EP2006880A1 - Miniaturröntgenquelle mit Führungsvorrichtung für Elektronen und / oder Ionen - Google Patents

Miniaturröntgenquelle mit Führungsvorrichtung für Elektronen und / oder Ionen Download PDF

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Publication number
EP2006880A1
EP2006880A1 EP07110601A EP07110601A EP2006880A1 EP 2006880 A1 EP2006880 A1 EP 2006880A1 EP 07110601 A EP07110601 A EP 07110601A EP 07110601 A EP07110601 A EP 07110601A EP 2006880 A1 EP2006880 A1 EP 2006880A1
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EP
European Patent Office
Prior art keywords
miniature
cathode
ray source
wall
anode
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.)
Withdrawn
Application number
EP07110601A
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English (en)
French (fr)
Inventor
Godefridus Hendricus Maria Gubbels
Frank Simonis
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
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Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
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Priority to EP07110601A priority Critical patent/EP2006880A1/de
Priority to PCT/NL2008/050400 priority patent/WO2008156361A2/en
Publication of EP2006880A1 publication Critical patent/EP2006880A1/de
Withdrawn legal-status Critical Current

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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00X-ray tubes
    • H01J35/02Details
    • H01J35/04Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00X-ray tubes
    • H01J35/02Details
    • H01J35/14Arrangements for concentrating, focusing, or directing the cathode ray
    • H01J35/147Spot size control
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00X-ray tubes
    • H01J35/02Details
    • H01J35/04Electrodes ; Mutual position thereof; Constructional adaptations therefor
    • H01J35/08Anodes; Anti cathodes
    • H01J35/112Non-rotating anodes
    • H01J35/116Transmissive anodes
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00X-ray tubes
    • H01J35/02Details
    • H01J35/16Vessels; Containers; Shields associated therewith
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J35/00X-ray tubes
    • H01J35/32Tubes wherein the X-rays are produced at or near the end of the tube or a part thereof which tube or part has a small cross-section to facilitate introduction into a small hole or cavity
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2235/00X-ray tubes
    • H01J2235/08Targets (anodes) and X-ray converters
    • H01J2235/086Target geometry

