US3388256A - Light amplifier including a layer for converting x-rays to visible radiation - Google Patents

Light amplifier including a layer for converting x-rays to visible radiation Download PDF

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US3388256A
US3388256A US385887A US38588764A US3388256A US 3388256 A US3388256 A US 3388256A US 385887 A US385887 A US 385887A US 38588764 A US38588764 A US 38588764A US 3388256 A US3388256 A US 3388256A
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layer
photoconductive
radioluminescent
rays
electrode
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US385887A
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Kohashi Tadao
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/12—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof structurally associated with, e.g. formed in or on a common substrate with, one or more electric light sources, e.g. electroluminescent light sources, and electrically or optically coupled thereto
    • H01L31/14—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof structurally associated with, e.g. formed in or on a common substrate with, one or more electric light sources, e.g. electroluminescent light sources, and electrically or optically coupled thereto the light source or sources being controlled by the semiconductor device sensitive to radiation, e.g. image converters, image amplifiers or image storage devices
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05G—X-RAY TECHNIQUE
    • H05G1/00—X-ray apparatus involving X-ray tubes; Circuits therefor
    • H05G1/08—Electrical details
    • H05G1/64—Circuit arrangements for X-ray apparatus incorporating image intensifiers

Definitions

  • the primary object of the present invention is to provide a light intensifier of the kind specified in which radiation energy is more efficiently utilized than ever, the sensitivity of the photoconductive element is never lowered by mechanical working, and impedance conditions are also improved.
  • radioluminescent layer in the device for converting the incident X-rays to visible radiation which then impinge upon a photoconductor-electroluminescent light amplifier.
  • FIG. 1 is a longitudinal sectional view of a light intensifier embodying the present invention, with the electrical supply circuit shown diagrammatically;
  • FIG. 2 is a perspective view of another embodiment of the invention, partly cut away to show the internal construction, with the electric supply circuit shown diagrammatically.
  • a photoconductive layer is low in transmittivity of optical rays. As a result, a photoconductive layer effectively absorbs the energy of optical rays irradiating the same. In other words, a photo conductive layer has a high utilization factor of optical ray energ and is effectively excited thereby. Thus a photoconductive layer has a high photoconductive sensitivity, in general.
  • a photoconductive layer shows a certain degree of photoconductivity with respect to radiations, such as a-rays, 'y-rays, etc.
  • radiations such as a-rays, 'y-rays, etc.
  • the high transmittivity of such radiation causes the same to pass through the photo conductive layer, with only a small portion being absorbed in the latter, resulting in low energy utilization factor.
  • the photoconduction sensitivity of the photoconductive layer is inherently lower when excited by such radiations than when excited by optical rays, and consequently, the photoconductivity with respect to such radiations is usually extremely low.
  • a light intensifier for radiation of the kind specified above in order to obtain a high white-to-black ratio (contrast ratio) of the output image produced in the electroluminescent layer, it is required that the electroluminescent layer has a low impedance, and the photoconductive layer has a high dark impedance.
  • Conventional light intensifiers for radiations are driven by alternating current energy, and consequently, the above-mentioned impedance conditions are satisfied by a large electric capacity of a thin electroluminescent layer, and a small electric capacity of a thick photoconductive layer, with mechanically formed groove openings of V-shapes and a decreased space factor of electrodes provided on the photoconductive layer.
  • the specific dielectric constant which determines the electric capacity of the photoconductive layer is usually higher than 10.
  • Conventional photoconductive layers with groove openings formed directly therein cannot have an electric capacity other than that limited by the specific dielectric constant inherent in the material and the geometrical shape of the photoconductive layer.
  • the present invention contemplates overcoming the above-mentioned difiiculties inevitable in conventional light intensifiers for radiations.
  • the present invention is characterized in that a phototransparent electrode is disposed on one side of the electroluminescent layer, and on the other side, by intermediation of an opaque layer, a current diffusion layer, and other necessary layers, a radioluminescent layer is disposed for emitting optical rays by excitation with the radiation, which layer is provided with groove-shaped or pore-shaped openings, and has a second electrode disposed on the top thereof, and in that a photoconductive layer is arranged in electrical contact with the abovementioned second electrode and secured to the opening side of the radioluminescent layer covering the same.
  • Voltage is applied across the photo-transparent electrode and the second electrode, and the photoconductive layer is excited by radiation directly, while the radiation passing through at least portions of the photoconductive layer and/or the electrodes causes the radioluminescent layer to emit optical rays, such emitted optical rays exciting the photoconductive layer for responding to the same.
  • the light intensifier shown comprises a photo-transparent supporter plate 1 of transparent glass plate, for example, and it may be of a leadcontaining glass capable of absorbing X-rays.
