Patent Publication Number: US-2022230831-A1

Title: X-ray tube and method of manufacturing x-ray tube

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation application of PCT Application No. PCT/JP2020/027168, filed Jul. 10, 2020 and based upon and claiming the benefit of priority from Japanese Patent Application No. 2019-203791, filed Nov. 11, 2019; and No. 2020-011831, filed Jan. 28, 2020, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to an X-ray tubes and a method of manufacturing the X-ray tube. 
     BACKGROUND 
     In X-ray tubes for analysis and other applications, the envelope, which maintains a vacuum inside, is made of metal and an insulator such as ceramics, glass or the like. Each of the members of the X-ray tube is joined by brazing, welding, or glass sealing during the assembly process to create a structure that maintains a vacuum. In particular, brazing or welding is used to join ceramic and metal components, and to join metal components to each other. 
     For each component, the dimensional tolerance is set, but, particularly, in engaging parts and joint parts, backlashes are created. Further, as the dimensional tolerances and the backlashes accumulate in accordance with the number of assembled parts, the focal error with respect to the anode target and the backlash in the distance to the cathode electron gun become significant in the finished shape, which may result in large variations in the shape of the focal point. 
     The shape of the focal point affects not only the analysis performance but also the lifetime of the X-ray tube. For example, if the focal point is smaller than a necessary size, the X-ray intensity and resolution as analytical performance enhances, but the temperature of the focal plane rises, which accelerates the melting of the focal plane and shortens the lifetime of the X-ray tube. On the other hand, if the focal point is large, the lifetime of the X-ray tube becomes longer, but the X-ray intensity and resolution as resolution performance become lower. 
     Under these circumstances, there has been a demand for an X-ray tube that can reduce the variation in the shape of the focal point in an anode target spot shape, and a method of manufacturing such an X-ray tube. 
     One of embodiments described herein aims to provide an X-ray tube that can absorb the effects of the dimensional tolerances of parts and the backlashes during assembly, and reduce the variation of the focal shape in the anode target, and a method of manufacturing such an X-ray tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view showing a schematic configuration of an X-ray tube according to an embodiment. 
         FIG. 2  is a longitudinal cross-sectional view showing a schematic configuration of an envelope assembly shown in  FIG. 1 . 
         FIG. 3  is a longitudinal cross-sectional view showing a schematic configuration of a cathode assembly shown in  FIG. 1 . 
         FIG. 4  is a longitudinal cross-sectional view showing a schematic configuration of an anode assembly shown in  FIG. 1 . 
         FIG. 5  is a longitudinal cross-sectional view illustrating assembling of the cathode assembly to the envelope assembly. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an X-ray tube comprises an outer envelope that maintains a vacuum inside, an anode target provided inside the envelope and generating X-rays by collision of thermal electrons, and a cathode electron gun provided inside the envelope and emits thermal electrons toward the anode target, and the X-ray tube also comprises a cathode assembly including a metal-made support which holds the cathode electron gun at a distal end thereof, and an envelope assembly including a support fixing portion which fixes the support of the cathode assembly and constituting the envelope, and the support fixing portion being made of a metal into a cylindrical shape, and the support of the cathode assembly being fixed to an inner circumferential side thereof by welding. 
     According to another embodiment, a method of manufacturing an X-ray tube comprising an outer envelope that maintains a vacuum inside, an anode target provided inside the envelope and generating X-rays by collision of thermal electrons, and a cathode electron gun provided inside the envelope and emits thermal electrons toward the anode target, the X-ray tube comprising: a cathode assembly including a metal-made support which holds the cathode electron gun at a distal end thereof; an envelope assembly including a metal-made support fixing portion which fixes the support of the cathode assembly and a ceramic-made cylindrical envelope body, one end of the envelope body and an outer circumferential surface of the support fixing portion being joined together by a metal-made joint member; and an anode assembly including a metal-made bottomed cylindrical portion which constitutes a part of the envelope, holding the anode target on an inner bottom surface of the bottomed cylindrical portion, and including an X-ray transmission window on a side surface of the bottomed cylindrical portion, and the method comprises an insertion step of inserting the cathode assembly into the support fixing portion of the envelope assembly from the distal end thereof into the envelope assembly, a cathode assembly positioning step of positioning the cathode assembly by, after the insertion step, positioning the distal end of the cathode assembly at a predetermined position, a cathode assembly welding step of fixing by welding, after the cathode assembly positioning step, a rear end of the support of the cathode assembly to the support fixing portion of the envelope assembly. 