Definitions

  • the invention relates to a miniature X-ray source comprising a vacuum tube containing a cathode and an anode spaced apart from each other.
  • X-ray sources are known per se.
  • the sources are used for generating X-ray radiation by applying an electrical potential difference between the cathode and the anode so that electrons, emitted by the cathode are accelerated towards the anode.
  • the accelerated electrons impact at the anode causing X-ray radiation to be emitted if the energy of the impacting electron is high enough.
  • electron energies of 10 - 50 keV (requiring a potential difference or acceleration voltage of 10-50 kV) are desired for generating X-ray radiation with photon energies of 10- 50 keV, e.g. for use in (medical) imaging, inspection, detection, material analysis (diffraction, fluorescence, Auger), lithography (e.g.
  • Miniature X-ray sources i.e. with typical dimensions on the order of millimetres, e.g. smaller than 10 mm, are also known. These known miniature X-ray devices, e.g. for medical application, can only be operated at low acceleration voltages, e.g. up to 20 kV. To generate high energy X-ray radiation, i.e. radiation with X-ray photon energy higher than 20 keV, high acceleration voltages are needed, i.e. voltages higher than 20kV. The reduced size of the miniature X-ray device, however, results in local high electrical fields strengths initiating destroying electrical breakthroughs.
  • the object of the invention is to provide the miniature X-ray source with which it is possible to generate high energy X-ray radiation.
  • the object of the invention is to provide the miniature X-ray source with the reduced risk of electrical breakthroughs.
  • the object of the invention is to provide further miniaturisation of the X-ray source.
  • the miniature X-ray source is provided with the guiding means for guiding electrons and/or ions to prevent the electrons and/or ions from impacting at least a part of a wall of the vacuum tube.
  • the guiding means are arranged for guiding electrons and/or ions to prevent the electrons and/or ions from impacting the wall of the vacuum tube in a region of the vacuum tube where, in use, an electric field is present.
  • the guiding means guide electrons and/or ions away from the wall of the vacuum tube, e.g. in the region of the vacuum tube where, in use, the electric field is present. Hence, the risk of electrons and/or ions impacting the wall of the vacuum tube, e.g. in the region of the vacuum tube where, in use, the electric field is present, is reduced. Thus, by reducing the chance of electrons and/or ions impacting the wall at these locations, the guiding means reduce the risk of electrical breakthrough and/or electrical charging of the wall.
  • the acceleration voltage between the anode and the cathode may be increased, e.g. until an acceptable level of breakthrough-risk is attained.
  • the miniature X-ray source according to the invention to generate high energy X-ray radiation, e.g. with a photon energy of 30 keV or more, preferably 40 keV or more, most preferably 50 keV or more.
  • the guiding means may comprise a directional barrier interposed between the cathode and the anode wherein the barrier is arranged to transmit, in use, electrons emitted by the cathode towards the anode, and wherein the barrier is arranged to, in use, substantially prevents electrons and/or ions to pass the barrier in the direction of the anode towards the cathode.
  • Electrons impacting on the anode may, instead of X-ray radiation, also cause electrons or ions to be emitted (or reflected) by the anode. Since the directional barrier substantially prevent electrons and/or ions to pass the barrier in the direction of the anode towards the cathode, substantially none of these electrons and/or ions can impact the cathode or the inner wall of the vacuum tube between the cathode and the directional barrier. The directional barrier, thus, reduces the risk of electrical breakthrough and/or electrical charging of the wall of the vacuum tube.
  • the directional barrier is an electrically conducting diaphragm comprising an aperture, wherein the diaphragm is arranged to be maintained at the same electric potential as the anode.
  • the diaphragm makes that the accelerating electrical field is maintained between the cathode and the diaphragm, and that substantially no electrical field is present between the diaphragm and the anode. Since there is substantially no electrical field between the diaphragm and the anode, electrical breakthrough will not occur between the diaphragm and the anode.
  • the diaphragm substantially prevents electrons and/or ions to pass the barrier in the direction of the anode towards the cathode, substantially none of these electrons and/or ions can impact the cathode or the inner wall of the vacuum tube between the cathode and the directional barrier, i.e. in the region of the vacuum tube where, in use, the electric field is present.
  • the anode and the diaphragm together form the, electrically conducting, walls of a chamber which is preferably closed except for the aperture.
  • a chamber is created in which substantially no electrical field is present. Electrons and/or ions emitted or reflected by the anode are highly likely to strike a wall of the chamber. The risk that such electron or ion exits the chamber through the aperture is very small.
  • the guiding means may comprise electron focussing means for directing, in use, the electrons emitted by the cathode in a direction towards the anode, such that substantially all electrons emitted by the cathode are prevented from impacting the at least a part of the wall of the vacuum tube.
