US 4,503,551 AGranted

Semiconductor-gated ionographic method and apparatus

AssigneeSRI International

InventorsIvor Brodie, Malcolm Thackray

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Abstract

Radiographic imaging method and apparatus are disclosed which include a gas gap formed between closely spaced dielectric and photoconductor surfaces, across which gap a uniform strength electric field is applied. Counting gas is supplied to the gas gap, and penetrating radiation, such as X-ray radiation, is directed onto the photoconductor through an object to be examined. Photons absorbed in the photoconductor induce electron-hole pairs resulting in increased localized conductivity thereof and localized intensification of the electric field across the gas gap to a level for production of gas discharge across the gap. Ion amplification by Townsend cascade enhances charge transfer in the gas gap. An apertured platen may be provided against which dielectric imaging paper is held by gas pressure to facilitate formation of the narrow, substantially uniform width, gas gap. A charge image is produced on the dielectric imaging surface which then is developed using conventional xerographic developing techniques.

Claims4

Dependent claims

In a radiographic imaging method employing radiation such as x-rays, or the like, for producing an electrostatic charge image of radiation penetrating an object, the combination comprising,

establishing an electric field across a narrow gas gap formed between substantially plane surfaces of spaced photoconductor and flexible dielectric members,
holding said flexible dielectric member flat against one face of a platen formed within apertures which extend therethrough to the opposite face by supplying an ionizing gas to the gas gap at a subatmospheric pressure while maintaining gas pressure at the opposite face of the platen at a pressure less than the subatmospheric gas gap pressure to urge the flexible dielectric member into surface contact with the platen and,
gating localized gas ionization in the gas gap by absorption of penetrating radiation in the photoconductor member for the formation of electron-hole pairs and increased localized electric field strength across the gas gap to a level for localized gas ionization within the gas gap, charged particles of one polarity produced by said gated gas ionization being accelerated by said electric field onto said dielectric member for production of a latent electrostatic charge image thereon, the production of the latent electrostatic image on said dielectric member including gas ion amplification by Townsend dicharge in the gas gap.

Dependencies are inferred from the claim text.