occur in the coolant  7  in the cooling passage  30   a,  the X-ray tube  30  can further be cooled. 
     In the meantime, in this example, the third conduit  11   c  is liquid-tightly attached to the other opening of the first divisional part  20   a,  and the other end portion of the third conduit  11   c  is directly attached to the intake port of the cooling passage  30   a.  Thereby, the coolant  7 , which has been cooled through the radiator  130 , can be introduced into the cooling passage  30   a.    
     Next, another modification of the rotating-anode X-ray tube apparatus  1  according to the second embodiment will be described. Incidentally, in this another modification, too, the same advantageous effects as in the second embodiment can be obtained. 
     As illustrated in  FIG. 4 , the X-ray tube  30  may include a cooling passage  30   b  which radiates at least part of the heat which is produced by the X-ray tube  30  itself. The cooling passage  30   b  includes an intake port for taking in a cooling (another coolant)  70 , and a discharge port for discharging the coolant  70 . In this case, the conduit  11  can be directly attached to both the intake port and the discharge port of the cooling passage  30   b.  Since the coolant  7  and coolant  70  can be used together and forced convection can be caused to occur in the coolant  70  in the cooing passage  30   b,  the X-ray tube  30  can further be cooled. 
     In this example, an insulation oil is used as the coolant  7 , and a water-based coolant is used as the coolant  70 . The coolant  70  is filled in the cooling passage  30   b  and conduit  11 , and absorbs at least part of the heat produced by the X-ray tube  30 . 
     The conduit  11  is made to communicate with the cooling passage  30   b  of the X-ray tube  30  through the housing  20 . To be more specific, one end portion of the first conduit  11   a  is made to communicate with the discharge port of the cooling passage  30   b,  and the other end portion of the third conduit  11   c  is made to communicate with the intake port of the cooling passage  30   b.  The circulating pump  120  circulates the coolant  70 . The radiator  130  radiates the heat of the coolant  70 . 
     Next, a rotating-anode X-ray tube assembly according to a third embodiment will be described. In this embodiment, the same functional parts as in the above-described first embodiment are denoted by like reference numerals, and a detailed description thereof is omitted. 
     As illustrated in  FIG. 5 , the coupling surface between the first divisional part  20   a  and second divisional part  20   c  is located on one plane, and is inclined to the axis a on a side opposite to the case of the first and second embodiments. In this embodiment, in an attitude in which the axis a is parallel to the horizontal line, the X-ray radiation window  20   w  is located on the upper side of the anode target  35  and the cathode  36  is located on the right side of the anode target  35 , the coupling surface is inclined in a lower-right direction. 
     The second divisional part  20   c  is formed so as not to affect the prevention of X-ray leakage. Specifically, the coupling surface between the first divisional part  20   a  and second divisional part  20   c  is located in a region where X-rays are shielded by the anode target  35 . 
     The X-ray shielding member  60  (first divisional part  20   a ) extends in the direction along the axis a toward the second divisional part  20   c  side beyond an extension line of the surface of the target layer  35   a.  Thus, the X-ray shielding member  60 , together with the anode target  35 , can prevent leakage of X-rays. 
     By detaching the second divisional part  20   c  from the first divisional part  20   a,  the X-ray tube  30  and stator coil  90  can be exposed in a direction along the axis a and in a direction (downward) perpendicular to the axis a. Thus, the efficiency of manufacture of the rotating-anode X-ray tube assembly  10  can be enhanced. For example, after fixing the X-ray tube  30  to the first divisional part  20   a,  the stator  90  can be fixed to the first divisional part  20   a.  Incidentally, by varying the attitude of the first divisional part  20   a  where necessary, it becomes possible to make it easier to fix the X-ray tube  30  and stator coil  90  to the first divisional part  20   a.    
     In addition, in this embodiment, too, the mounting portion  20   e  is formed on the first divisional part  20   a.  In this case, two mounting portions  20   e  are formed on the first divisional part  20   a  with an interval in the direction along the axis a. 
     According to the rotating-anode X-ray tube assembly  10  of the third embodiment with the above-described structure, the rotating-anode X-ray tube assembly  10  includes the rotating-anode X-ray tube  30 , stator coil  90 , housing  20 , X-ray radiation window  20   w,  and coolant  7 . 
     The housing  20  includes the first divisional part  20   a  and second divisional part  20   c.  The first divisional part  20   a  includes the X-ray radiation port  20   o   1 , and the X-ray tube  30  is directly or indirectly fixed to the first divisional part  20   a.  The second divisional part  20   c  is located on the side opposite to the anode target  35  with respect to the anode target rotating mechanism  14 , and is coupled to the first divisional part  20   a.  The coupling surface between the first divisional part  20   a  and second divisional part  20   c  is located on one plane, and is inclined to the axis a, with the exclusion of the direction perpendicular to the axis a. 