  • the light intensifier further comprises a photo-transparent electrode 2 formed by a metal oxide film, such as of tin oxide, sprayed onto the supporter plate 1, an electroluminescent layer 3 of ZnS:Cu, Al powder for example, mixed with a bonding agent, such as epoxy resin, having a thickness of 40a or so, ZnS:Cu, Al being luminant in response to green colors to change in electric field, and intermediate layers 41 and 42, layer 41 being an insulating or semiconductive opaque layer of black paint or the like, having a thickness of about 5 to 10 for example.
  • the layer 41 serves to isolate optically the electroluminescent layer 3 from a photoconductive layer 7, to be described later.
  • the layer 42 is a current diffusion layer for facilitating mechanical working of open portions 52 of a radioluminescent layer 50 to be described later and also for causing diffusion of the photo-current to prevent striping of output image L.
  • This layer is formed by powder of non-linear resistance material, such as CdszCl for example, mixed with bonding material, such as epoxy resin for example, and has a thickness of about to 300 for example.
  • the radioluminescent layer 59 is rendered luminant by excitation of radiation, and is provided with open portions 52 in the form of parallel V-shaped grooves.
  • the tops of the grooves are provided with electrodes 6 formed by metal vaporizing, adhesive silver paint, or the like.
  • the photoconductive layer 7 is secured to the radioluminesceut layer 50 at its side face 51 to cover the same and, at the same time, is in electrical contact with the electrodes 6.
  • the photoconductive layer 7 may be formed by vacuum vaporization, or by spraying a mixture of photoconductive powder and bending material, such as epoxy resin, diluted with a solvent, such as diacetone alcohol, to form a thin layer.
  • the photoconductive layer 7 is formed with a photoconductive material of the CdS series activated by Cu, Cl.
  • Photoconductive materials of the CdS series have photoconductivity even for X-rays, and have a high photoconductive sensitivity for optical ray excitation, its spectral distribution of photoconduction being in the range of 500 to 900 m
  • the radioluminescent layer 50 is required to emit optical rays by the X-ray (radiation) exciting, and also to excite the photoconductive layer 7 to respond by the emitted optical rays, thus varying the impedance. Consequently, the spectral energy distribution characteristics of the optical rays should be in overlapping relation at least partly with the spectral photoconductivity distribution characteristics.
  • the spectral energy distribution characteristics of optical rays of the layer 59 should at least partly be in 500 to 900 m
  • the spectral energy distribution characteristics should exist in the range or" the spectral photoconductivity distribution characteristics, and the maximum integral value should be obtained when the product of the respective response value (distributed value) for every wave length has been integrated against the desired wave lengths.
  • X-ray luminescent phosphor, (Cd, Zn)S solid solution of the CdS and ZnS activated with Ag satisfies the abovementioned condition.
  • the layer 7 is formed by spraying powdered CdSzCuCl, which is highly sensitive to orange light, mixed with a bonding agent, such as epoxy resin, etc., to form a suspension
  • the layer 50 may be formed by a powder of X-ray luminescent phosphor (Cd, Zn)S:Ag which is orange luminant, mixed with an adhesive agent, such as epoxy resin, polystyrol resin, etc.
  • the thickness of layer 59 is selected to be large enough to have an appropriately high impedance in comparison to that of the layer 3, to lower electroluminescent output in a dark state for improving whiteto-black ratio (Contrast ratio) of the output image L.
  • the layer 5t may be of about 300 to 400,11. thickness, and the conductive adhesive agent is applied over one face of layer 50 to a thickness of about to 40 Then, V-shaped grooves are cut therein at pitch spacings of about 600 to provide openings 52. With such a construction, the space factor of electrodes 6 is lower than 1, and therefore, the layer 50 shOWS further high impedance by virtue of openings 52.
  • the photoconductive layer 7 is formed thereon by spraying.
  • the electrodes 6 are all connected to a conductor 8 in parallel relation, while the transparent electrode 2 is connected to a conductor 10. Thus, the electrodes 6 and 2 are connected across an alternating current supply source 9.
  • the impedance (resistance) of the photoconductive layer 7 decreases by the X-ray excitation.
  • X-rays being of high transmittivity, pass through the layer 7, and through the opening sides 51 of the radioluminescent layer 59 and electrodes 6 to excite the layer 5% which in turn generates orange light L
  • the light L excites the photoconductive layer 7 covering the opening sides 51 to respond optically.
  • the layer 7 is of low transmittivity with respect to light, and in addition, the layer 59 shows a behavior as one kind of light integrant, the optical rays generated in the layer 50 are wholly absorbed by the layer 7 through the opening sides 51, except those which are absorbed in the layer 56 itself, and the optical excitation is accomplished effectively.
  • the photoconductive layer 7 is excited by X-rays directly, and also excited by the optical rays converted in the layer 50 from penetrating X-rays that would otherwise be lost, and operates with a higher sensitivity than ever.
  • the photocurrent flows from electrodes 6 along opening sides 51, and diffuses through the layer 42 to render the layer 3 luminant.
  • the X-ray image X has thus been converted and intensified to a visible image L on the layer 3.
  • the photoconductive layer and the radioluminescent layer are of different materials, and therefore, by appropriate construction of the radioluminescent layer, its dark impedance (impedance in a dark state) can be made high, in comparison to direct working on the photoconductive layer for provision of groove openings therein, even if their geometrical shapes are the same.
