EP0584871A1 - X-ray tube with anode in transmission mode - Google Patents
X-ray tube with anode in transmission mode Download PDFInfo
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- EP0584871A1 EP0584871A1 EP93202435A EP93202435A EP0584871A1 EP 0584871 A1 EP0584871 A1 EP 0584871A1 EP 93202435 A EP93202435 A EP 93202435A EP 93202435 A EP93202435 A EP 93202435A EP 0584871 A1 EP0584871 A1 EP 0584871A1
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- Prior art keywords
- ray tube
- target layer
- angle
- anode
- electrons
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
- H01J35/08—Anodes; Anti cathodes
- H01J35/10—Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
- H01J35/08—Anodes; Anti cathodes
- H01J35/10—Rotary anodes; Arrangements for rotating anodes; Cooling rotary anodes
- H01J35/101—Arrangements for rotating anodes, e.g. supporting means, means for greasing, means for sealing the axle or means for shielding or protecting the driving
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J35/00—X-ray tubes
- H01J35/02—Details
- H01J35/04—Electrodes ; Mutual position thereof; Constructional adaptations therefor
- H01J35/08—Anodes; Anti cathodes
- H01J35/112—Non-rotating anodes
- H01J35/116—Transmissive anodes
Definitions
- the invention relates to an X-ray tube with a transmission anode, which comprises a target layer made of one or more metals with a high atomic number that is hit by electrons in the operating state and a carrier layer made of one or more substances with a low atomic number connected to the target layer.
- Such X-ray tubes are known - for example from DE-OS 27 29 833, from US-PS 20 90 636 and from US-PS 3 894 239.
- the target layer should be as thick as possible in order to convert the impinging electrons as high as possible into X-ray quanta.
- this layer must be as thin as possible in order to weaken the X-ray quanta generated in it as little as possible.
- the carrier layer must be thin enough on the one hand to weaken the emerging X-rays as little as possible and on the other hand thick enough to ensure the mechanical stability and the dissipation of the thermal energy generated in the target layer.
- these X-ray tubes at least for a voltage range between 50 and 500 kV, which is important for medical, but also for industrial examinations - have hardly found their way into practice.
- X-ray tubes with anodes are used, in which the X-rays are emitted from the side of the anode on which the electrons strike. These anodes are therefore also referred to below as reflection anodes.
- the object of the present invention is to design an X-ray tube of the type mentioned at the outset, whose operating voltage is in the range between 50 kV and 500 kV, in such a way that with the electrical energy applied to operate the X-ray tube, more X-radiation is generated in the useful radiation beam than in the case of an X-ray tube Reflection anode.
- the angle ⁇ between the direction of incidence of the electrons and the direction of the X-rays emitted through the carrier layer in the useful beam is between 10 ° and 40 °.
- the invention is based on the knowledge that the intensity of the X-rays is very dependent on the angle that the emitted X-rays form with the direction of the electrons. Neglecting the weakening by the target results in a pronounced maximum intensity on the lateral surface of a cone, the central axis of which is formed by the direction of the electron beam generating the X-rays.
- the opening angle of this cone depends on the operating voltage, and the smaller the higher the operating voltage, the smaller it is. For an operating voltage of 60 kV, half the opening angle of the cone with the maximum intensity is approx. 40 °, and for an operating voltage of 500 kV approx. 10 °.
- the invention takes advantage of this knowledge by determining the angle between the light beam, i.e. selects the part of the X-ray radiation used outside the X-ray tube, and the direction of incidence of the electrons generating the X-ray radiation accordingly.
- the useful beam has an aperture angle that differs from zero at least in one direction.
- the angle between an X-ray beam in the center of the useful beam and the direction of incidence of the electrons must be chosen as specified in the claim.
- the useful beam In the previously known x-ray tubes with a transmission anode, the useful beam generally runs in the extension of the electron path, ie the angle ⁇ is zero.
- FIG. 7 of DE-OS 27 29 833 describes an X-ray tube with an annular anode, in which the X-radiation is generated by means of two groups of cathodes distributed over the circumference of the anode, which are arranged on both sides of a central plane running through the radiator. This results in an angle ⁇ of 45 °.
- the invention can be used in different X-ray tubes for different applications. According to a preferred development of the invention, it is provided that it is designed as a rotating anode X-ray tube and that the target layer (for example made of tungsten and / or rhenium) lies on the lateral surface of a truncated cone which encloses an angle with the direction of the X-rays used outside the X-ray tubes , which is smaller than the angle that exists between this direction and the direction of the incident electrons.
