US2842694A - X-ray apparatus - Google Patents

X-ray apparatus Download PDF

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US2842694A
US2842694A US318572A US31857252A US2842694A US 2842694 A US2842694 A US 2842694A US 318572 A US318572 A US 318572A US 31857252 A US31857252 A US 31857252A US 2842694 A US2842694 A US 2842694A
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cathode
anode
electrostatic lens
electrons
potential
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US318572A
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Hosemann Rolf
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Licentia Patent Verwaltungs GmbH
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Licentia Patent Verwaltungs GmbH
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00—X-ray tubes
    • H01J35/02—Details
    • H01J35/14—Arrangements for concentrating, focusing, or directing the cathode ray
    • H01J35/147—Spot size control

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  • the present invention relates to an X-ray apparatus and particularly to an X-ray apparatus having an X-ray tube having an electrostatic lens;
  • An X-ray apparatus comprises an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by the cathode and thus emitting X-rays, an electrostatic lens having a high refractive power and being arranged between the cathode and the anode, the electrostatic lens having a first portion, a third portion and a second portion arranged consecutively in the path of the electrons from the cathode to the anode and provided, respectively, with aligned openings, means for maintaining the first and second portions of the electrostatic lens substantially at the same potential as the anode, and means for maintaining the third portion of the electrostatic lens substantially at or near the potential of the cathode, whereby the electrons are strongly accelerated between the cathode and the first portion of the electrostatic lens, are subsequently brought substantially to a standstill while they approach the opening of the third portion of the electrostatic lens, and are finally accelerated again when they have passed the opening of the third portion of
  • the portions of the electrostatic lens are arranged closely to one another so as to obtain an electrostatic lens having a high refractive power.
  • the electrostatic lens is arranged at a distance from the anode being a minor fraction of the distance between the cathode and the anode.
  • a preferred embodiment of the present invention comprises a Wehnelt cylinder surrounding the cathode and having a potentialbeing preferably slightly lower than the potential of the cathode.
  • the cathode is formed as a flat spiral or a hairpin.
  • the electrostatic lens has a first and a second portion each formed by a disc having a central hollow projection provided with a first and second opening, respectively, said projections facing each other at a spacing distance, and a third portion formed as a disc located in the space between said first and second portions and provided with a third opening, said first, third and second openings being aligned with each other so as to be arranged consecutively in the path of the electrons from the cathode to the anode.
  • the single figure is a diagrammatic sectional elevation of an X-ray tube showing the wiring diagram of the connections of the electrodes of the tube.
  • the X-ray tube comprises an oblong envelope 20 one end of which carries an anode 2 whereas the opposite end forms a stem 22 provided with sealings 4, 7 and 5 leading to the electrodes of the tube to be described hereinafter.
  • the .sealings 7 carry conductors 24 leading to a cathode 3 shown as a hairpin. It should be understood however that the cathode may be formed by a flat spiral of very closely wound wire having an external diameter being preferably less than 3 mm.
  • the cathode 3 is surrounded by a Wehnelt cylinder 6 which is connected to a conductor 26 passing through the sealing 4.
  • an electrostatic lens generally denoted by 28 is arranged so that the distance thereof from the anode 2- amounts to approximately one fifth of the distance between the cathode 3 of the Wehnelt cylinder 6 and the anode 2.
  • the electrostatic lens comprises a first portion 30, a third portion 32 and a second portion 34.
  • the first and second portions 30 and 34 form a single metallic piece connected by a conductor 36 to the anode 2.
  • the first portion 30 includes a disc having a central hollow projection 38 provided with a first opening 40
  • the second portion 34 includes a similar disc having a central hollow projection 42 provided with a second opening 44.
  • the third portion 32 of the electrostatic lens 28 consists also of metal and is formed as a disc insulated from the first and second portions 30 and 34 and having a central opening 46 termed hereinafter the third opening.
