WO2022070098A1

WO2022070098A1 - Field emission x-ray tube assembly and a method of making same

Info

Publication number: WO2022070098A1
Application number: PCT/IB2021/058942
Authority: WO
Inventors: Cheng Qian
Original assignee: Ncx Corporation
Priority date: 2020-09-30
Filing date: 2021-09-29
Publication date: 2022-04-07
Also published as: TW202232546A

Abstract

A field emission X-ray tube assembly having a metal body incorporating a glass window and a method of forming such devices.

Description

FIELD EMISSION X-RAY TUBE ASSEMBLY AND A METHOD OF MAKING SAME

BACKGROUND

Field of the Disclosure

The present application relates to field emission X-ray devices and, more particularly, to field emission X-ray devices having metal bodies incorporating a glass window and methods of forming such devices.

Description of Related Art

Field emission X-ray tubes convert electrical input power into X-rays. Field emission X-ray tube bodies are generally made of glass or metal. Glass body X-ray tubes can be baked at relatively high temperatures (e.g., up to 600°C) so that all of the components within the X-ray tube may be de-gassed completely, especially those including cathodes made from carbon nanotubes, which absorb numerous different gases on their surfaces and also within their cylinder structures. Baking the tube assemblies at high temperatures under high vacuum is a is necessary step during the manufacturing process of a field emission X-ray tube assembly.

A metal body X-ray tube not only has a greater mechanical strength than an X-ray tube having a glass body, but also allows for baking the assembly at temperatures higher than the melting point of certain glasses. However, because most metals block X-rays much more than glass, the metal body X-ray tube needs a window that allows the X-rays generated from an anode inside the X-ray tube to pass therethrough. Windows in metal body tube assemblies are generally made of a metal, but that metal is usually different from the metal used in the body, which creates difficulties with sealing between the window and the body due to the different thermal expansion of the two different metals during the baking process.

Typical metal windows are a thin aluminum or a thin beryllium, while the metal used for body is made of, for example, stainless steel, nickel alloys, or other metals and alloys of similar strength and characteristics. X-ray tube assemblies with aluminum or beryllium windows cannot be baked at temperatures higher than 350°C, which is much lower than the temperature used for baking a glass body X- ray tube. Baking under 350°C significantly increases the baking time, decreases manufacturing efficiency, and increases the cost of the final product. Moreover, baking at such low temperatures cannot completely remove the residue gases absorbed by the components within the X-ray tube, thereby increasing the arcing rate in the subsequent manufacturing steps and decreasing the life time and the yield of X-ray tube assemblies.

Thus, there is a need for an X-ray tube assembly having a metal body and an X-ray transparent window that can be effectively manufactured with higher bake-out temperatures to improve de-gassing efficiency and to decrease the arcing rate of the X-ray tube in order to improve the operational life of the X- ray tube. SUMMARY OF THE DISCLOSURE

The above and other needs are met by aspects of the present disclosure which includes, without limitation, the following example embodiments and, in one particular aspect, a field emission X-ray tube assembly including an X-ray tube cathode assembly having a first electrical potential and including an electron emitting surface having an electron beam axis, an X-ray tube anode spaced apart from the cathode assembly and having a second electrical potential which is more positive than the first electrical potential, and including an X-ray target surface generally facing the electron emitting surface of the cathode and intersecting the electron beam axis at a focal point, a generally hermetically -sealed metallic housing surrounding the cathode assembly and the anode, spaced apart from the electron emitting surface and the X- ray target surface, and an X-ray transparent glass window coupled to the housing, the window having a center point, wherein the focal point and the center point define an X-ray beam centerline.

Another example aspect provides a method of forming a field emission X-ray tube assembly. The method includes disposing an X-ray tube cathode assembly having a first electrical potential and an electron emitting surface having an electron beam axis within a metallic housing, disposing an X-ray tube anode having a second electrical potential which is more positive than the first electrical potential, and including an X-ray target surface generally facing the electron emitting surface of the cathode and intersecting the electron beam axis at a focal point within the metallic housing, wherein the anode is spaced apart from the cathode assembly, and disposing an X-ray transparent glass window within a wall of the metallic housing, wherein the window has a center point and is located in the housing such that the focal point and the center point define an X-ray beam centerline.