- the target layer for example made of tungsten and / or rhenium
- the anode has the shape of a bowl which is symmetrical with respect to its axis of rotation, the inner surface of which is provided with the target layer and faces the electron-emitting electron source and the useful beam of rays is preferably emitted from the outer surface at an angle of 90 ° to the axis of rotation.
- the transmission anode shown in FIG. 1 comprises a target layer 1 made of a metal with a high atomic number, which is applied to a carrier layer 2 made of a material with a low atomic number.
- the target layer 1 can consist, for example, of tungsten or rhenium or of an alloy of these metals; other metals suitable for the target layer 1 are platinum or thorium.
- the carrier layer 2 can consist of graphite or beryllum and have such a thickness that, on the one hand, there is sufficient mechanical stability and the X-ray radiation, if possible is weakened little.
- the arrow 3 denotes an electron beam which strikes the target layer 1 at an angle ⁇ with the normal. This creates X-rays that spread on a sphere around the point of impact.
- theoretical and experimental studies have shown that neglecting the weakening by the target layer results in the greatest intensity of X-rays, which spread on the surface of a cone (with its tip in the electron impingement point and its axis of symmetry parallel to the direction of the electron beam) with a certain aperture angle ⁇ .
- the upper limit beam 4a and the lower limit beam 4b of this cone are shown in FIG. 1.
- Half the opening angle ⁇ of this cone depends on the operating voltage, whereby the table applies approximately: U / kV 60-100 100-150 150-200 200-350 350-500 ⁇ 40 ° - 35 ° 35 ° - 30 ° 30 ° - 25 ° 25 ° - 20 ° 20 ° - 15 °
- the x-ray tube must be designed so that the direction of the useful beam coincides with the direction of one of the beams on the cone jacket.
- the X-rays generated in the target layer can run at different angles to the layer planes, the drawing showing the smallest angle ⁇ 1 and the largest angle ⁇ 2.
- ⁇ 2 90 ° - ⁇ + ⁇ (2)
- a is the relative atomic weight
- Z is the atomic number of the metal from which the target layer is made.
- ⁇ is the angle of incidence of the electrons, ie the angle that the direction of the electron beam 3 forms with the normal to the target layer. If the target layer consists of an alloy of two or more metals, the mass of the target layer per unit area is calculated by using each metal of the alloy calculates the value w according to equation (3) and the calculated values are weighted according to the respective alloy proportion.
- the intensity of the X-ray radiation in the useful beam bundle is significantly greater than for an X-ray tube with a reflection anode, with which the angle between Electron incidence direction and beam exit direction is approx. 90 °.
- the X-ray tube is operated at a voltage other than that for which it is designed, these intensity advantages decrease.
- the x-ray tube comprises a tube bulb 5 made of glass, in which a cathode arrangement 6 and an anode arrangement 7 are located.
- the anode arrangement comprises a transmission anode 2 which is fastened in a known manner to a rotor 8 which is rotatably mounted in the interior of the X-ray tube.
- the rotor is driven by a stator arranged outside the glass bulb and not shown in FIG. 2.
- the transmission anode comprises a carrier body 2 made of graphite and has a bowl or plate shape which is open towards the cathode arrangement 6.
- a target layer 1 made of rhenium is applied to the carrier body 2. If the X-ray tube is intended for the purposes of computer tomography and is accordingly designed for an operating voltage of 150 kV and if the electron beam 3 strikes the layer at an angle of 40 ° with the normal direction, then the mass of this layer, based on the unit area, is according to equation (3) 0.024 g / cm2. This is achieved by a 11.5 ⁇ m thick rhenium layer.
- the X-ray tube is located inside a housing, of which part of the housing wall 10 is shown in FIG. 2 only on the right side.
- the housing wall comprises a lining made of an X-ray absorbing material, for example lead of sufficient thickness.
- a radiation exit window 11 made of a material transparent to the X-rays, e.g. made of aluminum, so that useful radiation can only escape in this area.
- the useful radiation then runs perpendicular to the axis of rotation at an angle of 30 ° to the direction of the electron beam.
- an almost flat fan-shaped bundle of rays is masked out perpendicular to the plane of the drawing in FIG. 2 through the radiation exit window. In this case, the main direction of expansion of the radiation exit window likewise runs perpendicular to the plane of the drawing.
- the invention was explained above on the basis of a rotating anode X-ray tube with a glass bulb intended for medical examinations, the invention can also be used in other embodiments.
- a fixed anode can be used instead of a rotating anode.