  • the three openings 40, 46 and 44 are aligned with one another so as to be arranged consecutively in the path of the electrons traveling from the cathode 3 to the anode 2 where they cause an X-ray radiation leaving the envelope 20 through the X-ray window 8 preferably formed by a dome-shaped part having a very small wall thickness preferablyamounting to a few thousandths of a millimeter. In the drawing the wall thickness of the window 8 is shown on a greatly enlarged scale.
  • the distance between the first opening 40 and the second opening 44 is very small and amounts to 8 mm. or less so that the'electrostatic lens 28 has a high refractive power and a focal length of a few mm.
  • the electrodes of the X-ray tubes are supplied with potentials as follows:
  • the primary 50 of a transformer 52 is connected to a voltage source 9.
  • the transformer 52 has two secondaries l0 and 11.
  • One end 54 of the secondary 10 is grounded and connected by a conductor 56 with-the anode 2 of the tube.
  • the secondary 10 is connected through the conductor 26 to the Wehnelt cylinder 6 and through a resistor 12 to the midpoint 60 of the other secondary 11 which is connected through the conductors 24 with the cathode 3.
  • the secondary 10 generates a high voltage applied to the Wehnelt cylinder 6 and the cathode 3 with respect to the anode 2 whereas the secondary 11 generates only a voltage which is sufiicient to produce a heating current in the hairpin cathode 3.
  • a conductor 13 leads from a tap 62 of the secondary 10 being rather close to the end 58 thereof to the third The other end 58 of portion 32 of the electrostatic lens which is therefore maintained at a potential being substantially equal to those of the Wehnelt cylinder 6 and the cathode 3.
  • the potential of the Wehnelt cylinder 6 is preferably chosen so as to be slightly lower than that of the cathode 3 so that the Wehnelt cylinder 6 acts as a tele-lens on the electrons.
  • a potential field is built up having'the effect of a lens of positive refractive power so that the electrons. emitted by the glow cathode 3 are concentrated at a single point lying far in front of the cathode 3.
  • the electrons are strongly accelerated between the cathode 3 and the first portion 30 of the electrostatic lens 28.
  • the electrons When the electrons have passed the opening 40 in the first portion 30 they are brought substantially to a standstill by the third portion 32 which is at a potential substantially equalling that of the cathode 3 and the Wehnelt cylinder 6.
  • the electrons are accelerated again when they traverse the distance between the second opening 46 and the second opening 44 so that they are concentrated so as to form a fine focal spot at the-anode 2.
  • the potential of the third portion 32 can be adjusted.
  • the resistor 12 By a suitable choice of the resistor 12 the proper potential of the Wehnelt cylinder 6 is obtained at a predetermined anode current.
  • An X-ray apparatus comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, saidelectrostatic lens being substantially closer to said anode than to said cathode' and having a first portion, a third portion and a second portion arranged consecutively in the path of the electrons from said cathode to said anode and provided, respectively, with aligned'openings; means for maintaining said-first and second portions of said electrostatic lens substantially at the same potential as said anode; and means for maintaining said third portion of said electrostatic lens substantially'at the potential of said cathode, whereby "the electrons are strongly accelerated between'said cathode and said first portion of said electrostatic lens, are subsequently brought substantially to a stand
  • An X-ray apparatus comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens being substantially closer to said anode than to said cathode and having a first portion, a third portion and a second portion arranged consecutively in the path of the electrons from said cathode to said anode and provided, respectively with aligned openings; means for maintaining said first and second portions of said electrostatic lens substantially at the same potential as said anode; and means for maintaining said third portion of said electrostatic lens substantially at the potential of said cathode, whereby the electrons are strongly accelerated between said cathode
  • An X-ray apparatus comprising, in combination,'an X-raytube including a cathode emitting electrons and'an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens having a first portion, a third, portion and a second portion arranged consecutively in the path of the electrons from said cathode to said anode and provided, respectively, with aligned openings, said portions of said electrostatic lens being arranged closely to one another, said electrostatic lens being arranged at a distance from said anode being a minor fraction of the distance between said cathode and said anode; means for maintaining said first'and second portions of said electrostatic lens substantially at the same potential as said ano