  • the photoconductive layer when the photoconductive layer is formed by a photoconductive powder of the CdS series mixed with an adhesive agent, its specific dielectric constant can be made low to a certain extent by use of an adhesive agent of low specific dielectric constant E, such as, for example, polystyrol of E:2.5.
  • an adhesive agent of low specific dielectric constant E such as, for example, polystyrol of E:2.5.
  • the mixture proportion by volume of photoconductive powder should be about but the specific dielectric constant of photoconductive particles is higher than 10, and consequently, the specific dielectric constant of the photo conductive layer is naturally higher than 10.
  • the radioluminescent layer 50 serves as an impedance. Radioluminescent particles are commingled in the layer 50, but in this case, the mixture proportion is never limited from the requirement of mutural contact of the particles as in the case of photoconductive layer. If the radioluminescent particles, such as CdZnStAg, have a specific dielectric constant of 10 or so, and an adhesive agent, such as polystyrol, of low specific dielectric constant of 2.5 or so, is used, there being no limit on the mixture proportion by volume, the specific dielectric constant can be made lower than 10, and as low as 2.5 or so, by decreasing the proportion by volume of fluorescent particles.
  • the dark impedance is considered from the side of electric capacity, but below is considered from the side of dark resistance.
  • Radioluminescent particles such as (Cd.Zn)S:Ag
  • photoconductive materials such as CdS:CuCl, have a dark resistance lower than the former. -It is, therefore, clear that the present invention is superior to the well-known art, with respect to the specific resistance also.
  • the open portions 52 are in the form of equal-spaced parallel grooves, but may be of other form, such as concentric circles or spirals, and they are not necessarily V-shaped, but may be circular are or rectangular in cross-Section.
  • the photoconductive layer 7 is secured to and covers the V-shaped opening sides 51, but X-rays or other radiations of high transmittivity can pass through the layer 7 even when it is substantially thick, and the photoconductive layer 7 is allowed to fill up the openings 52.
  • the photoconductive layer 7 covers the electrodes 6 in FIG. 1, it is not required, but the only requirement is that the layer 7 is in electrical connection with electrodes 6. Consequently, electrodes 6 may be exposed beyond the layer 7.
  • FIG. 2 shows another embodiment of the invention, in which the open portions are of pore shape.
  • the same reference numerals are used for indicating parts corresponding to those in FIG. I.
  • the open portions are regularly distributed conical pores, with their tip portions extending into the current diffusing layer 42.
  • the photoconductive layer 7 lills up the conical-pore openings, and covers the opening sides 51, and further covers and is secured to the electrode 6 of net form.
  • the photoconductive layer 7 may not fill up the open portions, but merely cover the opening sides 51, in electrical contact with the electrode 6.
  • the shape of the pores need not be conical, but may be cylindrical, square-columnar, semi-spherical, or the like.
  • the groove or conical openings extend into the current diffusing layer 42, and this is desirable for effectively utilizing the impedance change in the photoconductive layer 7, and also for preventing striping or spotting of the output image by effective diffusion of the photocurrent, but this is not limitative.
  • the groove openings may extend to mid portions of the radioluminescent layer 50, or to its face in contact with the layer 42.
  • the current diffusing layer 42 may be omitted, if required.
  • the electrodes 6 are X-ray transmittive (radiation transmittive), and the opening sides 51 form inclined surfaces, and therefore, the radioluminescent layer 50 is excited to become luminant by both of the X-rays (radiations) that pass through the portions of electrodes 6 and photoconductive layer 7, obtaining the desirable results, but the present invention is never limited to such a case only.
  • the objects of the present invention can be accomplished principally by the radioluminescent layer 50 being excited to emit optical rays by radiation that passes through either the portion of electrodes 6 or the portion of the photoconductive layer 7.
  • the essential condition of the present invention is to have the radioluminescent layer excited to emit optical rays by the radiation that has passed through at least either portion of the photoconductive layer 7 or electrodes 6. It is natural that substances of the electrodes and photoconductive layer as well as shape of the open portions should be selected to satisfy the above condition.
  • the photoconductive layer may be a sintered layer, when glass enamel or other adhesive agents durable to high temperature are employed in the radioluminescent layer.
  • the electroluminescent layer is rendered lnminant by a direct current, such as a vaporized electroluminescent layer, it may be connected to a DC. supply source for effecting direct current operation.
  • the radioluminescent layer may be formed without employing an adhesive agent, but by sintering, etc.
  • a light intensifier for radiations comprising an electroluminescent layer, a photo-transparent first electrode disposed on one side of said electroluminescent layer, a radioluminescent layer mounted on the other side of said electroluminescent layer, a plurality of recessions in said radioluminescent layer on the far side thereof from said electroluminescent layer, at least one second electrode disposed on the top portion of the recessed radioluminescent layer, a photoconductive layer covering the recessed surface of said radioluminescent layer as well as its recessed portions, said photoconductive layer being electrically connected with said second electrode, and an electric voltage source applied across said phototransparent first electrode and said second electrode.