     The coupling surface between the first divisional part  20   a  and second divisional part  20   c  is inclined in a lower-right direction. In this case, too, the same advantageous effects as in the above-described first embodiment can be obtained. 
     From the above, the rotating-anode X-ray tube assembly  10  can be obtained which can prevent leakage of X-rays, has high product reliability, has a good manufacturing yield, and can suppress an increase in manufacturing cost and power consumption. 
     Next, a rotating-anode X-ray tube assembly according to Comparative Example 1 will be described. 
     As illustrated in  FIG. 6 , the rotating-anode X-ray tube assembly  10  is, in general terms, an anode-grounding-type X-ray tube assembly constructed like the rotating-anode X-ray tube assembly according to the above-described first embodiment. However, the coupling surface between the first divisional part  20   a  and second divisional part  20   c  is parallel to the axis a of the X-ray tube  30 . 
     Thus, such a special structure is adopted that an X-ray shielding member  60  is provided on the first divisional part  20   a,  an X-ray shielding member  80  is provided on the second divisional part  20   c,  and the X-ray shielding member  60  and X-ray shielding member  80  oppose each other. The reason for this is that it is highly possible that X-rays leak from the coupling surface of the housing  20 . In the case of Comparative Example 1, however, an increase in processing cost of the housing  20  will occur. The second divisional part  20   c  includes the X-ray radiation port  20   o   1  and through-hole  20   o   2 . The X-ray radiation window  20   w  is attached to the second divisional part  20   c,  and closes the X-ray radiation port  20   o   1 . 
     According to the rotating anode X-ray tube assembly  10  of the comparative example 1 with the above-described structure, the stator coil  90  cannot be disposed in the first divisional part  20   a,  after disposing only the X-ray tube  30  in the first divisional part  20   a.  It is necessary to dispose the X-ray tube  30  and stator coil  90  as one body in the first divisional part  20   a  in the state in which the stator coil  90  is inserted over the X-ray tube  30 . 
     The gap between the X-ray tube  30  and the stator coil  90  cannot be confirmed. Since it is difficult to correct the relative position between the X-ray tube  30  and stator coil  90 , problems may arise with the rotational characteristics of the anode target rotating mechanism  14  of the X-ray tube  30  and the cooling capability of the X-ray tube  30 . 
     In addition, there may be a need to set a wide gap between the X-ray tube  30  and stator coil  90 . This may lead to degradation in the efficiency of rotary drive by a produced magnetic field of the stator coil  90 , and to an increase in power consumption of the stator coil  90 . 
     Further, since the through-hole  20   o   2  is formed in the second divisional part  20   c,  skill is required to couple the first divisional part  20   a  and the second divisional part  20   c.    
     Moreover, it is possible that the X-ray tube  30  and stator coil  90 , on the one hand, which are installed in the first divisional part  20   a,  and the second divisional part  20   c,  on the other hand, interfere during working, and are mutually damaged. After the assembling in the housing, it is not possible to confirm whether the X-ray tube, stator coil, second divisional part, etc. have been damaged. Thus, there is concern that a problem will arise in a subsequent manufacturing process or during the use by the user. 
     Next, a rotating-anode X-ray tube assembly according to Comparative Example 2 will be described. 
     As illustrated in  FIG. 7 , the shape of the rotating-anode X-ray tube assembly  10  is substantially rotation-symmetric with respect to the axis of the X-ray tube  30 . The housing  20  is cylindrical and includes, on its side, a projection portion to which a high-voltage receptacle is attached, and an X-ray radiation port. 
     The structure of the rotating-anode X-ray tube assembly  10  of Comparative Example 2 is described below. 
     The rotating-anode X-ray tube assembly  10  is, in general terms, a neutral-grounding-type X-ray tube assembly including the housing  20 , X-ray tube  30 , coolant  7  (insulation oil), high-voltage insulation member  6 , stator coil  90 , and receptacles  300 ,  400 . 
     The housing  20  includes a cylindrically formed housing body  20   n,  and cover parts (side plates)  20   f,    20   g,    20   h.  In a direction along the axis a of the X-ray tube  30 , a peripheral edge portion of the cover part  20   f  is in contact with a stepped portion of the housing body  20   n.  A rubber member  2   a  is formed of an O-ring and is provided between the housing body  20   n  and the cover part  20   f.  A C type retaining ring  20   i  is fitted in the groove portion of the housing body  20   n.    