  • the electron focussing means are arranged for directing, in use, the electrons emitted by the cathode in a direction towards the anode, such that substantially all electrons emitted by the cathode are prevented from impacting the wall in the region of the vacuum tube where, in use, the electric field is present.
  • the electrons emitted by the cathode will follow a path such that they do not impact the inner wall of the vacuum tube between the cathode and the anode, thus reducing the risk of electrical breakthrough.
  • the electron focussing means direct the electrons emitted by the cathode in a direction such that substantially all electrons emitted by the cathode are transmitted by the directional barrier.
  • substantially no electrons emitted by the cathode can impact the inner wall of the vacuum tube between the cathode and the directional barrier, the directional barrier itself or the vacuum tube after collision with the directional barrier. Since, electrons impacted at the vacuum tube are likely to act as electron source and may therefore function as the origin of electrical breakthrough, the electron focusing means, thus, reduce the risk of electrical breakthrough.
  • the directional barrier allows the electrons emitted by the cathode to be transmitted towards the anode, so that efficiency of the X-ray source is not, at least hardly, adversely affected by the presence of the barrier.
  • the electron focussing means are arranged for directing substantially all electrons emitted by the cathode through the aperture in the direction of the anode.
  • substantially all electrons emitted by the cathode pass through the aperture and are effectively caught downstream of the aperture, e.g. in the chamber, so that these electrons cannot cause electrical breakthrough.
  • the electron focussing means comprise an electric and/or magnetic lens. Hence it is possible to in a simple manner direct the electrons emitted by the cathode in a direction such that substantially all electrons emitted by the cathode are transmitted by the directional barrier.
  • the cathode is concave, in a direction towards the anode, wherein the concave shape acts as the electric lens for directing, in use, the electrons emitted by the cathode in a direction such that substantially all electrons emitted by the cathode are transmitted by the directional barrier.
  • a grid shaped electron absorbing element is disposed between the cathode and the directional barrier for absorbing any electrons being reflected from the barrier towards the cathode or the wall of the vacuum tube.
  • the cathode is of a cold cathode type comprising carbon nanotubes for emitting electrons.
  • the use of the cold cathode poses less thermal load to the X-ray source which enables further miniaturisation of the X-ray source.
  • the carbon nanotubes are aligned mono-wall nanotubes, aligned multi-wall nanotubes, randomised mono-wall nanotubes or randomised multi-wall nanotubes.
  • the nanotubes provide an efficient source of electrons for the cathode of the miniature X-ray source.
  • the miniature X-ray source may comprise a tubular housing of an electrically isolating material having an electrically conducting first cap or first plug associated with the anode at a first end and an electrically conducting second cap or second plug associated with the cathode at the other, second end.
  • the electrically isolating material may for instance be a ceramic material, such as aluminium oxide (alumina) or another material defect free material such as diamond or mono crystalline quartz.
  • a particularly suitable material is optically transparent alumina, which appears to have a high dielectric strength.
  • the vacuum tube e.g. the tubular housing
  • the vacuum tube is at least partly made of an electrically isolating material.
  • an electric field is generated, e.g. adjacent the anode and/or cathode which may be at a potential difference with an outer side of the vacuum tube.
  • the vacuum tube comprises an inner wall, of a first material and an outer wall of a second material.
  • a dielectric constant of the first material is higher than a dielectric constant of the second material
  • a dielectric strength of the second material is higher than a dielectric strength of the first material.
  • the dielectric strength is the maximum electric field strength that a material can withstand without electrical breakthrough, i.e. without experiencing failure of its insulating properties.
  • the first material may be a ceramic material, such as aluminium oxide (alumina), and the second material may be a polymeric material, such as polyethylene.
  • the thickness of the inner wall and the outer wall is such that the electric field strength inside the inner wall is smaller than the electric field strength in the outer wall. It will be appreciated that it is, thus, possible to ensure that by choosing the desired thickness for the inner and outer wall the electric field strength inside the inner wall can be kept smaller than the dielectric strength of the first material, and the electric field strength inside the outer wall can be kept smaller than the dielectric strength of the second material. Hence, it is possible to provide a wall of the vacuum tube comprising the inner and the outer wall, such that the total wall thickness is minimized, while breakthrough across the wall is substantially prevented. Thus, further miniaturisation of the miniature X-ray source may be achieved.
  • a triple junction may be shielded by an electrically conducting, e.g. metal, layer at the outside surface of the electrically isolating tubular housing.
