US3543034A - X-ray image transducer tube having crenelated fluorescent layer ahead of solid-state image intensifier - Google Patents

Description

Nov. 24, 1970 J. FINKLE 3,543,034

X-RAY IMAGE TRANSDUCER TUBE HAVING CRENELATED FLUORESCENT LAYER AHEAD 0F SOLID-STATE IMAGE INTENSIFIER Filed March 14, 1969 Bose in if n JACK FIN/(LE I BY m 72 f ,3 mar! 91 x E ATTORNEY I INVENTOR;

United States Patent 3,543,034 X-RAY IMAGE TRANSDUCER TUBE HAVING CRENELATED FLUORESCENT LAYER AHEAD OF SOLID-STATE IMAGE INTENSIFIER Jack Finkle, 918 E. 14th St., Brooklyn, N.Y. 11230 Continuation-impart of applications Ser. No. 306,897, Sept. 5, 1963, and Ser. No. 459,529, May 24, 1965. This application Mar. 14, 1969, Ser. No. 807,201

Int. Cl. H01j 31/50 U.S. Cl. 250-213 6 Claims ABSTRACT OF THE DISCLOSURE An evacuated envelope contains, at an entrance end transparent to incident X-rays, a receiving unit for X- rays ahead of an image-intensifier structure responsive to both ultraviolet and luminous radiation for emitting an electron beam conforming to the intensity pattern of the incident X-rays, the receiving unit being transparent to X rays and including a crenelated light-reflecting layer with forwardly facing depressions occupied by a fluorescent mass which, on being excited by the incident X-rays, emits concentrated bundles of light rays which reach the intensifier together with the generating X-rays.

This application is a continuation-in-part of my prior applications Ser. No. 459,529, fi-led May 24, 1965, and Ser. No. 306,897, filed Sept. 5, 1963, now Pat. No. 3,436,550.

In my last-mentioned application I have disclosed an image intensifier to be used in a system for visualizing X- ray images by electronic means. This image intensifier includes, within an evacuated envelope, a photoelectroluminescent phosphor layer and a photoconductive layer disposed, with interposition of a barrier layer opaque to visible light but transparent to ultraviolet radiation, between a pair of conductive layers connected across a source of alternating voltage. An image-receiving unit ahead of this intensifier structure includes a fluorescent layer excitable by impinging X-rays whose output energizes the photoconductive layer of the intensifier to modulate the alternating-current field developed across the electroluminescent phoshpor layer which is stimulated both by the applied potential and by the penetrating X- rays to trigger the emission of a conforming electron pattern from an adjoining photocathode.

The general object of my present invention is to provide an improved receiving unit for an image transducer of this type, designed to amplify the luminous radiation impinging upon the photoconductor of the intensifier.

This object is realized, pursuant to my present invention, by providing the light-reflecting layer preceding the photoconductor with a multiplicity of depressions of substantially paraboloidal shape which are formed in a crenelated forward surface of that layer, i.e. a surface confronting the image-intensifier structure. Advantageously, this light-reflective layer is formed as a thin metallic coating on a base plate of glass or other radiationpermeable material having a crenelated front surface, the limited thickness of this deposit enabling substantially unimpeded propagation of X-rays toward the following intensifier. In principle, however, it is also possible to make the base itself of X-ray-transparent but lightrefiecting material so that the reflecting layer becomes self-supporting and no special carrier therefor is required. The depressions of the crenelated surface are filled with a fluorescent mass excitable by the impinging X-rays to produce concentrated bundles or pencils of light rags generally paralleling the exciting X-rays so that the combination thereof impinges upon the intensifier structure to generate the corresponding electron pattern.

3,543,034 Patented Nov. 24, 1970 The invention will be described in greater detail with reference to the accompanying drawing the sole FIGURE of which is a somewhat diagrammatic illustration of a representative embodiment shown in longitudinal section.

As shown in the drawing, a Farnsworth-type tube 35 having the usual evacuated envelope is provided with a composite receiving, image-intensifying and electronemissive structure disposed near a radiation-transparent entrance end of the tube. This structure includes a multiplicity of layers transparent to X-rays, namely a base plate 2, a light reflector 36 deposited thereon, another base plate 3, a conductive layer 4, a photoconductive layer 5 and a high-resistance barrier layer 39 opaque to visible light. Layer 39 carries a photoelectroluminescent phosphor layer 6 adjoining another conductive layer 7 which is transparent to luminous radiation emitted by layer 6. A further base plate 8 serves together with plate 3 as a support for the multilayer stack sandwiched therebetween. Electrodes 4 and 7 may comprise an easily volatilzing metal, such as aluminum, silver or gold, deposited in vacuo with a thickness on the order of 0.1 mm.; the same applies to reflecting layer 36. A pattern of incident X- rays has been diagrammatically indicated at 1.