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Description

June 11. 1968 TADAO KOHASHI 3,388,256
LIGHT AMPLIFIER INCLUDING A LAYER FOR CONVERTING XRAYS TO VISIBLE RADIATION Filed. July 29, 1964 INVENTOR 13.4.3.0 KOA 8.511.;
MMM MW ATTORNEY United States Patent 3,388,256 LIGHT AMPLIFIER INCLUDING A LAYER FOR CONVERTING X-RAYS T0 VISIBLE RADIATION Tadao Kohashi, Yokohama, Japan, assiguor to Matsushita Electric Industrial Co., Ltd, Osaka, Japan, a corporation of Japan Filed July 29, 1964, Ser. No. 385,887 Claims priority, application Japan, Aug. 2, 1963, ass/41,543 3 Claims. (Cl. 250213) This invention relates to light intensifiers for radiations, and particularly for those having high transmittivity, such as X-rays, 'y-rays, etc.
The primary object of the present invention is to provide a light intensifier of the kind specified in which radiation energy is more efficiently utilized than ever, the sensitivity of the photoconductive element is never lowered by mechanical working, and impedance conditions are also improved.
The above objects are accomplished by the inclusion of a radioluminescent layer in the device for converting the incident X-rays to visible radiation which then impinge upon a photoconductor-electroluminescent light amplifier.
There are other objects and particularities of the present invention, which will be made obvious in the following descriptions, with reference to the accompanying drawings, in which:
FIG. 1 is a longitudinal sectional view of a light intensifier embodying the present invention, with the electrical supply circuit shown diagrammatically; and
FIG. 2 is a perspective view of another embodiment of the invention, partly cut away to show the internal construction, with the electric supply circuit shown diagrammatically.
In general, a photoconductive layer is low in transmittivity of optical rays. As a result, a photoconductive layer effectively absorbs the energy of optical rays irradiating the same. In other words, a photo conductive layer has a high utilization factor of optical ray energ and is effectively excited thereby. Thus a photoconductive layer has a high photoconductive sensitivity, in general.
On the other hand, a photoconductive layer shows a certain degree of photoconductivity with respect to radiations, such as a-rays, 'y-rays, etc. However, the high transmittivity of such radiation causes the same to pass through the photo conductive layer, with only a small portion being absorbed in the latter, resulting in low energy utilization factor.
In addition, the photoconduction sensitivity of the photoconductive layer is inherently lower when excited by such radiations than when excited by optical rays, and consequently, the photoconductivity with respect to such radiations is usually extremely low.
In a light intensifier for radiation of the kind specified above, in order to obtain a high white-to-black ratio (contrast ratio) of the output image produced in the electroluminescent layer, it is required that the electroluminescent layer has a low impedance, and the photoconductive layer has a high dark impedance. Conventional light intensifiers for radiations are driven by alternating current energy, and consequently, the above-mentioned impedance conditions are satisfied by a large electric capacity of a thin electroluminescent layer, and a small electric capacity of a thick photoconductive layer, with mechanically formed groove openings of V-shapes and a decreased space factor of electrodes provided on the photoconductive layer.
in general, however, the mechanical working for providing the groove openings in a photoconductive layer is apt to break the photoconductive material forming the 3,388,256 Patented June 11, 1968 layer, and such a breakage in the surface of the photoconductive layer at the side of groove openings extremely lowers the photoconduction sensitivity. Any mechanical working is thus undesirable for the purpose of highly sensitive operation.
Particularly with regard to the above-mentioned impedance conditions, the specific dielectric constant which determines the electric capacity of the photoconductive layer is usually higher than 10. Conventional photoconductive layers with groove openings formed directly therein cannot have an electric capacity other than that limited by the specific dielectric constant inherent in the material and the geometrical shape of the photoconductive layer.
The present invention contemplates overcoming the above-mentioned difiiculties inevitable in conventional light intensifiers for radiations.