  • tubular triple junctions of electrical conductor e.g. metal
  • electrical conductor e.g. metal
  • electrical insulator e.g. aluminum
  • vacuum e.g., water
  • tubular triple junction may be formed where the electrically conducting first and/or second cap or plug, the electrically isolating tubular housing and the vacuum meet.
  • tubular triple junction thus poses a risk for electrical breakthrough. Since, according to the fifth aspect of the invention, the tubular triple junction may be shielded by an electrically conducting, e.g.
  • a high electrical resitivity coating (resistivity in the rang 10 6 -10 10 ohm ⁇ cm may be applied on the inner side and/or outer side of the vacuum tube, e.g. on the electrically isolating tubular housing.
  • the high resistivity coating may be electrically conducting connected to the anode and the cathode, e.g. at the first end of the tubular housing and the second end of the tubular housing, respectively.
  • the high resistivity coating may enforce a gradual linear voltage distribution along the wall of the vacuum tube, e.g. along the isolating tubular housing (glass or ceramic) as a result of a small electric current (e.g. 0.1 to 100 ⁇ A) that may flow through the high resistivity coating.
  • the high resistivity coating substantially completely covers the vacuum tube between the anode and the cathode.
  • the high resistivity coating substantially completely covers the tubular housing between a first electrically conducting layer associated with the triple junction associated with the anode and a second electrically conducting layer associated with the triple junction associated with the cathode.
  • first, second, third, fourth, fifth and sixth aspect of the invention may be practiced separately or in any combination thereof.
  • Fig. 1a shows a schematic sectional view of a first embodiment of a miniature X-ray source 1 according to the invention.
  • the source 1 comprises an anode 2 and a cathode 4.
  • the source 1 further comprises a housing in the form of a vacuum tube 8 enclosing an inner space 10 in which a vacuum is present.
  • This miniature X-ray source may e.g. be of generally cylindrical design, having a diameter of approximately 1-2.5 mm and a length of less than approximately 3 cm, preferably less than approximately 2 cm.
  • the miniature X-ray source 1 further comprises a diaphragm 12 comprising an aperture 14.
  • the diaphragm is made of an electrically conducting material.
  • the anode 2, a tubular extension 2' of the anode 2, and the diaphragm 12 together form electrically conducting walls of a chamber 16 which is closed except for the aperture 14.
  • the anode 2,2' and the diaphragm 12 may be considered to form an electrically conducting box 2,2',12 with the aperture 14 as entrance for the accelerated electrons.
  • the miniature X-ray source explained so far can be operated as follows.
  • the cathode 4 is maintained at earth potential (0 V), and the anode is maintained at a high voltage, e.g. 60 kV.
  • a power supply line 6 is drawn electrically conducting connected to the anode 2.
  • the cathode 4 may also be supplied with a power supply line.
  • the cathode is directly connected to earth, e.g. through an electrically conducting cooling fluid, such as water. Maintaining the cathode 4, i.e. the electron emitter at earth electric potential helps providing an electrical field inside the X-ray source which is substantially mainly axial and directed towards the anode 2, as the surroundings of the tubular housing 18 are also likely at earth electric potential. It will be appreciated that maintaining the cathode at earth electric potential will also be beneficial in the following examples of Figs. 3 , 4 and 5 , of tubular miniature X-ray source.
  • the cathode 4 When the high electrical potential difference is maintained between the cathode 4 and the anode 2, the cathode 4 will emit electrons which, due to the electric field caused by the electric potential difference, will be accelerated towards the anode 2.
  • At least a portion of the electrons emitted by the cathode 4 passes through the aperture 14 and impacts on the anode 2.
  • X-ray radiation is generated.
  • This X-ray radiation passes through the wall 2' of the box and through the wall of the vacuum tube 8.
  • substantially a point-source of X-ray radiation is obtained.
  • Some electrons impacting on the anode may, instead of X-ray radiation, also cause electrons or ions to be emitted (or reflected) by the anode. These electrons and/or ions may travel in the direction of the wall of the vacuum tube or in the general direction of the cathode 4.
  • the diaphragm blocks the path of flight of at least a portion of the electrons and/or ions travelling in the general direction of the cathode 4. Hence, these electrons and/or ions will be prevented from impacting the cathode 4 or the inner wall of the vacuum tube 8 between the cathode 4 and the diaphragm 12, where in this case an electric field is present. Hence, these electrons and/or ion will not form electron sources, so that the risk of electrical breakthrough is reduced.
  • the diaphragm 12 forms a directional barrier interposed between the cathode 4 and the anode 2 wherein the barrier is arranged to transmit, in use, electrons emitted by the cathode 4 towards the anode 2, and wherein the barrier is arranged to, in use, substantially prevent electrons and/or ions to pass the barrier in the direction of the anode 2 towards the cathode 4