  • An X-ray apparatus comprising, in combination, an X-ray tube including a cathode emittingelectrons and an anode struck by the electrons-emittedby said cathode and thus emitting X-rays; an electrostatic lens having a high refractive power and a short focal length and beingfarranged between said cathode and said anode, said electrostatic lens being substantially closerto said anode'than to said cathode and having a firstand' a second portion each formed 'by a disc-having'a central hollowprojection provided with a'first'and second opening, respectively,
  • An X-ray apparatus comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens being substantially closer to said anode than to said cathode and having a first and a second portion each formed by a disc having a central hollow projection provided with a first and second opening, respectively, said projections facing each other at a spacing distance, and a third portion formed as a disc located in the space between said first and second portions and provided with a third opening, said first, third and second openings being aligned with each other so as to be arranged consecutively in the path of the electrons from said cathode to said
  • An X-ray apparatus comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens having a first and a second portion each formed by a disc having a central hollow projection provided with a first and second opening, respectively, said projections facing each other at a spacing distance, and a third portion formed as a disc located in the space between said first and second portions and provided with a third opening, said first, third and second openings being aligned with each other so as to be arranged consecutively in the path of the electrons from said cathode to said anode, said portions of said electrostatic lens being arranged closely to

Description

July 8, 1958 R. HOSEMANN 2,842,694
X-RAY APPARATUS Filed Nov. 4, 1952 4 38 35 32 f I 26 7 6 2; {f z r 30 29 4 5 I 4' I34 Inventor": Rom HOSEMAP/l/ United States Patent Application November 4, 1952, Serial No. 318,572
Claims priority, application Germany November 8, 1951 9 Claims. (Cl. 313-57) The present invention relates to an X-ray apparatus and particularly to an X-ray apparatus having an X-ray tube having an electrostatic lens;
The present application is a continuation-in-part of the copending application Serial No. 300,587, filed July 24,-1952, for X-Ray Tube, now Patent No. 2,683,223.
It is an object of the present invention to provide an X-ray apparatus having a focal spot which is as small as possible.
It is another object of the present invention to provide an X-ray apparatus which is suitable for microscopic investigations.
An X-ray apparatus according to the present invention comprises an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by the cathode and thus emitting X-rays, an electrostatic lens having a high refractive power and being arranged between the cathode and the anode, the electrostatic lens having a first portion, a third portion and a second portion arranged consecutively in the path of the electrons from the cathode to the anode and provided, respectively, with aligned openings, means for maintaining the first and second portions of the electrostatic lens substantially at the same potential as the anode, and means for maintaining the third portion of the electrostatic lens substantially at or near the potential of the cathode, whereby the electrons are strongly accelerated between the cathode and the first portion of the electrostatic lens, are subsequently brought substantially to a standstill while they approach the opening of the third portion of the electrostatic lens, and are finally accelerated again when they have passed the opening of the third portion of the electrostatic lens and are under the influence of the potential of the anode so that a punctiform focal spot is generated on the anode.
Preferably the portions of the electrostatic lens are arranged closely to one another so as to obtain an electrostatic lens having a high refractive power.
'In a preferred embodiment of the present invention the electrostatic lens is arranged at a distance from the anode being a minor fraction of the distance between the cathode and the anode. V p
A preferred embodiment of the present invention comprises a Wehnelt cylinder surrounding the cathode and having a potentialbeing preferably slightly lower than the potential of the cathode.
Preferably the cathode is formed as a flat spiral or a hairpin.
In a preferred embodiment of the present invention the electrostatic lens has a first and a second portion each formed by a disc having a central hollow projection provided with a first and second opening, respectively, said projections facing each other at a spacing distance, and a third portion formed as a disc located in the space between said first and second portions and provided with a third opening, said first, third and second openings being aligned with each other so as to be arranged consecutively in the path of the electrons from the cathode to the anode.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method of operation, to-
gether with additional objects and advantages thereof,
will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:
The single figure is a diagrammatic sectional elevation of an X-ray tube showing the wiring diagram of the connections of the electrodes of the tube.
