Target assembly, X-ray device, structure measurement device, structure measurement method, and method for modifying target assembly

Abstract

A target assembly for an X-ray device is provided, the target assembly including a target housing, an entrance passage formed in an entrance portion of the target housing for accepting an incident electron beam, a target member for generating X-rays under illumination by the electron beam through the entrance passage, and an exit passage formed in an exit portion of the target housing for allowing the generated X-rays to exit the target assembly, the exit passage being covered by an X-ray transmissive window. In the assembly, the exit passage includes an exit aperture formed therein and configured to limit generation of X-rays due to scattered electrons reflected from the target member impinging on the interior of the aperture. Target assemblies, X-ray devices, structural measurement devices, structural measurement methods, and methods of modifying a target assembly are also provided.

Description

[Technical Field]

[0001] The present invention relates to a target assembly for an X-ray device, and more particularly to a target assembly for an X-ray device that is a reflective target assembly.

[0002] The invention also relates to an X-ray device comprising a target assembly, a structure measurement device comprising an X-ray device, a method for measuring a structure using an X-ray device, and a method for modifying a target assembly for an X-ray device. [Background technology]

[0003] In the production of x-rays, particularly for use in imaging or structural measurement techniques, it is common to apply an electron beam to an x-ray producing target to produce the desired x-ray beam.

[0004] However, depending on the structure of the housing that contains the target, unwanted secondary images may be observed, which tend to reduce the clarity and fidelity of the image. Furthermore, the presence of such secondary images may lead to poor results when reconstructing volumetric data (e.g., volumetric images) from the acquired images using reconstruction techniques such as CT (computed tomography).

[0005] Therefore, there is a need for a target assembly for an x-ray device that can improve image clarity and fidelity and provide reliable volumetric reconstruction, particularly by suppressing incidents of secondary images. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided a target assembly for an X-ray device.

[0007] The target assembly includes a target housing.

[0008] The target assembly includes an entrance passage. The inlet passage is formed in the inlet portion of the target housing. The entrance passage receives an incident electron beam. The target assembly includes a target member.

[0009] The target member is for producing x-rays under electron beam illumination. Electron beam illumination is via an entrance path. The target assembly includes an exit path. An exit passage is formed within the exit portion of the target housing. The exit path allows the generated x-rays to exit the target assembly. The exit path is covered by an X-ray transparent window. The exit path includes an exit aperture. An outlet hole is formed in the outlet portion. The exit path is configured to limit the generation of x-rays by electrons reflected from the target member impinging on the interior of the aperture.

[0010] In some embodiments, the exit hole is non-cylindrical.

[0011] In some embodiments, the exit aperture increases in cross-section in a direction away from the x-ray entrance side of the aperture. In some embodiments, the exit hole is conical.

[0012] In some embodiments, the exit aperture has a cone angle that matches the cone angle defined between the x-ray incidence point on the target and the exit aperture of the exit aperture.

[0013] In some embodiments, the outlet portion has a plug that provides an outlet hole.

[0014] In some embodiments, the outlet hole is provided with a liner that is composed primarily of a material having an atomic number lower than the atomic number of the predominant material of a surface of the exit part inward of the liner. In some embodiments, the liner is constructed from a material that has an atomic number lower than the atomic number of the predominant material of the surface of the interior outlet portion of the liner. In some embodiments, the atomic number is optionally less than 16. In some embodiments, the liner extends substantially around the cross section of the hole.

[0015] In some embodiments, the exit hole is lined with aluminum, beryllium, or carbon.

[0016] In some embodiments, the liner has a wall thickness greater than the electron penetration depth with which the target is designed to operate.

[0017] In some embodiments, the liner has a wall thickness greater than 10 microns. In some embodiments, the liner has a wall thickness greater than 15 microns. In some embodiments, the liner has a wall thickness greater than 25 microns. In some embodiments, the liner has a wall thickness greater than 50 microns. In some embodiments, the liner has a wall thickness greater than 100 microns.

[0018] In some embodiments, the liner has a wall thickness that is less than 2 mm. In some embodiments, the liner has a wall thickness that is less than 1 mm. In some embodiments, the liner has a wall thickness that is less than 500 microns. In some embodiments, the liner has a wall thickness that is less than 250 microns.

[0019] In some embodiments, the liner has a projection portion that extends inward of the exit aperture. In some embodiments, the liner is disposed between the entrance aperture and the target member. In some embodiments, the projection portion has an aperture for admitting the electron beam to the target.

[0020] In some embodiments, the protruding portion is shaped to conform to the surface of the target member, and is optionally spaced from the surface of the target member by less than 2 mm, optionally less than 1 mm, optionally less than 500 microns.

[0021] In some embodiments, the inlet path is along an inlet hole in the inlet portion.

[0022] In some embodiments, the inlet path is along the centerline of the inlet hole.

[0023] In some embodiments, the inlet hole has a circular cross section.

[0024] In some embodiments, the apertures in the protruding portions have a circular cross section.