  • the diaphragm 12 at the same electrical potential as the anode 2 also causes that between the anode 2 and the diaphragm 12 no electrical field is present. Thus, electrons and/or ions impacting the wall of the vacuum tube 8 (or the wall 2') between the anode 2 and the diaphragm 12 will not cause electrical breakthrough.
  • the diaphragm 12 may also be separate from the anode 2, while the diaphragm 12 is maintained at the same electric potential as the anode 2.
  • the diaphragm 12 thus forms guiding means for guiding electrons and/or ions to prevent the electrons and/or ions from impacting a wall of the vacuum tube 8, in this example in a region of the vacuum tube where, in use, an electric field is present.
  • the diaphragm is not electrically conductive it will, nevertheless, prevent at least some electrons and/or ions from impacting a wall of the vacuum tube 8.
  • the vacuum tube 8 comprises a tubular housing 18.
  • the vacuum tube 8 further has an electrically conducting first plug 20 at a first end and an electrically conducting second plug 22 at the other, second end.
  • first plug 20 is formed by the anode.
  • second plug 22 is formed by the cathode.
  • the first and second plug 20,22 are joined to the tubular housing 18 in a vacuum tight manner, e.g. by laser welding or brazing.
  • the vacuum tube may comprise an electrically conducting first cap, e.g. acting as or being part of the anode, at the first end and an electrically conducting second cap, e.g. acting as or forming part of the cathode, at the second end.
  • the vacuum tube 8, more specifically the tubular housing 18, comprises an inner wall 24, of a first material and an outer wall 26 of a second material.
  • the first and second material are selected such that a dielectric constant of the first material is higher than a dielectric constant of the second material, and that a dielectric strength of the second material is higher than a dielectric strength of the first material.
  • the first material may be a ceramic material, such as aluminium oxide (alumina) or boron nitride or another material defect free material such as glass, diamond or mono crystalline quartz. It is known that optically transparent alumina provides a high dielectric strength.
  • the second material may be a polymeric material, such as polyethylene. In the example of Fig. 1a the inner wall 24 is alumina and the outer wall 26 is polyethylene.
  • the thickness of the inner wall 24 and the outer wall 26 is such that the electric field strength inside the inner wall 24 is smaller than the electric field strength in the outer wall 26. It will be appreciated that it is, thus, possible to ensure that by choosing the desired thickness for the inner and outer wall the electric field strength inside the inner wall can be kept smaller than the dielectric strength of the first material, and the electric field strength inside the outer wall can be kept smaller than the dielectric strength of the second material. Thus, the region of high electrical field strengths is removed from the first material with a lower dielectric strength to the second material with the higher dielectric strength.
  • the optimum thicknesses of the inner wall 24 and outer wall 26, e.g. for a given total wall thickness may be determined by the following method.
  • An inner tubular wall with inner radius r1 and dielectric constant ⁇ iw and outer radius r2 covered with a outside wall with inner radius r2, dielectric constant ⁇ ow and outer radius r3 results in radial electrical field variation as a function of the radius r according to the following equations.
  • E iw V 13 / ⁇ iw r K
  • E ow V 13 / ⁇ ow r K
  • V 13 is the electrical potential difference across the (total of the inner and outer) tubular wall
  • E iw is the maximum electric field in the inner layer
  • E ow is the maximum electric field in the outer layer
  • K 1/ ⁇ iw ln (r2/r1) +1/ ⁇ ow ln (r3/r2).
  • Fig. 2 shows a graph in which the highest electric field value occurring in a tubular wall comprising the inner wall and the outer wall is demonstrated.
  • the inner wall 24 is alumina and the outer wall 26 is polyethylene, having dielectric constants of approximately 8 and 2, respectively.
  • the dielectric strength values of optically transparent alumina and polyethylene are approximately 50 kV/mm and 160 kV/mm, respectively.
  • Fig. 2 shows a graph in which the highest electric field value occurring in a tubular wall with an inner radius of 0.25 mm and an outer radius of 1 mm, i.e. a wall thickness of 0.75 mm, when 50 kV is applied across the wall.
  • the highest electrical field value is shown in the inner tubular wall 24 of alumina with an inner radius of 0.25 and an outer radius of r2 (lower curve in Fig. 2).
  • Fig. 2 further shows the highest electrical field value in the outer tubular wall 26 of polyethylene with an inner radius of r2 and an outer radius of 1 mm (upper curve in Fig. 2 ). Both the highest electrical field values in the inner and outer wall are shown as a function of r2.
  • the outer radius r2 of the inner wall ranges from 0.25 mm (only polyethylene) to 1 mm (only alumina) and the inner radius of the outer wall ranges from 0.25 mm (only polyethylene) to 1 mm (only alumina).
  • the outer radius of the inner wall of alumina approaches 1 mm, i.e. a wall thickness of the alumina inner wall of approximately 0.75 mm, the highest electric field in the inner wall exceeds the dielectric strength of alumina, so that electrical breakthrough in the inner wall might occur.
