DE1957152A1 - X-ray picture tube - Google Patents

Description

PATENTANWÄLTE V1 P236 D DR. CLAUS REINLÄNDER

DIPL ING. KLAUS BERNHARDT α q γ _{ί λ} γ ο

D-8 MONKS 60 ISO / I 0 £

BÄCKERSTRASSE3.

VARIAN ASSOCIATES PaIo Altο / California, USA

X-ray picture tube (addendum to patent ... (patent application P 1614986.3)

Priority: November 15, 1968 - United States v. America Serial No. 776,089

summary

An X-ray picture tube is described in which one Oxygenated vanadium barrier is provided between the scintillator tube and the photocathode.

State of the art

In the main patent, an X-ray picture tube is described and claimed, which consists of an evacuated vessel with a X-ray transparent recording window through which X-ray images can pass, an X-ray sensitive one Fluorescent layer that forms a collecting screen inside the vessel around the X-ray images and convert them into optical images, one Photocathode, with which the optical images are converted into electron images, and an electrode structure, with which the electron images are accelerated and focused on a fluorescent screen in order to achieve an intensified To generate an optical image for viewing, which corresponds to the X-ray image, is based on its particularity

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the main pat ent is that the photocathode 'as a layer is formed directly on the X-ray sensitive fluorescent layer, so that the sensitivity of the image intensifier tube is increased.

It is known between the X-ray sensitive fluorescent layer, which is also known for short as a scintillator and the photocathode to provide a buffer layer made of glass to prevent chemical reactions between the scintillator layer and to prevent the photocathode.

According to a particularly advantageous embodiment of the subject matter of the main patent, this buffer layer could be used to prevent a chemical reaction could be dispensed with, which made it possible to achieve a considerably higher sensitivity of the X-ray picture tube will.

However, it has been shown that at relatively low X-ray exposure, for example 30 Hillir X-rays per minute and moreover, there is an interaction between the scintillator hit and the photocathode, which results in a progressive one Defocusing of the electron image within the input layers leads. Seems as seen from the fluorescent screen of the tube then the x-ray image will fold and become blurred. The edge of the picture moves inward, making the picture as a whole is contracted.

The invention is intended to avoid this disadvantage of the known tube, but with the disadvantages of the conventional ones vitreous buffer layers are avoided. '

According to the invention this object is achieved in that a ' improved barrier is used between the scintillator and the photocathode of an X-ray picture tube.

In particular, the invention is intended to make available an X-ray picture tube with which an X-ray exposure

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amplified and transformed by more than 30 millirX-rays can, with an improved barrier between an alkali halide scintillator and an alkali antimonide photocathode is used to prevent noticeable defocusing, without resulting in a noticeable corresponding reduction in sensitivity.

According to the invention, this object is achieved in an X-ray picture tube with a scintillator and a photocathode in that that a barrier is connected between the scintillator and the photocathode, the weight of which is predominantly made of oxidized Vanadium consists.

The invention will be explained in more detail with reference to the drawing; show it:

1 schematically shows an X-ray system with an X-ray picture tube according to the invention, and

FIG. 2 shows a section through the part of the X-ray picture tube enclosed in FIG. 1 by the line 2-2.

Fig. 1 shows an X-ray system with an X-ray source, which projects an X-ray beam against an object. An X-ray picture tube is placed behind the object and takes its X-ray image. Such a system is, for example, described in "X-Ray Image Intensification With A Large Diameter Image Intensifier Tube" American Journal cf Roentgenology Radium Therapy and Nuclear Medicine, Vol. 85, pp. 323-341, February 1961.

The X-ray picture tube consists of a dielectric evacuated flask 1, which is about 43 cm. (17 nominal) long and 25 cm (10 in) in diameter. The front part of the tube has a novel input packing 2, which is shown in more detail in FIG. The tube also consists of an electrode focusing electrode 3, an anode A and a fluorescent viewing screen 5. The inlet packing consists of one part of the tube piston which forms the inlet packing support layer 6 on the same side

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consists of aluminum, which is transparent to incident X-rays. A scintillator made of a layer 7 of cesium iodide and sodium has been deposited on the surface of the support layer 6. If desired, thallium can be used instead of the sodium. A barrier consists of a layer _r which consists predominantly of vanadium pentoxide by weight and contains a smaller amount of phosphorus pentoxide ·; this layer is deposited directly on the scintillator. Finally, a photocathode made of a layer 9 of cesium antimonide has been deposited on the barrier. Any precipitate is created using evaporation techniques.

During operation, the X-ray source penetrates X-rays through the object being observed. The local attenuation of the X-rays depends on both the thickness and the also the ordinal number of the elements that make up the object under consideration. 'The intensity pattern of the X-ray according to the penetration of the object thus contains information relating to the structure of the object. The x-ray then occurs through the support layer 6 of the tube inlet packing and hits the scintillator 7 "as symbolized by the arrow 10 in FIG Fig. 2 is indicated. Within the scintillator 7, the X-ray photons are absorbed and re-emitted as optical photons, typically in the blue frequency range. The optical photons pass through the barrier 7 at around $ 75-80 Transmission through. The optical photons then hit the photocathode 9 where they generate electrons e. The electrons are captured by the photocathode in a pattern or image emitted according to the initial impinging X-ray image, The electrons are then on high. Speed within the X-ray picture tube accelerated and through the anode 4 on the Fluorescence viewing screen 5 focused where viewed with the eye or other suitable optical pickup will. ■

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The surprising success achieved through the use of Vanadium pentoxide as a barrier between the scintillator and the photocathode, extensive investigations followed with other materials, for example tin oxide and tungsten trioxide, Silicon oxide, silicon dioxide, platinum and aluminum - one such Success is surprising because vanadium pentoxide is an opaque, Semiconducting material and not a transparent dielectric, like glass, used to be a buffer layer was used between zinc sulfide phosphors and photocathodes.

Since vanadium pentoxide is naturally red-yellow, only an extremely thin layer can be applied if the optical transmission of the barrier is not to fall _{below a still permissible value t.} It has been found that a layer thickness between 20 and 200 AU gives satisfactory results, whereby satisfactory results are understood to mean that the optical transmission is sufficient and that there is no adverse interaction between the scintillator and the photocathode, which results from electronic defocusing within the incoming parcel noticeable.

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Claims (10)

Claims X-ray picture tube according to patent ... (patent application P 1614986.3), characterized in that between the X-ray sensitive fluorescent layer, which forms a collecting screen within the vessel to record the X-ray images and convert them into optical images, and the photocathode, with which the optical images into electron images are converted, a barrier is arranged, the weight of which consists predominantly of oxidized vanadium. 2. Tube according to claim 1, characterized in that the transmittance of the barrier is in the visible range about 75-80%. - 3. Pipes according to claim 1 or 2, characterized in that the barrier has a thickness between 20 and 200 AU. 4. Tube according to claim 1, 2 or 3, characterized in that that the barrier to the lower weight fraction of phosphorus pentoxide consists. 5. Tube according to one of claims 1 to 4, characterized in that that the scintillator consists of an alkali halide. 6. Tube according to claim 5, characterized in that the scintillator consists of cesium godide. 7. Tube according to claim 6, characterized in that the '. Scintillator also contains thallium or sodium. 00 9838/1372 8. Tube according to one of claims 1 to 7, characterized in that the photocathode consists of alkali antimonide ". 9. Tube according to claim 8, characterized in that the
Cesium antimonide photocathode ". 10. Tube according to one of claims 1 "to 9, characterized in that that the barrier consists of vanadium pentoxide. BATH
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