[0025] In some embodiments, the target member has a rod-shaped target portion, hi some embodiments, the rod-shaped target portion is positioned to be in the path of the incident electron beam.

[0026] In some embodiments, the target housing is radiopaque.

[0027] In some embodiments, the body of the target assembly is made of tungsten copper. In some embodiments, substantially all of the target assembly is made of tungsten copper.

[0028] In some embodiments, the window is made of beryllium, aluminum, graphite, or diamond.

[0029] According to a second aspect of the present invention, there is provided an X-ray apparatus comprising a target assembly, the X-ray apparatus comprising an electron beam generator, the electron beam generator being arranged to generate an electron beam, the electron beam being incident on a target member.

[0030] In some embodiments, the x-ray device further comprises an electron lens configured to focus the electron beam to a focal point on the target member.

[0031] According to a third aspect of the present invention, there is provided a structure measurement apparatus, comprising an X-ray device. The structure measurement device includes an X-ray detector positioned to measure the structure of an object, the object being interposed between the X-ray device and the X-ray detector.

[0032] According to a fourth aspect of the present invention, there is provided a method for measuring a structure, the method comprising the steps of measuring a structure of an object using an X-ray device and an X-ray detector, the object being positioned between the X-ray device and the X-ray detector.

[0033] According to a fifth aspect of the present invention, there is provided a method of modifying a target assembly for an X-ray device. The target assembly comprises a target housing. The target assembly comprises an entrance passage formed in an entrance portion of the target housing. The entrance passage is for receiving an incident electron beam. The target assembly comprises a target member for generating X-rays under electron beam illumination. The electron beam illumination is via the entrance passage. The target assembly comprises an exit passage formed in an exit portion of the target housing. The exit passage allows generated X-rays to exit the target assembly. The exit passage is covered by an X-ray transparent window. The exit passage comprises an exit aperture formed in the exit portion. The modifying includes the step of limiting generation of X-rays by scattered electrons reflected from the target member impinging inside the aperture.

[0034] In one embodiment, the modification includes modifying the exit hole to be non-cylindrical.

[0035] In one embodiment, the modifying comprises modifying the exit aperture to increase in cross section in a direction from the x-ray entrance side of the exit aperture.

[0036] In one embodiment, the modification includes modifying the exit hole to be conical.

[0037] In one embodiment, the modifying includes modifying the exit hole to have a cone angle that matches a cone angle defined between the x-ray incidence point on the target and the exit aperture of the exit hole.

[0038] In one embodiment, the modification comprises providing a plug in the exit hole.

[0039] In one embodiment, the modification includes providing a liner in the outlet hole, the liner being predominantly composed of a material having an atomic number lower than the atomic number of the predominant material of a surface of the interior outlet portion of the liner. In one embodiment, the modification includes providing a liner in the outlet hole, the liner being composed of a material having an atomic number lower than the atomic number of the predominant material of a surface of the interior outlet portion of the liner. In one embodiment, the atomic number is optionally less than 16. In one embodiment, the liner extends substantially around a cross section of the hole.

[0040] In one embodiment, the modification includes providing an aluminum, beryllium, or carbon liner in the exit hole.

[0041] In one embodiment, the liner has a wall thickness greater than the electron penetration depth at which the target is designed to operate.

[0042] In one embodiment, the liner has a wall thickness greater than 10 microns. In one embodiment, the liner has a wall thickness greater than 15 microns. In one embodiment, the liner has a wall thickness greater than 25 microns. In one embodiment, the liner has a wall thickness greater than 50 microns. In one embodiment, the liner has a wall thickness greater than 100 microns.

[0043] In one embodiment, the liner has a wall thickness that is less than 2 mm. In one embodiment, the liner has a wall thickness that is less than 1 mm. In one embodiment, the liner has a wall thickness that is less than 500 microns. In one embodiment, the liner has a wall thickness that is less than 250 microns.

[0044] In one embodiment, the liner has a protruding portion extending inward of the exit bore. In one embodiment, the protruding portion is located between the entrance bore and the target member. In one embodiment, the protruding portion has an aperture. In one embodiment, the aperture is for admitting the electron beam to the target member.

[0045] In one embodiment, the protruding portion is shaped to conform to the surface of the target member. In one embodiment, the protruding portion is spaced less than 2 mm from the surface of the target member. In one embodiment, the protruding portion is spaced less than 1 mm from the surface of the target member. In one embodiment, the protruding portion is spaced less than 500 microns from the surface of the target member.

[0046] In one embodiment, the inlet path is along an inlet hole in the inlet portion.

[0047] In one embodiment, the inlet path is along the centerline of the inlet hole.

[0048] In one embodiment, the inlet hole has a circular cross section.

[0049] In one embodiment, the aperture in the protruding portion has a circular cross section.

[0050] In one embodiment, the target member has a rod-shaped target portion, hi one embodiment, the rod-shaped target portion is positioned to be in the path of the incident electron beam.

[0051] In one embodiment, the target housing is radiopaque.

[0052] In one embodiment, the target assembly is made of tungsten copper.

