CA1089909A - Internally shielded x-ray tube - Google Patents
Internally shielded x-ray tubeInfo
- Publication number
- CA1089909A CA1089909A CA286,034A CA286034A CA1089909A CA 1089909 A CA1089909 A CA 1089909A CA 286034 A CA286034 A CA 286034A CA 1089909 A CA1089909 A CA 1089909A
- Authority
- CA
- Canada
- Prior art keywords
- target
- envelope
- ray
- ray tube
- electron gun
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- X-Ray Techniques (AREA)
Abstract
ABSTRACT
The present invention provides an X-ray tube which produces less external stray radiation than conventional tubes. It includes the usual evacuated envelope, and an X-ray generating target located within the envelope. An electron gun is positioned within the envelope to direct a stream of electrons at the target. The X-rays generated at the target are passed through a window to a point of use beyond the envelope. The major improvement of the present invention consists in providing a high density attenuator within the envelope which has an axial bore in line with the direction of the electron stream and has at least a substantial portion of its axial length extending into the space between the target and the electron gun.
The configuration of the axial bore and its disposition as stated serves to attenuate the high energy photons which do not leave the envelope through the window.
The present invention provides an X-ray tube which produces less external stray radiation than conventional tubes. It includes the usual evacuated envelope, and an X-ray generating target located within the envelope. An electron gun is positioned within the envelope to direct a stream of electrons at the target. The X-rays generated at the target are passed through a window to a point of use beyond the envelope. The major improvement of the present invention consists in providing a high density attenuator within the envelope which has an axial bore in line with the direction of the electron stream and has at least a substantial portion of its axial length extending into the space between the target and the electron gun.
The configuration of the axial bore and its disposition as stated serves to attenuate the high energy photons which do not leave the envelope through the window.
Description
9~
SPECIFICATION
This invention is in the field of internally shielded X-ray tubes wherein a high density attenuating means is located in proximity to the path of electrons emanating from the tube's electron gun, and also at or near the target area thereby reducing S the need for large amounts oE external shielding.
In any X-ray tube, X-rays are produced by accelerating the electrons to a high velocity by an electrostatic field and then suddenly stopping them by collision with a solid target interposed in their path. The X-rays which result radiate in all directions from the spot of the target where the collisions take place. The X-rays are due to the rnutual interaction of the fast moving electrons with the electrons and positively charged nuclei which constitute the atoms of the targetO
The first high vacuum X-ray tube used a hot tungsten -~
fllament cathode and a solid tungsten targetO This hot cathode, high vacuum type of X-ray tube permitted stable and reproducible .
operation with relatively high voltages and large masses of metals~
The vacuum was sufficiently good so that positive ions did not play either an essential or a harmful role in the tube operation.
Notwithstanding the wide acceptance of such high vacuum X-ray tubes in recent years, these tubes still have stray radiation problerns resulting from high energy photons which are generated at the target and which do not find their way out the envelope through the window~ Consequently, it has been common practice tO
use large amounts of external shielding to attenuate these X-ray photons outside of the evacuated envelope,. The necessity of `, . .
..
such shielding significantly incre~ses the cost and the bulk of the X-ray tube.
The present invention provides a means for reducing the amount of external shielding required for high vacuum X-ray tubes by accomplishing the shielding internally.
To this end, there is provided according to the present invention an X-ray tube comprising an evacuated envelope, an X-ray generating target within said envelope, an electron gun positioned within said envelope to direct a stream of electrons at said target, window means arranged to direct the resulting X-rays from said target beyond said envelope, a sleeve com-posed o a high density attenuating material disposed about said target, said sleeve having an aperture therein permitting passage of X-rays rom said target through said window means, and high dsnsity attenuating means disposed behind and peripherally around said electron gun to attenuate stray high energy photons.
In one form of the invention, the target is substantially perpen-dicular to the stream of electrons and the high density attenuating means ~ -is positioned coaxially with the stream and also behind the target.
In another form of the invention, the target is posi~ioned at a smallangle to the hori~ontal and the high density attenuating means is positioned along the path of the stream of electrons and also behind the target.
