US3794872A

US3794872A - Moving target spring loaded x-ray tube

Info

Publication number: US3794872A
Application number: US00264805A
Authority: US
Inventors: D Haas; J Pichert
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-06-21
Filing date: 1972-06-21
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26

Abstract

A sealed-off X-ray tube having a flat target surface facing an electron beam source and carried by a rigid support mounted for sliding reciprocally lateral motion against a sliding surface. A bellows is sealed vacuum tight to the target and to the wall of the tube opposite the sliding surface so that the target, the bellows, and the envelope of the tube form a closed surface. Conduits extend through the sliding surface to direct the flow of cooling fluid against the back surface of the target and carry the fluid away. The axis of the target reciprocates laterally in a direction perpendicular to the axis of the tube but the target does not rotate on its own axis. The target may be moved manually or by motor and with a linear, or circular motion. Because of the movement of the target, virtually constant X-ray beams radiate through windows of the tube and the effective life of the target is substantially increased.

Description

United States Patent [191 Haas et al.

1 MOVING TARGET SPRING LOADED X-RAY Filed: June 21, 1972 Appl. N0.: 264,805

Related US. Application Data Continuation-impart of Ser. No. 138,627, April 29, 1971.

US. Cl. 313/60, 313/32 H0lj 35/10 Field of Search 313/60 References Cited UNITED STATES PATENTS 10/1936 Pohl ..3l3/60 2,133,606 10/1938 Du Mond ..313/60 Feb. 26, 1974 r m r Emm nenr ieys ek Assistant ExaminerDarwin R. Hostetter Attorney, Agent, or Firm-Frank R. Trifari 5 7] ABSTRACT A sealed-off X-ray tube having a flat target surface facing an electron beam source and carried by a rigid support mounted for sliding reciprocally lateral motion against a sliding surface. A bellows is sealed vacuum tight to the target and to the wall of the tube 0pposite the sliding surface so that the target, the bellows, and the envelope of the tube form a closed surface. Conduits extend through the sliding surface to direct the flow of cooling fluid against the back surface of the target and carry the fluid away. The axis of the target reciprocates laterally in a direction perpendic'ular to the axis of the tube but the target does not rotate on its own axis. The target may be moved manually or by motor and with a linear, or circular motion. Because of the movement of the target, virtually constant X-ray beams radiate through windows of the tube and the effective life of the target is substantially increased.

.10, (l aimalt yrawi Eigu 24s lO2-- -T 1 MOVING TARGET SPRING LOADED X-RAY TUBE This is a continuation-in-part of application Ser. No. 138,627 filed Apr. 29, 1971 now U.S. Pat. No. 3,689,790.

1. Field of the Invention This invention relates to the field of moving target X-ray tubes and particularly to tubes suitable for continuous operation for X-ray diffraction.

2. Background of the Invention Only threetypes of general commercial X-ray diffraction tubes are manufactured today. These are the sealed-off tube, the rotating anode units, and the microfocus units. Sealed-off tubes, which are by far the most numerous, have fixed electrodes and are noted for their reliability, long life (which averages about 5,000 hours), reproduceable focus spots, and low cost. Typically they have a maximum specific loading of about 400 watts/mm for fine focus tubes and a maximum total loading of about 2,000 watts/mm? Rotating anode tubes are noted for their brightness on fine focus spots. They have a maximum specific loading of about 7 kw/mm which is'substantially higher than'the maximum specific loading of sealed-off tubes, and their maximum total loading is from 6 to 30 kw for commercial tubes and up to 50 kw for experimental tubes. The typical minimum focus size is 1 mm X 0.1 mm. Microfocus units are noted for their brightness in very small focal spots which are typically less than 0.1 mm in maximum dimension. Their maximum specific load ing may be of the order of 30 kwlmm which is four times as high as that of the rotating anode tubes, but their maximum total loading is of the order of only 500 watts. The minimum size of the focal spot is about 0.01 mm.