     An X-ray tube and a method of manufacturing the X-ray tube according to one embodiment will be described in detail below with reference to the accompanying drawings. In addition, in some cases, in order to make the description clearer, the widths, thicknesses, shapes, etc., of the respective parts are schematically illustrated in the drawings, compared to the actual modes. However, the schematic illustration is merely an example, and adds no restrictions to the interpretation of the invention. Besides, in the specification and drawings, the same or similar elements as or to those described in connection with preceding drawings or those exhibiting similar functions are denoted by like reference numerals, and a detailed description thereof is omitted unless otherwise necessary. 
     As shown in  FIG. 1 , an X-ray tube  1  comprises an envelope  3  that maintains a vacuum inside, an anode target  5  and a cathode electron gun  7 , installed inside the envelope  3 , and it generates an X-ray  4  by allowing thermal electrons  2  emitted from the cathode electron gun  7  to collide with the anode target  5 . 
     The X-ray tube  1  is constituted by three assemblies: an envelope assembly  11 , a cathode assembly  13 , and an anode assembly  15 . 
     As shown in  FIG. 2  and  FIG. 1 , the envelope assembly  11  comprises an envelope body  17 , a support fixing section  19  that fixes a support member (to be described later) of the cathode assembly  13 , a first joint member  21  provided at one end of the envelope body  17  to join the envelope body  17  and the support fixing section  19  together, and a second joint member  23  provided at the other end of the envelope body  17 . 
     The envelope body  17  is made of ceramics into a cylindrical shape. On one end  17   a  and the other end  17   b  of the main body  17 , metallizing portions  18  are formed respectively to be formed into metal surfaces. 
     The support fixing portion  19  is made of stainless steel or the like into a cylindrical shape. As shown in  FIG. 1 , the cathode assembly  13  is inserted inside the support fixing section  19 , and an inner circumferential surface  19   a  of the support fixing section  19  is a sliding surface of the cathode assembly  13 . 
     The first joint member  21  is made of a metal such as Kovar (KOV) and is placed between the one end  17   a  of the envelope body  17  and an outer circumferential surface  19   b  of the support fixing section  19 , so as to seal the space therebetween as a part of the envelope  3  (see  FIG. 1 ). This joint member  21  has a ring-like shape. 
     An end (inner circumferential end)  21   a  of the first joint member  21  on a support fixing section  19  side is brazed to the outer circumferential surface  19   b  of the support fixing section  19 . Another end (outer circumferential end)  21   b  of the first joint member  21  on an envelope body  17  side is brazed to the one end  17   a  of the envelope body. 
     Further, to the other end  17   b  of the envelope body  17 , one end  23   a  of the second joint member  23  is brazed. The second joint member  23  is made of a metal such as Kovar (KOV), and is formed into an annular shape along the form of the other end  17   b  of the envelope body  17 , and here in this embodiment, it has a ring-like shape. 
     As shown in  FIG. 3  and  FIG. 1 , the cathode assembly  13  comprises a cathode electron gun  7  and a support  27  which supports the cathode electron gun  7 . 
     The support  27  is made of a metal such as stainless steel into a cylindrical shape, and holds the cathode electron gun  7  at a distal end  27   a  thereof. As shown in  FIG. 1 , the support  27  is inserted to the inner circumference of the support fixing portion  19  of the envelope assembly  11 , and a rear end  27   b  of the support  27  is welded to an outer end  19   c  of the support fixing section  19 . 