[0053] In one embodiment, the window is made of beryllium, aluminum, graphite, or diamond. In one embodiment, the method further includes applying an incident electron beam to the target member and observing a reduction in x-ray production due to electrons reflected from the target member impinging on the inside of the hole.

[0054] In one embodiment, the method further includes applying an incident electron beam to the target member and observing a reduced intensity of a ghost image of a test object. In one embodiment, the ghost image is positioned on a circular locus surrounding a true image of the test object on the image plane. In one embodiment, the test object is positioned between the target member and the image plane.

[0055] In one embodiment, the method further includes adjusting the configuration of the exit aperture to observe a reduced intensity of the ghost image of the object under inspection.

[0056] According to a sixth aspect of the present invention, there is provided a method of modifying an x-ray apparatus comprising a target assembly and an electron beam generator arranged to generate an electron beam incident on the target member, the method comprising modifying the target assembly in accordance with a method for modifying a target assembly for an x-ray apparatus.

[0057] In one embodiment, the x-ray device further comprises an electron lens configured to focus the electron beam to a focal point on the target member. [Brief explanation of the drawings]

[0058] For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Figure 1] FIG. 1 shows a schematic diagram of an X-ray device in which the present invention can be implemented. [Figure 2] FIG. 2 is a diagram showing a cross section of an X-ray target assembly that may illustrate the problems that the present invention can address. [Figure 3] FIG. 3 shows a cross section of a target assembly for an X-ray device according to a first embodiment of the present invention. [Figure 4] FIG. 4 shows a cross section of a target assembly for an X-ray device according to a second embodiment of the present invention. [Figure 5] FIG. 5 illustrates a liner that can be used in connection with embodiments of the present invention. [Figure 6] FIG. 6 is a cross-sectional view of the liner of FIG. [Figure 7] FIG. 7 is a series of images showing an X-ray image of a radiopaque ball showing a ghost image produced using a conventional target assembly, along with an X-ray image produced using the target assembly shown in FIG. 3 and an image of the radiopaque ball obtained using the target assembly of FIG. 4. DETAILED DESCRIPTION OF THE INVENTION

[0059] FIG. 1 is a schematic diagram of an X-ray structural measurement system 1 that can be used to measure or image an object S.

[0060] The structural measurement system 1 is configured to receive a beam of X-rays B propagating towards an object S. x The object S is illuminated by an X-ray beam B. x The object S is supported by a stage 20 arranged to support the object S on the path of the X-ray beam B. x subsequently strike the X-ray detector 30 and provide information about the structure of the object S.

[0061] The X-ray structure measurement system 1 is controlled by a controller 40 connected to the X-ray source 10, the stage 20, and the detector 30 by data / control lines. x The X-ray source 10 and stage 20 can control the operation and parameters of the stage 20, the position and operation of the stage 20, the operation of the detector 30, as well as receiving image information from the detector 30 and receiving status information from the X-ray source 10 and stage 20.

[0062] In the example of Figure 1, the structural measurement system is a computerized tomography system, and the object S is measured by a beam Bx A sequence of images of object S is acquired as it rotates on stage 20 within a path of 100° F. Some or all of the image sequences are then combined using computed tomography techniques known to those skilled in the art to generate three-dimensional structural information, also referred to as volumetric structural information, about the internal structure and external contours of object S.

[0063] In the example of FIG. 1, the X-ray source 10 and detector 30 are configured to receive an X-ray beam B propagating from the X-ray source 10 to the detector 30. x The stage 20 remains in a fixed position relative to the stage 20 in the path of the X-ray source 10. The stage 20 may, for example, still support the object S and direct the X-ray beam B between the X-ray source 10 and the detector 30. x In another configuration, the stage 20 allows rotation about a first axis perpendicular to the path of the X-ray beam BX and also about a second axis perpendicular to the path of the X-ray beam BX. x Alternatively, the stage 20 may be a stage that allows tilting about a second axis that is perpendicular to the path of the beam B and perpendicular to the first axis. Such a stage with both rotation and tilt capabilities can refine the position of the object or acquire images used for volume reconstruction from a wider range of directions intersecting the object. In a further configuration, the stage 20 may be equipped with a linear axis that can translate the object S in one, two, or three degrees of linear motion, thereby adjusting the beam B. x To achieve the desired position of the object S in the path of the beam B x This allows for the translation of the object S within the path of

[0064] 1 can also be applied to X-ray structural measurement systems that do not provide volumetric reconstruction and can only provide two-dimensional images. In such configurations, the stage 20 can have the same or similar configuration as described above to allow images to be obtained from a wider range of directions across the object. Alternatively, in such configurations, the stage 20 may not be present or may be replaced by a sample holder with a fixed or adjustable position.

[0065] In another arrangement operating according to principles equivalent to those described with reference to Figure 1, the object S remains stationary while the X-ray source 10 and detector 30 are arranged to rotate together about one or more axes of rotation, with one or two axes of rotation in an opposed relationship about the object S. Such rotation can be provided, for example, by locating the source 10 and detector 30 on opposite sections of a rotating support or rotating gantry, with the object S supported on a stage or sample holder as described above with respect to the axes of rotation.