Rotating anode units and microfocus units require not only the electrical and coolant sources of sealed-off tubes but also complex vacuum pumps. Therefore, these units are either sold or individually made as complete systems, which are far more costly than an X-ray generator using asealed-off tube. A large number of rotating anode and microfocus X-ray units are discussed or referred to in a special report by DeBarr, A. E. and MacArthur, I. British Journal of Applied Physs.JLRLQQQ0259i One of the re ere ces. sited.

therein DuMond, J. W. M. and Youtz, J P., Review of Scientific Instruments, 8, 291 (1937) describes a large, demountable X-ray generator with an anode mounted on gimbals at the end of a long supporting pipe to pivot with a circular motion about the beam axis, but most of the generators with moving anodes have axially flanged disc anodes that rotate on an axis perpendicular to the tube axis.

Most sealed-off tubes have been made for years with four windows through which X-ray beams could radiate from the target area on the internal anode. A tube of this type is shown in U. S. Pat. 2,665,391. Usually the cross-section of the electron beam at the area of impact on the target is an elongated rectangle having a length to width ratio in the range from about 4:1 to about :1, although in some cases the beam is circular. If the tube has four windows, they are normally placed so that two of them are in line with the long dimension of the impact area and the other two are at 90 to the long dimension.

Sealed-off X-ray tubes have been made according to certain specific sizes and configurations, and there are many X-ray generators built to conform to the tube sizes and configurations. Such generators are, for example, of the type shown in U. S. Pat. No. 2,453,798. In addition to the generators themselves, there are numerous pieces of auxiliary equipment built specifically to fit onto these generators. Examples of such auxiliary equipment include the diffraction apparatus shown in U.S. Pat. No. 2,549,987, the powder diffraction camera shown in U. S. Pat. No. 2,514,791, and the alignment apparatus shown in U. S. Pat. No. 2,709,752.

Therefore, it is one of the objects of the present invention to provide a sealed-off X-ray tube having a movable target in an envelope that will fit onto existing X-ray generators built for fixed-target, sealed-off tubes and can be used with existing auxiliary equipment.

All of the windows of sealed-off tubes are normally placed so that only those X-rays emitted at relatively low take-off angles from the target, i.e. paths that are either parallel or nearly parallel to the surface of the target, pass through the windows. These take-off angles are of the order of 0 to about 15, and it is important that the target area from which X-rays are emitted at such low angles be as smooth as possible since any roughness would constitute peaks of solid target material extending into the path of the emitted X-rays. As a result, sealed-off X-ray tubes eventually become unusable either because the cathode material is used up or the target becomes eroded. Normally the cathode lasts much longer than the target, and it is erosion of the latter that usually determines the end point of the life at the tube.

It is another important object of the present invention to increase substantially the life of a sealed-off X-ray tube by making the target movable so that different areas can be utilized in succession until each in turn becomes eroded to the point where it can no longer function satisfactorily.

X-ray diffraction apparatus is inherently sensitive to certain variations in the X-ray source. This makes it important that any movable target be so constructed as to present, at all times, virtually a constant electron optical environment to the electron beam so that the resultant impact point will generate, as nearly as possible, a constant amount of radiation both in terms of intensity and of orientation or direction.

It is therefore another object of the present invention to provide an X-ray tube with a target which is a small portion of a spherical surface concentric with the pivot point about which the target moves.

It is therefore another object of the present invention to provide an X-ray tube with a target which is a small portion of the total surface.