The present invention is characterized in that a phototransparent electrode is disposed on one side of the electroluminescent layer, and on the other side, by intermediation of an opaque layer, a current diffusion layer, and other necessary layers, a radioluminescent layer is disposed for emitting optical rays by excitation with the radiation, which layer is provided with groove-shaped or pore-shaped openings, and has a second electrode disposed on the top thereof, and in that a photoconductive layer is arranged in electrical contact with the abovementioned second electrode and secured to the opening side of the radioluminescent layer covering the same. Voltage is applied across the photo-transparent electrode and the second electrode, and the photoconductive layer is excited by radiation directly, while the radiation passing through at least portions of the photoconductive layer and/or the electrodes causes the radioluminescent layer to emit optical rays, such emitted optical rays exciting the photoconductive layer for responding to the same.
Taking X-ray as an example of radiations, the invention will now be described.
Referring to FIG. 1, the light intensifier shown comprises a photo-transparent supporter plate 1 of transparent glass plate, for example, and it may be of a leadcontaining glass capable of absorbing X-rays. The light intensifier further comprises a photo-transparent electrode 2 formed by a metal oxide film, such as of tin oxide, sprayed onto the supporter plate 1, an electroluminescent layer 3 of ZnS:Cu, Al powder for example, mixed with a bonding agent, such as epoxy resin, having a thickness of 40a or so, ZnS:Cu, Al being luminant in response to green colors to change in electric field, and intermediate layers 41 and 42, layer 41 being an insulating or semiconductive opaque layer of black paint or the like, having a thickness of about 5 to 10 for example. The layer 41 serves to isolate optically the electroluminescent layer 3 from a photoconductive layer 7, to be described later. The layer 42 is a current diffusion layer for facilitating mechanical working of open portions 52 of a radioluminescent layer 50 to be described later and also for causing diffusion of the photo-current to prevent striping of output image L. This layer is formed by powder of non-linear resistance material, such as CdszCl for example, mixed with bonding material, such as epoxy resin for example, and has a thickness of about to 300 for example.
The radioluminescent layer 59 is rendered luminant by excitation of radiation, and is provided with open portions 52 in the form of parallel V-shaped grooves. The tops of the grooves are provided with electrodes 6 formed by metal vaporizing, adhesive silver paint, or the like. The photoconductive layer 7 is secured to the radioluminesceut layer 50 at its side face 51 to cover the same and, at the same time, is in electrical contact with the electrodes 6.
In the embodiment shown, the photoconductive layer 7 may be formed by vacuum vaporization, or by spraying a mixture of photoconductive powder and bending material, such as epoxy resin, diluted with a solvent, such as diacetone alcohol, to form a thin layer.
It is now assumed that the photoconductive layer 7 is formed with a photoconductive material of the CdS series activated by Cu, Cl. Photoconductive materials of the CdS series have photoconductivity even for X-rays, and have a high photoconductive sensitivity for optical ray excitation, its spectral distribution of photoconduction being in the range of 500 to 900 m The radioluminescent layer 50 is required to emit optical rays by the X-ray (radiation) exciting, and also to excite the photoconductive layer 7 to respond by the emitted optical rays, thus varying the impedance. Consequently, the spectral energy distribution characteristics of the optical rays should be in overlapping relation at least partly with the spectral photoconductivity distribution characteristics. Thus, if the spectral photoconductivity distribution characteristics are in the above-mentioned range of 500 to 900 m the spectral energy distribution characteristics of optical rays of the layer 59 should at least partly be in 500 to 900 m For the most desirable case, the spectral energy distribution characteristics should exist in the range or" the spectral photoconductivity distribution characteristics, and the maximum integral value should be obtained when the product of the respective response value (distributed value) for every wave length has been integrated against the desired wave lengths.
For photoconductive materials of the CdSzCuCl series, X-ray luminescent phosphor, (Cd, Zn)S (solid solution of the CdS and ZnS) activated with Ag satisfies the abovementioned condition. For example, when the layer 7 is formed by spraying powdered CdSzCuCl, which is highly sensitive to orange light, mixed with a bonding agent, such as epoxy resin, etc., to form a suspension, the layer 50 may be formed by a powder of X-ray luminescent phosphor (Cd, Zn)S:Ag which is orange luminant, mixed with an adhesive agent, such as epoxy resin, polystyrol resin, etc. The thickness of layer 59 is selected to be large enough to have an appropriately high impedance in comparison to that of the layer 3, to lower electroluminescent output in a dark state for improving whiteto-black ratio (Contrast ratio) of the output image L.
