EP0323365A1 - Rotary anode for an X-ray tube - Google Patents

Rotary anode for an X-ray tube Download PDF

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Publication number
EP0323365A1
EP0323365A1 EP88403377A EP88403377A EP0323365A1 EP 0323365 A1 EP0323365 A1 EP 0323365A1 EP 88403377 A EP88403377 A EP 88403377A EP 88403377 A EP88403377 A EP 88403377A EP 0323365 A1 EP0323365 A1 EP 0323365A1
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European Patent Office
Prior art keywords
target
slots
anode
depth
ray tube
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EP88403377A
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German (de)
French (fr)
Inventor
Michel Laurent
Pierre Nouahlaguet
Claude Mathieu
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General Electric CGR SA
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General Electric CGR SA
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Publication of EP0323365A1 publication Critical patent/EP0323365A1/en
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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
    • H01J2235/00—X-ray tubes
    • H01J2235/08—Targets (anodes) and X-ray converters
    • H01J2235/083—Bonding or fixing with the support or substrate
    • H01J2235/084—Target-substrate interlayers or structures, e.g. to control or prevent diffusion or improve adhesion

Definitions

  • the invention relates to a rotating anode for an X-ray tube, and in particular to means for preventing the uncontrolled creation of cracks in a target carried by the anode.
  • X-radiation is commonly obtained by electron bombardment of the anode. More precisely, the electron bombardment is concentrated on a small surface, called the focal point, of a target which the anode comprises, this focal point becoming the source of the X-ray radiation.
  • the target is generally made of a material not only of high atomic number to favor the production of X-rays, but also of a refractory material and good conductor of heat, such as for example tungsten, or molybdenum, or their alloys , etc ...
  • a common solution is to scroll the target under the focus or impact of the electron beam.
  • This scrolling of the target is obtained by a rotation of the anode about an axis of symmetry of the latter, the anode generally having the shape of a disc.
  • the scrolling of the target, under the focal point created at the impact of the electron beam, generates on the target and around the axis of symmetry, a focal ring several millimeters wide.
  • the rapid rotation of the anode (several thousand revolutions per minute) is necessary to distribute the heat flux over the focal ring.
  • the temperature of the focal point remains much higher than the temperature of the rest of the focal ring, which itself has a temperature much higher than that of the rest of the anode disc.
  • each point of this focal ring receives a "thermal impulse" at each revolution of the anode.
  • the fluctuations due to these pulses can be considered insignificant. beyond a surface layer whose thickness is of the order of 100 microns; so that it is mainly this surface layer which undergoes, at the rate of rotation, a succession of thermal shocks, and consequently, significant mechanical stresses.
  • the authors of the invention have thought that the focal crown is subjected to a significant compression, due to the expansion of the target material, and that probably the target material leaves the elastic range of the material, so that a tensile stress resulting from cooling can cause cracks in the surface of the material from which the target is made.
  • the invention relates to a rotating anode for an X-ray tube, which is arranged in a new way which avoids random and uncontrolled formation of cracks in the target.
  • a rotating anode for an X-ray tube comprising a target intended to be subjected to electronic bombardment in order to produce X-radiation, is characterized in that the surface of the target is hollowed out by a plurality of slots equidistant and arranged symmetrically with respect to an axis of symmetry of the anode.
  • the single figure shows a rotating anode 1 for an X-ray tube in itself conventional (not shown).
  • the anode 1 is formed according to a disc having an axis of symmetry 3 and an approximately frustoconical shape; that is to say that a face 4 is formed of a flat central part 5 surrounded by a sloping part 6 which joins the peripheral circular edges 7 of the anode disc 1.
  • the central part 5 has a hole 8, arranged along the axis of symmetry 3, and intended for the passage of a support axis (not shown) used to carry the rotating anode 1 in a conventional manner .
  • the rotating anode 1 is of the type comprising a base body 15 or substrate, in graphite for example, on which an intermediate layer is deposited attachment 16 in rhenium for example; a layer of target material 17, for example of tungsten, being deposited on the bonding layer 16.
  • the layer 17 of target material has been formed in one or more layers, deposited according to a conventional method such as, for example, electrolytic deposition, or chemical vapor deposition (CVD) or also by the method of deposition by plasma torch projection. , etc ...
  • a conventional method such as, for example, electrolytic deposition, or chemical vapor deposition (CVD) or also by the method of deposition by plasma torch projection. , etc ...