Since the target of the X-ray tube of the present invention can be moved from one location to another, it can be overloaded by being subjected to an electron beam of much higher intensity than would be permissible in the case of a fixed anode. This not only results in the generation of higher intensity X-rays but makes possible, for the first time, long life sealed-off mi- .crofocus tubes. For example, a target capable of fitting into the envelope of a standard sealedoff tube but op-' erated with an electron gun capable of forming a microfocus spot will have as many as or more positions that can form impact points for the microfocus beam. These spots can be spaced along a spiral path to cover a large part of the surface of the target. The expected lifetime of each target position before the tiny impact area becomes pitted or eroded is of the order of 100 to 300 hours. Since there may be room for 100 or more such impact areas the total time before the anode is used up may exceed the life of the cathode so that contrary to the practice at the present time, the cathode may form the life-limiting factor of the tube. However, it is expected that the filament can easily last more than 1,000 hours. Therefore, a sealed-off tube according to the present invention and built in microfocus form will have such a long life that it is economic to throw it away like an ordinary worn out sealed-off tube and unlike existing microfocus units that must be dismantled and rebuilt.

BRIEF DESCRIPTION OF THE INVENTION The tube of the present invention comprises an evacuated envelope, part of which is normally made of rigid metal with four X-ray permeable windows in it. The body of this metal portion is a hollow cylinder closed at one end by a rigid metal wall andsealed at the other end to a glass insulating cylinder that supports the filament, or cathode, and provides a long enough leakage path to permit a high voltage to be applied between the cathode and the anode.

The anode assembly is suspended within the tube from the rigid wall opposite the cathode. At the end of the anode facing the cathode is a spherical target surface, the perimeter of which is sealed to one end of a bellows. The other end of the bellows is sealed to the rigid end wall of the tube to form part of the vacuumtight structure. Within the bellows is a rigid member that supports the target and simultaneously serves as a conduit for cooling fluid. The complete cooling conduit consists of a concentric set of hollow pipes, the inner one of'which extends near the back surface of the target to direct cooling fluid against the target. Surrounding the inner pipe is an outer pipe which serves as the exit conduit for fluid that has adsorbed heat from the target. The entire cooling conduit system ridigly supports the target and is sealed water-tight so that none ofthe cooling fluid reaches the inner surface of the sur rounding bellows.

The concentric cooling and support conduit structure extends through a spherical bearing, the outer race of which is rigidly held in the end wall of the tube. The spherical bearing permits the anode assembly, which includes the target, its associated rigid conduit and support structure, and the bellows, to pivot in any direction around a complete circle. The maximum angle of deflection is determined by the geometry of the tube but is normally of the order of about 7. In addition to its primary purpose of serving as part of the vacuumtight tube enclosure, the bellows also prevents the target from rotating about its own axis. For this reason the motion of the target may be described as a precessing motion.

The stem of the central support structure extends beyond the intake and outlet coolant connections and may be attached to a rotary driving device comprising a motor and an eccentric support for a second spherical bearing. The precessional motion of the entire anode, or, more specifically, the deflection angle of the anode assembly, is determined by the relative geometry of the two spherical bearings. Instead of using a motor to cause the stern of the support structure to precess, the same motion may be produced by manually moving the stem to certain prescribed locations. These locations may be determined by a detent structure. As a further alternative, the extent of offset of the second spherical bearing may be varied continuously as the anode assembly precesses, thereby causing the center of the target to follow a spiral path.

In an alternative embodiment the target surface is flat.

The concentric cooling and support conduit structure extends through a spring and a spring retaining member which are fastened at the end wall of the tube. The spring which is compressed by the spring retaining member against a flange on the anode assembly maintains the anode assembly which includes the target, its associated rigid conduit and support structure, and the bellows, in substantially a stable position in the direction of the axis of the tube.

The stem of the central support structure extends beyond the intake and outlet coolant connections and may be attached to a reciprocal driving device comprising a motor and a driver. Instead of using a motor to cause the stem of the support structure to reciprocally move, the same motion may be produced by manually moving the stem to certain prescribed locations. These locations may be determined by a detent structure.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in connection with the drawings in which:

FIG. 1 is a side view of a sealed-off tube constructed according to the invention with part of the side wall broken away to show the interior construction;

FIG. 2 is an end view of the tube in FIG. 1;

FIG. 3 is a cross-sectional view of the anode of the tube in FIG. 1;