[0066] In the configuration shown in Figure 1, the x-ray source 10 has a vacuum enclosure 15 containing a filament 11 and a target 13. During operation, the filament 11 is heated and given a negative potential which causes it to emit electrons by the process of thermionic emission. The electrons thus generated are referred to as electron beam B in Figure 1. e , and strikes a target 13 comprising an X-ray generating material such as tungsten, rhodium or molybdenum, silver, copper or gold, and electron beam B e As a result of the X-rays hitting the target 13, a beam of X-rays BX is emitted from the target 13. The choice of target material can affect the X-ray emission spectrum and is selected accordingly depending on the desired characteristics of the X-ray beam.

[0067] Electron beam B to target 13 eTo facilitate the incidence of electrons, the target 13 can be connected to earth or to a potential different from earth, for example, a positive potential that is more positive than the negative potential of the filament 11, to attract the electrons propagating from the filament 11.

[0068] The grid electrode 12 surrounding the filament 11 has a similar or slightly negative potential to the filament 11, providing a local negative potential around the filament 11 to repel the electrons emitted by the filament, and the electron beam B 1 moving away from the filament. e and regulates the electron beam current from the filament 11.

[0069] The anode electrode 17 disposed between the filament 11 and the target 13 may be connected to earth or may be connected to the electron beam B e The electrons may be at an adjustable potential to further control their flux and energy.

[0070] An electrostatic lens 14 is disposed between the filament 11 and the target 13 and on the target side of the anode electrode 17. A potential is applied to the electrostatic lens 14 to deflect the electron beam B 1 impinging on the target 13. e The electrostatic lens 14 has a shape of a plurality of cylinders, and the plurality of cylinders can control the focus of the electron beam B. e The annular aperture has a gap disposed and sized between them to allow the electron beam to pass through. If the cylinders are at different potentials, the gap between the cylinders can act as a lens to converge or diverge the electron beam. The annular aperture can, in an alternative configuration, be used as an electrostatic lens, as will be understood by those skilled in the art.

[0071] The filament 11, grid electrode 12, anode electrode 17, target 13, and electrostatic lens 14 are all shown contained within an enclosure 15, which can be sealed to support an internal vacuum. However, in an alternative configuration, the electrostatic lens 14 can be replaced by a magnetic lens, such as a focusing coil. To avoid heat and sealing complications, such coils can be located outside the tubular section of the enclosure 14 made of a non-magnetic material.

[0072] The enclosure 15 can be made of virtually any airtight material and can be formed of sections of different materials such as metal, glass, plastic, etc. Airtight seals can be provided between the different sections.

[0073] The enclosure 15, due to its overall airtight construction, can thereby be placed in a relative vacuum by pumping at a pump-out port (not shown), which allows the electron beam B e to propagate freely from the filament 11 to the target 13 without substantial absorption. Forming part of the enclosure 15 is a window 16, which is formed of a material different from the material forming the rest of the enclosure 15, such as beryllium, aluminum, graphite or diamond, which is relatively transparent to X-rays but relatively opaque to electrons. The window 16 thereby allows the X-ray beam B e to pass through. x can pass outside the enclosure 115 without substantial absorption.

[0074] The entire measurement system 1 is typically provided with a surrounding, radiopaque enclosure (not shown) that serves to prevent X-rays generated by the source 10 from leaking outside the measurement system.

[0075] In Figure 1, the support arrangement for the target 13 is not shown. Figure 2 shows a cross-section of a typical configuration for supporting an X-ray generating target within a target housing so that an X-ray beam can be generated. The configuration of Figure 2 thus constitutes a target assembly into which an electron beam can be introduced and from which an X-ray beam can be emitted. Such a housing forms the upper portion of the vacuum enclosure 15 shown in Figure 1 and is hermetically connected to the remainder of the vacuum enclosure 15, which contains the components that generate and direct the electron beam, namely, the electron lens 14, the anode electrode 17, the filament 11, and the grid electrode 12.

[0076] 2 supports a rotating X-ray target 930 on an axis 935, which allows the target 930 to be rotated about the axis 935 either by a rotation drive (not shown) or manually. The target 930 can thus be rotated. This is useful, for example, if irradiation by the electron beam results in erosion of the point of the target where the electron beam struck, so that an undamaged portion of the target can be brought into the path of the beam.

[0077] The target 930 is supported in a target housing 901, which includes an entrance portion 920 for accepting the electron beam, an exit portion 910 for allowing the X-ray beam generated by the incidence of the electron beam on the target 930 to exit the housing, and a mounting portion 950 for connecting the target housing 901 to the remainder of the vacuum enclosure 15, which houses the aforementioned components for generating and directing the electron beam.

[0078] 2, the electron beam can be introduced into the target housing 910 along an electron beam tube 960 having a connecting portion 970 configured to engage a socket 955 formed in a mounting portion 950 of the target housing 901. The connection is made gas-tight by a suitable seal inserted between the end of the tube 960 and the socket 955 to maintain a vacuum through which the electron beam propagates from the electron beam tube 960 to the interior of the target housing 901.