Referring now to the drawing the X-ray tube comprises an oblong envelope 20 one end of which carries an anode 2 whereas the opposite end forms a stem 22 provided with sealings 4, 7 and 5 leading to the electrodes of the tube to be described hereinafter. The .sealings 7 carry conductors 24 leading to a cathode 3 shown as a hairpin. It should be understood however that the cathode may be formed by a flat spiral of very closely wound wire having an external diameter being preferably less than 3 mm.
The cathode 3 is surrounded by a Wehnelt cylinder 6 which is connected to a conductor 26 passing through the sealing 4.
Between the cathode 3 and the anode 2 an electrostatic lens generally denoted by 28 is arranged so that the distance thereof from the anode 2- amounts to approximately one fifth of the distance between the cathode 3 of the Wehnelt cylinder 6 and the anode 2. The electrostatic lens comprises a first portion 30, a third portion 32 and a second portion 34. In the shown embodiment the first and second portions 30 and 34 form a single metallic piece connected by a conductor 36 to the anode 2. Preferably the first portion 30 includes a disc having a central hollow projection 38 provided with a first opening 40 whereas the second portion 34 includes a similar disc having a central hollow projection 42 provided with a second opening 44. The third portion 32 of the electrostatic lens 28 consists also of metal and is formed as a disc insulated from the first and second portions 30 and 34 and having a central opening 46 termed hereinafter the third opening. The three openings 40, 46 and 44 are aligned with one another so as to be arranged consecutively in the path of the electrons traveling from the cathode 3 to the anode 2 where they cause an X-ray radiation leaving the envelope 20 through the X-ray window 8 preferably formed by a dome-shaped part having a very small wall thickness preferablyamounting to a few thousandths of a millimeter. In the drawing the wall thickness of the window 8 is shown on a greatly enlarged scale.
The distance between the first opening 40 and the second opening 44 is very small and amounts to 8 mm. or less so that the'electrostatic lens 28 has a high refractive power and a focal length of a few mm.
The electrodes of the X-ray tubes are supplied with potentials as follows: The primary 50 of a transformer 52 is connected to a voltage source 9. The transformer 52 has two secondaries l0 and 11. One end 54 of the secondary 10 is grounded and connected by a conductor 56 with-the anode 2 of the tube. the secondary 10 is connected through the conductor 26 to the Wehnelt cylinder 6 and through a resistor 12 to the midpoint 60 of the other secondary 11 which is connected through the conductors 24 with the cathode 3. It should be understood that the secondary 10 generates a high voltage applied to the Wehnelt cylinder 6 and the cathode 3 with respect to the anode 2 whereas the secondary 11 generates only a voltage which is sufiicient to produce a heating current in the hairpin cathode 3.
A conductor 13 leads from a tap 62 of the secondary 10 being rather close to the end 58 thereof to the third The other end 58 of portion 32 of the electrostatic lens which is therefore maintained at a potential being substantially equal to those of the Wehnelt cylinder 6 and the cathode 3.
The operation of this device is as follows:
If the transformer 52 is switched on the cathode 3 emits electrons which cause directly in front of the cathode apotential field having the efiect of a lens with slightly negative refractive power. The potential of the Wehnelt cylinder 6 is preferably chosen so as to be slightly lower than that of the cathode 3 so that the Wehnelt cylinder 6 acts as a tele-lens on the electrons. On the front surface of the Wehnelt cylinder 6 facing the anode 2 a potential field is built up having'the effect of a lens of positive refractive power so that the electrons. emitted by the glow cathode 3 are concentrated at a single point lying far in front of the cathode 3.
The electrons are strongly accelerated between the cathode 3 and the first portion 30 of the electrostatic lens 28. When the electrons have passed the opening 40 in the first portion 30 they are brought substantially to a standstill by the third portion 32 which is at a potential substantially equalling that of the cathode 3 and the Wehnelt cylinder 6. Finally the electrons are accelerated again when they traverse the distance between the second opening 46 and the second opening 44 so that they are concentrated so as to form a fine focal spot at the-anode 2.
By adjusting the tap 62 the potential of the third portion 32 can be adjusted. By a suitable choice of the resistor 12 the proper potential of the Wehnelt cylinder 6 is obtained at a predetermined anode current.