     The distal end  27   a  of the support  27  has a concave electron gun holding section  27   c , where the cathode electron gun  7  is placed, and is flush with the distal end of the cathode electron gun  7  or either side protrudes. 
     The support  27  has a cylindrical shape, and a ceramic sealing member  29  is provided inside the cylinder at a position corresponding to the support fixing section  19  of the envelope assembly  11 . Wires  7   a  and  7   b  of the cathode electron gun  7  pass through the sealing member  29  inside the support  27 , and are withdrawn out from the envelope  3 . 
     As shown in  FIG. 4  and  FIG. 1 , the anode assembly  15  includes a bottomed cylindrical section  31  made of a metal such as pure copper, which forms part of the envelope  3 . The bottomed cylindrical section  31  includes a cylindrical side surface portion  31   a  and a bottom portion  31   b  that seals one end of the cylindrical section, and the anode target  5  is held on the inner bottom surface of the bottom portion  31   b . In the side surface portion  31   a , an X-ray transmission window  33  is provided. The X-ray transmission window  33  is made of a light element such as beryllium (Be). 
     As shown in  FIG. 1 , to the end surface  31   c  of the bottomed cylindrical section  31 , the other end  23   b  of the second joint member  23  is fixed by welding. 
     Next, a method of manufacturing the X-ray tube  1  of this embodiment will be described. 
     First, the manufacturing of each of the assemblies  11 ,  13  and  15  will be described. 
     As shown in  FIG. 2 , in the envelope assembly  11 , the metallizing portion  18  is formed at each of the one end  17   a  and the other end  17   b  of the cylindrical envelope body  17 , and the end (outer circumferential end)  21   b  of the first joint member  21  is positioned to the one end  17   a , and the one end  23   a  of the second joint member  23  to the other end  17   b  at respective predetermined positions using a jig or the like. 
     Next, the cylindrical support fixing section  19  is slid into the one end (inner circumferential end)  21   a  of the first joint member  21  and positioned at a predetermined position using a jig or the like. Here, the support fixing section  19  is positioned so that a distance H 2  between the other end  17   b  of the envelope body  17  and the outer end  19   c  of the support fixing section  19  becomes a predetermined distance. 
     After positioning the support fixing portion  19 , the one end  17   a  of the cylindrical envelope body  17  and the other end  21   b  of the first joint member  21  are brazed together, and so are between the other end  17   b  of the envelope body  17  and the one end  23   a  of the second joint member  23 , and between the one end  21   a  of the first joint member  21  and the outer circumferential surface  19   b  of the support fixing section  19 , to be fixed. 
     As shown in  FIG. 3 , in the cathode assembly  13 , the cathode electron gun  7  is installed at the distal end  27   a  of the support  27 , and the wires  7   a  and  7   b  of the electron gun are drawn out of the support  27  through the sealing member  29 . 
     As shown in  FIG. 4 , the anode assembly  15  is formed into a bottomed cylindrical shape, and the anode target  5  is placed on the inner surface of the bottom portion  31   b . In the side surface portion  31   a , the X-ray transmission window  33  is formed. 
     Next, the assembling of each of the assemblies  11 ,  13  and  15  will be described. 
     As shown in  FIG. 2 , in the envelope assembly  11 , a positioning jig  35  is placed on the other end of the envelope body  17 . The positioning jig  35  is configured to define the distance between the cathode electron gun  7  of the cathode assembly  13  and the anode target  5  to be a predetermined distance H 3  when assembling the cathode assembly  13  and the anode assembly  15  to the envelope assembly  11 , as shown in  FIG. 1 . In order to achieve this, the positioning jig  35  positions the cathode electron gun  7  of the cathode assembly  13  with relative to the envelope assembly  11 . 