- an X-ray tube with a glass bulb an X-ray tube with a metal bulb can also be used, in which the cathode and / or anode are connected to the metal bulb via insulators.
- the X-ray tube can also be used for non-destructive examinations in the industrial sector; In the range of tube voltages (200 - 500 kV) used for this purpose, the efficiency is particularly high.
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- X-Ray Techniques (AREA)
Abstract
Description
Die Erfindung betrifft eine Röntgenröhre mit einer Transmissionsanode, die eine im Betriebszustand von Elektronen getroffene Targetschicht aus einem oder mehreren Metallen mit hoher Ordnungszahl und eine mit der Targetschicht verbundene Trägerschicht aus einem oder mehreren Stoffen mit niedriger Ordnungszahl umfaßt.The invention relates to an X-ray tube with a transmission anode, which comprises a target layer made of one or more metals with a high atomic number that is hit by electrons in the operating state and a carrier layer made of one or more substances with a low atomic number connected to the target layer.
Solche Röntgenröhren sind bekannt - beispielsweise aus der DE-OS 27 29 833, aus der US-PS 20 90 636 und aus der US-PS 3 894 239. Für die Dicke der beiden Schichten ergeben sich einander widersprechende Forderungen. Einerseits soll die Targetschicht möglichst dick sein, um die auftreffenden Elektronen zu einem möglichst hohen Prozentsatz in Röntgenquanten umzuwandeln. Andererseits muß diese Schicht möglichst dünn sein, um die darin erzeugten Röntgenquanten möglichst wenig zu schwächen. Die Trägerschicht muß einerseits dünn genug sein, um die austretenden Röntgenstrahlen möglichst wenig zu schwächen und andererseits dick genug, um die mechanische Stabilität und die Ableitung der in der Targetschicht erzeugten thermischen Energie zu gewährleisten.Such X-ray tubes are known - for example from DE-OS 27 29 833, from US-PS 20 90 636 and from US-
Wohl wegen dieser einander widersprechenden Forderungen haben diese Röntgenröhren - jedenfalls für einen Spannungsbereich zwischen 50 und 500 kV, der für medizinische, aber auch für industrielle Untersuchungen wichtig ist - kaum Eingang in die Praxis gefunden. Für diese Zwecke werden Röntgenröhren mit Anoden eingesetzt, bei denen die Röntgenstrahlen von der Seite der Anode emittiert werden, auf die die Elektronen auftreffen. Diese Anoden werden deshalb im folgenden auch als Reflexionsanoden bezeichnet.Probably because of these contradicting requirements, these X-ray tubes - at least for a voltage range between 50 and 500 kV, which is important for medical, but also for industrial examinations - have hardly found their way into practice. For this purpose, X-ray tubes with anodes are used, in which the X-rays are emitted from the side of the anode on which the electrons strike. These anodes are therefore also referred to below as reflection anodes.
Bei allen Röntgenröhren wird in dem Spannungsbereich bis zu 500 kV nur ein Kleiner Teil der aufgebrachten elektrischen Energie in Röntgenstrahlung umgesetzt; der Rest der aufgewandten Energie führt zur Erwärmung der Anode. Von der erzeugten Röntgenstrahlung wird außerhalb der Röntgenröhre wiederum nur ein kleiner Bruchteil als Nutzstrahlenbündel ausgenutzt.With all X-ray tubes, only a small part of the electrical energy applied is converted into X-rays in the voltage range up to 500 kV; the rest of the energy used leads to the heating of the anode. Only a small fraction of the X-rays generated is used outside the X-ray tube as a useful beam.
Aufgabe der vorliegenden Erfindung ist es, eine Röntgenröhre der eingangs genannten Art, deren Betriebsspannung im Bereich zwischen 50 kV und 500 kV liegt, so auszugestalten, daß mit der zum Betrieb der Röntgenröhre aufgebrachten elektrischen Energie im Nutzstrahlenbündel mehr Röntgenstrahlung erzeugt wird als bei einer Röntgenröhre mit Reflexionsanode.The object of the present invention is to design an X-ray tube of the type mentioned at the outset, whose operating voltage is in the range between 50 kV and 500 kV, in such a way that with the electrical energy applied to operate the X-ray tube, more X-radiation is generated in the useful radiation beam than in the case of an X-ray tube Reflection anode.
Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß der Winkel ϑ zwischen der Einfallsrichtung der Elektronen und der Richtung der durch die Trägerschicht hindurch emittierten Röntgenstrahlen im Nutzstrahlenbündel zwischen 10° und 40° beträgt.This object is achieved according to the invention in that the angle ϑ between the direction of incidence of the electrons and the direction of the X-rays emitted through the carrier layer in the useful beam is between 10 ° and 40 °.
Die Erfindung basiert auf der Erkenntnis, daß die Intensität der Röntgenstrahlung sehr stark von dem Winkel abhängig ist, den die emittierte Röntgenstrahlung mit der Richtung der Elektronen einschließt. Unter Vernachlässigung der Schwächung durch das Target ergibt sich ein ausgeprägtes Intensitätsmaximum auf der Mantelfläche eines Kegels, dessen Mittelachse durch die Richtung des die Röntgenstrahlen erzeugenden Elektronenstrahls gebildet wird. Der Öffnungswinkel dieses Kegels ist von der Betriebsspannung abhängig, und zwar wird er umso kleiner, je höher die Betriebsspannung ist. Für eine Betriebsspannung von 60 kV beträgt der halbe Öffnungswinkel des Kegels mit der maximalen Intensität ca. 40°, und für eine Betriebsspannung von 500 kV ca. 10°.The invention is based on the knowledge that the intensity of the X-rays is very dependent on the angle that the emitted X-rays form with the direction of the electrons. Neglecting the weakening by the target results in a pronounced maximum intensity on the lateral surface of a cone, the central axis of which is formed by the direction of the electron beam generating the X-rays. The opening angle of this cone depends on the operating voltage, and the smaller the higher the operating voltage, the smaller it is. For an operating voltage of 60 kV, half the opening angle of the cone with the maximum intensity is approx. 40 °, and for an operating voltage of 500 kV approx. 10 °.
Die Erfindung nutzt diese Erkenntnis dadurch aus, daß sie den Winkel zwischen dem Nutzstrahlenbündel, d.h. dem außerhalb der Röntgenröhre ausgenutzten Teil der Röntgenstrahlung, und der Einfallsrichtung der die Röntgenstrahlung erzeugenden Elektronen entsprechend wählt.The invention takes advantage of this knowledge by determining the angle between the light beam, i.e. selects the part of the X-ray radiation used outside the X-ray tube, and the direction of incidence of the electrons generating the X-ray radiation accordingly.
In der Regel hat das Nutzstrahlenbündel zumindest in einer Richtung einen von Null verschiedenen Öffnungswinkel. In diesem Fall muß der Winkel zwischen einem Röntgenstrahl im Zentrum des Nutzstrahlenbündels und der Einfallsrichtung der Elektronen so gewählt sein, wie im Anspruch angegeben.As a rule, the useful beam has an aperture angle that differs from zero at least in one direction. In this case, the angle between an X-ray beam in the center of the useful beam and the direction of incidence of the electrons must be chosen as specified in the claim.
Bei den bisher bekannten Röntgenröhren mit Transmissionsanode verläuft das Nutzstrahlenbündel in der Regel in der Verlängerung der Elektronenbahn, d.h. der Winkel ϑ ist Null.In the previously known x-ray tubes with a transmission anode, the useful beam generally runs in the extension of the electron path, ie the angle ϑ is zero.
Jedoch gibt es auch Röntgenröhren mit einer Transmissionsanode, bei denen der Winkel ϑ von Null verschieden ist. So ist aus der US-PS 3 894 239 eine Drehanoden-Röntgenröhre mit einer Transmissionsanode bekannt, bei der ein Elektronenbündel etwa senkrecht auf eine Targetschicht auftrifft, die gegenüber dem Strahlenaustrittsfenster um ca. 80° geneigt. ist. Dadurch soll das in der Targetschicht erzeugte kontinuierliche Bremsstrahlungsspektrum wesentlich stärker geschwächt werden als die in der Targetschicht erzeugte Fluoreszenzstrahlung.However, there are also X-ray tubes with a transmission anode in which the angle ϑ is different from zero. A rotating anode x-ray tube with a transmission anode is known from US Pat. No. 3,894,239, in which an electron beam strikes approximately perpendicularly on a target layer which is inclined by approximately 80 ° with respect to the radiation exit window. is. The aim of this is to weaken the continuous brake radiation spectrum generated in the target layer much more than the fluorescence radiation generated in the target layer.
