Patent Number: 045490830
Section: claims

1. An X-ray imaging device for directly displaying X-ray images on a screen, comprising: a layer of phosphor crystals arranged on said screen;  at least one cathode for emitting electrons which impinge on said phosphor screen, said crystals being excited by said electrons so as to display said X-ray image by a steady cathodoluminescence;  wherein said phosphor crystal excitation is controlled by the persistent polarization and depolarization thereof, said crystals emitting said steady cathodoluminescence only when depolarized and said crystals comprising a material which is depolarized when X-rays irradiate said persistently polarized crystals. 2. An X-ray image device according to claim 1, wherein said phosphor screen is continuously and uniformly irradiated by electrons which are emitted from said at least one cathode and which have been accelerated by a potential in a predetermined voltage range subsequent to the momentary application of a negative electric field which has been applied across said phosphor screen; wherein, when X-rays momentarily irradiate said phosphor screen, the areas of said phosphor screen which have been irradiated by said X-rays continuously emit cathodoluminescence until said negative electric field is again momentarily applied across said phosphor screen. 3. An X-ray imaging device according to claim 2, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal. 4. An X-ray imaging device according to claim 1, wherein said cathodoluminescence intensity and X-ray image contrast on said phosphor screen are improved by application of a predetermined potential to one of either collecting electrodes, electrodes which are placed in front of said at least one cathode, or electrodes placed in front of said phosphor screen. 5. An X-ray imaging device according to claim 4, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal. 6. An X-ray imaging device according to claim 1, wherein said phosphor screen is placed on a face plate and comprises a powder of phosphor crystals which emit brilliant cathodoluminescence when incident electrons have penetrated thereinto, and which are persistently polarized when an external electric field has been applied thereto and which are depolarized when subsequently irradiated by X-rays. 7. An X-ray imaging device according to claim 6, wherein said face plate of said device comprises a glass plate which has a low X-ray absorption coefficient. 8. An X-ray imaging device according to claim 6, wherein said phosphor crystals comprise an oxide, oxysulfide, oxyhalide, aluminate, silicate, or halide of at least one element selected from gadolinium, lanthanum, yttrium and lutetium, which has been activated with at least one element selected from terbium, praseodymium, cerium, europium, dysprosium, and samarium. 9. An X-ray imaging device according to claim 6, wherein said phosphor crystals comprise zinc sulfide or zinc-cadmium sulfides containing one of either copper or silver as an activator and one of either a group III-a or a VII-a element as a coactivator. 10. An X-ray imaging device according to claim 6, wherein said phosphor crystals comprise zinc silicate which has been activated with one of either manganese or calcium tungstate. 11. An X-ray imaging device according to claim 6, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal. 12. An X-ray imaging device according to claim 1, wherein said phosphor screen is placed on a face plate and comprises a thin film of phosphor crystals which emit brilliant cathodoluminescence when incident electrons have penetrated thereinto, and which are persistently polarized when an external electric field has been applied thereto and which are depolarized when subsequently irradiated by X-rays. 13. An X-ray imaging device according to claim 12, wherein said phosphor crystals comprise an oxide, oxysulfide, oxyhalide, aluminate, silicate, or halide of at least one element selected from gadolinium, lanthanum, yttrium and lutetium, which has been activated with at least one element selected from terbium, praseodymium, cerium, europium, dysprosium, and samarium. 14. An X-ray imaging device according to claim 12, wherein said phosphor crystals comprise zinc sulfide or zinc-cadmium sulfides containing one of either copper or silver as an activator and one of either a group III-a or a VII-a element as a coactivator. 15. An X-ray imaging device according to claim 12, wherein said phosphor crystals comprise zinc silicate which has been activated with one of either manganese or calcium tungstate. 16. An X-ray imaging device according to claim 12, wherein said face plate of said device comprises a glass plate which has a low X-ray absorption coefficient. 17. An X-ray imaging device according to claim 1, wherein said phosphor crystals comprise an oxide, oxysulfide, oxyhalide, aluminate, silicate, or halide of at least one element selected from gadolinium, lanthanum, yttrium and lutetium, which has been activated with at least one element selected from terbium, praseodymium, cerium, europium, dysprosium, and samarium. 18. An X-ray imaging device according to claim 1, wherein said phosphor crystals comprise zinc sulfide or zinc-cadmium sulfides containing one of either copper or silver as an activator and one of either a group III-a or a VII-a element as a coactivator. 19. An X-ray imaging device according to claim 1, wherein said phosphor crystals comprise zinc silicate which has been activated with one of either manganese or calcium tungstate. 20. An X-ray imaging device according to claim 1, further comprising a means for deriving a time varying signal corresponding to said displayed X-ray images, said means for deriving including a means for generating and controlling a read electron beam which is scanned over said phosphor screen and including a current detecting means for generating a signal corresponding to current flowing in collecting electrodes which are disposed in said device, wherein said signal generated by said current detecting means comprises said time varying signal.