  • the inner radius of the outer wall of polyethylene is less than approximately 0.3 mm or exceeds approximately 0.7 mm (crosshatched in Fig. 2 ), i.e. a wall thickness of the outer wall of polyethylene of more than approximately 0.65 mm or less than approximately 0.3 mm, the highest electric field in the outer wall exceeds the dielectric strength of polyethylene, so that electrical breakthrough in the outer wall might occur.
  • Fig. 2 suggests that for the tubular wall with the inner wall of alumina and the outer wall of polyethylene, wherein the total wall has an inner radius of 0.25 mm and an outer radius of 1 mm, the thickness of the outer wall is preferably between approximately 0.3 and 0.7 mm, more preferably approximately 0.5 mm (near the minimum of the upper curve of Fig. 2 ). Accordingly, the thickness of the inner wall is preferably between approximately 0.05 and 0.45 mm, more preferably approximately 0.25 mm.
  • Fig. 1b shows a schematic sectional view of a variation of the embodiment according to Fig. 1a .
  • the source 1 is further provided with a tubular electrical conductor 27.
  • the tubular conductor 27 is placed between the inner and outer wall 24,26. It will be appreciated that the tubular conductor 27 may also be arranged on the inside of the inner wall 24 or on the outside of the outer wall.
  • the tubular conductor 27 is electrically connected to the cathode 4. It will be appreciated that the tubular conductor 27 may also be maintained at an electric potential different from that of the cathode 4.
  • the tubular conductor 27 shapes the electric field around the cathode 4 such that the tubular conductor 27 acts as an electric lens.
  • the electric lens is dimensioned such that substantially all electrons emitted by the cathode 4 are aimed through the aperture 14 in the direction of the anode 2.
  • substantially all electrons emitted by the cathode 4 are prevented from impacting the wall of the vacuum tube 8 in the region between the diaphragm 12 and the cathode 4, i.e. in the region of the vacuum tube 8 where, in use, the electric field is present.
  • these electrons will not form electron sources at the inner side of the inner wall 24, so that the risk of electrical breakthrough is reduced. Further the risk of electrically charging the inner wall 24 is reduced.
  • the electric lens forms electron focussing means for directing, in use, the electrons emitted by the cathode 4 in a direction towards the anode 2, such that substantially all electrons emitted by the cathode 4 are prevented from impacting the wall of the vacuum tube 8, in this example in the region of the vacuum tube where, in use, the electric field is present.
  • the electric lens thus forms guiding means for guiding electrons and/or ions to prevent the electrons and/or ions from impacting a wall of the vacuum tube 8, e.g. in a region of the vacuum tube where, in use, an electric field is present.
  • the electric lens may be used to reduce the risk of electrical breakthrough independently of the directional barrier.
  • Fig. 3 shows a schematic sectional view of a second embodiment of a miniature X-ray source 1 according to the invention.
  • the source 1 also comprises the anode 2, the cathode 4. and the vacuum tube 8 enclosing the inner space 10 in which a vacuum is present.
  • the anode 2,2' and the diaphragm 12 also form the electrically conducting box 2,2',12 with the aperture 14 as entrance for the accelerated electrons.
  • the cathode 4 is provided with a bore 40 which is in communication with a longitudinal bore 42 through which the inner space 10 can be evacuated. After evacuation a seal 44 may be sealed, e.g. by melting, welding, etc.
  • the inner space 10 also comprises a getter material 46 for absorbing any free particles in the inner space for reducing the vacuum pressure inside the inner space 10.
  • the getter material 46 is positioned at the cathode 4.
  • the anode 2 comprises a window 28 coated with a high molecular mass electrical conductive coating, such as e.g. a 1-20 ⁇ m thick layer of tungsten, for generating X-ray radiation when impacted by electrons.
  • the window 28 may be substantially, or at least partially, transparent to X-rays, e.g. alumina.
  • the source 1 further comprises an exit window 31 which is substantially, or at least partially, transparent to X-ray radiation.
  • the X-ray radiation exits the source 1 mainly through the exit window.
  • substantially a directional source of X-ray radiation is obtained. This may e.g. be particularly useful in imaging or detection.
  • the cathode 4 is of the cold cathode type.
  • the cathode 4 comprises a section 32 comprising carbon nanotubes for emitting electrons.
  • the carbon nanotubes may be aligned mono-wall nanotubes, aligned multi-wall nanotubes, randomised mono-wall nanotubes or randomised multi-wall nanotubes.
  • section 32 substantially acts as a randomly oriented source of electrons, emitting electrons both towards the anode 2 and towards the tubular housing 18.
  • the cathode 4 is concave, in a direction towards the anode 2.
  • the cathode 4 thus, has a ring-shaped projection 34 which shapes the electric field around the cathode 4, more in particular around the electron source section 32, such that the projection 34 acts as the electric lens.
  • the electric lens is dimensioned such that substantially all electrons emitted by the cathode 4 are aimed through the aperture 14 in the direction of the anode 2.
  • substantially all electrons emitted by the cathode 4 are prevented from impacting the wall of the vacuum tube 8 in the region between the diaphragm 12 and the cathode 4, i.e. in the region of the vacuum tube 8 where, in use, the electric field is present.
  • these electrons will not form electron sources at the wall, so that the risk of electrical breakthrough is reduced. Further the risk of electrically charging the inner wall 24 is reduced.