  • the layer of target material 17 or target has a thickness E1 of between 300 microns and 700 microns.
  • the thickness E1 of the target 17 can be different and the target 17 can be formed according to a massive structure, formed for example directly by the base body 15 itself made of target material ; or the target 17 can be attached to the base body 15.
  • the layer 17 of target material constitutes a target intended to be bombarded by an electron beam (not shown) in order to conventionally produce X-radiation.
  • the target 17 is intended to be subjected to electronic bombardment over a small surface where a focal point 18 is formed, from which the rotation of the rotating anode 1 around the axis of symmetry 3 generates a focal ring 19 (shown in dotted lines).
  • the layer 17 of target material is deposited on the whole of the sloping part 6, but this layer 17 can be deposited on a more reduced surface, so as to constitute the target according to a ring corresponding substantially to focal ring 19.
  • the surface 21 of the target 17 is hollowed out by a plurality of slots F1, F2, F3,. .., Fn equidistant and arranged symmetrically with respect to the axis of symmetry 3.
  • the length L of the slots F1 to Fn extends radially and corresponds to generatrices of the cone.
  • the usefulness of the slots F1 to Fn is manifested above all with regard to the bombarded surfaces, that is to say of the focal ring 19, and the length L of the slots F1 to Fn can be limited and correspond substantially to a width 1 of the focal ring 19.
  • the slits F1 to Fn have a depth P less than the thickness E1 of the target 17, so as to leave a sufficient quantity of target material between a bottom 23 of the slits F1 to Fn and the substra or base body 15.
  • the depth P of the slits F1 to Fn must be equal to or greater than the thickness of the surface layer, estimated at around 100 microns, which was cited in the preamble as being the layer beyond which the thermal fluctuations are insignificant.
  • the depth P a value between 1/3 and 2/3 of the thickness E1 of the target material layer 17; that is to say that for a thickness E1 of 300 microns, the depth P can be between 100 microns and 200 microns.
  • the slots F1 to Fn are radial, so that they make it possible to release the mechanical stresses without hampering the heat exchanges.
  • the spacing of the slots F1 to Fn is a compromise between the concern to slightly decrease the x-ray yield of the target 17 (the yield is reduced if the slots F1 to Fn are too tight), and the concern to give the slots F1 at Fn maximum efficiency.
  • width 12 of the slots F1 to Fn must be as narrow as possible, taking into account the technological considerations of implementation. These technological considerations can also lead to increasing the length L of the slots F1 to Fn beyond the strictly necessary length.
  • the plane of the slots can be inclined relative to the plane normal to the surface 21 of the target.
  • An example of the inclination of a slot is given at a third slot F3 by an axis 27 parallel to the depth P3 of this third slot and forming an angle of inclination ⁇ 1, with a second axis 28 symbolizing a normal plane to the surface 21.
  • the angle of inclination ⁇ 1 is to be determined according to the width 12 and the depth P of a slot F1 to Fn: it may be mentioned, only by way of nonlimiting example, that the tilt angle ⁇ 1 can have a value of 15 ° for a depth P of 150 microns and a width 12 of the slot F3 of about 50 microns.
  • angle of inclination ⁇ 1 must remain relatively small, so as not to hinder the heat exchanges which, in the nonlimiting example shown in the figure, are essentially carried out in directions parallel to the axis of symmetry 3 and in radial directions (since all the points of the focal ring 19 are at close temperature) .
  • the production of the slots F1 to Fn in the surface 21 of the target 17 constitutes a simple and easy to implement solution to the problem of aging of the anodes represented by cracking of the targets.
  • the length L of the slots F1 to Fn extends in radial directions.
  • the orientation of the length of these slots may be different, in particular in the case where the target is formed on the edge or around the rotating anode disc: in this case, the length slots is parallel to the axis of symmetry or axis of rotation of the anode; such an arrangement of the target being common in the case of rotating anodes for mammography.

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  • X-Ray Techniques (AREA)

Abstract

The rotary anode (1) for an X-ray tube has a circular carbon base (15), with a partly sloping top surface (6) giving the form of a flattened truncated cone. This slope carries an intermediate layer of rhenium (16) on which is deposited a target layer (17) of tungsten. Radial slots (F1-n) are cut into the tungsten at intervals of between five and ten degrees, to a depth of between one and two thirds of its thickness. These may be inclined (27,28) to avoid problems of obliquely incident electrons, and are kept as narrow as possible to avoid loss of target efficiency. In operation, compression stresses due to surface expansion, particularly in the beam impact zone ring (19), are relieved by the radial slots. Cracking of the target material is thus prevented.

