EP0096824A1 - Fine focus X-ray tube and method for the production of a finely focused electron emission from an X-ray filament cathode - Google Patents

Fine focus X-ray tube and method for the production of a finely focused electron emission from an X-ray filament cathode Download PDF

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Publication number
EP0096824A1
EP0096824A1 EP83105571A EP83105571A EP0096824A1 EP 0096824 A1 EP0096824 A1 EP 0096824A1 EP 83105571 A EP83105571 A EP 83105571A EP 83105571 A EP83105571 A EP 83105571A EP 0096824 A1 EP0096824 A1 EP 0096824A1
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EP
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Prior art keywords
cathode
ray tube
hot cathode
grid
electron
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EP83105571A
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German (de)
French (fr)
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EP0096824B1 (en
Inventor
Alfred Dipl.-Ing. Reinhold
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Feinfocus Verwaltungs & Co KG GmbH
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Feinfocus Verwaltungs & Co KG 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
    • 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
    • H01J35/06—Cathodes
    • H01J35/064—Details of the emitter, e.g. material or structure
    • 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
    • H01J35/06—Cathodes
    • H01J35/066—Details of electron optical components, e.g. cathode cups

Definitions

  • the invention relates to a fine focus X-ray tube, in the evacuated flask of which a hot cathode surrounded by a grid and an anode equipped with a target, electromagnetic electron beam focusing and deflecting device and an entrance aperture are accommodated and a method for forming a microfocus of the electron emission of an X-ray tube hot cathode.
  • X-ray tubes were developed whose glow cathodes were made from ever finer wires and which were shaped like pointed needles to cover the electron exit surface - at the needle tip - to be made as small as possible. This is the only way to believe the optics rule - the smaller and more point-like the light source, the higher the resolution - corresponds to can and to be able to achieve sharp X-ray images.
  • the invention is based on the finding that the longer the cross-section of the filament and the lower its temperature, at least at the surface, the longer the service life of a hot cathode, and that a microfocus can be formed on this surface of a relatively thick wire , if it is only possible to expose a location on the surface to special physical conditions that do not exist on other parts of the surface and that are preferably suitable for electron emission.
  • the invention consists in using a glow wire whose dimensions are large compared to the dimensions of the electron exit surface.
  • the grid offers itself as a simple, existing component if it is only dimensioned in a suitable manner.
  • the filament is cooled (to different extents) in such a way that at the location of the electron exit surface the highest temperature prevails on the surface of the filament.
  • This method can be implemented with a fine focus X-ray tube, which is characterized in that the hot cathode consists of a wire whose dimensions are large compared to the dimensions of the electron exit surface and that a device for achieving an increased surface temperature is provided at the point where the electric field between the anode and cathode reaches its highest value.
  • the device for achieving an elevated temperature is a device which strongly absorbs radiation and which partially surrounds the hot cathode. Because with this device, an enormous increase in the intensity of the electron emission can be achieved with the least effort.
  • This device can be the grid present in the X-ray tube anyway, if it is only adapted in a special way to this purpose of heat absorption.
  • a fine-focus X-ray tube is characterized in that the grating is designed as a thick-walled, rotationally symmetrical body which partially surrounds the hot cathode and has the shape of a hollow cylinder with an inward projection on the end face, the outside of which widens in a funnel shape, the latter Funnel includes an angle of 100 ° to 140 0 , and that the hot cathode with its point emerging most from the interior of the grid is arranged in the axis of the grid in a plane which lies in the region of the lower edge of the funnel-shaped part of the end face.
  • the hot cathode can be designed such that the hot cathode consists of a U-shaped or V-shaped wire.
  • a tiny spot is then formed in the tip of the bend of the filament, which is least affected by the cooling effect and which, since it is also located at the location of the highest field strength, is a location of particularly intense electron emission .
  • the cooling effect of the surface parts of the hot cathode is the cause of the significant increase in the life of the hot cathode.
  • a further increase in the intensity of the X-rays which goes far beyond what is to be expected after the increase in electron emission, can be achieved in that the target has a spherically curved surface and the target angle has a value between 0 ° and 10.
  • This increase is unexpected, because up to now the experts have used different target angles according to Heel's teaching.
  • Here shows the interaction of the measures according to the invention on the cathode with the measures according to the invention on the anode, an increase in intensity by more than an order of magnitude, without any particular effort being made and without a loss in service life.
  • the hot cathode consists of a wire whose dimensions are large compared to the dimensions of the electron exit area, this wire being bent in a substantially U-shaped manner, that the grid as one Thick-walled, rotationally symmetrical body that surrounds the hot cathode is formed in the form of a hollow cylinder with an inward projection on the end face, the outside of which widens in a funnel shape, this funnel enclosing an angle of 100 to 140 °, - this grid serves on the one hand electric field formation, on the other hand as a radiation-absorbing body, which in turn emits radiation on its outward-facing sides - and that the hot cathode at its most distant point from the inside of the grid is arranged in the plane of the grid in a plane which is in the area the bottom edge of the funnel shaped side surface.
  • the target has a spherically curved surface and the target
  • the piston of the X-ray tube consists of two parts 1, 2.
  • the part 1 receives the cathode, consisting of the filament 3, which serves as an emitter for the electron current 11, the contacts 12, 13 for the filament 3 and the base 14 and the grid 4, which is also carried by the base 14 and which is connected via the connection contact 15 to a voltage source, not shown.
  • the part 2 serving as the anode accommodates in its interior focusing coils 5, deflection coils 6 provided with an air gap 26 and is provided with the target head 7, which receives the target 8 (the anti-cathode) and a shield 16 in its interior, which provides an opening for has the exit of the X-rays 10 generated at the target 8, which exit through the exit window 9.
  • the target head is cooled by a cooling liquid which flows into or out of a cooling space through the tubes 17. exit.
  • the piston of the x-ray tube has a vacuum connection 18.
  • the electrical connections for the focusing coil 5 and the deflection coils 6 are designated 19 to 22.
  • FIG. 2 the structure of the cathode and grid is shown in an enlarged view.
  • the filament 3 Via the connection contacts 12, 13, which end in clamping devices 27, 28 for the U-shaped filament (emitter) 3, the filament 3 is supplied with voltage, which makes this filament glow.
  • the two clamping devices 27, 28 are accommodated in a holder 29 which also supports the grating 4 by means of the insulating ring 30.
  • This grid 4 is designed as a thick-walled hollow cylinder, which has on its one end, surrounding the filament 3, an inward projection 34, which is formed on the outside in the form of a funnel 31, which has an opening angle ⁇ of 100 ° to 140 ° , preferably 120 °.
  • This funnel 31 merges on its inside into a cylindrical surface 32, the rounded edge 33.
  • the plane 35 in which the surface part of the heating wire 3 is located, which emits electrons. Due to the special geometric design of the grid, on the one hand generates an electric field, which has its peak value in the axis 36 where the axis 36 breaks through the surface of the heating wire 3 facing the target. On the other hand, the special geometric design of the grating 4 ensures that more radiation is emitted to the grating from all surface parts of the filament 3 than from the location of the filament at which the geometric axis breaks through the surface of the heating wire 3 facing the target. As a result, the surface of the heating wire is cooled everywhere, but the cooling is lowest at the location where the geometric axis 36 breaks through the surface of the heating wire facing the target 8.
  • the diameter D of the heating wire is chosen to be more than 0.17 mm, the inside diameter Ri is chosen to be greater than 0.1 D. These dimensions are significantly larger than the dimensions previously used for fine focus X-ray tubes.
  • the inner diameter Ri and the outer diameter Ra can also have significantly larger values. - In some cases, it is useful to provide the ring-shaped grid 4, which is solid like a block, with an additional apron 37 in order to increase the outward heat radiation. This apron 37 is advantageously made in one piece with the grid 4 and essentially represents a solid hollow cylinder.
  • the heating wire 3 instead of the heating wire 3, other shapes for the emitter can also be used, e.g. Emitters in the forms shown in FIGS. 5 and 6. These emitters made of solid material are also heated until they glow by current flowing through them.
  • FIG. 3 shows the detail 1 from FIG. 1, namely a part of the target head 7 and the target 8 in cross section.
  • the target 8 is designed as a solid block, which has a cylindrical or spherical surface on the side facing the electron stream 11.
  • the inside of the target head 7 is provided with a lining 16 made of lead.
  • the target head 7 has a lateral opening which is closed by the radiation exit window 9 for the emerging X-rays 10.
  • the values set on the target 8 are explained in more detail with reference to FIG. 4 (detail IV): the electron beam axis E of the electron beam with the electron beam diameter De runs parallel to the tube axis 36.
  • the point of impact of the electron beam axis E and the target radius of curvature R is chosen so that a target angle a of 10 ° results. Since, with the measures according to the invention, a very thinly focused electron beam already hits the target 8, the optical focal spot width BFo is very small.
  • the target angle A maximum intensity of X-rays of up to 10 ° is reached, the cause of which has not yet been scientifically clarified. It is assumed that conditions similar to those that occur with total reflection in the optics occur here.
  • the hot cathode does not necessarily have to consist of a current-carrying wire, it can also be heated indirectly, e.g. be heated inductively. In this case too, it is important that the dimensions of the hot cathode, which may well have the shape of a needle or a nail, are large compared to the dimensions of the electron exit area and that a point with a higher surface temperature than the other surface parts is indicated on the hot cathode the point at which the electric field between the anode and cathode reaches its highest value. However, there are also ways of heating the cathode both directly through a current flowing through it and additionally indirectly.