It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of X-ray apparatuses differing from the types described above.
While the invention has been illustrated and described as embodied in an X-ray apparatus having an X-ray tube having an electrostatic lens, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.
Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.
'What is claimed as new and desired to be secured by Letters Patent is:
1. An X-ray apparatus, comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, saidelectrostatic lens being substantially closer to said anode than to said cathode' and having a first portion, a third portion and a second portion arranged consecutively in the path of the electrons from said cathode to said anode and provided, respectively, with aligned'openings; means for maintaining said-first and second portions of said electrostatic lens substantially at the same potential as said anode; and means for maintaining said third portion of said electrostatic lens substantially'at the potential of said cathode, whereby "the electrons are strongly accelerated between'said cathode and said first portion of said electrostatic lens, are subsequently brought substantially to a standstill while they approach said opening of said third portion of said electrostatic lens, and are finally accelerated again when ey havepassedsaid opening ofsaid third portion f said electrostaticlens and are under the influence of the potential of said anode so that a punctiform focal spot is generated on said anode.
2. An X-ray apparatus, comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens being substantially closer to said anode than to said cathode and having a first portion, a third portion and a second portion arranged consecutively in the path of the electrons from said cathode to said anode and provided, respectively with aligned openings; means for maintaining said first and second portions of said electrostatic lens substantially at the same potential as said anode; and means for maintaining said third portion of said electrostatic lens substantially at the potential of said cathode, whereby the electrons are strongly accelerated between said cathode and said first portion of said electrostatic lens, are subsequently brought substantially to a standstill while they approach said opening of said third portion of said electrostatic lens, and are finally accelerated again when they have passed said opening of said third portion of said electrostatic lens and are under the influence ofthe potential of said anode so that a punctiform focal spot is generated on said anode.
3. An X-ray apparatus, comprising, in combination,'an X-raytube including a cathode emitting electrons and'an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens having a first portion, a third, portion and a second portion arranged consecutively in the path of the electrons from said cathode to said anode and provided, respectively, with aligned openings, said portions of said electrostatic lens being arranged closely to one another, said electrostatic lens being arranged at a distance from said anode being a minor fraction of the distance between said cathode and said anode; means for maintaining said first'and second portions of said electrostatic lens substantially at the same potential as said anode; and means for'maintaining said third portion of said electrostatic lens substantially at the potential of said cathode, whereby the electrons are strongly accelerated between said cathode and said firstportion of said electrostatic lens, are subsequently brought substantially to a standstill While they approach said opening'of said third portion of said electrostatic lens, and are finally accelerated again when they have passed said opening ofsaid third portion of said electrostatic lens and are under the influence of the potential of said anode so that a punctiform focal spot is generated on said anode.
4. An X-ray apparatus, comprising, in combination, an X-ray tube including a cathode emittingelectrons and an anode struck by the electrons-emittedby said cathode and thus emitting X-rays; an electrostatic lens having a high refractive power and a short focal length and beingfarranged between said cathode and said anode, said electrostatic lens being substantially closerto said anode'than to said cathode and having a firstand' a second portion each formed 'by a disc-having'a central hollowprojection provided with a'first'and second opening, respectively,
said projections facing each other at a spac'ing distance,
and a third portion formed as a disc located in the'spacc between said first and secondportions and provided" with a third opening, said first, third and second'openings'being aligned with each otherso as to be arranged consecutively in the path of the electrons from said cathode to said anode; means for maintaining said first and second portions of said electrostatic lens substantially at the same potential as said anode; and means for maintaining said third portion of said electrostatic lens substantially at the potential of said cathode, whereby the electrons are strongly accelerated between said cathode and said first portion of said electrostatic lens, are subsequently brought substantially to a standstill while they approach said opening of said third portion of said electrostatic lens, and are finally accelerated again when they have passed said openings of such third portion of said electrostatic lens and are under the influence of the potential of said anode so that a punctiform focal spot is generated on said anode.