Description

L'invention concerne une anode tournante pour tube à rayons X, et en particulier des moyens pour éviter la création anarchique de fissures dans une cible portée par l'anode.The invention relates to a rotating anode for an X-ray tube, and in particular to means for preventing the uncontrolled creation of cracks in a target carried by the anode.

Avec les tubes à rayons X, le rayonnement X est couramment obtenu par un bombardement électronique de l'anode. Plus précisément, le bombardement électronique est concentré sur une petite surface, appelée foyer, d'une cible que comporte l'anode, ce foyer devenant la source du rayonnement X.With X-ray tubes, X-radiation is commonly obtained by electron bombardment of the anode. More precisely, the electron bombardment is concentrated on a small surface, called the focal point, of a target which the anode comprises, this focal point becoming the source of the X-ray radiation.

Une faible part de l'énergie électrique dépensée pour accélérer les électrons (environ 1%) est transfor­mée en rayons X, le reste de cette énergie est dissipé en chaleur. Cette chaleur, dont l'évacuation pour la plus grande partie se fait par rayonnement, peut con­duire à la détérioration de l'anode, et plus particuliè­rement à la détérioration de la cible, par fusion par exemple, à l'endroit où est formé le foyer.A small part of the electrical energy expended to accelerate the electrons (about 1%) is transformed into X-rays, the rest of this energy is dissipated into heat. This heat, most of which is evacuated by radiation, can lead to deterioration of the anode, and more particularly to deterioration of the target, for example by fusion, at the place where the foyer.

Aussi, la cible est généralement constituée en un matériau non seulement à haut numéro atomique pour favoriser la production de rayons X, mais aussi en un matériau réfractaire et bon conducteur de la chaleur, comme par exemple le tungstène, ou le molybdène, ou leurs alliages, etc...Also, the target is generally made of a material not only of high atomic number to favor the production of X-rays, but also of a refractory material and good conductor of heat, such as for example tungsten, or molybdenum, or their alloys , etc ...

Cependant quel que soit le matériau dont est constitué la cible, les puissances instantanées mises en jeu (de l'ordre de 100 KW) créent des contraintes importantes dans les couches superficielles de ce matériau.However, whatever the material of which the target is made, the instantaneous powers involved (of the order of 100 KW) create significant constraints in the surface layers of this material.

En vue de diminuer la température au foyer, une solution courante consiste à faire défiler la cible sous le foyer ou impact du faisceau d'électrons. Ce défile­ment de la cible est obtenu par une rotation de l'anode autour d'un axe de symétrie de cette dernière, l'anode ayant généralement la forme d'un disque. Le défilement de la cible, sous le foyer créé à l'impact du faisceau d'électrons, engendre sur la cible et autour de l'axe de symétrie, une couronne focale large de plusieurs milli­mètres.In order to decrease the temperature at the focus, a common solution is to scroll the target under the focus or impact of the electron beam. This scrolling of the target is obtained by a rotation of the anode about an axis of symmetry of the latter, the anode generally having the shape of a disc. The scrolling of the target, under the focal point created at the impact of the electron beam, generates on the target and around the axis of symmetry, a focal ring several millimeters wide.

La rotation rapide de l'anode (plusieurs milliers de tours par minute) est nécessaire pour répartir le flux thermique sur la couronne focale. Mais la tempéra­ture du foyer reste très supérieure à la température du reste de la couronne focale, qui elle-même a une tempé­rature très supérieure à celle du reste du disque d'anode.The rapid rotation of the anode (several thousand revolutions per minute) is necessary to distribute the heat flux over the focal ring. However, the temperature of the focal point remains much higher than the temperature of the rest of the focal ring, which itself has a temperature much higher than that of the rest of the anode disc.