Weiterhin ist in Fig. 7 der DE-OS 27 29 833 eine Röntgenröhre mit einer ringförmigen Anode beschrieben, bei der die Röntgenstrahlung mittels zweier auf den Umfang der Anode verteilter Gruppen von Kathoden erzeugt wird, die beiderseits einer durch den Strahler verlaufenden Mittelebene angeordnet sind. Dadurch ergibt sich jeweils ein Winkel ϑ von 45°.Furthermore, FIG. 7 of DE-OS 27 29 833 describes an X-ray tube with an annular anode, in which the X-radiation is generated by means of two groups of cathodes distributed over the circumference of the anode, which are arranged on both sides of a central plane running through the radiator. This results in an angle ϑ of 45 °.
In keiner dieser Veröffentlichungen wird die Tatsache ausgenutzt, daß die Röntgenstrahlung in einem Winkelbereich zwischen 15° (bei hohen Röhrenspannungen) und 40° (bei niedrigen Röhrenspannungen) besonders intensiv ist.Neither of these publications takes advantage of the fact that the X-rays are particularly intense in an angular range between 15 ° (at high tube voltages) and 40 ° (at low tube voltages).
Schließlich ist aus der WO 92/03837 eine Röntgenröhre mit einer Reflexionsanode bekannt, bei der die Elektronen unter einem Winkel von 10° (statt üblicherweise 70° - 90°) auf die Anode auftreffen und bei der das Nutzstrahlenbündel unter einem Winkel von 5° - 15° in Bezug auf die Anode verläuft. Dabei kann sich aber das Strahlenaustrittsfenster stark durch Streuelektronen erwärmen.Finally, from WO 92/03837 an X-ray tube with a reflection anode is known, in which the electrons strike the anode at an angle of 10 ° (instead of usually 70 ° - 90 °) and in which the useful beam is at an angle of 5 °. 15 ° with respect to the anode. However, the radiation exit window can heat up considerably due to scattered electrons.
In Ausgestaltung der Erfindung ist vorgesehen, daß das für die Röntgenstrahlenausbeute wesentliche Gewicht w der Targetschicht pro Flächeneinheit - ausgedrückt in Gramm/cm² - zumindest annähernd der Beziehung genügt:
wobei A die relative Atommasse und Z die Ordnungszahl des Metalls der Targetschicht ist, U die Betriebsspannung in kV, für die die Röntgenröhre ausgelegt ist, und β der Winkel ist, den die Einfallsrichtung der Elektronen mit der Normalen auf die Targetschicht einschließt. Für eine Röntgenröhre mit einer Targetschicht aus Wolfram ergibt sich daraus für eine Betriebsspannung U = 100 kV eine Masse pro Flächeneinheit von 0,017 g/cm² bzw. eine Dicke von 8,6 µm (für β=0°).In an embodiment of the invention it is provided that the weight w of the target layer per unit area, which is essential for the X-ray yield - expressed in grams / cm 2 - at least approximately satisfies the relationship:
where A is the relative atomic mass and Z is the atomic number of the metal of the target layer, U is the operating voltage in kV for which the X-ray tube is designed, and β is the angle that is the direction of incidence of the electrons with the normal to the target layer. For an X-ray tube with a target layer made of tungsten, this results in a mass per unit area of 0.017 g / cm² or a thickness of 8.6 µm for an operating voltage U = 100 kV (for β = 0 °).
Die Erfindung kann bei unterschiedlichen Röntgenröhren für unterschiedliche Anwendungszwecke eingesetzt werden. Nach einer bevorzugten Weiterbildung der Erfindung ist vorgesehen, daß sie als Drehanoden-Röntgenröhre ausgebildet ist und daß die Targetschicht (beispielsweise aus Wolfram und/oder Rhenium) auf der Mantelfläche eines Kegelstumpfes liegt, der mit der Richtung der außerhalb der Röntgenrohre ausgenutzten Röntgenstrahlen einen Winkel einschließt, der Kleiner ist als der Winkel, der zwischen dieser Richtung und der Richtung der einfallenden Elektronen besteht. Die Anode hat dabei die Form einer zu ihrer Drehachse symmetrischen Schüssel, deren mit der Targetschicht versehene Innenfläche der die Elektronen emittierenden Elektronenquelle zugewandt ist und deren Nutzstrahlenbündel vorzugsweise unter einem Winkel von 90° zur Drehachse aus der Außenfläche emittiert wird.The invention can be used in different X-ray tubes for different applications. According to a preferred development of the invention, it is provided that it is designed as a rotating anode X-ray tube and that the target layer (for example made of tungsten and / or rhenium) lies on the lateral surface of a truncated cone which encloses an angle with the direction of the X-rays used outside the X-ray tubes , which is smaller than the angle that exists between this direction and the direction of the incident electrons. The anode has the shape of a bowl which is symmetrical with respect to its axis of rotation, the inner surface of which is provided with the target layer and faces the electron-emitting electron source and the useful beam of rays is preferably emitted from the outer surface at an angle of 90 ° to the axis of rotation.