FIG. 4 is a cross-sectional view of the tube in FIG. 1 along the line 44 and showing one position of the target within the tube; and

FIG. 5 illustrates a series of target areas on the target in FIG. 4;

FIG. 6 is a side view of a sealed-off tube of an alternate embodiment constructed according to the invention with partthe side wall broken away to show the interior construction;

FIG. 7 is an end view of the tube in FIG. 6;

FIG. 8 is a cross-sectional view of the anode of the tube in FIG. 6;

FIG. 9 is a cross-sectional view of the tube in FIG. 6 along the line 99 and showing one position of the target within the tube; and

FIG. 10 illustrates a series of target areas on the target in FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION The X-ray tube in FIG. 1 is in the form of an elongated cylinder with a metal body 11 at one end. The body is a rigid structure with a circularly cylindrical channel extending through it. Extending from one end of this hollow metal body and sealed to it is a hollow cylindrical tube 12, the other end of which is sealed to a re-entrant glass cylinder 13 that forms a support for a filamentary cathode 14 within the cylindrical portion 12. At the bottom end of the glass member is a seal-off nipple 16 which is the remnant of an exhaust tubulation through which air is removed from the body of the X-ray tube during the final stage of manufacture. The cathode is surrounded by a beam-forming electrode structure 17 which helps to define the focus of electrons emitted by the cathode. Various known embodimerits of beam-forming structures may be ued to produce electron beams of any desired focal qualities from regular focus to microfocus.

At the top of the body 11 is a rigid disc 18 on which the anode structure is supported. The rim of the disc 18 is sealed to the body 11. The anode structure comprises a bellows 19, one end of which is sealed to the disc 18, a target 21, and various support and coolant conduit members. The periphery of the target is sealed to a connecting ring 22 to which the bellows 19 is also sealed, and these components, together with the body 11, the tube 12, the re-entrant glass cylinder 13, and the disc 18 form the complete vacuum-tight enclosure.

The target 21 has a spherical, convex front surface 23 and a back surface that is almost concentric with the front surface.

The support and coolant conduit members in the complete anode structure include a support post 24 that extends through the inner part 26 of a spherical bearing. The outer part of the bearing is a race 27 which is press-fitted into a recess in the disc 18. The post 24 is hollow and has conduits in it, one of which is connected to an inlet pipe 28 and the other to an outlet pipe 29. The inlet pipe 28 is shown connected by a flexible hose 31 to another pipe 32 that extends into the member 11. A similar hose, which is not shown, would also connect the pipe 29 to another pipe 33 which is supported in the opposite side of the member 11.

The central portion of the post 24 extends into a second spherical bearing comprising a spherical segment 34 held in a race 36 in an eccentric connector 37. Thelatteris attached to the output shaft 38 of a motor 39.

The post 24 is shown tilted slightly to one side so that its axis 41 is at an angle of about 7 with respect to the axis 42 that extends through the center of the spherical race 27. The axes 41 and 42 cross each other at the pivot point 43 which is also the center of the spherical segment 26, and the axis 42 continues through the 'center of the output shaft 38 of the motor. A sheet metal cap 44 is attached to the upper surface of the disc 18 and the member 11 and supports the motor 39. This shell 44 has two

slots

46 and 47 to permit the inlet hose 31 and the outlet hose 30 to pass through in order to make connection with the

pipes

28 and 29.

Electrons from the cathode 14 are formed into a beam 48 on the axis 42. This beam strikes whichever part of the spherical surface 23 happens to be on the axis 42. The electrons striking this impact area cause the emission of X-rays in all directions, but only certain X-rays are able to escape from the cylindrical member 12. These are the X-rays that can pass through any one of four windows. of which only three windows 49-51 are shown in the drawing. X-rays can actually be emitted at a grazing angle and still pass through the windows 49-51. The grazing angle is parallel to the surface 23 within the area struck by the beam 48. However, the centers of the windows 49 51 lie on a plane slightly below this level so that a line through the centersof these windows and intersecting the axis 42 at the surface 23 would make an angle of about 6 with respect to that part of the surface 23 of the target. This is the same angular relationship that is present in existing fixed anode tubes of the same external configuration. Specifically, the windows 49 -.51 are so located that the plane passing through their centers is at a predetermined distance from the bottom surface 52 of the member 11. Apparatus in which tubes of this type may be used are provided with receptacles that have matching surfaces and ports spaced according to this dimension.

