U.S. patent number 3,794,872 [Application Number 05/264,805] was granted by the patent office on 1974-02-26 for moving target spring loaded x-ray tube.
Invention is credited to David J. Haas, Jerome Pichert.
United States Patent |
3,794,872 |
Haas , et al. |
February 26, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
MOVING TARGET SPRING LOADED X-RAY TUBE
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.
Inventors: |
Haas; David J. (Stamford,
CT), Pichert; Jerome (Centerport, NY) |
Family
ID: |
23007679 |
Appl.
No.: |
05/264,805 |
Filed: |
June 21, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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138627 |
Apr 29, 1971 |
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Current U.S.
Class: |
378/141; 313/32;
378/126; 378/125 |
Current CPC
Class: |
H01J
35/24 (20130101) |
Current International
Class: |
H01J
35/00 (20060101); H01J 35/24 (20060101); H01j
035/10 () |
Field of
Search: |
;313/60 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lake; Roy
Assistant Examiner: Hostetter; Darwin R.
Attorney, Agent or Firm: Trifari; Frank R.
Parent Case Text
This is a continuation-in-part of application Ser. No. 138,627
filed Apr. 29, 1971 now U.S. Pat. No. 3,689,790.
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 vacuum-tight
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.
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 defined plane.
Description
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 three types 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.sup.2 for fine focus
tubes and a maximum total loading of about 2,000 watts/mm.sup.2.
Rotating anode tubes are noted for their brightness on fine focus
spots. They have a maximum specific loading of about 7 kw/mm.sup.2,
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 .times. 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 loading may be of the order of 30 kw/mm.sup.2, 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 a sealed-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 Physics, 1, p. 305 (1950). One of the references
cited 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 20:1,
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.degree. 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.degree. to about 15.degree.,
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 microfocus tubes. For
example, a target capable of fitting into the envelope of a
standard sealed-off tube but operated with an electron gun capable
of forming a microfocus spot will have as many as 100 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 and sealed 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 vacuum-tight
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 of the cooling fluid reaches the inner
surface of the surrounding 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.degree.. In addition to its primary purpose of
serving as part of the vacuum-tight 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 stem 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 4--4 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 part the
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 9--9 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 embodiments 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. The latteris 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.degree. 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 centers of these windows and intersecting the axis
42 at the surface 23 would make an angle of about 6.degree. 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 pre-determined 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 inpact area
57 follows a different circle 59 also indicated in dotted
lines.
FIG. 5 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 20 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 a tube 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
vacuum-tight 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 attachcd 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 111 and supports the motor 139. This shell 144
has two slots 146 and 147 to permit the inlet hose 131 and the
outlet hose 130 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.degree. 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 arrows. 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
121-123 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 20 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.
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