     In the direction along the axis a of the X-ray tube  30 , a peripheral edge portion of the cover part  20   g  is in contact with a stepped portion of the housing body  20   n.  The cover part  20   g  includes an opening portion  20   k  through which the coolant  7  comes in and goes out. A vent hole  20   m,  through which air as an atmosphere comes in and goes out, is formed in the cover part  20   h.  A C type retaining ring  20   j  is fitted in a groove portion of the housing body  20   n.  A seal portion of a rubber member  2   b  is formed like an O-ring. 
     A fixed shaft of the X-ray tube  30  is fixed to the container  32  and high-voltage insulation member  6 . The high-voltage insulation member  6  is directly fixed to the housing  20 , or indirectly fixed to the housing  20  via the stator coil  90 . The high-voltage insulation member  6  is configured to effect electrical insulation between the fixed shaft (X-ray tube  30 ), and the housing  20  and stator coil  90 . 
     The rotating-anode X-ray tube assembly  10  further includes X-ray shielding members  510 ,  520  and  530 . 
     The X-ray shielding member  510  is provided on one side of the housing  20  and shields X-rays which are radiated from the target layer  35   a.  The X-ray shielding member  510  includes a first shielding portion  511  and a second shielding portion  512 . 
     The X-ray shielding member  520  is formed in a cylindrical shape. One end portion of the X-ray shielding member  520  is close to the first shielding portion  511 . The X-ray shielding member  530  is formed in a cylindrical shape and is provided in a cylindrical portion  20   r  of the housing  20 . One end portion of the X-ray shielding member  530  is close to the X-ray shielding member  520 . 
     A holding member  3  and rubber members  2   d,    2   e  are provided between the X-ray tube  30  and the housing  20 . The stator coil  90  is fixed to the housing body  20   n.  The receptacle  300  for the anode is located inside a cylindrical portion  20   q  of the housing  20  and is attached to the cylindrical portion  20   q.  A ring nut  310  is fastened to a stepped portion of the cylindrical portion  20   q  and pushes the receptacle  300 . The receptacle  400  for the cathode is located inside the cylindrical portion  20   r  of the housing  20  and is attached to the cylindrical portion  20   r.  A ring nut  410  is fastened to a stepped portion of the cylindrical portion  20   r  and pushes the receptacle  400 . 
     According to the rotating-anode X-ray tube assembly  10  of the comparative example with the above-described structure, the end portion of the anode of the X-ray tube can relatively easily be fixed to the high-voltage insulation member  6  which is attached to the cylindrical housing  20 . However, the cathode side of the X-ray tube is merely elastically supported and fixed to the cylindrical housing  20  via the holding member  3  and rubber members  2   d,    2   e.    
     In the meantime, in recent years, in an X-ray tube assembly for CT photography use, etc., with an increase in complexity of the shape of the X-ray tube  30 , an increase in weight of the X-ray tube  30 , and an increase in rotational speed of a rotating frame to which the X-ray tube assembly is mounted, there may be a case which cannot be coped with by the fixing structure of the X-ray tube to the housing in the above-described comparative example. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     For example, in the above embodiments, the X-ray shielding member  60  is stuck to only the inner surface of the first divisional part  20   a,  but the embodiments are not limited to this example. The X-ray shielding member may be stuck to the inner surface of the second divisional part  20   c.  In this case, it is possible to contribute to further reduction in the amount of leakage of scattered X-rays. 
     The X-ray shielding member ( 60 ) does not need to be stuck to the inner surface of the housing  20 , and may be disposed within the housing  20  while being spaced apart from the inner surface of the housing  20 . 
     It is desirable that the entire surface of the X-ray shielding member ( 60 ) be coated with an organic coating film. The reason for this is that, for example, when the coolant  7  is a water-based coolant, if the X-ray shielding member is in a state of immersion in the water-based coolant, such problems will arise that the lead, of which the X-ray shielding member is formed, is gradually corroded and dissolved during use and the electrical conductivity of the coolant  7  increases, or that a deposit containing lead as a main component forms on a metallic outer surface of the X-ray tube  30 . 
     The embodiments of the invention are applicable not only to the above-described rotating-anode X-ray tube assembly  10  and rotating-anode X-ray tube apparatus  1 , but also to various kinds of rotating-anode X-ray tube assemblies and rotating-anode X-ray tube apparatuses. For example, the rotating-anode X-ray tube assembly is not limited to a rotating-anode X-ray tube assembly of an anode-grounding type, but may be a rotating-anode X-ray tube assembly of a cathode-grounding type or a rotating-anode X-ray tube assembly of a neutral-grounding type.