FIG. 2 shows an end view of the tube in FIG. 1 and illustrates one way in which coolant connections are made. The sides of the body 11 are flat and form a square. The

pipes

32 and 33 are at diametrically opposite corners of the square and connect with fluid passages (not shown) that emerge from the body 11 in the same locations as the fluid passages in present-day sealed-off X-ray tubes having fixed anodes. The flexible hose 31 that connects the pipe 32 to the inlet pipe 28 is shown, as is a similar hose 30 that connects the outlet pipe 29 to the pipe 33. These flexible hoses are made relatively long so that they will be flexible enough to accommodate movement of the anode structure.

FIG. 3 is a cross-sectional view of the anode portion alone. In this enlarged view the target 23 is shown centered in the hollow metal body 11 rather than being at an angle thereto.

The surface 23 of the target is rigidly attached to the end cap 22 which in turn is positioned by an internal spider 53 which in this case has three points to position the end cap with respect to the hollow center support post 24. The axis 41 of the support post passes directly through the center of the spherical surface 23 and these components are rigidly joined together with each other and with the outer race 27 of the main spherical bearing before the final finishing of the spherical surface 23. In this way the spherical surface may be made precisely concentric with the pivot point 43 at the center of the spherical segment 26 of the main spherical bearing.

Surrounding the support post 24 is a hollow tubular member 54 which is also sealed vacuum tight to the cylindrical part 22 of the target. At the upper end of the support post 24 above the spherical segment 26 is an entrance port for the coolant inlet pipe 28. The end of the inlet pipe is slightly bevelled to direct coolant, usually water, down through the center of the support post 24 in the direction indicated by the arrows. At the bottom, the coolant flows radially outwardly and against the concave inner surface 56 of the target to cool the target by direct flow of the coolant. Thereafter, the coolant flows up between the post 24 and the surrounding tube 54 to the outlet pipe 29 which is sealed at the upper end of the outer pipe and is also slightly bevelled to facilitate entry of the coolant.

The bellows 19 is directly sealed to the disc 18 and to the cylindrical part 22 of the target but is not subjected to any coolant pressure since the support post 24, the surrounding hollow pipe 54, the inlet and

outlet pipes

28 and 29, and the target components 21-23 form a sealed conduit system. As a result, the bellows is only subjected to atmospheric pressure which is the difference in pressure between the inside of the bellows and the evacuated part of the tube which is. outside of the bellows.

FIG. 4 shows a view of the target surface 23 looking directly upwardly along the axis of the hollow cylindrical tube 12 when the target is displaced a maximum amount in one direction. In this drawing the target is displaced upwardly. The impact area of the electron beam is indicated by a small rectangle 57 which, as may be seen, is located on the axis of the cylindrical tube 12.,

However, this impact point does not strike the center of the target 23 because the latter is displaced upwardly a distance d. As the target 23 precesses along a circular path, its center follows the circle 58 indicated in dotted lines but the center of impact area 57 follows a different circle 59 also indicated in dotted lines.

FIG. shows the locus traced out by the impact point 57 as target 23 precesses. The impact point 57 is indicated in the same position as shown in FIG. 4. Other impact areas are indicated by horizontal lines spaced around the circle 59 drawn through the centers of all of these lines. It is clear that there can easily be or more entirely separate impact areas each of which can be used until it becomes eroded. Thus, the tube has a life that may, at least theoretically, be 20 times as great as the life of an ordinary sealed-off X-ray tube with a fixed target.