In a further modified form of the invention, the target means and the high d0nsity attenuating means are part of the same integral structure. -Other features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although ~ - `
variations and modifications may be effected without departing from the ; spirit and scope of the novel concepts of the disclosure, and in which:
_3_ 9~}9 Figure 1 is a vertical cross-sectional view of one form of X-ray tube which can be used in accordance with the present invention;
Figure 2 is a fragmentary cross-sectional view of the target area of a modiEied form of ~he present invention; and Figure 3 is a partial cross-sectional view of still another form of the invention wherein the target area and the shielding means are integral with each other.
In Figure 1 reference numeral 10 indicates generally an improved X-ray tube according to the present invention having a solid ceramic insulator base 11 through which there extends an electron gun generally indicated at reference numeral 12, said electron gun including a heated filament 13 for generating electrons, and a focusing electrode 14 which directs a stream of such elec-lS trons toward an anode assembly including an X-ray attenuating anode tip 15 having an axial bore 16 through which the beam of . . . :
electrons is passedO The anode assernbly also includes an anode body 17 having an axial bore 18 in registry with the bore 16 to direct the bearn of electrons toward a target 19 composed of a heavy metal or heavy ceramic of high atomic weight. As is well known in the art, any target material should have a high atomic number to give best X-ray efficiency, a high melting point and high thermal conductivity to permit maximum energies for a given . .
size of focal spot, and a low vapor pressure to reduce the rate of ~evaporation of the metal cn the walls of the ceramic envelope.
The high energy electron beam striking the target 19 causes X-ray radiation in all directions from the spot on the target - ~' - 4 ~
:: ;~-where the collisions take place~ The X-ray tube of Figure 1 is provided with a window 20 composed of a material such as beryllium or ceramic which is transparent ~o X-ray radiation and through which the X-rays can leave the confines of the tube to the area at which they are used. Regardless of the spatial orientation of the target area and the window, however, there is unavoidably some X-ray radiation back into the bore 18, behind the target 19, and even back into the electron gun assembly~ To attenuate such radiation, I provide a target backing composed of a high density X-ray a~tenuating means such as tungsten, tantalum, depleted uranium, zirconium or an attenuating ceramic material such as uranium oxideO For tubes operating a~ a reasonably high power level, it is highly desirable to use a composite of the attenuating material and a good heat conductor such as coF~3er. Such a composite is illustrated in Figure 1 whexe the target 19 is shown, backed by a copper layer 27 having contact passages 28 formed ~therein, and the copper in turn being backed by an attenuating layer 290 An additional copper layer 30 is formed over the attenuating layer 290 An exhaust tube 23 also is confined within the target backing 27. The exhaust tube 23 is used to evacuate the interior OI the tube to a high vacuum whereupon it is sealed :~ off by closing the end of the OHFC copper tube, and covered with . a tube cap 24~ Radiation which is directed back along the path of the electron beam is attenuated by the anode support 17 and anode tip 15 which is also composed of a heavy metal or ceramic OI the type mentionedO Finally, radiation which proceeds far enough to ~ . .
. '.
l _ 5 _ :-.
- ~l(31 3g9~
`
strike the electron gun assembly 12 is attenuated by means of a - ring 25 and a disk 26 composed of the high density material and surrounding the focusing electrode 140 With the attenuating means disposed throughout the tube as mentioned, very little stray radia-tion escapes and any external shielding for the tube can be reduced to a minimum~ -In the form of the invention shown in Figure 2, there is provided an anode housing 31 composed of copper or other highly heat conductive materialO A target structure consisting of a target plate 32 is disposed at a small angle to the horizontal with respect to the electron beam which is directed at it in the direction of the arrow 33D The target 32 is supported on a target .
support 34 composed of copper, a copper attenuating material composite or one of the aforementioned high density ~attenuating materials~ One or more fluid flow passages 35 iS provided in the target support to cool the target structure during operationr A . .
line 36 is provided to connect the interior of ~he tube assembly to a source of high vacuum (not shown). .:
The target 32 is substantially surrounded by a sleeve ~ .