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  • X-Ray Techniques (AREA)

Abstract

In an X-ray tube having a glow cathode for emitting an electron beam, an anode, focusing and deflecting coils and a target in an evacuated envelope, the cathode is a U-bent filament the dimensions of which are large in relation to the electron emitting area. The cathode is heated by passing electric current through it and is differentially cooled so that a small surface area at the site of electron emission is at a substantially higher temperature than remaining surface areas of the cathode. Cooling is effected by a thick-walled cylindrical grid which surrounds the cathode and has at its outer end an annular inward projection which absorbs heat rays from the cathode. The grid has a funnel-shaped outer end surface having an included angle of about 100 DEG to 140 DEG . The electron emitting surface of the cathode lies approximately in a plane defined by the inner peripheral edge of the funnel-shaped end surface of the grid. The electric field applied to the cathode has its highest value at the small electron emitting surface of the cathode.

Description

Die Erfindung betrifft eine Feinfokus-Röntgenröhre, in deren evakuiertem Kolben eine von einem Gitter umgebene Glühkathode und eine mit Target, elektromagnetischen Elektronenstrahlbündelungs- und-ablenkungsvorrichtung und einer Eintrittsblende ausgestattete Anode untergebracht sind und ein Verfahren zur Bildung eines Mikrofokus der Elektronenemission einer Röntgenröhren-Glühkathode.The invention relates to a fine focus X-ray tube, in the evacuated flask of which a hot cathode surrounded by a grid and an anode equipped with a target, electromagnetic electron beam focusing and deflecting device and an entrance aperture are accommodated and a method for forming a microfocus of the electron emission of an X-ray tube hot cathode.

In dem Bestreben, das Auflösungsvermögen bei Röntgengeräten zu steigern, um immer kleinere Details in Röntgenaufnahmen zu erkennen, z.B. feinste Haarrisse in Turbinenschaufeln, wurden Röntgenröhren entwickelt, deren Glühkathoden aus immer feineren Drähten hergestellt wurden und die wie spitze Nadeln geformt wurden, um die Elektronenaustrittsfläche - an der Nadelspitze - möglichst klein zu gestalten. Nur so glaubte man bisher der Regel aus der Optik, - je kleiner und punktförmiger die Lichtquelle, um so höher das Auflösungsvermögen -, entsprechen zu können und scharfe Röntgenbildaufnahmen erzielen zu können.In an effort to increase the resolving power of X-ray devices in order to detect ever smaller details in X-rays, e.g. the finest hairline cracks in turbine blades, X-ray tubes were developed whose glow cathodes were made from ever finer wires and which were shaped like pointed needles to cover the electron exit surface - at the needle tip - to be made as small as possible. This is the only way to believe the optics rule - the smaller and more point-like the light source, the higher the resolution - corresponds to can and to be able to achieve sharp X-ray images.