A photocathode 9, disposed forwardly of base plate 8, comprises an electron-emissive layer generating an electron beam 40 in response to light emitted by phosphor layer 6; this electron-emissive layer may consist of a material also responsive to incident X-rays, e.'g. bismuth, in which case the rate of electron emission is further increased.

The fluorescent mass 37 in the depressions of crenelated layer 36 may consist of one or more phosphors, with or without an activator, designed to emit high-actinic light when struck by X-rays; calcium tungstate with a lead activator may be mentioned by way of example. The indentations should, of course, be spaced closely enough along the surface of base 2 to provide a mosaic of light bundles with the desired degree of resolution.

The electron beam 40 is focused by several accelerating anodes 10,- connected to respective taps of a potentiometer 41, and by an electromagnetic coil 11 upon a target electrode 34 emitting secondary electrons after a certain delay whereby the generated electron image is stored for a predetermined period. Electrode 34 is preceded by a field-equalizing grid 12 and is followed by a further accelerating anode 16. The secondary electron beam 18 travels within a conductive shield constituted by a graphite coating 17 (known as Aguadag) on the inner surface of tube 35; this section of the tube is surrounded by a focusing coil 19 and by a deflecting yoke 21 connected to a sweep circuit not shown. A conventional beam-scanning assembly at the far end of tube 35 includes an electron-multiplier structure 23 with an entrance orifice in a shield plate 20 and an output lead 24, together with a source of biasing potential represented by a potentiometer 43. Though an image-dissector type of scanner is shown by way of example, other conventional scanning means (e.g., of the Vidicon or image-orthicon types) may be employed with the same receiving and intensifier assembly.

A generator 31 of alternating current is connected across the two layer electrodes 4, 7 in series with a switch 38 and in parallel with a D-C source of biasing voltage 33, the latter lying in series with another switch 32. The polarity of battery 33 is so chosen that electrode 7, and therefore also the adjoining phosphor layer 6, is more highly positive than electrode 4 and adjoining photoconductive layer 5 upon closure of circuit breaker 32. Battery 33 and switch 32 are bridged by a condenser 30.

The general mode of operation of the system herein disclosed, apart from the intervening storage of the electron image on target 34, is the same as in the device of my prior application Ser. No. 306,897 (now Pat. No. 3,436,550), to which reference may alsobe made for suitable operating voltages and for preferred compositions of electroluminiscent layer 6. The present system, however, sharpens the contrasts between lighter and darker areas of the incident X-ray image 1 by virtue of its array of closely spaced luminous pencils emitted by the crenelated layer 36 with intensities depending upon the impinging mosaic of ultraviolet radiation.

I claim:

.1. An image transducer responsive to X-rays, comprising:

an evacuated envelope having an entrance end transparent to incident X-rays;

a receiving unit in said envelope disposed adjacent said entrance end for irradiation by said X-rays, said unit having a radiation-permeable base with a crenelated light-reflecting surface remote from said entrance end forming a multiplicity of depressions of substantially paraboloidal shape, and a fluorescent mass excitable by said X-rays filling said depressions to produce concentrated bundles of light rays generally paralleling the exciting X-rays;

an image-intensifier structure in said envelope confronting said crenelated surface for receiving said light rays therefrom together with X-rays trans luminating said unit, said structure including an emissive layer for producing, in response to said X-rays and light rays, an electron beam conforming to the intensity pattern of the incident X-rays; and

output means in said envelope for converting said electron beam into a visible picture.

2. An image transducer as defined in claim 1 wherein said base is provided with a metallic deposit of lightrefiecting character lining said depressions.

3. An image transducer as defined in claim 1 wherein said output means comprises beam-scanning means and a target ahead of said beam-scanning means for storing energy of said electron beam and generating a pattern of secondary electrons directed toward said beam-scanning means.

4. An image transducer as defined in claim 3 wherein said structure comprises a photoconductive layer proximal to said unit, and an electroluminescent layer interposed between said emissive layer and said photoconductive layer for joint excitation by an electric field emanating from the latter and by penetrating X-rays from said entrance end.

5. An image transducer as defined in claim 4 wherein said structure further comprises a barrier layer opaque to said light rays but transparent to said X-rays between said photoconductive and electroluminescent layers.

6. An image transducer as defined in claim 4 wherein said structure further comprises a pair of conductive layers bracketing said photoconductive and electroluminescent layers, and a source of alternating voltage connected across said conductive layers.

References Cited UNITED STATES PATENTS 2,804,560 8/ 1957 Sheldon 250-213 3,345,534 10/1967 Charles 250-213 ARCHIE R. BORCHELT, Primary Examiner M. ABRAMSON, Assistant Examiner

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