For example, the layer 5t) may be of about 300 to 400,11. thickness, and the conductive adhesive agent is applied over one face of layer 50 to a thickness of about to 40 Then, V-shaped grooves are cut therein at pitch spacings of about 600 to provide openings 52. With such a construction, the space factor of electrodes 6 is lower than 1, and therefore, the layer 50 shOWS further high impedance by virtue of openings 52. After the radioluminescent layer 50 and electrodes 6 have thus been formed, the photoconductive layer 7 is formed thereon by spraying. The electrodes 6 are all connected to a conductor 8 in parallel relation, while the transparent electrode 2 is connected to a conductor 10. Thus, the electrodes 6 and 2 are connected across an alternating current supply source 9.
When an X-ray image X is projected onto the intensifier as shown by arrows, the impedance (resistance) of the photoconductive layer 7 decreases by the X-ray excitation. X-rays, being of high transmittivity, pass through the layer 7, and through the opening sides 51 of the radioluminescent layer 59 and electrodes 6 to excite the layer 5% which in turn generates orange light L The light L excites the photoconductive layer 7 covering the opening sides 51 to respond optically. Since the layer 7 is of low transmittivity with respect to light, and in addition, the layer 59 shows a behavior as one kind of light integrant, the optical rays generated in the layer 50 are wholly absorbed by the layer 7 through the opening sides 51, except those which are absorbed in the layer 56 itself, and the optical excitation is accomplished effectively.
Consequently, the photoconductive layer 7 is excited by X-rays directly, and also excited by the optical rays converted in the layer 50 from penetrating X-rays that would otherwise be lost, and operates with a higher sensitivity than ever. The photocurrent flows from electrodes 6 along opening sides 51, and diffuses through the layer 42 to render the layer 3 luminant. The X-ray image X has thus been converted and intensified to a visible image L on the layer 3.
According to the invention, mechanical Working for providing openings is done only in the radioluminescent layer, but not in the photoconductive layer which can be formed by vaporizing or spraying, and consequently, the photoconductive sensitivity is never damaged. In addition, the photoconductive layer and the radioluminescent layer are of different materials, and therefore, by appropriate construction of the radioluminescent layer, its dark impedance (impedance in a dark state) can be made high, in comparison to direct working on the photoconductive layer for provision of groove openings therein, even if their geometrical shapes are the same.
For example, when the photoconductive layer is formed by a photoconductive powder of the CdS series mixed with an adhesive agent, its specific dielectric constant can be made low to a certain extent by use of an adhesive agent of low specific dielectric constant E, such as, for example, polystyrol of E:2.5. However, unless photoconductive particles have good mutual contact, high photoconductive sensitivity cannot be obtained. Usually, the mixture proportion by volume of photoconductive powder should be about but the specific dielectric constant of photoconductive particles is higher than 10, and consequently, the specific dielectric constant of the photo conductive layer is naturally higher than 10.
According to the present invention, however, the radioluminescent layer 50 serves as an impedance. Radioluminescent particles are commingled in the layer 50, but in this case, the mixture proportion is never limited from the requirement of mutural contact of the particles as in the case of photoconductive layer. If the radioluminescent particles, such as CdZnStAg, have a specific dielectric constant of 10 or so, and an adhesive agent, such as polystyrol, of low specific dielectric constant of 2.5 or so, is used, there being no limit on the mixture proportion by volume, the specific dielectric constant can be made lower than 10, and as low as 2.5 or so, by decreasing the proportion by volume of fluorescent particles.
In the foregoing description, the dark impedance is considered from the side of electric capacity, but below is considered from the side of dark resistance.
Radioluminescent particles, such as (Cd.Zn)S:Ag, are of an insulating nature, and have an extremely high specific resistance. On the other hand, photoconductive materials, such as CdS:CuCl, have a dark resistance lower than the former. -It is, therefore, clear that the present invention is superior to the well-known art, with respect to the specific resistance also.
'In the embodiment shown in FIG. 1, the open portions 52 are in the form of equal-spaced parallel grooves, but may be of other form, such as concentric circles or spirals, and they are not necessarily V-shaped, but may be circular are or rectangular in cross-Section.