The angular position of the target as it moves around a circle may be determined by stepping the shaft 38 of the motor 39 in FIG. 1 to certain specific locations or it may be done by moving the upper end of the support post 24 by hand. In the latter case it may be desirable to provide a detent ring adjacent the upper end of the support post to fix the locations to which the post can move.

As the post is moving by the motor 39, it is also possible to allow the motor to rotate continuously at a speed of approximately one revolution per second to perhaps six revolutions per second. The higher the speed of rotation the greater the chance of encountering resonant vibrations, but the cooling effect on the target 23 is better when the electron beam does not strike one spot for a very long time.

It is also possible to adjust the eccentricity of the eccentric connector 37 to change continuously so that the center of the target 23 will follow a spiral path instead of a circular or linear one. In this way, and by means of a slight and well-known change in the electron optical structure around the filament 14, a sharply focused beam, which is also referred to as a microfocus beam may be directed to as many as 100 different locations over the surface of the target. Each of these locations could accept normal beam intensity for as much as 100 hours or more and the tube life would be many times as great as the life of a normal tube with a fixed anode or atube that was made in a demountable form, as micro-focus tubes normally are.

In an alternate embodiment, the'X-ray tube in FIG. 6 is in the form of an elongated cylinder with a metal body 111 at one end. The body is a rigid structure with a circularly cylindrical channel extending through it. Extending from one end of this hollow metal body and sealed to it is a hollow cylindrical tube 112, the other end of which is sealed to a re-entrant glass cylinder 113 that forms a support for a filamentary cathode 114 within the cylindrical portion 112. At the bottom end of the glass member is a seal-off nipple 116 which is the remnant of an exhaust tubulation through which air is removed from the body of the X-ray tube during the final stage of manufacture. The cathode is surrounded by a beam forming electrode structure 117 which helps to define the focus of electrons emitted by the cathode. Various known embodiments of beam-forming structures may be used to produce electron beams of any desired focal quality from regular focus to microfocus.

At the top of the body 111 is a rigid disc 118 on which the anode structure is supported. The rim of the disc 118 is sealed to the body 111. The anode structure comprises a bellows 119, one end of which is sealed to the disc 118, a target 121, and various support and coolant conduit members. The periphery of the target is sealed to a connecting ring 122 to which the bellows 119 is also sealed, and these components, together with the body 111, the tube 112, the re-entrant glass cylinder 113, and the disc 118 form the complete vacuumtight enclosure.

The target 121 has a flat front surface 123 and a back surface that is parallel with the front surface.

The support and coolant conduit members in the complete anode structure include a support post 124 that extends through a spring retaining member 126 which is mated to a shoulder 127 of the disc 118 by the threaded portions or other known means. A spring 101 is compressed by the spring retaining member 126 against the flange 102 of the support post 124 and the flange 102 is'in turn held firmly against the top surface 103 of the disc 118. The target 121 is thus maintained for movement only in a lateral direction i.e. in a direction perpendicular to the axis of the tube 112 and is prevented from twisting by the attached bellows 119. The post 124 is hollow and has conduits in it, one of which is connected to an inlet pipe 128 and the other to an outlet pipe 129. The inlet pipe 128 is shown connected by a flexible hose 131 to another pipe 132 that extends into the member 111. A similar hose, which is not shown, would also connect the pipe 129 to another pipe 133 which is supported in the opposite side of the member 111.

The central portion of the post 124 forms a follower 106 which extends into a guide comprising an inverted cup 134 supported from an eccentric connector 137. The latter is attached to the output shaft of a motor 139.

A sheet metal cap 144 is attached to the upper surface of the disc 118 and the member 1 l l and supports the motor 139. This shell 144 has two

slots

146 and 147 to permit the inlet hose 131 and the outlet hose to pass through in order to make connection with the

pipes

128 and 129. Likewise the spring retaining member 118 has two

slots

108 and 109 to permit the inlet hose 131 and the outlet hose 130 to pass through for connection with the

pipes

128 and 129.