  • the miniature X-ray source 1 comprises a first electrically conducting, e.g. metal, shield 36 around the tubular housing 18 adjacent the anode 2. Further, the miniature X-ray source 1 comprises a second electrically conducting, e.g. metal, shield 38 around the tubular housing 18 adjacent the cathode 2.
  • the end of the first shield 36 towards the cathode 4 extends around the outside of the tubular housing 18 as far as the end of the anode 2.
  • the risk of electrical breakthrough is reduced.
  • the second shield 38 may also be dimensioned such that the second shield 38 acts as an electric lens.
  • this electric lens is dimensioned such that aids in aiming substantially all electrons emitted by the cathode 4 through the aperture 14 in the direction of the anode 2.
  • Fig. 4 shows a schematic sectional view of a second embodiment of a miniature X-ray source 1 according to the invention.
  • the source 1 also comprises the anode 2, the cathode 4 and the vacuum tube 8 enclosing the inner space 10 in which a vacuum is present.
  • the anode 2,2' and the diaphragm 12 also form the electrically conducting box 2,2',12 with the aperture 14 as entrance for the accelerated electrons.
  • the anode 2 comprises the window 28 coated with the high atomic mass electrical conductive coating, such as e.g a 1-10 ⁇ m thick layer of tungsten.
  • the miniature X-ray source 1 also comprises the first electrically conducting shield 36 around the tubular housing 18 adjacent the anode 2 and the second electrically conducting shield 38 around the tubular housing 18 adjacent the cathode 2.
  • the first and second shield 36, 38 are formed by a metallic coating on the outer side of the vacuum tube 8.
  • the first shield 36 is electrically connected to the anode 2, e.g. via the tubular portion 2'.
  • the second shield 38 is electrically connected to the cathode 4.
  • a high-resistivity coating 48 is applied on the outer side of the vacuum tube 8, in electrical connection with the first and second shield 36,38 respectively.
  • An electrical resistivity of the high-resistivity coating is preferably in the rang 10 6 -10 10 ohm/cm. It will be appreciated that the high-resistivity coating 48 may also be applied on the inner side of the vacuum tube 8, in electrical connection with the anode and the cathode. Thus, the high-resistivity coating may enforce a gradual linear voltage distribution along the isolating tubular housing 18 as a result of a small electric current (e.g. 0.1 to 100 ⁇ A) that may flow through the high-resistivity coating.
  • a small electric current e.g. 0.1 to 100 ⁇ A
  • the anode 2 is maintained at earth electric potential and the cathode 4 is maintained at a negative high voltage, e.g. -60 kV.
  • a negative high voltage e.g. -60 kV.
  • Fig. 5 shows a schematic sectional view of an array of miniature X-ray sources 1 according to a fourth embodiment of invention.
  • Such array may e.g. be desirable when a small X-ray source is required with a large surface area of substantially homogeneous X-ray radiation.
  • the sources 1 also comprises the anode 2, the cathode 4 and the vacuum tube 8 enclosing the inner space 10 in which a vacuum is present.
  • the anode 2,2' and the diaphragm 12 also form the electrically conducting box 2,2',12 with the aperture 14 as entrance for the accelerated electrons.
  • the anode 2 comprises the window 28 coated with the high molecular mass electrical conductive coating, such as e.g.
  • the ring-shaped projection 34 which shapes the electric field around the cathode 4, more in particular around the electron source section 32, such that the projection 34 acts as an electric lens is not integral with the cathode 4, but designed as a separate part.
  • the ring-shaped part 34 may be maintained at an electronic potential that differs from the electric potential of the cathode 4.
  • the ring-shaped part 34 may e.g. be electrically conducting connected to a voltage supply line 35.
  • Fig. 5 the beam of electrons emitted by the cathode 4, transmitted through the aperture 14 and impacted on the anode 2 is indicated with broken lines.
  • the invention is by no means limited to the above exemplary embodiments.
  • a miniature X-ray source for providing X-ray radiation which is emitted intermittently, e.g. by sequentially switching a supply power to the cathode and/or the anode on and off.
  • an electric lens is used for preventing electrons emitted by the cathode from impacting the wall of the vacuum tube in the region where, in use, the electric field is present. It will be appreciated that alternatively, or additionally, a magnetic lens may be used.
  • the cold cathode comprises carbon nanotubes as electron source.
  • Alternative “hot” or “cold” electron sources can also be used, such as metal-insulator-metal stacks (MIM), piezo-electric crystals or thermionic surfaces (e.g a tungsten filament).
  • the exit window is flat. It will be appreciated that the exit window can also have other shapes such as conical or dome-shaped.
  • the diaphragm and the anode form a substantially cylindrical box. It will be appreciated that also other shapes are possible.
  • the box may e.g. be conical, frustoconical, dome-shaped, block-shaped, pyramidal, etc.
  • an, e.g. grid shaped, electron absorbing element is disposed between the cathode and the directional barrier for absorbing any electrons being reflected from the barrier towards the cathode.
  • the grid-shaped absorbing element may e.g. be maintained at an electrical potential which is slightly higher than that of the anode.