[0079] Entrance section 920 includes an entrance passage 925 formed as an entrance hole between socket 955 and the location where target 930 is located. The interior of electron beam tube 960 is aligned with entrance passage 925 so that the electron beam can be incident on target 930 at a desired incident location.

[0080] The exit portion 910 is disposed adjacent to the target member 930 and includes an exit path 915 formed by an exit aperture. The exit path 915 extends between the surface of the target housing 901 from which the x-rays are to be emitted and the target member 930.

[0081] Covering the exit hole exit aperture 912, which defines the exit path 915, is an x-ray transmissive window 940, which is formed of an x-ray transparent material such as beryllium. The window 940 is secured above the exit hole 915 exit aperture 912 by a mounting plate 945. The mounting plate 945 is attached to a flat surface of the target housing 901 in which the exit aperture 912 is formed, thus ensuring that the transmissive window 940 is positioned above the exit opening 912.

[0082] The mounting plate 945 has a recess positioned facing the surface of the target housing 901 to receive the transmission window 940, such that the surface of the transmission window 940 is substantially flush with the surrounding surface of the mounting plate 945. The mounting plate 945 has an opening 949 formed in the form of a through-hole extending from the recess to the opposite surface of the mounting plate 945, and is arranged to be aligned with and positioned over the exit aperture 912, with the x-ray transmissive window 940 between the opening 949 and the exit aperture 912, such that the generated x-rays pass from the exit hole 915 through the transmission window 940 and then through the opening 949. Thus, the generated x-rays can be directed towards the object under investigation.

[0083] A first seal 946 in the form of an O-ring is provided between the x-ray transmissive window 940 and the mounting plate 945, and a second seal 947, also in the form of an O-ring, is provided between the mounting plate 945 and the surface of the target housing 901. The mounting plate 945 is secured to the target housing 901 by suitable fasteners, exemplified in FIG. 2 by mounting screws 948, one or more of which may be provided to hermetically secure the mounting plate 945 to the remainder of the target housing 901, as required.

[0084] 2, the electron beam arrives through the electron beam tube 960 and passes through an entrance path 925 defined by the entrance aperture to impinge on the target member 930. The x-rays thereby generated are emitted from the target member 930 and directed along an exit path 915 through an x-ray transmissive window 940 toward the object under investigation. The configuration of FIG. 2 therefore operates in a so-called reflection mode, where the path of the x-ray radiation is along a different direction than the direction of the incident electron beam to the target. This is in contrast to a so-called transmission mode arrangement, where the x-ray radiation is along substantially the same direction as the direction of the incident electron beam.

[0085] 2, at least the body of the target housing 901 is typically formed from tungsten copper, such as an 80% tungsten / 20% copper alloy or another tungsten copper alloy with a high percentage of tungsten that exhibits low thermal expansion. Other components, such as the electron beam tube 960, connecting portion 970, and mounting plate 945, are also formed from such tungsten copper or another suitable material.

[0086] When the target assembly of FIG. 2 is operated, unwanted secondary images of the object being observed may appear in the acquired image data.

[0087] For example, imaging a 1 mm diameter tungsten copper sphere using such a conventional target at 120 kV and 6 W beam energy results in the image shown in Figure 7a. In Figure 7a, a circular secondary image can be observed surrounding the image of the 1 mm diameter tungsten copper sphere, which can be understood as a superposition of a faint (ghost) image of the tungsten copper sphere positioned on a circular trajectory or path around the center of the emitted x-ray beam. Depending on the intensity of the effect, it may be necessary to stretch the image contrast to make the effect shown in Figure 7a clearly visible to the eye. The presence of such secondary images, whether visible or not, can reduce image contrast and fidelity and prevent proper volumetric reconstruction using standard computed tomography techniques.

[0088] Therefore, in accordance with the present invention, the target assembly 900 shown in FIG. 2 is modified to arrive at a first embodiment of the present invention, as shown in FIG.

[0089] The first embodiment of the present invention, target assembly 100 shown in Figure 3, corresponds substantially in structure and function to target assembly 900 shown in Figure 2, except as described below. Accordingly, parts of target assembly 100 that are assigned the reference numeral 1XX should be considered to correspond directly in structure and function to the analogous parts 9XX shown in Figure 2.

[0090] The target assembly 100 shown in FIG. 3 is provided with an insert 180. The insert 180 is configured in the form of a plug and is made of a material similar to or the same as the target housing 901. For example, the insert 180 may be made of tungsten copper. The insert 180 is sized in length and outer diameter to fit within the exit bore of the target housing 101 and has a tapered interior bore between an entrance aperture 181 closest to the target member 130 and an exit aperture 182 of the insert 180 furthest from the target member 130. In the embodiment of FIG. 3, the tapered exit bore 185 is conical with a linearly tapered interior surface, but may also have a curved or stepped interior taper.