Es gelingt auch, auf diesem Wege das Auflösungsvermögen eines Röntgengerätes erheblich zu steigern, doch nur um den Preis einer geringeren Elektronenemission und um den Preis einer stark verkürzten Lebensdauer der Glühkathode. Die geringere Elektronenemission führt dazu, daß man in der medizinischen Anwendung von Röntgengeräten längere Expositionszeiten benötigt und dadurch den Patienten stärker belastet, während in der Anwendung von Röntgengeräten zur Materialprüfung dem Durchdringungsvermögen Grenzen gesetzt sind, die Untersuchungen erheblich längere Zeit in Anspruch nehmen und die Einsatzmöglichkeiten am bewegten Untersuchungsobjekt erheblich eingeschränkt werden. Die stark verkürzte Lebensdauer der Glühkathode macht deren häufiges Auswechseln erforderlich, ein Vorgang, bei dem nach dem Auswechseln die Röntgenröhre erst wieder evakuiert werden muß, ehe sie erneut einsatzbereit ist. Das ist ein zeitaufwendiger Vorgang, der das Verhältnis von Benutzungszeit zu Stillstandszeit sehr ungünstig beeinflußt.It is also possible to significantly increase the resolving power of an X-ray device in this way, but only at the price of a lower electron emission and at the price of a greatly shortened life of the hot cathode. The lower electron emission means that longer exposure times are required in the medical application of X-ray devices and thus put more strain on the patient, while in the use of X-ray devices for material testing the penetration capacity is limited, the examinations take considerably longer time and the possible uses moving examination object can be significantly restricted. The greatly shortened life of the hot cathode necessitates frequent replacement, a process in which the X-ray tube has to be evacuated again before it is ready for use again. This is a time-consuming process that affects the ratio of usage time to downtime very unfavorably.

Maßnahmen am Target der Röntgenröhre zur Verbesserung der Auflösung führten weder zur Vermeidung der aufgezeigten Nachteile an der Kathode noch zu einer wesentlichen Verbesserung der Intensität der emittierten Röntgenstrahlen, wohl aber zu einem vorzeitigen Verschleiß der Targetoberfläche. Hier am Target hielt die Fachwelt bisher strikt die von Heel aufgestellte Regel ein, daß der Targetwinkel (Winkel zwischen der Senkrechten zur Elektroneneinfallsridn tung und der Targetoberfläche) zwischen 10° und 400 liegen solle, weil bei 300 bis 33° Targetwinkel ein Maximum der Intensität der Röntgenstrahlungsabstrahlung liegt. Da hier am Target keine Verbesserungen möglich erschienen, richteten sich die Versuche zur Verbesserung der Intensität auf die Kathode der Röntgenröhren und endeten an den aufgezeigten Grenzen.Measures on the target of the X-ray tube to improve the resolution did not lead to avoiding the disadvantages on the cathode shown, nor to a substantial improvement in the intensity of the emitted X-rays, but did lead to premature wear of the target surface. The experts stopped here at the target been strictly the erected Heel rule, that the target angle (angle tung between the perpendicular to the Elektroneneinfallsridn and the target surface) should between 10 ° and 40 0 are because at 30 0 to 33 ° target angle is a maximum of the intensity of X-ray radiation. Since no improvements seemed possible at the target, the attempts to improve the intensity were directed towards the cathode of the X-ray tubes and ended at the limits shown.

Es ist die Aufgabe der Erfindung, die Intensität der Elektronenemission aus einem Mikrofokus einer Glühkathode bei gleichzeitiger Steigerung deren Lebensdauer erheblich zu erhöhen und die Intensität der Röntgenstrahlenemission in unerwarteter Weise zu steigern.It is the object of the invention to considerably increase the intensity of the electron emission from a microfocus of a hot cathode while simultaneously increasing its service life and to increase the intensity of the X-ray emission in an unexpected manner.

Der Erfindung liegt die Erkenntnis zugrunde, daß die Lebensdauer einer Glühkathode um so höher ist, je stärker der Querschnitt des Glühdrahtes ist und um so niedriger dessen Temperatur zumindest an der Oberfläche ist, und daß auf dieser Oberfläche eines relativ dicken Drahtes sich ein Mikrofokus ausbilden läßt, wenn es nur gelingt, einen Ort der Oberfläche besonderen physikalischen Bedingungen auszusetzen, die an anderen Teilen der Oberfläche nicht herrschen und die zur Elektronenemission bevorzugt geeignet sind.The invention is based on the finding that the longer the cross-section of the filament and the lower its temperature, at least at the surface, the longer the service life of a hot cathode, and that a microfocus can be formed on this surface of a relatively thick wire , if it is only possible to expose a location on the surface to special physical conditions that do not exist on other parts of the surface and that are preferably suitable for electron emission.

Die Erfindung besteht darin, daß man einen Glühdraht verwendet, dessen Dimensionen groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind.The invention consists in using a glow wire whose dimensions are large compared to the dimensions of the electron exit surface.