37 composed of high density attenuating materials such as tungsten, tantalum, depleted uranium, zirconium, or uranium o~ide. The sleeve 37 is provided with an apexture 38 along a. relatively :;
llmited portion of its circumference to provide for egress of the X-rays generated by the electron beam striking the target 32. An X-ray pervious windo~7 39 directs the X-ray radiation out of the - .
tube to its point of useO A mounting flange 40 is provided to .;
;: :
- 6 ~
.
~ 99~ :
mount the anode structure onto a ceramic insulator of the type shown in Figure lo A furthex modified form of the invention is illustrated in Figure 3~ In this form, there is provided a high density zirconium or uranium oxide ceramic insulator 41 in which there is disp~sed an electron gun 42 including a heated filament 43 and a focusing electrode 44~ The anode structure in this embodiment talces the form of an anode body member 45 composed of copper or the like and having a flange portion 46 for mounting against the -ceramic insulator 410 A line 47 communicates the interior of the X-ray tube to a source of vacuumD
In the form of the invention shown in Figure 3, the target and the shield are part of ~he same integral structure , consisting of a cylindrical portion 48~ surrounding the path of electron flow from the electron gun, and terminating in a generally spherical head 49 in ~hich there is provided an inclined target face 50~ Co~ling passages 51 are provided in this portion of the anode to abstract heat from the target area. A window 52 directs the X-ray radiation from the target area 50 outwardly. Additional protection against X-ray radiation is provided by means of a ring $3 of X-ray attenuating material located about the focusing ring 44.
In any of the forms of the invention shown, the ceramic insulator itself can include a~tenua~ing oxides such as uranium-~: :
, o~{ide, zirconium oxide or other high density, vacuum stable 25 ~ materials. The ceramic then absorbs secondary X-rays generate~
:
o n the parts of the tube centèred within the ceramic and still ~
. .
further reduces ~he stray radiation.
,: : : ~ ,', ., , ; .
. .. . ..... . .
~99~
The improved X-ray tubes of the present invention reduce the cost of shielding and drastically reduce shielding weight for the same amount of stray radiation~ ~urthermore, from a product safety standpoint, the shielding is failsafe as it cannot be removed without making the X~ray tube inoperative~
` .. .... .. .
.
. ~
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':' . :
SPECIFICATION
This invention is in the field of internally shielded X-ray tubes wherein a high density attenuating means is located in proximity to the path of electrons emanating from the tube's electron gun, and also at or near the target area thereby reducing S the need for large amounts oE external shielding.
In any X-ray tube, X-rays are produced by accelerating the electrons to a high velocity by an electrostatic field and then suddenly stopping them by collision with a solid target interposed in their path. The X-rays which result radiate in all directions from the spot of the target where the collisions take place. The X-rays are due to the rnutual interaction of the fast moving electrons with the electrons and positively charged nuclei which constitute the atoms of the targetO
The first high vacuum X-ray tube used a hot tungsten -~
fllament cathode and a solid tungsten targetO This hot cathode, high vacuum type of X-ray tube permitted stable and reproducible .
operation with relatively high voltages and large masses of metals~
The vacuum was sufficiently good so that positive ions did not play either an essential or a harmful role in the tube operation.
Notwithstanding the wide acceptance of such high vacuum X-ray tubes in recent years, these tubes still have stray radiation problerns resulting from high energy photons which are generated at the target and which do not find their way out the envelope through the window~ Consequently, it has been common practice tO
use large amounts of external shielding to attenuate these X-ray photons outside of the evacuated envelope,. The necessity of `, . .
..
such shielding significantly incre~ses the cost and the bulk of the X-ray tube.
The present invention provides a means for reducing the amount of external shielding required for high vacuum X-ray tubes by accomplishing the shielding internally.
To this end, there is provided according to the present invention an X-ray tube comprising an evacuated envelope, an X-ray generating target within said envelope, an electron gun positioned within said envelope to direct a stream of electrons at said target, window means arranged to direct the resulting X-rays from said target beyond said envelope, a sleeve com-posed o a high density attenuating material disposed about said target, said sleeve having an aperture therein permitting passage of X-rays rom said target through said window means, and high dsnsity attenuating means disposed behind and peripherally around said electron gun to attenuate stray high energy photons.