[0091] The degree of taper of the internal bore 185 of the insert 180 is selected to match the desired cone angle of the x-rays emitted from the target member 130, which is typically dictated by the geometry of the rest of the x-ray structure measurement apparatus into which the target assembly 100 is incorporated. For example, the cone angle may be selected to completely fill the x-ray sensitive surface of the detector at the intended distance of the detector from the target.

[0092] In the configuration of FIG. 3, the insert 180 extends from directly adjacent the transmission window 140 to directly adjacent the target member 130, although the insert 180 may be axially shortened if desired.

[0093] In the absence of insert 180, electrons that strike target member 130 and then scatter off the target on member 130 may strike the inner surface of target housing 901, generating unwanted electrons that are then emitted through transmission window 140. Such are hypothesized to be the origin of the secondary image shown in FIG. 7a when target assembly 900 of FIG. 2 is in operation.

[0094] By providing the insert 180 in the target assembly 100, a non-cylindrical exit hole is provided, which limits the possibility that electrons scattered or reflected from the target material will impinge on the interior of the hole and generate a secondary source of x-rays therein.

[0095] The arrangement shown in Figure 3 therefore reduces the incidence of undesirable secondary images.

[0096] This can be seen, for example, with reference to Figure 7b, which shows the effect of introducing a tapered insert 180, as shown and described in relation to Figure 3, into the x-ray target assembly used to generate Figure 7a. By introducing the insert 180, the occurrence of undesired secondary images is almost completely eliminated, even when contrast is stretched. Thus, the contrast and fidelity of the image are improved, and volumetric reconstruction by standard computed tomography techniques may be more successful.

[0097] A second embodiment of the present invention will now be described with reference to Figure 4. Again, parts similar in structure and function to the target assembly 900 shown in Figure 2 are designated with reference numerals 2XX and correspond to similar parts 9XX shown in Figure 3.

[0098] 4 includes a liner 280 inside the exit hole 215. The liner 280 is formed of a material having an atomic number lower than that of the primary material of the body of the target housing 201. Since the target housing 201 is made of tungsten copper in this embodiment, the liner 280 may be formed of a material with an atomic number less than 16, for example, and may be preferably formed of aluminum, beryllium, or carbon.

[0099] In this embodiment, the liner 280 has a cylindrical outer surface and a cylindrical inner surface and a wall thickness greater than the electron penetration depth at which the target is designed to operate. In particular, in the embodiment of FIG. 4, the liner may have an outer diameter of 4 mm and an inner diameter of 3 mm. Accordingly, the liner 280 may have a wall thickness of 1 mm. In other configurations, the wall thickness may be greater than 10 microns, greater than 15 microns, greater than 25 microns, greater than 50 microns, or greater than 100 microns. Furthermore, for ease of manufacturing, the liner has a wall thickness less than 2 mm, optionally less than 1 mm, optionally less than 500 microns, or optionally less than 250 microns. The liner extends between adjacent the transmission window 240 and adjacent the target member 230 and substantially lines or coats the exit hole 215 of the target housing 201.

[0100] The liner 280 also has a projection portion 258 that projects across the electron beam entrance path 225 from a cylindrical insert portion 284 that is shaped and dimensioned to fit within the exit aperture 215. A circular aperture 286 is formed in the projection portion 285 and is sized to allow the electron beam to pass through the projection portion 285. Shapes of the aperture 286 formed in the projection portion 285 other than circular are contemplated.

[0101] Liner 280 functions to absorb scattered electrons, thereby preventing them from reaching the surface of exit hole 215 of target housing 201 with enough energy to generate x-rays. By adjusting the thickness of liner 280, the degree of reduction of unwanted x-rays can be controlled.

[0102] 4, the protruding portion 285 extending from the insert portion 284 of the liner 280 is shaped to conform to the surface of the target member 230, thereby providing a slight clearance between the target member 230 and the protruding portion 285. In the embodiment of FIG. 4, the protruding portion 285 is shaped to have a substantially cylindrical transverse cut-out from the generally cylindrical axial shape of the liner 280.

[0103] Such a shape preferably has a high degree of symmetry about the longitudinal axis of liner 280, at least for insert portion 284, although other shapes besides a cylinder are contemplated for liner 280, such as a regular polygonal prism. The exterior shape of liner 280 in cross section preferably matches the cross-sectional shape of outlet hole 215, although the interior cross-sectional shape may be the same or different. In the embodiment of FIG. 4, insert portion 284 is cylindrically symmetric about its longitudinal axis.

[0104] 5 and 6 show different views of the liner 280, with FIG. 5 showing the liner 280 alone, i.e., removed from the exit hole 215, and FIG. 6 showing a cross-sectional view of the liner 280, showing a substantially cylindrical insert portion 284 and a protruding portion 285 having an aperture 286 cut out to accommodate the target member 230.