Die Erfindung wird nachstehend anhand der Zeichnungen näher erläutert. Es zeigen
- Fig. 1
- eine Prinzipzeichnung eines Teils einer Transmissionsanode und
- Fig. 2
- eine Drehanoden-Röntgenröhre mit einer erfindungsgemäßen Transmissionsanode.
- Fig. 1
- a schematic diagram of part of a transmission anode and
- Fig. 2
- a rotating anode X-ray tube with a transmission anode according to the invention.
Die in Fig. 1 dargestellte Transmissionsanode umfaßt eine Targetschicht 1 aus einem Metall mit einer hohen Ordnungszahl, die auf eine Trägerschicht 2 aus einem Stoff mit einer niedrigen Ordnungszahl aufgebracht ist. Die Targetschicht 1 kann beispielsweise aus Wolfram oder Rhenium oder aus einer Legierung dieser Metalle bestehen; andere für die Targetschicht 1 geeignete Metalle sind Platin oder Thorium. Die Trägerschicht 2 kann aus Graphit oder Beryllum bestehen und eine solche Dicke aufweisen, daß sich einerseits eine genügende mechanische Stabilität ergibt und die Röntgenstrahlung möglichst wenig geschwächt wird.The transmission anode shown in FIG. 1 comprises a
Mit dem Pfeil 3 ist ein Elektronenstrahl bezeichnet, der unter einem Winkel β mit der Normalen auf die Targetschicht 1 auftrifft. Dadurch wird Röntgenstrahlung erzeugt, die sich auf einer Kugel um den Auftreffpunkt ausbreitet. Theoretische und experimentelle Untersuchungen haben jedoch gezeigt, daß bei Vernachlässigung der Schwächung durch die Targetschicht die Röntgenstrahlung, die sich auf dem Mantel eines Kegels (mit seiner Spitze im Elektronenauftreffpunkt und seiner Symmetrieachse parallel zur Elektronenstrahlrichtung) mit einem bestimmten Öffnungswinkel ϑ ausbreitet, die größte Intensität hat. Von diesem Kegel sind in Fig. 1 der obere Grenzstrahl 4a und der untere Grenzstrahl 4b dargestellt. Der halbe Öffnungswinkel ϑ dieses Kegels hängt von der Betriebsspannung ab, wobei näherungsweie die Tabelle gilt:
Deshalb muß die Röntgenröhre so gestaltet werden, daß die Richtung des Nutzstrahlenbündels mit der Richtung eines der Strahlen auf dem Kegelmantel zusammenfällt. Die in der Targetschicht erzeugte Röntgenstrahlung kann dabei unter verschiedenen Winkeln zu den Schichtebenen verlaufen, wobei die Zeichnung den kleinsten Winkel α₁ und den größten Winkel α₂ zeigt. Für diese Winkel gelten die Gleichungen
Die für die Strahlenausbeute optimale Masse der Targetschicht pro Flächeneinheit errechnet sich angenähert nach der Beziehung
Dabei ist a die relative Atommasse (atomic weight) und Z die Ordnungszahl (atomic number) des Metalls, aus dem die Targetschicht besteht. β ist der Einfallswinkel der Elektronen, d.h. der Winkel, den die Richtung des Elektronenstrahls 3 mit der Normalen auf die Targetschicht bildet. Wenn die Targetschicht aus einer Legierung aus zwei oder mehreren Metallen besteht, errechnet sich die Masse der Targetschicht pro Flächeneinheit, indem man für jedes Metall der Legierung den Wert w entsprechend Gleichung (3) berechnet und die berechneten Werte entsprechend dem jeweiligen Legierungsanteil gewichtet summiert.Therefore, the x-ray tube must be designed so that the direction of the useful beam coincides with the direction of one of the beams on the cone jacket. The X-rays generated in the target layer can run at different angles to the layer planes, the drawing showing the
The optimal mass of the target layer per unit area for the radiation yield is calculated approximately according to the relationship
Here, a is the relative atomic weight and Z is the atomic number of the metal from which the target layer is made. β is the angle of incidence of the electrons, ie the angle that the direction of the
Wenn die Strahlenaustrittsrichtung entsprechend der Tabelle gewählt und die Dicke der Targetschicht entsprechend Gleichung (3) bemessen ist, ist - bei gleicher Röhrenspannung und bei gleichem Röhrenstrom - die Intensität der Röntgenstrahlung im Nutzstrahlenbündel signifikant größer als bei einer Röntgenröhre mit Reflexionsanode, bei der der Winkel zwischen Elektroneneinfallsrichtung und Strahlenaustrittsrichtung ca. 90° beträgt. Die Zunahme der Intensität ist umso ausgeprägter, je größer die Röhrenspannung ist. - Betreibt man allerdings die Röntgenröhre bei einer anderen Spannung als derjenigen, für die sie ausgelegt ist, dann nehmen diese Intensitätsvorteile ab.If the beam exit direction is selected in accordance with the table and the thickness of the target layer is dimensioned in accordance with equation (3), the intensity of the X-ray radiation in the useful beam bundle is significantly greater than for an X-ray tube with a reflection anode, with which the angle between Electron incidence direction and beam exit direction is approx. 90 °. The greater the tube voltage, the more pronounced the increase in intensity. - However, if the X-ray tube is operated at a voltage other than that for which it is designed, these intensity advantages decrease.