Auf diese Weise erreicht man, daß trotz der Verwendung eines sehr stabilen Glühdrahtes, der infolge seiner Querschnittsgröße und seiner Oberflächentemperatur eine lange Lebensdauer aufweist, ein Mikrofokus geschaffen ist, der sich durch eine besonders hohe Intensität der Elektronenemission auszeichnet. Durch die Anordnung der Elektronenemissionsstelle in zwei Feldern, einem elektrischen Feld und einem Temperaturfeld an der Oberfläche des Glühdrahtes, deren Spitzenwerte an ein und denselben Ort fallen, läßt sich auf dem Glühdraht ein Fokus intensiver Elektronenemission von sehr kleinen Abmessungen schaffen, obwohl der Durchmesser des Glühdrahtes viel größer ist.In this way it is achieved that, despite the use of a very stable glow wire, which due to its cross-sectional size and its surface temperature has a long service life, a microfocus is created which is characterized by a particularly high intensity of the electron emission. By arranging the electron emission point in two fields, an electric field and a temperature field on the surface of the filament, the peak values of which fall in one and the same place, a focus of intense electron emission of very small dimensions can be created on the filament, although the diameter of the filament is much larger.

Dabei braucht man den winzigen Fleck erhöhter Temperatur nicht einmal durch äußere Strahlungseinwirkung, z.B. durch Lichteinstrahlung, Infraroteinstrahlung oder mittels eines Lasers, zu schaffen, dieser Ort erhöhter Temperatur läßt sich viel einfacher, aber ebenso wirkungsvoll dadurch schaffen, daß man die Glühkathode mit einem Wärmestrahlung absorbierenden Körper so (teilweise) umgibt, daß von allen Orten der Oberfläche des Glühdrahtes mehr Strahlung absorbiert wird als von dem Ort er Elektronenaustrittsfläche. Hierzu bietet sich das Gitter als einfaches, sowieso vorhandenes Bauelement an, wenn man es nur in geeigneter Weise dimensioniert.You don't even need the tiny spot of elevated temperature due to external radiation, e.g. to create by light irradiation, infrared irradiation or by means of a laser, this place of elevated temperature can be created much more simply, but just as effectively, by surrounding the hot cathode with a body absorbing heat radiation in such a way that from all places the surface of the glow wire more radiation is absorbed than from the location of the electron exit surface. For this purpose, the grid offers itself as a simple, existing component if it is only dimensioned in a suitable manner.

Durch diese StrahlungsabsorPtion, aber auch mit anderen Maßnahmen der Kühlung läßt sich erreichen, daß man den Glühdraht so (unterschiedlich stark) kühlt, daß am Ort der Elektronenaustrittsfläche die höchste Temperatur an der Oberfläche des Glühdrahtes herrscht.Through this radiation absorption, but also with other cooling measures, it can be achieved that the filament is cooled (to different extents) in such a way that at the location of the electron exit surface the highest temperature prevails on the surface of the filament.

Dieses Verfahren läßt sich mit einer Feinfokus-Röntgenröhre realisieren, die sich dadurch auszeichnet, daß die Glühkathode aus einem Draht besteht, dessen Dimensionen groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind und daß eine Vorrichtung zur Erzielung einer erhöhten Oberflächentemperatur an derjenigen Stelle vorgesehen ist, an der das elektrische Feld zwischen Anode und Kathode seinen höchsten Wert erreicht.This method can be implemented with a fine focus X-ray tube, which is characterized in that the hot cathode consists of a wire whose dimensions are large compared to the dimensions of the electron exit surface and that a device for achieving an increased surface temperature is provided at the point where the electric field between the anode and cathode reaches its highest value.

Dabei ist es zweckmäßig, wenn die Vorrichtung zur Erzielung einer erhöhten Temperatur eine Strahlung stark absorbierende Vorrichtung ist, welche die Glühkathode teilweise umgibt. Denn mit dieser Vorrichtung läßt sich bei geringstem Aufwand eine enorme Steigerung der Intensität der Elektronenemission erzielen.It is expedient if the device for achieving an elevated temperature is a device which strongly absorbs radiation and which partially surrounds the hot cathode. Because with this device, an enormous increase in the intensity of the electron emission can be achieved with the least effort.

Diese Vorrichtung kann das sowieso in der Röntgenröhre vorhandene Gitter sein, wenn es nur in besonderer Weise diesem Zweck der Wärmeabsorption angepaßt ist. Eine solche Feinfokus-Röntgenröhre zeichnet sich dadurch aus, daß das Gitter als ein starkwandiger, die Glühkathode teilweise umgebender, rotationssymmetrischer Körper ausgebildet ist, der die Form eines Hohlzylinders mit an der Stirnseite nach innen gerichtetem Vorsprung aufweist, dessen Außenseite sich trichterförmig erweitert, wobei dieser Trichter einen Winkel von 100° bis 1400 einschließt, und daß die Glühkathode mit ihrer am weitesten aus dem Inneren des Gitters austretenden Stelle in der Achse des Gitters in einer Ebene angeordnet ist, die im Bereich der Unterkante des trichterförmigen Teiles der Stirnseitenfläche liegt.This device can be the grid present in the X-ray tube anyway, if it is only adapted in a special way to this purpose of heat absorption. Such a fine-focus X-ray tube is characterized in that the grating is designed as a thick-walled, rotationally symmetrical body which partially surrounds the hot cathode and has the shape of a hollow cylinder with an inward projection on the end face, the outside of which widens in a funnel shape, the latter Funnel includes an angle of 100 ° to 140 0 , and that the hot cathode with its point emerging most from the interior of the grid is arranged in the axis of the grid in a plane which lies in the region of the lower edge of the funnel-shaped part of the end face.