Electrons from the cathode 114 are formed into a beam 148 on the axis 142 of the X-ray tube. This beam strikes whichever part of the surface 123 which happens to be on the axis 142. The electrons striking this impact area cause the emission of X-rays in all directions, but only certain X-rays are able to escape from the cylindrical member 112. These are the X-rays that can pass through any one of four windows, of which only three windows 149-151 are shown in the drawing. X-rays can actually be emitted at a grazing angle and still pass through the windows 149-151. The grazing angle is parallel to the surface 123 within the area struck by the beam 148. However, the centers of the windows 149 151 lie on a plane slightly below this level so that a line through the centers of these windows and intersecting the axis 142 at the surface 123 would make an angle of about 6 with respect to that part of the surface 123 of the target. This is the same angular relationship that is present in existing fixed anode tubes of the same external configuration. Specifically, the windows 149 151 are so located that the plane passing through their centers is at a pre-determined distance from the bottom surface 152 of the member 111. Apparatus in which tubes of this type may be used are provided with receptacles that have matching surfaces and ports spaced according to this dimension.

FIG. 7 shows an end view of the tube in FIG. 6 and illustrates one way in which coolant connections are made The sides of the body 111 are flat and form a square. The

pipes

132 and 133 are at diametrically opposite corners of the square and connect with fluid passages (not shown) that emerge from the body 111 in the same locations as the fluid passages in present-day sealed-off X-ray tubes having fixed anodes. The flexible hose 131 that connects the pipe 132 to the inlet pipe 128 is shown, as is a similar hose 130 that connects the outlet pipe 129 to the pipe 133. These flexible hoses are made relatively long so that they will be flexible enough to accomodate movement of the anode structure.

FIG. 8 is a cross-sectional view of the anode portion alone. The surface 123 of the target is rigidly attached to the connecting ring 122 which in turn is pOsitioned.

by an internal spider 153.

The support post 124 includes a hollow tubular member 154 which is also sealed vacuum tight by the connecting ring 122 to the cylindrical part of the target. At the upper end of the support post 124 above the flange 102 is an entrance port for the coolant inlet pipe 128. The end of the inlet pipe is slightly bevelled to direct coolant, usually water, down through the center of the suport post 124 in the direction indicated by the ar-' rows. At the bottom, the coolant flows radially outwardly and against the inner surface 156 of the target to cool the target by direct flow of the coolant. Thereafter the coolant flows up a concentric outer channel of post 124 which is also slightly bevelled at the top to facilitate exit of the coolant.

The bellows 119 is directly sealed to the disc 118 and to the cylindrical part of the target where it is held by the connecting ring 122 but is not subjected to any coolant pressure since the support post 124, including the surrounding hollow pipe 154, the inlet and

outlet pipes

128 and 129, and the target components l21-123 form a sealed conduit system. As a result, the bellows is only subjected to atmospheric pressure which is the difference in pressure between the inside of the bellows and the evacuated part of the tube which is outside the bellows.

FIG. 9 shows a view of the target surface 123 looking directly upwardly along the axis of the hollow cylindrical tube 112 when the target is displaced in one direction. In this drawing the target is displaced upwardly. The impact area of the electron beam is indicated by a small rectangle 157 which, as may be seen, is located on the axis of the cylindrical tube 112. However, this impact point does not strike the center of the target 123 because the latter is displaced upwardly a distance d. As the target 123 is displaced downwardly, new loci are traced out which are shown in FIG. 10.

FIG. 10 shows the locus traced out by the impact point 157 as the target 123 is displaced linearly in one direction. The impact point 157 is indicated in the same position as shown in FIG. 9. Other impact areas are indicated by horizontal lines in the rectangle 159 drawn through the periphery of all of these lines. It is clear that there can easily be or more entirely separate impact areas each of which can be used until it becomes eroded. Thus, the tube has a life that may, at least theoretically, be 20 times as great as the life of an ordinary sealed-off X-ray tube with a fixed target.