The present disclosure thus includes, without limitation, the following example embodiments:

Example Embodiment 1: A field emission X-ray tube assembly comprising an X-ray tube cathode assembly having a first electrical potential and including an electron emitting surface having an electron beam axis; an X-ray tube anode spaced apart from the cathode assembly and having a second electrical potential more positive than the first electrical potential, and including an X-ray target surface generally facing the electron emitting surface of the cathode and intersecting the electron beam axis at a focal point; a hermetically -sealed metallic housing surrounding the cathode assembly and the anode, and spaced apart from the electron emitting surface and the X-ray target surface; and an X-ray transparent glass window coupled to the housing, the window having a center point, wherein the focal point and the center point define an X-ray beam centerline.

Example Embodiment 2: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the metallic housing comprises a nickel-cobalt ferrous alloy, a stainless steel, a titanium, or a titanium alloy.

Example Embodiment 3: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the window is coupled to the housing via welding. Example Embodiment 4: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the housing comprises a window mounting frame for securing the window to the housing.

Example Embodiment 5: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the window mounting frame comprises an outer rim affixed to a wall of the metallic housing and defining an opening through the housing; and a flange sized and shaped to correspond to a size and shape of the outer rim, wherein the flange is configured to sealingly engage the window with the outer rim and housing, thereby covering the opening.

Example Embodiment 6: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the glass window comprises a borosilicate glass or other lead-free glass.

Example Embodiment 7: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the glass window is disposed proximate to a distal end of the housing.

Example Embodiment 8: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the glass window is disposed in a sidewall of the housing.

Example Embodiment 9: The field emission X-ray tube assembly of any preceding example embodiment, or combinations thereof, wherein the cathode assembly comprises a carbon nanotube cathode, a gate structure, and electrostatic optics for focusing the electron beam.

Example Embodiment 10: A method of forming a field emission X-ray tube assembly, comprising disposing an X-ray tube cathode assembly having a first electrical potential and an electron emitting surface having an electron beam axis within a metallic housing; disposing an X-ray tube anode having a second electrical potential more positive than the first electrical potential, and including an X-ray target surface generally facing the electron emitting surface of the cathode and intersecting the electron beam axis at a focal point within the metallic housing, the anode being spaced apart from the cathode; and disposing an X- ray transparent glass window within a wall of the metallic housing, the window having a center point and being located in the housing such that the focal point and the center point define an X-ray beam centerline.

Example Embodiment 11: The method of any preceding example embodiment, or combinations thereof, wherein disposing the X-ray transparent glass window within a wall of the metallic housing comprises welding an edge of the glass window to an edge of an opening formed in the wall of the housing.

Example Embodiment 12: The method of any preceding example embodiment, or combinations thereof, wherein disposing the X-ray transparent glass window within a wall of the metallic housing, comprises forming an opening in the wall of the housing; securing an outer rim of a window mounting frame about a perimeter of opening in the housing wall; and securing a flange sized and shaped to correspond to a size and shape of the outer rim to the outer rim so as to sealingly engage the window between the outer rim and the flange. Example Embodiment 13: The method of any preceding example embodiment, or combinations thereof, further comprising evacuating an environment within the housing and hermetically sealing the assembly.

Example Embodiment 14: The method of any preceding example embodiment, or combinations thereof, wherein the metallic housing surrounds the cathode assembly and the anode and is spaced apart from the electron emitting surface and the X-ray target surface.

Example Embodiment 15: The method of any preceding example embodiment, or combinations thereof, further comprising de-gassing the field emission X-ray tube assembly.

Example Embodiment 16: The method of any preceding example embodiment, or combinations thereof, wherein the de-gassing comprises baking the tube assembly at a temperature of up to 600°C.