     More specifically, as shown in  FIG. 5 , the positioning jig  35  is attached to the second joint member  23  of the envelope assembly  11 , and as indicated by a reference symbol A in  FIG. 1 , the support  27  of the cathode assembly  13  is inserted to the inside of the cylindrical support fixing section  19 . The support  27  is configured to insert the cathode electron gun  7  to the inside of the envelope body  17 . 
     Next, as indicated by a reference symbol B in  FIG. 1 , a lower end of the support  27  which holds the cathode electron gun  7  is placed to abut against the positioning jig  35  to position the cathode assembly  13 . 
     As shown in  FIG. 1 , after positioning the support  27  of the cathode assembly  13  with respect to the support fixing section  19 , the rear end  27   b  of the support  27  and the outer end  19   c  of the support fixing section  19  are fixed together at the position by welding. 
     Next, as shown in  FIG. 1 , in the envelope body  17  of the envelope assembly  11 , the end surface  31   c  of the bottomed cylindrical section  31  of the anode assembly  15  is fixed to the other end  23   b  of the second joint member  23  by welding. 
     In the above-described manner, the envelope assembly  11 , the cathode assembly  13 , and the anode assembly  15  are assembled to manufacture the X-ray tube  1 . 
     The function of the X-ray tube  1  will now be described. 
     As shown in  FIG. 1 , thermal electrons  2  generated from the cathode electron gun  7  are accelerated by high voltage and collide with the anode target  5  to generate X-rays  4 . The thus generated X-rays  4  are extracted through the X-ray transmission window  33  and used for analysis. 
     The effect of the X-ray tube  1  in this embodiment will now be described. 
     As shown in  FIG. 1 , in the envelope  3 , the distance H 3  between the cathode electron gun  7  and the anode target  5  can be adjusted by positioning the support  27  that holds the cathode electron gun  7  with respect to the support fixation part  19  of the envelope assembly  11  by sliding thereon as shown in  FIG. 5 . Therefore, it is possible to accurately and easily position the cathode electron gun  7  with relative to the anode target  5 . 
     In particular, by positioning the cathode electron gun  7  directly with respect to the anode target  5 , the influence of the dimensional tolerance, if any, on the distance H 1  of the ceramic-made envelope body  17  can be reduced. 
     The positioning of the support  27  that holds the cathode electron gun  7  can be achieved by placing the distal end  27   a  of the support  27  to abut on the positioning jig  35  corresponding to the position of the anode target  5 , thereby making it easy to carry out the positioning. 
     According to this embodiment, the X-ray tube can be manufactured so accurately that the distance between the cathode electron gun  7  and the anode target  5 , which affects the shape of the focal point of the X-ray tube is set within an error range of 0.1 mm. 
     As shown in  FIG. 2 , in the envelope assembly  11 , the support fixing section  19 , the envelope body  17 , and the first joint member  21  are fixed by brazing. Here, the other end  17   b  of the envelope body  17  and the outer end  19   c  of the support fixing section  19  are positioned to set the distance therebetween to be H 2 . Thus, the dimensional accuracy of the envelope assembly  11  can be improved, and the distance H 3  (see  FIG. 1 ) between the cathode electron gun  7  and the anode target  5  when the cathode assembly  13  is assembled can be further accurately set. 
     In the X-ray tube  1  of this embodiment, among the parts related to the distance H 3  between the cathode electron gun  7  and the anode target  5 , which affects the shape of the focal point, those other than the envelope body  17 , which is made of ceramics, are all metal parts. Therefore, precise processing and jointing can be easily achieved. 
     According to this embodiment, the X-ray tube  1  is constituted by three assemblies: an envelope assembly  11 , a cathode assembly  13 , and an anode assembly  15 , and it is assembled while positioning each of the assemblies  11 ,  13 , and  15 . Therefore, it is possible to carry out efficient manufacturing. 
     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.