In dieser Röntgenröhre kann die Glühkathode so ausgeführt sein, daß die Glühkathode aus einem U- oder V-förmig gebogenen Draht besteht. In Zusammenwirken mit dem als Kühlvorrichtung wirkenden Gitter bildet sich dann in der Spitze der Biegung des Glühdrahtes ein winziger Fleck aus, der von der Kühlwirkung am wenigsten erfaßt wird und der, da er gleichzeitig am Ort der höchsten Feldstärke liegt, ein Ort besonders intensiver Elektronenemission ist. So wird hier völlig unerwartet an einer keineswegs spitzen Elektrode von bisher ungeeignet erscheinender Form und Größe ein Mikrofokus erzielt, dessen Wirkungsgrad der Emission die spitzgeformten bekannten Elektroden wesentlich übertrifft. Die Kühlwirkung gerade der Oberflächenteile der Glühkathode ist die Ursache für die bedeutende Erhöhung der Lebensdauer der Glühkathode.In this X-ray tube, the hot cathode can be designed such that the hot cathode consists of a U-shaped or V-shaped wire. In cooperation with the grid acting as a cooling device, a tiny spot is then formed in the tip of the bend of the filament, which is least affected by the cooling effect and which, since it is also located at the location of the highest field strength, is a location of particularly intense electron emission . In this way, a microfocus is achieved completely unexpectedly on an electrode that has in no way been pointed and of a shape and size that previously appeared unsuitable, the efficiency of the emission of which significantly exceeds that of the known electrodes. The cooling effect of the surface parts of the hot cathode is the cause of the significant increase in the life of the hot cathode.

Eine weitere Steigerung der Intensität der Röntgenstrahlung, die weit über das hinausgeht, was nach der Steigerung der Elektronenemission zu erwarten ist, ist dadurch erreichbar, daß das Target eine sphärisch gekrümmte Oberfläche aufweist und der Targetwinkel einen Wert zwischen 0° und 10 hat. Diese Steigerung ist unerwartet, weil bisher die Fachwelt gemäß der Lehre von Heel andere Targetwinkel benutzte. Hier zeigt das Zusammenwirken der erfindungsgemäßen Maßnahmen an der Kathode mit den erfindungsgemäßen Maßnahmen an der Anode eine Steigerung der Intensität um mehr als eine Größenordnung, ohne daß ein besonderer Aufwand getrieben wurde und ohne daß eine Einbuße an Lebensdauer entsteht.A further increase in the intensity of the X-rays, which goes far beyond what is to be expected after the increase in electron emission, can be achieved in that the target has a spherically curved surface and the target angle has a value between 0 ° and 10. This increase is unexpected, because up to now the experts have used different target angles according to Heel's teaching. Here shows the interaction of the measures according to the invention on the cathode with the measures according to the invention on the anode, an increase in intensity by more than an order of magnitude, without any particular effort being made and without a loss in service life.

Die besten Ergebnisse wurden mit einer Feinfokus-Röntgenröhre erzielt, die sich dadurch auszeichnet, daß die Glühkathode aus einem Draht besteht, dessen Dimensionen groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind, wobei dieser Draht im wesentlichen U-förmig gebogen ist, daß das Gitter als ein starkwandiger rotationssymmetrischer, die Glühkathode umgebender Körper ausgebildet ist, der in Form eines Hohlzylinders mit an der Stirnseite nach innen gerichtetem Vorsprung ausgebildet ist, dessen Außenseite sich trichterförmig erweitert, wobei dieser Trichter einen Winkel von 100 bis 140° einschließt, - dieses Gitter dient einerseits der elektrischen Feldausbildung, andererseits als ein strahlungsaufnehmender Körper, der an seinen nach außen gerichteten Seiten wiederum Strahlung abgibt -, und daß die Glühkathode an ihrer am weitesten aus dem Inneren des Gitters austretenden Stelle in der Achse des Gitters in einer Ebene angeordnet ist, die im Bereich der Unterkante der trichterförmigen Seitenfläche liegt. Bei dieser Feinfokus-Röntgenröhre weist das Target eine sphärisch gekrümmte Oberfläche auf und der Targetwinkel hat einen Wert zwischen 0° und 10°.The best results have been achieved with a fine-focus X-ray tube, which is characterized in that the hot cathode consists of a wire whose dimensions are large compared to the dimensions of the electron exit area, this wire being bent in a substantially U-shaped manner, that the grid as one Thick-walled, rotationally symmetrical body that surrounds the hot cathode is formed in the form of a hollow cylinder with an inward projection on the end face, the outside of which widens in a funnel shape, this funnel enclosing an angle of 100 to 140 °, - this grid serves on the one hand electric field formation, on the other hand as a radiation-absorbing body, which in turn emits radiation on its outward-facing sides - and that the hot cathode at its most distant point from the inside of the grid is arranged in the plane of the grid in a plane which is in the area the bottom edge of the funnel shaped side surface. With this fine focus X-ray tube, the target has a spherically curved surface and the target angle has a value between 0 ° and 10 °.

Das Wesen der Erfindung ist nachstehend anhand eines in der Zeichnung schematisch dargestellten Ausführungsbeispieles näher erläutert. Es zeigen:

  • Fig.1 einen Querschnitt durch die Feinfokus-Röntgenröhre,
  • Fig.2 einen Querschnitt durch die Kathode und die Anordnung des Gitters,
  • Fig.3 einen Querschnitt durch einen Teil der Röntgenröhre im Bereich des Targets,
  • Fig.4 einen Teil des Targets,
  • Fig.5 eine andere Ausbildung des Glühdrahtes,
  • Fig.6 eine weitere Ausbildung des Glühdrahtes.
The essence of the invention is explained below with reference to an embodiment shown schematically in the drawing. Show it:
  • 1 shows a cross section through the fine focus X-ray tube,
  • 2 shows a cross section through the cathode and the arrangement of the grid,
  • 3 shows a cross section through part of the X-ray tube in the region of the target,
  • 4 shows part of the target,
  • 5 another design of the filament,
  • 6 shows a further embodiment of the filament.