On observe que chaque point de cette couronne focale reçoit une "impulstion thermique" à chaque tour de l'anode. Avec les matériaux généralement utilisés pour l'émission d'un rayonnement X sous l'effet d'un bombardement électronique, c'est à dire les matériaux cibles tels que le tungstène par exemple, les fluctua­tions dues à ces impulsions peuvent être considérées comme insignifiantes au delà d'une couche superficielle dont l'épaisseur est de l'ordre de 100 microns ; de sorte que c'est principalement cette couche superfi­cielle qui subit, au rythme de la rotation, une succes­sion de chocs thermiques, et par suite, de contraintes mécaniques importantes.It is observed that each point of this focal ring receives a "thermal impulse" at each revolution of the anode. With the materials generally used for the emission of X-rays under the effect of electronic bombardment, that is to say the target materials such as tungsten for example, the fluctuations due to these pulses can be considered insignificant. beyond a surface layer whose thickness is of the order of 100 microns; so that it is mainly this surface layer which undergoes, at the rate of rotation, a succession of thermal shocks, and consequently, significant mechanical stresses.

D'autre part, à une autre échelle de temps, celle d'une pose qui peut durer par exemple de 0,1 seconde à 1 seconde ou même plus, toute la couronne focale reçoit un flux thermique important, qui ne diffuse que graduelle­ment dans l'ensemble du disque d'anode.On the other hand, on another time scale, that of a pose which can last for example from 0.1 second to 1 second or even more, the entire focal ring receives a significant thermal flux, which diffuses only gradually throughout the anode disc.

Par suite, les auteurs de l'invention ont pensé que la couronne focale est soumise à une compression impor­tante, due à la dilatation du matériau cible, et que probablement le matériau cible sort du domaine d'élasti­cité du matériau, de sorte qu'une contrainte de traction qui résulte du refroidissement peut engendrer des fissures dans la surface du matériau dont est constitué la cible.Consequently, the authors of the invention have thought that the focal crown is subjected to a significant compression, due to the expansion of the target material, and that probably the target material leaves the elastic range of the material, so that a tensile stress resulting from cooling can cause cracks in the surface of the material from which the target is made.

Ces fissures tendent à augmenter en nombre et en importance avec le temps de fonctionnement, et elles deviennent préjudiciables au bon fonctionnement du tube à rayons X : ainsi par exemple, dans le cas d'une anode constituée d'un corps de base (en graphite par exemple) revêtu d'une couche de matériau émissif de rayons X ou matériau cible (en tungstène par exemple), ces fissures peuvent se prolonger jusqu'au graphite et il peut en résulter des décollements de la couche de tungstène, entraînant la destruction rapide du tube ; on note également que ces fissures, si elles sont trop nombreu­ses, tendent à diminuer la quantité de rayonnements X émis par le foyer.These cracks tend to increase in number and in importance with the operating time, and they become detrimental to the proper functioning of the X-ray tube: thus for example, in the case of an anode consisting of a basic body (in graphite for example) coated with a layer of X-ray emissive material or target material (in tungsten for example), these cracks can extend to graphite and this can result in detachments of the tungsten layer, leading to rapid destruction tube; it is also noted that these cracks, if they are too numerous, tend to decrease the amount of X-rays emitted by the hearth.

L'invention concerne une anode tournante pour tube à rayons X, agencée d'une manière nouvelle qui permet d'éviter la formation aléatoire et non contrôlée de fissures dans la cible.The invention relates to a rotating anode for an X-ray tube, which is arranged in a new way which avoids random and uncontrolled formation of cracks in the target.

Selon l'invention, une anode tournante pour tube à rayons X, comportant une cible destinée à être soumise à un bombardement électronique en vue de produire un rayonnement X, est caractérisée en ce que la surface de la cible est creusée par une pluralité de fentes équi­distantes et disposées de manière symétrique par rapport à un axe de symétrie de l'anode.According to the invention, a rotating anode for an X-ray tube, comprising a target intended to be subjected to electronic bombardment in order to produce X-radiation, is characterized in that the surface of the target is hollowed out by a plurality of slots equidistant and arranged symmetrically with respect to an axis of symmetry of the anode.

L'invention sera mieux comprise grâce à la descrip­tion qui suit, faite à titre d'exemple non limitatif, et à l'unique figure jointe qui montre schématiquement, par une vue en perspective, une anode tournante conforme à l'invention.The invention will be better understood thanks to the description which follows, given by way of nonlimiting example, and to the single attached figure which schematically shows, in a perspective view, a rotating anode in accordance with the invention.