As the post 124 is moved by the motor 139, it is also possible to allow the motor to move the post 124 in the X and Y direction simultaneously in a circle or spiral thus increasing the number of impact areas.

It should be noted that although specific embodiments have been disclosed, they are merely illustrative and are not intended to limit the scope of the invention.

1. A sealed-off X-ray tube, comprising:

an evacuated envelope having a rigid wall and an X-ray permeable window;

an electron beam source for generating an electron beam;

a target having a flat surface facing said electron beam, said surface defining a plane;

rigid support means slidably supporting said target from said rigid wall to permit said target to move only in directions which maintain said flat surface within said defined plane; and

a bellows sealed vacuum-tight to said rigid wall and vacuum-tight to said target.

2. A scaled-off X-ray tube as claimed in claim I wherein said support means includes a post rigidly attached at one end to said target; said post having a flange; and

a spring maintaining said flange in sliding contact with said rigid wall.

3. A sealed-off X-ray tube as claimed in claim 2 wherein said flange includes a sliding surface and wherein said rigid wall includes a sliding surface, both of which are in a plane parallel to said defined plane.

4. A sealed-off X-ray tube as claimed in claim 3 wherein said post has conduits for transporting coolant fluid to and from said target.

5. A sealed-off X-ray tube as claimed in claim 4 further comprising a motor in mechanical communication with said post for moving said post from one position to another thereby also moving said flat surface from one position to another within said defined plane.

6. A sealed-off X-ray tube as claimed in claim 5 wherein the shaft of said motor is eccentrically coupled with said post for circular movement of said post and flat surface without substantial rotation thereof.

7. A sealed-off X-ray tube as claimed in claim 1 further comprising a motor in mechanical communication with said rigid support meanS for moving said flat surface from one position to another within said defined plane.

8. A sealed-off X-ray tube as claimed in claim 7 wherein said motor is coupled with said rigid support means for movement of said flat surface in one dimension only.

9. A sealed-off X-ray tube as claimed in claim 7 wherein said motor is coupled with said rigid support means for movement of said flat surface in both dimensions of said defined plane.

10. A sealed-off X-ray tube as claimed in claim 9 wherein said motor is coupled with said rigid support means for gyratory movement of said flat surface within said'dcfined plane.

UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIQN PATENT NO. I 3 ,794,872

DATED February 26, 1974 INVENTOR(S) I DAVID J. HAAS, JEROME PICI-IERI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 9, line 19, "pOsitioned" should be positioned- Figure 8, the line indicated by reference numeral 103 on the right and the corresponding line on the left should extend to the left and right respectively across the dark and light hatched areas and the dark and light hatched areas below these extended lines should be blank.

Figure 10, the portions of the horizontal lines 157 lying outside the dashed rectangle 159 should be removed.

Claim 7, line 3, "meanS" should be -means--.

Signed and Sealed this First D y 0f March 1977 [SEAL] Arrest:

RUTH c. MASON C.MARSHALL DANN Arresting Officer Commissioner u/Parenrs and Trademarks

Claims

1. A sealed-off X-ray tube, comprising: an evacuated envelope having a rigid wall and an X-ray permeable window; an electron beam source for generating an electron beam; a target having a flat surface facing said electron beam, said surface defining a plane; rigid support means slidably supporting said target from said rigid wall to permit said target to move only in directions which maintain said flat surface within said defined plane; and a bellows sealed vacuum-tight to said rigid wall and vacuumtight to said target.

2. A sealed-off X-ray tube as claimed in claim 1 wherein said support means includes a post rigidly attached at one end to said target; said post having a flange; and a spring maintaining said flange in sliding contact with said rigid wall.

10. A sealed-off X-ray tube as claimed in claim 9 wherein said motor is coupled with said rigid support means for gyratory movement of said flat surface within said defined plane.