Der Kolben der Röntgenröhre besteht aus zwei Teilen 1,2. Das Teil 1 nimmt die Kathode, bestehend aus dem Heizfaden 3, der als Emitter für den Elektronenstrom 11 dient, den Anschlußkontakten 12,13 für den Heizfaden 3 und dem Sockel 14 und das Gitter 4 auf, welches ebenfalls vom Sockel 14 getragen wird und welches über den Anschlußkontakt 15 mit einer nicht dargestellten Spannungsquelle verbunden ist. Das als Anode dienende Teil 2 nimmt in seinem Inneren mit einem Luftspalt 26 versehene Fokussierspulen 5, Ablenkspulen 6 auf und ist mit dem Targetkopf 7 versehen, der in seinem Inneren das Target 8 (die Antikathode) und eine Abschirmung 16 aufnimmt, die eine Durchbrechung für den Austritt der am Target 8 erzeugten Röntgenstrahlen 10 aufweist, die durch das Austrittsfenster 9 austreten. Der Targetkopf wird durch eine Kühlflüssigkeit gekühlt, die durch die Rohre 17 in einen Kühlraum ein- bzw. austritt. Der Kolben der Röntgenröhre weist einen Vakuumanschluß 18 auf. Die elektrischen Anschlüsse für die Fokussierspule 5 und die Ablenkspulen 6 sind mit 19 bis 22 bezeichnet. Zwischen den beiden Teilen 1 und 2 des Kolbens der Röntgenröhre befindet sich eine Trennwand (Anode) 24, welche mit einer Durchlaßöffnung 25 für den Elektronenstrom 11 versehen ist.The piston of the X-ray tube consists of two parts 1, 2. The part 1 receives the cathode, consisting of the filament 3, which serves as an emitter for the electron current 11, the contacts 12, 13 for the filament 3 and the base 14 and the grid 4, which is also carried by the base 14 and which is connected via the connection contact 15 to a voltage source, not shown. The part 2 serving as the anode accommodates in its interior focusing coils 5, deflection coils 6 provided with an air gap 26 and is provided with the target head 7, which receives the target 8 (the anti-cathode) and a shield 16 in its interior, which provides an opening for has the exit of the X-rays 10 generated at the target 8, which exit through the exit window 9. The target head is cooled by a cooling liquid which flows into or out of a cooling space through the tubes 17. exit. The piston of the x-ray tube has a vacuum connection 18. The electrical connections for the focusing coil 5 and the deflection coils 6 are designated 19 to 22. Between the two parts 1 and 2 of the piston of the X-ray tube there is a partition (anode) 24, which is provided with a passage opening 25 for the electron current 11.

In Fig. 2 ist in vergrößerter Darstellung der Aufbau von Kathode und Gitter dargestellt. Über die Anschlußkontakte 12,13, die in Klemmvorrichtungen 27,28 für den U-förmig gebogenen Heizfaden (Emitter) 3 enden, wird dem Heizfaden 3 Spannung zugeführt, die diesen Heizfaden zum Glühen bringt. Die beiden Klemmvorrichtungen 27,28 sind dabei in einer Halterung 29 untergebracht, die mittels des Isolierringes 30 auch das Gitter 4 trägt. Dieses Gitter 4 ist als ein starkwandiger Hohlzylinder ausgebildet, der an seiner einen, den Heizfaden 3 umschließenden Stirnseite einen nach innen gerichteten Vorsprung 34 aufweist, der an seiner Außenseite in Form eines Trichters 31 ausgebildet ist, der einen Öffnungswinkel ß von 100° bis 140°, vorzugsweise 120°, aufweist. Dieser Trichter 31 geht auf seiner Innenseite in eine zylindrische Oberfläche 32 über, die abgerundete Kante 33, über. Im Bereich dieser abgerundeten Kante 33 befindet sich die Ebene 35, in welcher sich de*-nige Oberflächenteil des Heizdrahtes 3 befindet, der Elektronen emittiert. Durch die besondere geometrische Ausbildung des Gitters wird einerseits ein elektrisches Feld erzeugt, welches seinen Spitzenwert in der Achse 36 dort hat, wo die Achse 36 die dem Target zugewandte Oberfläche des Heizdrahtes 3 durchbricht. Andererseits ist durch die besondere geometrische Gestaltung des Gitters 4 erreicht, daß von allen Oberflächenteilen des Heizfadens 3 mehr Strahlung an das Gitter abgegeben wird als von demjenigen Ort des Heizfadens, an dem die geometrische Achse die dem Target zugewandte Oberfläche des Heizdrahtes 3 durchbricht. Hierdurch wird die Oberfläche des Heizdrahtes überall gekühlt, jedoch ist die Kühlung am geringsten an demjenigen Ort, an dem die geometrische Achse 36 die dem Target 8 zugewandte Oberfläche des Heizdrahtes durchbricht. Als Durchmesser D des Heizdrahtes wird ein solcher von mehr als 0,17 mm gewählt, der Innendurchmesser Ri ist größer als 0,1 D gewählt. Diese Abmessungen sind erheblich größer als die Abmessungen, die bisher für Feinfokus-Röntgenröhren verwendet werden. Der Innendurchmesser Ri und der Außendurchmesser Ra können aber auch noch erheblich größere Werte aufweisen. - In manchen Fällen ist es zweckmäßig, das massiv wie ein Klotz ausgebildete ringförmige Gitter 4 noch mit einer zusätzlichen Schürze 37 zu versehen, um die nach außen erfolgende Abstahlung von Wärme zu vergrößern. Diese Schürze 37 wird zweckmäßigerweise einstückig mit dem Gitter 4 hergestellt und stellt im wesentlichen einen massiven Hohlzyinder dar.In Fig. 2, the structure of the cathode and grid is shown in an enlarged view. Via the connection contacts 12, 13, which end in clamping devices 27, 28 for the U-shaped filament (emitter) 3, the filament 3 is supplied with voltage, which makes this filament glow. The two clamping devices 27, 28 are accommodated in a holder 29 which also supports the grating 4 by means of the insulating ring 30. This grid 4 is designed as a thick-walled hollow cylinder, which has on its one end, surrounding the filament 3, an inward projection 34, which is formed on the outside in the form of a funnel 31, which has an opening angle β of 100 ° to 140 ° , preferably 120 °. This funnel 31 merges on its inside into a cylindrical surface 32, the rounded edge 33. In the area of this rounded edge 33 there is the plane 35, in which the surface part of the heating wire 3 is located, which emits electrons. Due to the special geometric design of the grid, on the one hand generates an electric field, which has its peak value in the axis 36 where the axis 36 breaks through the surface of the heating wire 3 facing the target. On the other hand, the special geometric design of the grating 4 ensures that more radiation is emitted to the grating from all surface parts of the filament 3 than from the location of the filament at which the geometric axis breaks through the surface of the heating wire 3 facing the target. As a result, the surface of the heating wire is cooled everywhere, but the cooling is lowest at the location where the geometric axis 36 breaks through the surface of the heating wire facing the target 8. The diameter D of the heating wire is chosen to be more than 0.17 mm, the inside diameter Ri is chosen to be greater than 0.1 D. These dimensions are significantly larger than the dimensions previously used for fine focus X-ray tubes. The inner diameter Ri and the outer diameter Ra can also have significantly larger values. - In some cases, it is useful to provide the ring-shaped grid 4, which is solid like a block, with an additional apron 37 in order to increase the outward heat radiation. This apron 37 is advantageously made in one piece with the grid 4 and essentially represents a solid hollow cylinder.