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  • X-Ray Techniques (AREA)
EP07110601A 2007-06-19 2007-06-19 Miniaturröntgenquelle mit Führungsvorrichtung für Elektronen und / oder Ionen Withdrawn EP2006880A1 (de)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP07110601A EP2006880A1 (de) 2007-06-19 2007-06-19 Miniaturröntgenquelle mit Führungsvorrichtung für Elektronen und / oder Ionen
PCT/NL2008/050400 WO2008156361A2 (en) 2007-06-19 2008-06-19 Miniature x-ray source with guiding means for electrons and / or ions

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP07110601A EP2006880A1 (de) 2007-06-19 2007-06-19 Miniaturröntgenquelle mit Führungsvorrichtung für Elektronen und / oder Ionen

Publications (1)

Publication Number Publication Date
EP2006880A1 true EP2006880A1 (de) 2008-12-24

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP07110601A Withdrawn EP2006880A1 (de) 2007-06-19 2007-06-19 Miniaturröntgenquelle mit Führungsvorrichtung für Elektronen und / oder Ionen

Country Status (2)

Country Link
EP (1) EP2006880A1 (de)
WO (1) WO2008156361A2 (de)

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CN103715047A (zh) * 2012-10-02 2014-04-09 双叶电子工业株式会社 X射线管
GB2530254A (en) * 2014-09-12 2016-03-23 Xstrahl Ltd X-Ray system
EP3240010B1 (de) * 2014-12-25 2022-02-09 Meidensha Corporation Feldemissionsvorrichtung und reformierungsbehandlungsverfahren

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JP5871529B2 (ja) 2011-08-31 2016-03-01 キヤノン株式会社 透過型x線発生装置及びそれを用いたx線撮影装置
JP5875297B2 (ja) * 2011-08-31 2016-03-02 キヤノン株式会社 放射線発生管及びそれを用いた放射線発生装置、放射線撮影システム
JP5901180B2 (ja) 2011-08-31 2016-04-06 キヤノン株式会社 透過型x線発生装置及びそれを用いたx線撮影装置
JP5871528B2 (ja) * 2011-08-31 2016-03-01 キヤノン株式会社 透過型x線発生装置及びそれを用いたx線撮影装置
JP6549730B2 (ja) * 2015-12-25 2019-07-24 株式会社ニコン 荷電粒子装置、構造物の製造方法および構造物製造システム
CN105632856B (zh) * 2016-01-20 2018-06-19 西北核技术研究所 阳极箔产生等离子体加强箍缩聚焦的小焦斑x射线二极管

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CN103715047A (zh) * 2012-10-02 2014-04-09 双叶电子工业株式会社 X射线管
JP2014075188A (ja) * 2012-10-02 2014-04-24 Futaba Corp X線管
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GB2530254A (en) * 2014-09-12 2016-03-23 Xstrahl Ltd X-Ray system
EP3240010B1 (de) * 2014-12-25 2022-02-09 Meidensha Corporation Feldemissionsvorrichtung und reformierungsbehandlungsverfahren

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WO2008156361A2 (en) 2008-12-24

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