5. An X-ray apparatus, comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens being substantially closer to said anode than to said cathode and having a first and a second portion each formed by a disc having a central hollow projection provided with a first and second opening, respectively, said projections facing each other at a spacing distance, and a third portion formed as a disc located in the space between said first and second portions and provided with a third opening, said first, third and second openings being aligned with each other so as to be arranged consecutively in the path of the electrons from said cathode to said anode; means for maintaining said first and second portions of said electrostatic lens substantially at the same potential as said anode; and means for maintaining said third portion of said electrostatic lens substantially at the potential of said cathode, whereby the electrons are strongly accelerated between said cathode and said first portion of said electrostatic lens, are subsequently brought substantially to a standstill while they approach said opening of said third portion of said electrostatic lens, and are finally accelerated again when they have passed said opening of said third portion of said electrostatic lens and are under the influence of the potential of said anode so that a punctiform focal spot is generated on said anode.
6. An X-ray apparatus, comprising, in combination, an X-ray tube including a cathode emitting electrons and an anode struck by the electrons emitted by said cathode and thus emitting X-rays; a Wehnelt cylinder surrounding said cathode and having a potential slightly lower than the potential of said cathode; an electrostatic lens having a high refractive power and a short focal length and being arranged between said cathode and said anode, said electrostatic lens having a first and a second portion each formed by a disc having a central hollow projection provided with a first and second opening, respectively, said projections facing each other at a spacing distance, and a third portion formed as a disc located in the space between said first and second portions and provided with a third opening, said first, third and second openings being aligned with each other so as to be arranged consecutively in the path of the electrons from said cathode to said anode, said portions of said electrostatic lens being arranged closely to one another, said electrostatic lens being arranged at a distance from said anode being a minor fraction of the distance between said cathode and said anode; means for maintaining said first and second portions of said electrostatic lens substantially at the same potential as said anode; and means for maintaining said third portion of said electrostatic lens substantially at the potential of said cathode, whereby the electrons are strongly accelerated between said cathode and said first portion of said electrostatic lens, are subsequently brought substantially to a standstill while they approach said opening of said third portion of said electrostatic lens, and are finally accelerated again when they have passed said opening of said third portion of said electrostatic lens and are under the influence of the potential of said anode so that a punctiforrn focal spot is generated on said anode.
7. An X-ray apparatus as set forth in claim 1, wherein said cathode is formed as a hairpin.
8. An X-ray apparatus as set forth in claim 3, wherein said cathode is formed as a hairpin.
9. An X-ray apparatus as set forth in claim 6, wherein said cathode is formed as a hairpin.
References Cited in the file of this patent UNITED STATES PATENTS 2,112,034 Livingston Mar. 22, 1938 2,240,120 Nicoll Apr. 29, 1941 2,345,080 Von Ardenne Mar. 28, 1944 2,452,919 Gabor Nov. 2, 1948 2,531,583 Ott Nov. 28, 1950 2,581,243 Dodds Jan. 1, 1952 2,617,046 Douma Nov. 4, 1952 FOREIGN PATENTS 696,419 Germany Sept. 20, 1940
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US20140133635A1 (en) * 2005-10-25 2014-05-15 Edward James Morton Graphite backscattered electron shield for use in an x-ray tube
US9263225B2 (en) 2008-07-15 2016-02-16 Rapiscan Systems, Inc. X-ray tube anode comprising a coolant tube
US9420677B2 (en) 2009-01-28 2016-08-16 Rapiscan Systems, Inc. X-ray tube electron sources
US9726619B2 (en) 2005-10-25 2017-08-08 Rapiscan Systems, Inc. Optimization of the source firing pattern for X-ray scanning systems
US10483077B2 (en) 2003-04-25 2019-11-19 Rapiscan Systems, Inc. X-ray sources having reduced electron scattering
US10901112B2 (en) 2003-04-25 2021-01-26 Rapiscan Systems, Inc. X-ray scanning system with stationary x-ray sources
US10976271B2 (en) 2005-12-16 2021-04-13 Rapiscan Systems, Inc. Stationary tomographic X-ray imaging systems for automatically sorting objects based on generated tomographic images

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