La figure unique montre une anode tournante 1 pour un tube à rayons X en lui-même classique (non représen­té). Dans l'exemple non limitatif de la description, l'anode 1 est formée selon un disque ayant un axe de symétrie 3 et une forme approximativement troncônique ; c'est à dire qu'une face 4 est formée d'une partie centrale 5 plane entourée d'une partie pentue 6 qui rejoint les bords circulaires périphériques 7 du disque d'anode 1.The single figure shows a rotating anode 1 for an X-ray tube in itself conventional (not shown). In the nonlimiting example of the description, the anode 1 is formed according to a disc having an axis of symmetry 3 and an approximately frustoconical shape; that is to say that a face 4 is formed of a flat central part 5 surrounded by a sloping part 6 which joins the peripheral circular edges 7 of the anode disc 1.

Dans l'exemple non limitatif décrit, la partie centrale 5 comporte un trou 8, disposé selon l'axe de symétrie 3, et destiné au passage d'un axe support (non représenté) servant à porter l'anode tournante 1 de manière classique.In the nonlimiting example described, the central part 5 has a hole 8, arranged along the axis of symmetry 3, and intended for the passage of a support axis (not shown) used to carry the rotating anode 1 in a conventional manner .

Dans l'exemple non limitatif de la description, comme il apparaît sur la figure grace à un arraché, l'anode tournante 1 est du type comportant un corps de base 15 ou substrat, en graphite par exemple, sur lequel est déposée une couche intermédiaire d'accrochage 16 en rhénium par exemple ; une couche de matériau cible 17, en tungstène par exemple, étant déposée sur la couche d'accrochage 16.In the nonlimiting example of the description, as it appears in the figure thanks to a cutaway, the rotating anode 1 is of the type comprising a base body 15 or substrate, in graphite for example, on which an intermediate layer is deposited attachment 16 in rhenium for example; a layer of target material 17, for example of tungsten, being deposited on the bonding layer 16.

La couche 17 de matériau cible a été formée en une ou plusieurs couches, déposées selon une méthode classi­que telle que par exemple, dépôt électrolytique, ou dépôt chimique en phase vapeur (CVD) ou encore par la méthode de dépôt par projection au chalumeau à plasma, etc...The layer 17 of target material has been formed in one or more layers, deposited according to a conventional method such as, for example, electrolytic deposition, or chemical vapor deposition (CVD) or also by the method of deposition by plasma torch projection. , etc ...

Dans l'exemple non limitatif décrit la couche de matériau cible 17 ou cible a une épaisseur E1 comprise entre 300 microns et 700 microns.In the nonlimiting example described, the layer of target material 17 or target has a thickness E1 of between 300 microns and 700 microns.

Bien entendu dans l'esprit de l'invention, l'épa­isseur E1 de la cible 17 peut être différente et la cible 17 peut être constituée selon une structure massive, formée par exemple directement par le corps de base 15 lui même constitué en matériau cible ; ou encore la cible 17 peut étre rapportée sur le corps de base 15.Of course in the spirit of the invention, the thickness E1 of the target 17 can be different and the target 17 can be formed according to a massive structure, formed for example directly by the base body 15 itself made of target material ; or the target 17 can be attached to the base body 15.

La couche 17 de matériau cible consitue une cible destinée à être bombardée par un faisceau d'électrons (non représenté,) en vue de produire de manière classi­que un rayonnement X.The layer 17 of target material constitutes a target intended to be bombarded by an electron beam (not shown) in order to conventionally produce X-radiation.

En fait, la cible 17 est destinée à être soumise au bombardement électronique sur une faible surface où est constitué un foyer 18, à partir duquel la rotation de l'anode tournante 1 autour de l'axe de symétrie 3, engendre une couronne focale 19 (représentée en traits pointillés). Dans l'exemple non limitatif décrit, la couche 17 de matériau cible est déposée sur l'ensemble de la partie pentue 6, mais cette couche 17 peut être déposée sur une surface plus réduite, de sorte à consti­tuer la cible selon une couronne correspondant sensible­ment à la couronne focale 19.In fact, the target 17 is intended to be subjected to electronic bombardment over a small surface where a focal point 18 is formed, from which the rotation of the rotating anode 1 around the axis of symmetry 3 generates a focal ring 19 (shown in dotted lines). In the nonlimiting example described, the layer 17 of target material is deposited on the whole of the sloping part 6, but this layer 17 can be deposited on a more reduced surface, so as to constitute the target according to a ring corresponding substantially to focal ring 19.