In one form of the invention, the target is substantially perpen-dicular to the stream of electrons and the high density attenuating means ~ -is positioned coaxially with the stream and also behind the target.
In another form of the invention, the target is posi~ioned at a smallangle to the hori~ontal and the high density attenuating means is positioned along the path of the stream of electrons and also behind the target.
In a further modified form of the invention, the target means and the high d0nsity attenuating means are part of the same integral structure. -Other features and advantages of the invention will be readily apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings, although ~ - `
variations and modifications may be effected without departing from the ; spirit and scope of the novel concepts of the disclosure, and in which:
_3_ 9~}9 Figure 1 is a vertical cross-sectional view of one form of X-ray tube which can be used in accordance with the present invention;
Figure 2 is a fragmentary cross-sectional view of the target area of a modiEied form of ~he present invention; and Figure 3 is a partial cross-sectional view of still another form of the invention wherein the target area and the shielding means are integral with each other.
In Figure 1 reference numeral 10 indicates generally an improved X-ray tube according to the present invention having a solid ceramic insulator base 11 through which there extends an electron gun generally indicated at reference numeral 12, said electron gun including a heated filament 13 for generating electrons, and a focusing electrode 14 which directs a stream of such elec-lS trons toward an anode assembly including an X-ray attenuating anode tip 15 having an axial bore 16 through which the beam of . . . :
electrons is passedO The anode assernbly also includes an anode body 17 having an axial bore 18 in registry with the bore 16 to direct the bearn of electrons toward a target 19 composed of a heavy metal or heavy ceramic of high atomic weight. As is well known in the art, any target material should have a high atomic number to give best X-ray efficiency, a high melting point and high thermal conductivity to permit maximum energies for a given . .
size of focal spot, and a low vapor pressure to reduce the rate of ~evaporation of the metal cn the walls of the ceramic envelope.
The high energy electron beam striking the target 19 causes X-ray radiation in all directions from the spot on the target - ~' - 4 ~
:: ;~-where the collisions take place~ The X-ray tube of Figure 1 is provided with a window 20 composed of a material such as beryllium or ceramic which is transparent ~o X-ray radiation and through which the X-rays can leave the confines of the tube to the area at which they are used. Regardless of the spatial orientation of the target area and the window, however, there is unavoidably some X-ray radiation back into the bore 18, behind the target 19, and even back into the electron gun assembly~ To attenuate such radiation, I provide a target backing composed of a high density X-ray a~tenuating means such as tungsten, tantalum, depleted uranium, zirconium or an attenuating ceramic material such as uranium oxideO For tubes operating a~ a reasonably high power level, it is highly desirable to use a composite of the attenuating material and a good heat conductor such as coF~3er. Such a composite is illustrated in Figure 1 whexe the target 19 is shown, backed by a copper layer 27 having contact passages 28 formed ~therein, and the copper in turn being backed by an attenuating layer 290 An additional copper layer 30 is formed over the attenuating layer 290 An exhaust tube 23 also is confined within the target backing 27. The exhaust tube 23 is used to evacuate the interior OI the tube to a high vacuum whereupon it is sealed :~ off by closing the end of the OHFC copper tube, and covered with . a tube cap 24~ Radiation which is directed back along the path of the electron beam is attenuated by the anode support 17 and anode tip 15 which is also composed of a heavy metal or ceramic OI the type mentionedO Finally, radiation which proceeds far enough to ~ . .
. '.
l _ 5 _ :-.
- ~l(31 3g9~
`
strike the electron gun assembly 12 is attenuated by means of a - ring 25 and a disk 26 composed of the high density material and surrounding the focusing electrode 140 With the attenuating means disposed throughout the tube as mentioned, very little stray radia-tion escapes and any external shielding for the tube can be reduced to a minimum~ -In the form of the invention shown in Figure 2, there is provided an anode housing 31 composed of copper or other highly heat conductive materialO A target structure consisting of a target plate 32 is disposed at a small angle to the horizontal with respect to the electron beam which is directed at it in the direction of the arrow 33D The target 32 is supported on a target .
support 34 composed of copper, a copper attenuating material composite or one of the aforementioned high density ~attenuating materials~ One or more fluid flow passages 35 iS provided in the target support to cool the target structure during operationr A . .
line 36 is provided to connect the interior of ~he tube assembly to a source of high vacuum (not shown). .:
The target 32 is substantially surrounded by a sleeve ~ .