Man kann anstelle des Heizddrahtes 3 auch andere Formen für den Emitter verwenden, z.B. Emitter in den Formen, wie sie in Fig. 5 und 6 dargestellt sind. Diese aus massivem Material hergestellten Emitter werden ebenfalls bis zum Glühen durch durchfließenden Strom erhitzt.Instead of the heating wire 3, other shapes for the emitter can also be used, e.g. Emitters in the forms shown in FIGS. 5 and 6. These emitters made of solid material are also heated until they glow by current flowing through them.

In Fig. 3 ist das Detail 1 aus Fig. 1 dargestellt, nämlich ein Teil des Targetkopfes 7 und das Target 8 im Querschnitt. Das Target 8 ist als ein massiver Klotz ausgeführt, der eine zylindrische oder sphärische Oberfläche auf der dem Elektronenstrom 11 zugekehrten Seite aufweist.FIG. 3 shows the detail 1 from FIG. 1, namely a part of the target head 7 and the target 8 in cross section. The target 8 is designed as a solid block, which has a cylindrical or spherical surface on the side facing the electron stream 11.

Die Innenseite des Targetkopfes 7 ist mit einer Auskleidung 16 aus Blei versehen. Der Targetkopf 7 weist eine seitliche Durchbrechung auf, die durch das Strahlenaustrittsfenster 9 für die austretenden Röntgenstrahlen 10 verschlossen ist. Die am Target 8 eingestellten Werte sind anhand der Fig. 4 (Detail IV) näher erläutert: Parallel zur Röhrenachse 36 verläuft die Elektronenstrahlachse E des Elektronenstrahles mit dem Elektronenstrahldurchmesser De. Der Auftreffpunkt der Elektronenstrahlachse E und der Targetkrümmungsradius R wird so gewählt, daß sich ein Targetwinkel a von maximal 10° ergibt. Da mit den erfindungsgemäßen Maßnahmen an der Kathode bereits ein sehr dünn gebündelter Elektronenstrahl auf das Target 8 fällt, ergibt sich eine sehr geringe Breite BFo des optischen Brennflecks. Bei einer Wahl des Targetwinkels von maximal 10° wird eine sehr hohe Intensität der Röntgenstrahlung erreicht, deren Ursache noch nicht wissenschaftlich geklärt werden konnte. Es wird angenommen, daß hier ähnliche Verhältnisse auftreten, wie sie bei der Totalreflexion in der Optik auftreten.The inside of the target head 7 is provided with a lining 16 made of lead. The target head 7 has a lateral opening which is closed by the radiation exit window 9 for the emerging X-rays 10. The values set on the target 8 are explained in more detail with reference to FIG. 4 (detail IV): the electron beam axis E of the electron beam with the electron beam diameter De runs parallel to the tube axis 36. The point of impact of the electron beam axis E and the target radius of curvature R is chosen so that a target angle a of 10 ° results. Since, with the measures according to the invention, a very thinly focused electron beam already hits the target 8, the optical focal spot width BFo is very small. When choosing the target angle A maximum intensity of X-rays of up to 10 ° is reached, the cause of which has not yet been scientifically clarified. It is assumed that conditions similar to those that occur with total reflection in the optics occur here.

Die Glühkathode braucht nicht unbedingt aus einem stromdurchflossenen Draht zu bestehen, sie kann auch indirekt beheizt werden, z.B. induktiv beheizt werden. Auch in diesem Falle ist es wichtig, daß die Dimensionen der Glühkathode, die durchaus die Form einer Nadel oder eines Nagels haben kann, groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind und daß man an der Glühkathode einen Punkt mit einer gegenüber den anderen Oberflächenteilen erhöhten Oberflächentemperatur an der Stelle hat, an der das elektrische Feld zwischen Anode und Kathode seinen höchsten Wert erreicht. Es gibt aber auch Möglichkeiten, die Kathode sowohl direkt durch einen hindurchfließenden Strom als auch zusätzlich indirekt zu beheizen.The hot cathode does not necessarily have to consist of a current-carrying wire, it can also be heated indirectly, e.g. be heated inductively. In this case too, it is important that the dimensions of the hot cathode, which may well have the shape of a needle or a nail, are large compared to the dimensions of the electron exit area and that a point with a higher surface temperature than the other surface parts is indicated on the hot cathode the point at which the electric field between the anode and cathode reaches its highest value. However, there are also ways of heating the cathode both directly through a current flowing through it and additionally indirectly.