Selon une caractéristique de l'invention, et en vue d'éviter une fissuration anarchique de la cible 17 sous l'effet du bombardement électronique, la surface 21 de la cible 17 est creusée par une pluralité de fentes F1, F2, F3, ..., Fn équidistantes et disposées de manière symétrique par rapport à l'axe de symétrie 3.According to a characteristic of the invention, and in order to avoid an uncontrolled cracking of the target 17 under the effect of electronic bombardment, the surface 21 of the target 17 is hollowed out by a plurality of slots F1, F2, F3,. .., Fn equidistant and arranged symmetrically with respect to the axis of symmetry 3.

Dans l'exemple non limitatif représenté à la figure où la cible 17 est formée sur une face 4 de l'anode 1, la longueur L des fentes F1 à Fn s'étend radialement et correspond à des génératrices du cône.In the nonlimiting example shown in the figure where the target 17 is formed on a face 4 of the anode 1, the length L of the slots F1 to Fn extends radially and corresponds to generatrices of the cone.

Mais, l'utilité des fentes F1 à Fn se manifeste surtout en regard des surfaces bombardées, c'est à dire de la couronne focale 19, et la longueur L des fentes F1 à Fn peut être limitée et correspondre sensiblement à une largeur 1 de la couronne focale 19.However, the usefulness of the slots F1 to Fn is manifested above all with regard to the bombarded surfaces, that is to say of the focal ring 19, and the length L of the slots F1 to Fn can be limited and correspond substantially to a width 1 of the focal ring 19.

Les fentes F1 à Fn ont une profondeur P inférieure à l'épaisseur E1 de la cible 17, de manière à laisser subsister une quantité suffisante de matériau cible entre un fond 23 des fentes F1 à Fn et le substra ou corps de base 15.The slits F1 to Fn have a depth P less than the thickness E1 of the target 17, so as to leave a sufficient quantity of target material between a bottom 23 of the slits F1 to Fn and the substra or base body 15.

En fait, la profondeur P des fentes F1 à Fn doit être égale ou supérieure à l'épaisseur de la couche, superficielle, estimée à environ 100 microns, qui a été citée dans le préambule comme étant la couche au delà de laquelle les fluctuations thermiques sont insignifian­tes.In fact, the depth P of the slits F1 to Fn must be equal to or greater than the thickness of the surface layer, estimated at around 100 microns, which was cited in the preamble as being the layer beyond which the thermal fluctuations are insignificant.

En pratique un compromis satisfaisant est atteint en conférant à la profondeur P une valeur comprise entre 1/3 et 2/3 de l'épaisseur E1 de la couche de matériau cible 17 ; c'est à dire que pour une épaisseur E1 de 300 microns, la profondeur P peut être comprise entre 100 microns et 200 microns.In practice, a satisfactory compromise is achieved by giving the depth P a value between 1/3 and 2/3 of the thickness E1 of the target material layer 17; that is to say that for a thickness E1 of 300 microns, the depth P can be between 100 microns and 200 microns.

Dans l'exemple non limitatif décrit, les fentes F1 à Fn sont radiales, de sorte qu'elles permettent de libérer les contraintes mécaniques sans entraver les échanges thermiques.In the nonlimiting example described, the slots F1 to Fn are radial, so that they make it possible to release the mechanical stresses without hampering the heat exchanges.

L'espacement des fentes F1 à Fn est un compromis entre le souci de diminuer peu le rendement du rayonne­ment X de la cible 17 (le rendement est diminué si les fentes F1 à Fn sont trop serrées), et le souci de donner aux fentes F1 à Fn une efficacité maximum.The spacing of the slots F1 to Fn is a compromise between the concern to slightly decrease the x-ray yield of the target 17 (the yield is reduced if the slots F1 to Fn are too tight), and the concern to give the slots F1 at Fn maximum efficiency.

Nous avons constaté qu'un écartement angulaire α compris entre environ 5° et 10° était correct, mais bien entendu on peut sortir de ces limites.We found that an angular spacing α between about 5 ° and 10 ° was correct, but of course we can get out of these limits.

Il est à noter que la largeur 12 des fentes F1 à Fn doit être aussi étroite que possible, compte tenu des considérations technologiques de réalisation. Ces onsidérations technologiques peuvent conduire également à augmenter la longueur L des fentes F1 à Fn au delà de la longueur strictement nécessaire.It should be noted that the width 12 of the slots F1 to Fn must be as narrow as possible, taking into account the technological considerations of implementation. These technological considerations can also lead to increasing the length L of the slots F1 to Fn beyond the strictly necessary length.