37 composed of high density attenuating materials such as tungsten, tantalum, depleted uranium, zirconium, or uranium o~ide. The sleeve 37 is provided with an apexture 38 along a. relatively :;
llmited portion of its circumference to provide for egress of the X-rays generated by the electron beam striking the target 32. An X-ray pervious windo~7 39 directs the X-ray radiation out of the - .
tube to its point of useO A mounting flange 40 is provided to .;
;: :
- 6 ~
.
~ 99~ :
mount the anode structure onto a ceramic insulator of the type shown in Figure lo A furthex modified form of the invention is illustrated in Figure 3~ In this form, there is provided a high density zirconium or uranium oxide ceramic insulator 41 in which there is disp~sed an electron gun 42 including a heated filament 43 and a focusing electrode 44~ The anode structure in this embodiment talces the form of an anode body member 45 composed of copper or the like and having a flange portion 46 for mounting against the -ceramic insulator 410 A line 47 communicates the interior of the X-ray tube to a source of vacuumD
In the form of the invention shown in Figure 3, the target and the shield are part of ~he same integral structure , consisting of a cylindrical portion 48~ surrounding the path of electron flow from the electron gun, and terminating in a generally spherical head 49 in ~hich there is provided an inclined target face 50~ Co~ling passages 51 are provided in this portion of the anode to abstract heat from the target area. A window 52 directs the X-ray radiation from the target area 50 outwardly. Additional protection against X-ray radiation is provided by means of a ring $3 of X-ray attenuating material located about the focusing ring 44.
In any of the forms of the invention shown, the ceramic insulator itself can include a~tenua~ing oxides such as uranium-~: :
, o~{ide, zirconium oxide or other high density, vacuum stable 25 ~ materials. The ceramic then absorbs secondary X-rays generate~
:
o n the parts of the tube centèred within the ceramic and still ~
. .
further reduces ~he stray radiation.
,: : : ~ ,', ., , ; .
. .. . ..... . .
~99~
The improved X-ray tubes of the present invention reduce the cost of shielding and drastically reduce shielding weight for the same amount of stray radiation~ ~urthermore, from a product safety standpoint, the shielding is failsafe as it cannot be removed without making the X~ray tube inoperative~
` .. .... .. .
.
. ~
, ~
.' "''. ' '~
~ ' '' - 8 - ~
':' . :
Claims (2)
1. An X-ray tube comprising an evacuated envelope, an X-ray generating target within said envelope, an electron gun positioned within said envelope to direct a stream of electrons at said target, window means arranged to direct the resulting X-rays from said target beyond said envelope, a sleeve composed of a high density attenuating material disposed about said target, said sleeve having an aperture therein permitting passage of X-rays from said target through said window means, and high density attenuating means disposed behind and peripherally around said electron gun to attenuate stray high energy photons.
2. An X-ray tube according to claim 1 in which said target is disposed at an acute angle to the electron beam path.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US77184977A | 1977-02-25 | 1977-02-25 | |
US771,849 | 1977-02-25 |
Publications (1)
Publication Number | Publication Date |
---|---|
CA1089909A true CA1089909A (en) | 1980-11-18 |
Family
ID=25093129
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA286,034A Expired CA1089909A (en) | 1977-02-25 | 1977-09-02 | Internally shielded x-ray tube |
Country Status (1)
Country | Link |
---|---|
CA (1) | CA1089909A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1611590A2 (en) * | 2003-04-09 | 2006-01-04 | Varian Medical Systems, Inc. | X-ray tube having an internal radiation shield |
-
1977
- 1977-09-02 CA CA286,034A patent/CA1089909A/en not_active Expired
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1611590A2 (en) * | 2003-04-09 | 2006-01-04 | Varian Medical Systems, Inc. | X-ray tube having an internal radiation shield |
EP1611590A4 (en) * | 2003-04-09 | 2009-11-11 | Varian Med Sys Inc | X-ray tube having an internal radiation shield |
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