Example Embodiment 17: The method of any preceding example embodiment, or combinations thereof, wherein the de-gassing comprises baking the tube assembly under a vacuum.

These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying drawings, which are briefly described below. The present disclosure includes any combination of two, three, four, or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific embodiment description herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and embodiments, should be viewed as intended, namely to be combinable, unless the context of the disclosure clearly dictates otherwise.

It will be appreciated that the summary herein is provided merely for purposes of summarizing some example aspects so as to provide a basic understanding of the disclosure. As such, it will be appreciated that the above described example aspects are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. It will be appreciated that the scope of the disclosure encompasses many potential aspects, some of which will be further described below, in addition to those herein summarized. Further, other aspects and advantages of such aspects disclosed herein will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described aspects.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1 schematically illustrates an example of a field emission X-ray tube assembly according to one or more aspects of the present disclosure;

FIG. 2 schematically illustrates another example of a field emission X-ray tube assembly according to one or more aspects of the present disclosure; and FIG. 3 illustrates one example of a method of forming a field emission X-ray tube assembly, according to one or more aspects of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all aspects of the disclosure are shown. Indeed, the disclosure may be embodied in many different forms and should not be construed as limited to the aspects set forth herein; rather, these aspects are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

FIG. 1 illustrates one example of a field emission X-ray tube assembly 100 having a body 102 comprising a metal alloy, such as a nickel-cobalt ferrous alloy (e.g., Kovar® available from CRS Holdings, Inc. in Delaware) and a glass window 104 comprising a borosilicate glass. Generally, the nickel-cobalt ferrous alloy and the borosilicate glass have substantially similar thermal expansion characteristics (~5 x 10^-6 /K between 30°C and 200°C, to ~10 * 10^-6 /K at 800°C), which allows for a tight mechanical joint between the two materials over a range of temperatures. Specifically, the glass material used for the window 104 has a low thermal expansion similar to the nickel-cobalt ferrous alloy body 102, so that the sealing between the window and the body can withstand higher baking temperatures (e.g., up to 600°C) than between an aluminum window and metal body. In addition to borosilicate, other lead-free types of glass may be used and selected to have similar thermal expansion to the particular metal used for the housing (e.g., stainless steel, titanium, titanium alloy, etc.).

As shown in FIG. 1, the tube assembly 100 has a generally elongate tubular shape; however, the exact size and shape of the housing 102 will vary to suit a particular application. In one aspect, the window 104 is disposed in a distal end 124 of the housing 102; however, in other aspects, the window may be disposed within a side wall 120 of the housing 102. A cross-sectional shape of the body may be circular; however, in other embodiments it may be any combination of one or more polygonal and/or arcuate shapes. In some embodiments, the window 104 has a substantially planar shape, a dome shape, or an arcuate shape, depending on its location in the housing 102.

In various aspects, an X-ray tube cathode assembly 108, having a first electrical potential and including an electron emitting surface having an electron beam axis, is disposed within the housing 102. In some cases, the cathode assembly 108 includes a base 112 configured for interfacing with the housing 102 and including electrical connections (not shown) for providing a voltage to the cathode assembly. The field emission X-ray tube assembly 100 may utilize a cathode that uses field emitters comprising carbon nanotubes. The field emission X-ray tube assembly 100 also includes an X-ray tube anode 110 spaced apart from the cathode assembly 108 and having a second electrical potential which is more positive than the first electrical potential, and including an X-ray target surface generally facing the electron emitting surface of the cathode assembly and intersecting the electron beam axis at a focal point. In some cases, the anode 110 is disposed in an opposite end of the housing 102, proximate the window 104, which has a center point, where the focal point and the center point of the window define an X-ray beam centerline.