Pour réaliser les fentes F1 à Fn, plusieurs procé­dés en eux-mêmes connus peuvent être utilisés, tels que par exemple : par découpe mécanique, par fusion avec faisceau laser, ou encore par électro-érosion : il semble que ce dernier procédé soit actuellement particu­lièrement bien adapté à réaliser les fentes F1 à Fn très fines (largeur 12 de l'ordre de quelques 1/100 millimè­tre), et de géométrie quelconque.To make the slits F1 to Fn, several methods which are known per se can be used, such as for example: by mechanical cutting, by fusion with laser beam, or by electro-erosion: it seems that the latter method is currently particularly well suited to making very fine slots F1 to Fn (width 12 of the order of a few 1/100 millimeters), and of any geometry.

On peut même envisager des fentes F1 a Fn dont la profondeur P s'étend de manière non rectiligne, pour éviter l'atteinte du fond 23 par des électrons (non représentés) d'incidence oblique.One can even envisage slits F1 to Fn whose depth P extends in a non-rectilinear manner, to avoid reaching the bottom 23 by electrons (not shown) of oblique incidence.

En vue d'éviter le choc direct d'électrons dans le fond 23 des fentes F1 à Fn, le plan des fentes peut être incliné par rapport au plan normal à la surface 21 de la cible. Un exemple de l'inclinaison d'une fente est donné au niveau d'une troisième fente F3 par un axe 27 paral­lèle à la profondeur P3 de cette troisième fente et formant un angle d'inclinaison α 1, avec un second axe 28 symbolisant un plan normal à la surface 21. L'angle d'inclinaison α 1 est à déterminer selon la largeur 12 et la profondeur P d'une fente F1 à Fn : on peut citer, uniquement à titre d'exemple non limitatif, que l'angle d'inclinaison α 1 peut avoir une valeur de 15° pour une profondeur P de 150 microns et une largeur 12 de la fente F3 d'environ 50 microns.In order to avoid the direct shock of electrons in the bottom 23 of the slots F1 to Fn, the plane of the slots can be inclined relative to the plane normal to the surface 21 of the target. An example of the inclination of a slot is given at a third slot F3 by an axis 27 parallel to the depth P3 of this third slot and forming an angle of inclination α 1, with a second axis 28 symbolizing a normal plane to the surface 21. The angle of inclination α 1 is to be determined according to the width 12 and the depth P of a slot F1 to Fn: it may be mentioned, only by way of nonlimiting example, that the tilt angle α 1 can have a value of 15 ° for a depth P of 150 microns and a width 12 of the slot F3 of about 50 microns.

IL est à noter que l'angle d'inclinaison α 1 doit rester relativement faible, pour ne pas entraver les échanges thermiques qui, dans l'exemple non limita­tif représenté à la figure, se font essentiellement selon des directions parallèles à l'axe de symétrie 3 et selon des directions radiales (puisque tous les points de la couronne focale 19 sont à température voisine).It should be noted that the angle of inclination α 1 must remain relatively small, so as not to hinder the heat exchanges which, in the nonlimiting example shown in the figure, are essentially carried out in directions parallel to the axis of symmetry 3 and in radial directions (since all the points of the focal ring 19 are at close temperature) .

Il est à noter que les contraintes mécaniques, au contraire, qu'elles soient de compression ou de trac­tion, se font principalement tangentiellement, ce qui explique que les fissures, quand elles se produisent, sont généralement radiales.It should be noted that the mechanical stresses, on the contrary, whether they are compression or traction, are mainly tangential, which explains why the cracks, when they occur, are generally radial.