[0105] Applying the liner shown in FIG. 4 to the configuration of FIG. 2 under the same imaging conditions as described above in connection with FIG. 7a results in an image of the tungsten-copper sphere, as shown in FIG. 7c. Again, a significant reduction in the circular secondary image of the tungsten sphere can be observed. As with the first embodiment, the introduction of insert 280 significantly eliminates the occurrence of undesired secondary images, even at the expense of contrast stretching. Thus, the contrast and fidelity of the image are improved, making volumetric reconstruction by standard computed tomography techniques more successful.

[0106] Furthermore, with appropriate adaptation, the liner of Figure 4 can be provided inside the insert 180 shown in Figure 3. In such a configuration, a tapered liner of the thickness and material as described in connection with Figure 4 is provided within the tapered exit hole 185 of the insert 180, thereby absorbing any electrons that reach the surface of the tapered hole, even taking into account the tapered hole of the insert 180. By providing such a liner, even these electrons can be absorbed, further reducing the generation of unwanted secondary images.

[0107] Although the insert 180 and liner 280 are described above as being provided as separate components of the target assembly that may be integrated with the target assembly during manufacture, it is also possible to retrofit or retrofit such inserts or liners onto existing target assemblies to improve their imaging performance.

[0108] Furthermore, while insert 180 and liner 280 are described above as separate components applied to the target assembly, in an alternative configuration, element 180 shown in FIG. 3 can be provided as an integral part of the target housing rather than as an insert therein. This can be achieved, for example, by appropriately shaping the exit hole of the target housing to provide a suitable taper that increases in cross section in a direction away from the x-ray entrance side of the hole. Similarly, a liner such as that described in connection with FIG. 4 can be provided during manufacture by applying a suitable coating of lining material to the interior surface of the exit hole of the target assembly rather than as a separate applied part. Such a coating can be provided, for example, by coating techniques known in the art.

[0109] Accordingly, the above-described embodiments should be understood to be illustrative, while the scope of the claimed invention should be defined solely by the appended claims.

Claims

1. 1. A target assembly for an x-ray device comprising: target housing; an entrance passage formed in an entrance portion of the target housing for receiving an incident electron beam; a target member for producing x-rays under illumination by an electron beam via said entrance path; an exit path formed in an exit portion of the target housing to allow generated x-rays to exit the target assembly, the exit path being covered by an x-ray transmissive window, the exit path having an exit aperture formed therein, the exit aperture configured to limit generation of x-rays by scattered electrons reflected from the target member impinging on an interior side of the exit aperture; Equipped with A target assembly wherein the exit aperture is provided with a liner, the liner being composed primarily of or consisting of a material having an atomic number lower than the atomic number of the predominant material of the interior surface of the exit aperture of the target housing.

2. the exit hole is non-cylindrical; The target assembly of claim 1 .

3. the exit aperture increases in cross section in a direction from the X-ray entrance side of the exit aperture; 3. The target assembly according to claim 1 or 2.

4. the exit hole is conical; The target assembly of any one of claims 1 to 3.

5. the exit aperture has a cone angle that matches a cone angle defined between an x-ray emission point on a target and an exit aperture of the exit aperture. The target assembly of any one of claims 1 to 4.

6. the outlet portion having a plug providing the outlet hole; A target assembly according to any one of claims 1 to 5.

7. the liner has an atomic number less than 16; the liner extends substantially around a cross section of the outlet hole; A target assembly according to any preceding claim.

8. The outlet hole is provided with an aluminum, beryllium, or carbon liner. A target assembly according to any preceding claim.

9. the liner has a wall thickness greater than the electron penetration depth at which the target is designed to operate; 9. The target assembly according to claim 7 or 8.

10. the liner has a wall thickness of greater than 10 microns, greater than 15 microns, greater than 25 microns, greater than 50 microns, or greater than 100 microns; A target assembly according to any one of claims 7 to 9.

11. the liner has a wall thickness of less than 2 mm, less than 1 mm, less than 500 microns, or less than 250 microns; A target assembly according to any one of claims 7 to 10.

12. the liner has a protruding portion extending inward of the exit hole and positioned between the entrance hole and the target member; the protruding portion has an aperture for admitting the electron beam to a target; A target assembly according to any one of claims 7 to 11.

13. the protruding portion is configured to conform to the surface of the target member and is spaced from the surface of the target member by less than 2 mm, less than 1 mm, or less than 500 microns; The target assembly of claim 12.

14. the inlet path is along an inlet hole in the inlet portion; A target assembly according to any preceding claim.

15. the inlet path is along a centerline of the inlet hole; The target assembly of claim 14.

16. the inlet hole has a circular cross section; 16. A target assembly according to claim 14 or 15.

17. the aperture in the protruding portion has a circular cross section; 14. A target assembly according to claim 12 or 13.

18. the target member comprises a rod-shaped target portion positioned in the path of the incident electron beam; 18. A target assembly according to any preceding claim.

19. the target housing is radiopaque; 19. A target assembly according to any preceding claim.

20. the target assembly is made of tungsten copper; 20. A target assembly according to any preceding claim.

21. the X-ray transmissive window is made of beryllium, aluminum, graphite, or diamond; 21. A target assembly according to any preceding claim.