The X-ray transparent glass window 104 is coupled to the housing 102 via a window mounting frame 106, which sealingly secures the window 104 to the housing 102. The specific configuration of the window mounting frame 106 will vary to suit being disposed at a particular location on the housing 102 e.g., a sidewall 120 or distal end 124 thereof. In at least one aspect, the window mounting frame 106 includes an outer rim or first flange half 114 engaged with the housing 102 and running about an entire perimeter of an opening 118 formed in the housing and a mating outer flange or second flange half 116 that mates with the first flange half 114 to sealingly engage the window 104 to the housing 102 by sandwiching the window 104 between the flange halves. In some cases, the two flange halves are coupled to one another via mechanical fasteners, with any necessary gaskets, or welded together. The two flange halves 114, 116 are sized and shaped to correspond to one another, such that the window 104 covers the opening 118. The mounting frame may be configured to allow sliding movement of the window therein to compensate for any difference in thermal expansion between the window and housing, while maintaining a generally hermetically-sealed connection with the housing. Alternatively, the window may be coupled to the housing via bonding, for example, with an intermediate oxide layer.

The housing of the finished X-ray tube assembly is hermetically sealed and spaced apart from the electron emitting surface and the X-ray target surface. The housing 102 defines an interior environment 122 that is evacuated (e.g., under vacuum) prior to sealing.

FIG. 2 depicts an alternative X-ray tube assembly 300 also having a metallic housing 302 and a glass window 304 disposed on or in a sidewall 320 of the housing 302. The exact size and shape of the housing 302 will vary to suit a particular application. As shown in FIG. 2, the window 304 is disposed along the sidewall 320 of the housing 302. In some aspects, the window 304 is positioned over an opening in the housing sidewall 320 and welded or otherwise bonded thereto, eliminating the need for a mounting frame. In some aspects, the window 304 is positioned relative to the opening so as to overlap or abut with an edge(s) of the opening. For example, an edge(s) of the glass window may be welded to a corresponding edge(s) of the opening formed in the wall of the housing. The window 304 may have a polygonal and/or arcuate shape to accommodate a shape of the housing 302.

The X-ray tube assembly 300 further includes a cathode assembly 308 (e.g., one comprising carbon nanotubes) having a first electrical potential and including an electron emitting surface having an electron beam axis and an X-ray tube anode 310 spaced apart from the cathode assembly 308 and having a second electrical potential which is more positive than the first electrical potential, and including an X-ray target surface 311 generally facing the electron emitting surface of the cathode assembly 308 for generating X-rays 332 that exit the assembly 300 via the window 304. The cathode assembly 308 further includes a gate structure 326 and electrostatic optics 328 for focusing the electron beam 330. Like the assembly 100 of FIG. 1, the housing 302 of the finished X-ray tube assembly shown in FIG. 2 is hermetically sealed and spaced apart from the electron emitting surface and the X-ray target surface. FIG. 3 illustrates a method 200 of forming an X-ray tube assembly according to one or more aspects of the present disclosure. The method includes providing a metallic housing into which an X-ray tube cathode assembly is disposed at first location (e.g., a first end thereof) (step 210) and an X-ray tube anode is disposed at a second location (e.g., a second end thereof) (step 220). The order of steps 210 and 220 may be reversed to suit a particular application. An X-ray transparent glass window is disposed within a wall of the metallic housing (step 230). The window is disposed at a location on the housing so as to align a center point thereof with an X-ray beam centerline. In some cases, the window may be disposed within a sidewall of the housing or a distal end of the housing.

The window may be coupled to the housing via welding the glass directly to the housing body or using a mounting frame assembly having, for example, a flange arrangement comprising an outer rim or first flange half engaged with the housing and running about an entire perimeter of an opening formed in the housing and a mating outer flange or second flange half that mates with the first flange half to sealingly engage the window to the housing by sandwiching the window between the flange halves. In some cases, the two flange halves are coupled to one another via mechanical fasteners, with any necessary gaskets, or welded together.

The assembled X-ray tube is then exposed to one or more processes to evacuate an environment within the housing (e.g., by exposing the environment to a vacuum) and to hermetically seal the X-ray tube assembly (e.g., epoxy bonding the housing to a base of the cathode assembly) (step 240). At step 250, the field emission X-ray tube assembly is de-gassed. De-gassing may be carried out by baking the tube assembly at a temperature of up to 600°C under a high vacuum.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these disclosed embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that embodiments of the invention are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the invention. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the disclosure. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated within the scope of the disclosure. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one operation or calculation from another. For example, a first calculation may be termed a second calculation, and, similarly, a second step may be termed a first step, without departing from the scope of this disclosure. As used herein, the term “and/or” and the “/” symbol includes any and all combinations of one or more of the associated listed items.