Claims (8)

1. Feiniokus-Röntgenröhre, in deren evakuiertem Kolben eine von einem Gitter umgebene Glühkathode und eine mit Target, elektromagnetischen Elektronenstrahlbündelungs-und -ablenkungsvorrichtungen und einer Eintrittsblende ausgestattete Anode untergebracht sind,
dadurch gekennzeichnet,
daß die Glühkathode aus einem Draht besteht, dessen Dimensionen groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind
und daß eine Vorrichtung zur Erzielung einer erhöhten Oberflächentemperatur an derjenigen Stelle vorgesehen ist, an der das elektrische Feld zwischen Anode und Kathode seinen höchsten Wert erreicht.1. Feiniokus X-ray tube, in the evacuated flask of which a hot cathode surrounded by a grid and an anode equipped with a target, electromagnetic electron beam focusing and deflecting devices and an entrance aperture are accommodated,
characterized,
that the hot cathode consists of a wire whose dimensions are large compared to the dimensions of the electron exit surface
and that a device for achieving an increased surface temperature is provided at the point at which the electric field between the anode and cathode reaches its highest value. 2. Feinfokus-Röntgenröhre nach Anspruch 1,
dadurch gekennzeichnet,
daß die Vorrichtung zur Erzielung einer erhöhten Temperatur eine Strahlung stark absorbierende Vorrichtung ist, welche die Glühkathode teilweise umgibt.2. fine focus x-ray tube according to claim 1,
characterized,
that the device for attaining an elevated temperature is a radiation-strongly absorbing device which partially surrounds the hot cathode. 3. Feinfokus-Röntgenröhre nach Anspruch 1,
dadurch gekennzeichnet,
daß das Gitter als ein starkwandiger, die Glühkathode teilweise umgebender, rotationssymmetrischer Körper ausgebildet ist, der die Form eines Hohlzylinders mit an der Stirnseite nach innen gerichtetem Vorsprung aufweist, dessen Außenseite sich trichterförmig erweitert, wobei dieser Trichter einen Winkel von 100° bis 1400 einschließt, und daß die Glühkathode mit ihrer am weitesten aus dem Inneren des Gitters austretenden Stelle in der Achse des Gitters in einer Ebene angeordnet ist, die im Bereich der Unterkante des trichterförmigen Teiles der Stirnseitenfläche liegt.3. fine focus x-ray tube according to claim 1,
characterized,
that the grid is designed as a thick-walled, rotationally symmetrical body which partially surrounds the hot cathode and has the shape of a hollow cylinder with an inward projection on the end face, the outside of which widens in a funnel shape, this funnel enclosing an angle of 100 ° to 1400, and that the The hot cathode, with its point emerging most from the interior of the grid, is arranged in the axis of the grid in a plane which lies in the region of the lower edge of the funnel-shaped part of the end face. 4.Feinfokus-Röntgenröhre nach Anspruch 1,
dadurch gekennzeichnet,
daß die Glühkathode aus einem U- oder V-förmig gebogenen Draht besteht.4.Finfokus-X-ray tube according to claim 1,
characterized,
that the hot cathode consists of a U- or V-shaped wire. 5.Feinfokus-Röntgenröhre nach Anspruch 1,
dadurch gekennzeichnet,
daß das Target eine sphärisch gekrümmte Oberfläche aufweist und der Targetwinkel einen Wert zwischen 0° und 10° hat.5.Finfokus-X-ray tube according to claim 1,
characterized,
that the target has a spherically curved surface and the target angle has a value between 0 ° and 10 °. 6.Verfahren zur Bildung eines Mikrofokus der Elektronenemission einer Röntgenröhren-Glühkathode,
dadurch gekennzeichnet,
daß man einen Glühdraht verwendet, dessen Dimensionen groß gegenüber den Dimensionen der Elektronenaustrittsfläche sind,
daß man auf dem Glühdraht am Ort der Elektronenaustrittsfläche einen Ort erhöhter Temperatur schafft und daß man das elektrische Feld so gestaltet, daß es an diesem Ort erhöhter Temperatur seinen Spitzenwert erreicht.6.Method for forming a microfocus of the electron emission of an X-ray tube hot cathode,
characterized,
that one uses a glow wire whose dimensions are large compared to the dimensions of the electron exit surface,
that a location of elevated temperature is created on the glow wire at the location of the electron exit surface and that the electric field is designed in such a way that it reaches its peak value at this location of elevated temperature. 7.Verfahren nach Anspruch 6,
dadurch gekennzeichnet,
daß man den Ort erhöhter Temperatur dadurch schafft, daß man die Glühkathode mit einem Wärmestrahlung absorbierenden Körper so (teilweise) umgibt, daß von allen Orten der Oberfläche des Glühdrahtes mehr Strahlung absorbiert wird als von dem Ort der Elektronenaustrittsfläche.7.The method according to claim 6,
characterized,
that the location of elevated temperature thereby creates that one surrounds the hot cathode with a body absorbing heat radiation in such a way that more radiation is absorbed from all locations on the surface of the filament than from the location of the electron exit surface. 8. Verfahren nach Anspruch 6,
dadurch gekennzeichnet,
daß man den Glühdraht so (unterschiedlich stark) kühlt, daß am Ort der Eiektronenaustrittsfläche die höchste Temperatur an der Oberfläche des Glühdrahtes herrscht.8. The method according to claim 6,
characterized,
that the filament is cooled so (to different degrees) that the highest temperature prevails on the surface of the filament at the location of the electron exit surface.
EP83105571A 1982-06-16 1983-06-07 Fine focus x-ray tube and method for the production of a finely focused electron emission from an x-ray filament cathode Expired EP0096824B1 (en)

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AT83105571T ATE29088T1 (en) 1982-06-16 1983-06-07 FINE FOCUS X-RAY TUBE AND METHOD OF FORMING A MICROFOCUS OF THE ELECTRON EMISSION OF AN X-RAY TUBE GLOW CATHOD.

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DE3222511A DE3222511C2 (en) 1982-06-16 1982-06-16 Fine focus X-ray tube
DE3222511 1982-06-16

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EP0096824B1 EP0096824B1 (en) 1987-08-19

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Also Published As

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DE3222511C2 (en) 1985-08-29
JPH0618119B2 (en) 1994-03-09
JPS598251A (en) 1984-01-17
DE3222511A1 (en) 1983-12-22
US4573186A (en) 1986-02-25
EP0096824B1 (en) 1987-08-19
ATE29088T1 (en) 1987-09-15

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