La réalisation des fentes F1 à Fn dans la surface 21 de la cible 17, constitue une solution simple et de mise en oeuvre facile au problème du vieillissement des anodes que représente la fissuration des cibles. Dans l'exemple non limitatif décrit et représenté à la figure, la longueur L des fentes F1 à Fn s'étend dans des directions radiales. Mais, dans l'esprit de l'inv­ention l'orientation de la longueur de ces fentes peut être différente, notamment dans le cas où la cible est formée sur la tranche ou pourtour du disque d'anode tournante : dans ce cas, la longueur des fentes est parallèle à l'axe de symétrie ou axe de rotation de l'anode ; une telle disposition de la cible étant courante dans le cas d'anodes tournantes pour mammographie.The production of the slots F1 to Fn in the surface 21 of the target 17 constitutes a simple and easy to implement solution to the problem of aging of the anodes represented by cracking of the targets. In the nonlimiting example described and shown in the figure, the length L of the slots F1 to Fn extends in radial directions. However, in the spirit of the invention, the orientation of the length of these slots may be different, in particular in the case where the target is formed on the edge or around the rotating anode disc: in this case, the length slots is parallel to the axis of symmetry or axis of rotation of the anode; such an arrangement of the target being common in the case of rotating anodes for mammography.

Claims (7)

1. Anode tournante pour tube à rayons X comportant une cible (17) sous forme d'une couche en matériau émissif qui est portée par un substrat (15) et qui est formée autour d'un axe de symétrie (3) de l'anode (1), caractérisée en ce que la surface (21) de la cible (17) est creusée par une pluralité de fentes radiales (F1 à Fn) équidistantes et disposées de manière symétrique par rapport à l'axe de symétrie (3), la profondeur (P) desdites fentes (F1 à Fn) étant inférieure à l'épaisseur (E1) de la cible (17).1. Rotating anode for an X-ray tube comprising a target (17) in the form of a layer of emissive material which is carried by a substrate (15) and which is formed around an axis of symmetry (3) of the anode (1), characterized in that the surface (21) of the target (17) is hollowed out by a plurality of radial slots (F1 to Fn) equidistant and arranged symmetrically with respect to the axis of symmetry (3) , the depth (P) of said slots (F1 to Fn) being less than the thickness (E1) of the target (17). 2. Anode selon la revendication 1, caractérisée en ce que la profondeur (P) des fentes (F1 à Fn) est sensiblement comprise entre 1/3 et 2/3 de l'épaisseur (E1) de la cible (17).2. Anode according to claim 1, characterized in that the depth (P) of the slots (F1 to Fn) is substantially between 1/3 and 2/3 of the thickness (E1) of the target (17). 3. Anode selon la revendication 1 ou 2, caractérisée en ce que la profondeur (P) des fentes (F1 à Fn) est égale ou supérieure à cent microns.3. Anode according to claim 1 or 2, characterized in that the depth (P) of the slots (F1 to Fn) is equal to or greater than one hundred microns. 4. Anode selon l'une quelconque des revendications précédentes 1 à 3, caractérisée en ce que la profondeur des fentes (F1 à FN) n'est pas uniforme.4. Anode according to any one of the preceding claims 1 to 3, characterized in that the depth of the slots (F1 to FN) is not uniform. 5. Anode selon l'une quelconque des revendications précédentes 1 à 4, caractérisée en ce que le plan des fentes (F1 à Fn) est incliné par rapport à un plan (28) normal à la surface (27) de la cible (17).5. Anode according to any one of the preceding claims 1 to 4, characterized in that the plane of the slots (F1 to Fn) is inclined relative to a plane (28) normal to the surface (27) of the target (17 ). 6. Anode selon l'une quelconque des revendications précédentes, caractérisée en ce que les fentes (F1 à Fn) s'étendent radialement sur au moins la largeur de la couronne focale (19).6. Anode according to any one of the preceding claims, characterized in that the slots (F1 to Fn) extend radially over at least the width of the focal ring (19). 7. Anode selon l'une quelconque des revendications précédentes, caractérisé en ce que les fentes présentent entre elles un écartement angulaire α compris entre 5° et 10° .7. Anode according to any one of the preceding claims, characterized in that the slots have between them an angular spacing α of between 5 ° and 10 °.
EP88403377A 1987-12-30 1988-12-30 Rotary anode for an X-ray tube Withdrawn EP0323365A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8718367 1987-12-30
FR8718367A FR2625605A1 (en) 1987-12-30 1987-12-30 ROTATING ANODE FOR X-RAY TUBE

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EP0323365A1 true EP0323365A1 (en) 1989-07-05

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EP (1) EP0323365A1 (en)
JP (1) JPH01209641A (en)
FR (1) FR2625605A1 (en)

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US4991194A (en) 1991-02-05
JPH01209641A (en) 1989-08-23
FR2625605A1 (en) 1989-07-07

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