In Fig. 2 ist als Ausführungsbeispiel eine Drehanoden-Röntgenröhre mit einer erfindungsgemäßen Transmissionsanode dargestellt. Die Röntgenröhre umfaßt einen Röhrenkolben 5 aus Glas, in dem sich eine Kathodenanordnung 6 und eine Anodenanordnung 7 befinden. Die Anodenanordnung umfaßt eine Transmissionsanode 2, die in bekannter Weise an einem Rotor 8 befestigt ist, der im Innern der Röntgenröhre drehbar gelagert ist. Der Antrieb des Rotors erfolgt durch einen außerhalb des Glaskolbens angeordneten, in Fig. 2 nicht näher dargestellten Stator.2 shows a rotating anode X-ray tube with a transmission anode according to the invention as an exemplary embodiment. The x-ray tube comprises a
Die Transmissionsanode umfaßt einen Trägerkörper 2 aus Graphit und hat eine zur Kathodenanordnung 6 hin offene Schüssel- oder Tellerform. In dem vom Elektronenstrahl 3 aus einem an der Kathodenanordnung 6 befestigten Elektronenemitter bestrichenen Bereich der Transmissionsanode ist eine Targetschicht 1 aus Rhenium auf den Trägerkörper 2 aufgebracht. Wenn die Röntgenröhre für Zwecke der Computertomographie bestimmt ist und dementsprechend für eine Betriebsspannung von 150 kV ausgelegt ist und wenn der Elektronenstrahl 3 unter einem Winkel von 40° mit der normalen Richtung auf die Schicht trifft, dann beträgt die Masse dieser Schicht, bezogen auf die Flächeneinheit gemäß Gleichung (3) 0,024 g/cm². Dies wird durch eine 11,5 µm dicke Rheniumschicht erreicht.The transmission anode comprises a
Die Röntgenröhre befindet sich im Innern eines Gehäuses, von dem in Fig. 2 nur auf der rechten Seite ein Teil der Gehäusewand 10 dargestellt ist. Die Gehäusewand umfaßt eine Auskleidung aus einem die Röntgenstrahlung absorbierenden Material, beispielsweise Blei von genügender Dicke. Lediglich in Höhe der Targetschicht ist ein Strahlenaustrittsfenster 11 aus einem für die Röntgenstrahlung transparenten Material vorgesehen, z.B. aus Aluminium, so daß nur in diesem Bereich Nutzstrahlung austreten kann. Die Nutzstrahlung verläuft dann senkrecht zur Rotationsachse unter einem Winkel von 30° zur Richtung des Elektronenbündels. Bei Anwendung für CT-Untersuchungen wird durch das Strahlenaustrittsfenster ein nahezu ebenes fächerförmiges Strahlenbündel senkrecht zur Zeichenebene der Fig. 2 ausgeblendet. Die Hauptausdehnungsrichtung des Strahlenaustrittsfensters verläuft in diesem Fall ebenfalls senkrecht zur Zeichenebene.The X-ray tube is located inside a housing, of which part of the
Obwohl die Erfindung vorstehend anhand einer für medizinische Untersuchungen bestimmten Drehanoden-Röntgenröhre mit einem Glaskolben erläutert wurde, ist die Erfindung auch bei anderen Ausführungsformen verwendbar. Beispielsweise kann anstelle einer Drehanode eine Festanode verwendet werden. Anstelle einer Röntgenröhre mit Glaskolben kann auch eine Röntgenröhre mit Metallkolben verwendet werden, bei der Kathode und/oder Anode über Isolatoren mit dem Metallkolben verbunden sind. Die Röntgenröhre kann auch für zerstörungsfreie Untersuchungen im industriellen Bereich eingesetzt werden; in dem für diese Zwecke benutzten Bereich von Röhrenspannungen (200 - 500 kV) ergibt sich ein besonders hoher Wirkungsgrad.Although the invention was explained above on the basis of a rotating anode X-ray tube with a glass bulb intended for medical examinations, the invention can also be used in other embodiments. For example, a fixed anode can be used instead of a rotating anode. Instead of an X-ray tube with a glass bulb, an X-ray tube with a metal bulb can also be used, in which the cathode and / or anode are connected to the metal bulb via insulators. The X-ray tube can also be used for non-destructive examinations in the industrial sector; In the range of tube voltages (200 - 500 kV) used for this purpose, the efficiency is particularly high.