Further in FIG. 1, the photoconductive layer 7 is secured to and covers the V-shaped opening sides 51, but X-rays or other radiations of high transmittivity can pass through the layer 7 even when it is substantially thick, and the photoconductive layer 7 is allowed to fill up the openings 52. Although the photoconductive layer 7 covers the electrodes 6 in FIG. 1, it is not required, but the only requirement is that the layer 7 is in electrical connection with electrodes 6. Consequently, electrodes 6 may be exposed beyond the layer 7.
'FIG. 2 shows another embodiment of the invention, in which the open portions are of pore shape. In this figure, the same reference numerals are used for indicating parts corresponding to those in FIG. I.
Referring to FIG. 2, the open portions are regularly distributed conical pores, with their tip portions extending into the current diffusing layer 42. The photoconductive layer 7 lills up the conical-pore openings, and covers the opening sides 51, and further covers and is secured to the electrode 6 of net form.
Needless to sa the photoconductive layer 7 may not fill up the open portions, but merely cover the opening sides 51, in electrical contact with the electrode 6. The shape of the pores need not be conical, but may be cylindrical, square-columnar, semi-spherical, or the like.
In either of the above-described two embodiments, the groove or conical openings extend into the current diffusing layer 42, and this is desirable for effectively utilizing the impedance change in the photoconductive layer 7, and also for preventing striping or spotting of the output image by effective diffusion of the photocurrent, but this is not limitative. For example, the groove openings may extend to mid portions of the radioluminescent layer 50, or to its face in contact with the layer 42. Further, the current diffusing layer 42 may be omitted, if required.
Further in the embodiments shown, the electrodes 6 are X-ray transmittive (radiation transmittive), and the opening sides 51 form inclined surfaces, and therefore, the radioluminescent layer 50 is excited to become luminant by both of the X-rays (radiations) that pass through the portions of electrodes 6 and photoconductive layer 7, obtaining the desirable results, but the present invention is never limited to such a case only. Thus, the objects of the present invention can be accomplished principally by the radioluminescent layer 50 being excited to emit optical rays by radiation that passes through either the portion of electrodes 6 or the portion of the photoconductive layer 7.
From the foregoing, it is seen that the essential condition of the present invention is to have the radioluminescent layer excited to emit optical rays by the radiation that has passed through at least either portion of the photoconductive layer 7 or electrodes 6. It is natural that substances of the electrodes and photoconductive layer as well as shape of the open portions should be selected to satisfy the above condition.
The photoconductive layer may be a sintered layer, when glass enamel or other adhesive agents durable to high temperature are employed in the radioluminescent layer. Further, in case that the electroluminescent layer is rendered lnminant by a direct current, such as a vaporized electroluminescent layer, it may be connected to a DC. supply source for effecting direct current operation.
For use for -rays and other radiations than X-rays, appropriate materials should be employed, needless to say. The radioluminescent layer may be formed without employing an adhesive agent, but by sintering, etc.
What is claimed is:
.1. A light intensifier for radiations comprising an electroluminescent layer, a photo-transparent first electrode disposed on one side of said electroluminescent layer, a radioluminescent layer mounted on the other side of said electroluminescent layer, a plurality of recessions in said radioluminescent layer on the far side thereof from said electroluminescent layer, at least one second electrode disposed on the top portion of the recessed radioluminescent layer, a photoconductive layer covering the recessed surface of said radioluminescent layer as well as its recessed portions, said photoconductive layer being electrically connected with said second electrode, and an electric voltage source applied across said phototransparent first electrode and said second electrode.
2. The light intensifier according to claim 1, in which said recessions of radioluminescent layer are of groove shape.
3. The light intensifier according to claim 1, in which said recessions of radioluminescent layer are of pore shape.
References Cited UNITED STATES PATENTS 2,835,822 5/1958 William 250-213 2,975,294 3/1961 Kazan et al. 250213 2,999,941 9/1961 Klasens et al 250-213 3,064,133 11/1962 Murr et al. 250-2l3 3,210,551 9/ l965 Vaughn et al. 250-213 RALPH G. NILSON, Primary Examiner.
M. A. ABRAMSON, Assistant Examiner.