As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes”, and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

Claims

THAT WHICH IS CLAIMED:

1. A field emission X-ray tube assembly comprising: an X-ray tube cathode assembly having a first electrical potential and including an electron emitting surface having an electron beam axis; an X-ray tube anode spaced apart from the cathode assembly and having a second electrical potential more positive than the first electrical potential, and including an X-ray target surface generally facing the electron emitting surface of the cathode and intersecting the electron beam axis at a focal point; a hermetically -sealed metallic housing surrounding the cathode assembly and the anode, and spaced apart from the electron emitting surface and the X-ray target surface; and an X-ray transparent glass window coupled to the housing, the window having a center point, wherein the focal point and the center point define an X-ray beam centerline.

2. The field emission X-ray tube assembly of claim 1, wherein the metallic housing comprises a nickel-cobalt ferrous alloy, a stainless steel, a titanium, or a titanium alloy.

3. The field emission X-ray tube assembly of claim 1, wherein the window is coupled to the housing via welding.

4. The field emission X-ray tube assembly of claim 1, wherein the housing comprises a window mounting frame for securing the window to the housing.

5. The field emission X-ray tube assembly of claim 4, wherein the window mounting frame comprises: an outer rim affixed to a wall of the metallic housing and defining an opening through the housing; and a flange sized and shaped to correspond to a size and shape of the outer rim, wherein the flange is configured to sealingly engage the window with the outer rim and housing, thereby covering the opening.

6. The field emission X-ray tube assembly of claim 1, wherein the glass window comprises a borosilicate glass or other lead-free glass.

7. The field emission X-ray tube assembly of claim 1, wherein the glass window is disposed proximate to a distal end of the housing.

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8. The field emission X-ray tube assembly of claim 1, wherein the glass window is disposed in a sidewall of the housing.

9. The field emission X-ray tube assembly of claim 1, wherein the cathode assembly comprises a carbon nanotube cathode, a gate structure, and electrostatic optics for focusing the electron beam.

10. A method of forming a field emission X-ray tube assembly, comprising: disposing an X-ray tube cathode assembly having a first electrical potential and an electron emitting surface having an electron beam axis within a metallic housing; disposing an X-ray tube anode having a second electrical potential more positive than the first electrical potential, and including an X-ray target surface generally facing the electron emitting surface of the cathode and intersecting the electron beam axis at a focal point within the metallic housing, the anode being spaced apart from the cathode; and disposing an X-ray transparent glass window within a wall of the metallic housing, the window having a center point and being located in the housing such that the focal point and the center point define an X-ray beam centerline.

11. The method of claim 10, wherein disposing the X-ray transparent glass window within a wall of the metallic housing comprises welding an edge of the glass window to an edge of an opening formed in the wall of the housing.

12. The method of claim 10, wherein disposing the X-ray transparent glass window within a wall of the metallic housing, comprises: forming an opening in the wall of the housing; securing an outer rim of a window mounting frame about a perimeter of opening in the housing wall; and securing a flange sized and shaped to correspond to a size and shape of the outer rim to the outer rim so as to sealingly engage the window between the outer rim and the flange.

13. The method of claim 10, further comprising evacuating an environment within the housing and hermetically sealing the assembly.

14. The method of claim 10, wherein the metallic housing surrounds the cathode assembly and the anode and is spaced apart from the electron emitting surface and the X-ray target surface.

15. The method of claim 13, further comprising de-gassing the field emission X-ray tube assembly.

16. The method of claim 15, wherein the de-gassing comprises baking the tube assembly at a temperature of up to 600°C.

17. The method of claim 15, wherein the de-gassing comprises baking the tube assembly under a vacuum.

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