Claims (4)
dadurch gekennzeichnet, daß der Winkel ϑ zwischen der Einfallsrichtung der Elektronen und der Richtung der durch die Trägerschicht hindurch emittierten Röntgenstrahlen im Nutzstrahlenbündel zwischen 10° und 40° beträgt.X-ray tube with a transmission anode, which comprises a target layer made of one or more metals with a high atomic number that is hit by electrons in the operating state and a carrier layer made of one or more substances with a low atomic number connected to the target layer,
characterized in that the angle ϑ between the direction of incidence of the electrons and the direction of the X-rays emitted through the carrier layer in the useful beam is between 10 ° and 40 °.
dadurch gekennzeichnet, daß der Winkel ϑ und die Betriebsspannung U, für die die Röntgenröhre ausgelegt ist, zumindest näherungsweise der Beziehung genügen
characterized in that the angle ϑ and the operating voltage U, for which the x-ray tube is designed, at least approximately satisfy the relationship
dadurch gekennzeichnet, daß das Gewicht der Targetschicht pro Flächeneinheit - ausgedrückt in Gramm/cm² - zumindest annähernd der Beziehung genügt:
wobei A die relative Atommasse und Z die Ordnungszahl des Metalls der Targetschicht, U die Betriebsspannung in kV, für die die Röntgenröhre ausgelegt ist und β der Winkel ist, den die Einfallsrichtung der Elektronen mit der Normalen auf die Targetschicht einschließt.X-ray tube according to one of the preceding claims,
characterized in that the weight of the target layer per unit area - expressed in grams / cm² - at least approximately meets the relationship:
where A is the relative atomic mass and Z is the atomic number of the metal of the target layer, U is the operating voltage in kV for which the X-ray tube is designed and β is the angle which the direction of incidence of the electrons includes the normal to the target layer.
dadurch gekennzeichnet, daß sie als Drehanoden-Röntgenröhre ausgebildet ist und daß die Targetschicht (1) auf der Mantelfläche eines Kegelstumpfes liegt, der mit der Richtung der außerhalb der Röntgenröhre ausgenutzten Röntgenstrahlen einen Winkel (α₁) einschließt, der kleiner ist als der Winkel ϑ, der zwischen dieser Richtung und der Richtung der einfallenden Elektronen besteht.X-ray tube according to one of the preceding claims,
characterized in that it is designed as a rotating anode X-ray tube and that the target layer (1) on the outer surface of a truncated cone lies, which includes an angle (α₁) with the direction of the X-rays used outside the X-ray tube, which is smaller than the angle ϑ, which exists between this direction and the direction of the incident electrons.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE4228559 | 1992-08-27 | ||
DE4228559A DE4228559A1 (en) | 1992-08-27 | 1992-08-27 | X-ray tube with a transmission anode |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0584871A1 true EP0584871A1 (en) | 1994-03-02 |
EP0584871B1 EP0584871B1 (en) | 1996-11-20 |
Family
ID=6466593
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP93202435A Expired - Lifetime EP0584871B1 (en) | 1992-08-27 | 1993-08-18 | X-ray tube with anode in transmission mode |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0584871B1 (en) |
JP (1) | JPH06162972A (en) |
DE (2) | DE4228559A1 (en) |
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Also Published As
Publication number | Publication date |
---|---|
EP0584871B1 (en) | 1996-11-20 |
DE59304524D1 (en) | 1997-01-02 |
JPH06162972A (en) | 1994-06-10 |
DE4228559A1 (en) | 1994-03-03 |
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