Claims (1)

1. A LIGHT INTENSIFIER FOR RADIATIONS COMPRISING AN ELECTROLUMINESCENT LAYER, A PHOTO-TRANSPARENT FIRST ELECTRODE DISPOSED ON ONE SIDE OF SAID ELECTROLUMINESCENT LAYER, A RADIOLUMINESCENT LAYER MOUNTED ON THE OTHER SIDE OF SAID ELECTROLUMINESCENT LAYER, A PLURALITY OF RECESSIONS IN SAID RADIOLUMINESCENT LAYER ON THE FAR SIDE THEREOF FROM SAID ELECTROLUMINESCENT LAYER, AT LEAST ONE SECOND ELECTRODE DISPOSED ON THE TOP PORTION OF THE RECESSED RADIOLUMINESCENT LAYER, A PHOTOCONDUCTIVE LAYER COVERING THE RECESSED SURFACE OF SAID RADIOLUMINESCENT LAYER AS WELL AS ITS RECESSED PORTIONS, SAID PHOTOCONDUCTIVE LAYER BEING ELECTRICALLY CONNECTED WITH SAID SECOND ELECTRODE, AND AN ELECTRIC VOLTAGE SOURCE APPLIED ACROSS SAID PHOTOTRANSPARENT FIRST ELECTRODE AND SAID SECOND ELECTRODE.
US385887A 1963-08-02 1964-07-29 Light amplifier including a layer for converting x-rays to visible radiation Expired - Lifetime US3388256A (en)

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US3475411A (en) * 1966-12-27 1969-10-28 Varian Associates Mosaic x-ray pick-up screen for x-ray image intensifier tubes
US3590253A (en) * 1969-06-30 1971-06-29 Westinghouse Electric Corp Solid-state photoconductor-electroluminescent image intensifier

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4490615A (en) * 1981-10-30 1984-12-25 Radiographic Screen Oy X-ray intensifying screen

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US2835822A (en) * 1955-09-12 1958-05-20 Gen Electric X-ray fluoroscopic screen
US2975294A (en) * 1957-10-31 1961-03-14 Rca Corp Electroluminescent apparatus
US2999941A (en) * 1955-10-14 1961-09-12 Philips Corp Solid-state image intensifier
US3064133A (en) * 1959-12-01 1962-11-13 Rca Corp Layer type storage light amplifier
US3210551A (en) * 1952-04-18 1965-10-05 Westinghouse Electric Corp Electroluminescent image amplifier

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US3210551A (en) * 1952-04-18 1965-10-05 Westinghouse Electric Corp Electroluminescent image amplifier
US2835822A (en) * 1955-09-12 1958-05-20 Gen Electric X-ray fluoroscopic screen
US2999941A (en) * 1955-10-14 1961-09-12 Philips Corp Solid-state image intensifier
US2975294A (en) * 1957-10-31 1961-03-14 Rca Corp Electroluminescent apparatus
US3064133A (en) * 1959-12-01 1962-11-13 Rca Corp Layer type storage light amplifier

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3475411A (en) * 1966-12-27 1969-10-28 Varian Associates Mosaic x-ray pick-up screen for x-ray image intensifier tubes
US3590253A (en) * 1969-06-30 1971-06-29 Westinghouse Electric Corp Solid-state photoconductor-electroluminescent image intensifier

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DE1489118A1 (en) 1969-05-14
GB1080641A (en) 1967-08-23
NL6408728A (en) 1965-02-03

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