22. A target assembly according to any one of claims 1 to 21; an electron beam generator arranged to generate an electron beam incident on the target member; An X-ray device comprising:

23. further comprising an electron lens configured to focus the electron beam to a focal point on the target member.

23. The X-ray device of claim 22.

24. an X-ray device according to claim 23; an X-ray detector arranged to measure the structure of an object arranged between the X-ray device and the X-ray detector; A structural measurement device comprising:

25. Using the X-ray device and X-ray detector of claim 23, measuring a structure of an object placed between the X-ray device and the X-ray detector. A structural measurement method, including:

26. 1. A method of modifying a target assembly for an x-ray device, comprising: The target assembly comprises: target housing; an entrance passage formed in an entrance portion of the target housing for receiving an incident electron beam; a target member for producing x-rays under illumination by an electron beam via said entrance path; an exit pathway formed in an exit portion of the target housing to allow generated x-rays to exit the target assembly, the exit pathway being covered by an x-ray transmissive window, the exit pathway having an exit hole formed therein; a liner is provided at the exit hole, the liner consisting essentially of or consisting of a material having an atomic number lower than the atomic number of the predominant material of the interior surface of the exit hole of the target housing; the modification includes limiting the generation of the x-rays by scattered electrons reflected from the target member impinging on the inside of the exit aperture. method.

27. the modifying includes modifying the exit hole to be non-cylindrical.

27. The method of claim 26.

28. the modifying includes modifying the exit aperture so that a cross section in a direction from an X-ray entrance side of the exit aperture is enlarged.

28. The method of claim 26 or 27.

29. the modifying includes modifying the exit hole to be conical.

29. The method of any one of claims 26 to 28.

30. the modifying includes modifying the exit aperture to have a cone angle that matches a cone angle defined between an x-ray exit point on a target and an exit aperture of the exit aperture.

30. The method of any one of claims 26 to 29.

31. the modification includes providing a plug in the exit hole.

31. The method of any one of claims 26 to 30.

32. the modification includes providing a liner in the outlet hole, the liner consisting essentially of or consisting of a material having an atomic number lower than the atomic number of the predominant material of the surface of the outlet portion inside the liner, the atomic number being less than 16, and the liner extending substantially around a cross section of the outlet hole.

32. The method of any one of claims 26 to 31.

33. the modification includes providing an aluminum, beryllium, or carbon liner in the exit hole; 33. The method of any one of claims 26 to 32.

34. the liner has a wall thickness greater than the electron penetration depth at which the target is designed to operate; 34. The method of any one of claims 32 to 33.

35. the liner has a wall thickness of greater than 10 microns, greater than 15 microns, greater than 25 microns, greater than 50 microns, or greater than 100 microns; 35. The method of claim 32, 33 or 34.

36. the liner has a wall thickness of less than 2 mm, less than 1 mm, less than 500 microns, or less than 250 microns; 36. The method of claim 32, 33, 34 or 35.

37. the liner has a protruding portion extending inward of the exit hole and positioned between the entrance hole and the target member; the protruding portion has an aperture for admitting the electron beam to a target; 37. The method of any one of claims 26 to 36.

38. the protruding portion is configured to conform to the surface of the target member and is spaced from the surface of the target member by less than 2 mm, less than 1 mm, or less than 500 microns; 38. The method of claim 37.

39. the inlet path is along an inlet hole in the inlet portion; 39. The method of any one of claims 26 to 38.

40. the inlet path is along a centerline of the inlet hole; 40. The method of claim 39.

41. the inlet hole has a circular cross section; 41. The method of claim 40.

42. the aperture in the protruding portion has a circular cross section; 39. The method of any one of claims 37 or 38.

43. the target member comprises a rod-shaped target portion positioned in the path of the incident electron beam; 43. The method of any one of claims 26 to 42.

44. the target housing is radiopaque; 44. The method of any one of claims 26 to 43.

45. the target assembly is made of tungsten copper; 45. The method of any one of claims 26 to 44.

46. the X-ray transmissive window is made of beryllium, aluminum, graphite, or diamond; 46. ​​The method of any one of claims 26 to 45.

47. applying an incident electron beam to the target member; and observing a reduction in x-ray production due to the impact of electrons reflected from the target member onto the interior of the exit aperture.

47. The method of any one of claims 26 to 46.

48. applying an incident electron beam to the target member; observing a reduced intensity of the ghost image of the object of inspection, the ghost images are arranged on a circular locus surrounding a direct image of the object on an image plane; the inspection object is disposed between the target member and the imaging plane.

48. The method of any one of claims 26 to 47.

49. adjusting the exit aperture configuration to observe a reduced intensity of the ghost image of the inspected object.

49. The method of claim 48, further comprising:

50. 1. A method of modifying an X-ray device, the X-ray device comprising: A target assembly according to any one of claims 1 to 21; an electron beam generator arranged to generate an electron beam incident on the target member; The method includes modifying a target assembly according to any one of claims 26 to 49. method.

51. further comprising an electron lens configured to focus the electron beam to a focal point on the target member.

51. The method of claim 50.

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