CS240265B1 - from a cystic imaging - Google Patents

Abstract

The solution relates to a method of electrostatic imaging in the field of X-ray, ionizing and radioactive radiation, which makes it possible to obtain an electroradiogram even on those materials in which free charge carriers are not generated upon exposure to said radiation. The subject of the invention is a method of electrostatic imaging in the field of X-ray, ionizing and radioactive radiation, characterized in that a layer of material in which deep local trapping centers are formed after irradiation with actinic radiation, preferably X-ray radiation, is imagewise exposed to said actinic radiation, then the layer of material is homogeneously charged by a corona discharge and then homogeneously illuminated to remove the charge not present in said deep local trapping centers. The method according to the invention makes it possible to obtain an electroradiogram even on those materials in which free charge carriers are not generated upon exposure to said radiation.

Description

The subject of the invention is a method of electrostatic imaging in the field of X-ray, ionizing and radioactive radiation, characterized in that a material layer in which deep local capture centers are formed after irradiation with actinic radiation, preferably X-rays, is exposed to said actinic radiation. the layer of material is homogeneously charged with a corona discharge and then is homogeneously illuminated to discharge a charge not found in said deep local capture centers.

The method according to the invention makes it possible to obtain an electroradiogram even on those materials which do not generate free charge carriers upon exposure to the radiation.

The present invention relates to a method of electrostatic imaging in the field of X-rays, ionizing radiation and radioactive radiation, which makes it possible to obtain electradadiate on those materials which do not generate free charge carriers when exposed to said radiation.

Halogen-silver light-sensitive materials are nowadays used in many fields such as light detectors, dosimeters, photographic, reprography, X-ray, materials for detection of ionizing and radioactive radiation, etc. The static latent image generated after irradiation of the halogen-silver layer must be induced by chemical means wet (processed in liquid developers, fixers, washing baths, etc.).

This process, though not complicated, is quite lengthy. It is unnecessarily laborious if the records are intended for temporary storage. Its main disadvantage is the irreversibility and impossibility to further interfere with the recording of information.

In terms of static applications, recording media are increasingly used in which, due to radiation (we mean all types of radiation), there is a color change, an optical density change or a chemical reaction (S. Nešpůrek and M. Šorm, AO no. 1168 397, S. Nešpůrek, K. Ulbert and M. Šorm, AO No. 172689). Ideally, for a reversible process, a change in color or optical density occurs directly through a mechanism of physical character without minor chemical changes (G. H. Brown, Photochromism, J. Wiley and Sons, New York 1971).

These materials, photochromic, photorope etc. have recently become a serious competitor of halogen-silver recording media in terms of both sensitivity and resolution, and especially price. Replacement of silver in reprographic processes is becoming a topical problem of the present time. Electrophotographs (RM Schaffert, Electrophotography, Focal Press, New York 1975), also working in the field of visible radiation with sensitive media based on both inorganic substances such as selenium, zinc oxide and organic substances such as vinylcarbazole) with trinitrofluorenone.

In electroradiography (M. D. Phillips, Xeroradiography, Method and Device), where the pattern is displayed by shortwave or corpuscular radiation, sensitive media such as selenium, chalcogenic glasses, etc. are used.

The electrophotographic or electroradiographic imaging method can be briefly characterized as follows: sensitive layer prepared from the photo (the conductive substance is charged with positive or negative (depending on the nature of charge carriers in the dark and irradiation) corona discharge. charge and gas blocking contact.

Irradiation will result in a charge-free charge in the photo (radlo) conductor volume and thus a change in the electrical conductivity of the layer, as well as a change in the gas blocking contact to the ohmic contact, resulting in a strong charge injection from surface to volume.

The injected charge moves in the electric field of the surface charge through the volume of the layer to the grounded pad. In this way, the irradiated portions of the sensitive layer become electrically neutral, the non-irradiated portions remaining charged. A latent electrographic image is produced which can be induced by conventional electrostatic developing techniques using powder or liquid developers.

The basic condition of this procedure is the use of a sensitive layer prepared from a material in which free charge carriers are formed sufficiently after irradiation. This condition, together with the requirements imposed on other layer properties, such as stability, film-forming, adhesion to the substrate, etc., limits the choice of materials.

The situation is particularly critical in electroradiography, since there is only a limited amount of materials in which exposure to short-wave and corpuscular radiation generates a sufficient concentration of free charge carriers.

Therefore, new ways of obtaining radiograms are being sought. One of them is ionography (E. Criscuolo and D. OorConnor, U.S. Pat

9005-6, E.P. Muntz, A.P. Proudian, P.B. Scott, U.S. Patent No. 3,774,029, J.R. Baker, W. Busche, S.E. Indell, U.S. Pat.

No. 920,991, J. Müller, A. Rheude, M. Schmidt, U.S. Patent No. 4,074,433). It is based on the replacement of the electroradiographic sensitive medium with a layer of ionizable gas or liquid.

The charge from different parts of the dielectric surface is dissipated, due to the different ionization and hence the electrical conductivity of the gas or liquid caused by radiation, at a different speed, thereby producing a latent electrostatic image. Multiple ionization of gases can be utilized by accelerating the potential for enhancement (p. Matsumoto US Patent No. 4121101).

Ionography represents a challenging technical problem but is not insoluble, as documented in a number of patents (J. Pfeifer, A. Rheude, J. Muller, U.S. Pat. No. 4,061,915, JR Escke, SB Papadopaulos, U.S. Pat. No. 3,873,832), particularly in connection with classical electroradiography (I. Chudáček, K. Ulbert, D. Slavinská, O. Grogoň, J. Formánek, AO No. 224 750).

Electroradiographic methods employing fluorescent shortwave and corpuscular radiation transducers, such as ZnS / Cu layers, phosphorus-containing compounds, are interesting technical solutions (J.M. Houston, R.J. Young, N.R. Whetten, U.S. Pat.

940 620), for ultraviolet or visible radiation, respectively.

A number of other processes can be found in the patent literature that can be used to generate radiograms. In particular, the photocathode process (H. H. Yang, U.S. Patent No. 4,039,830), the exoelectron record (T. Ishii, U.S. Patent No. 4,163,898), the use of electroluminescence and thermoluminescence (M. Ikedo, Y. Yasuno, T. Tamashita, U.S. Patent No. 3,975,637), a thermoplastic record (M. Takenouchi, U.S. Patent No. ·

131,795) and others.

TaitO solutions, like ionograllies, are also usually technically very crushing, a number of parameters (eg distance, gas pressure, layer thickness) are critical, making it impossible to massively spread these techniques and thus to actually replace halogen-silver materials in radiography.

The object of the invention is a method of electrostatic imaging, characterized in that a layer of material in which, after irradiation with actinic radiation, preferably X-rays, deep local capture centers are formed, is imaged by said actinic radiation, then the material layer is homogeneously charged with corona and then homogeneously illuminated to discharge a charge not present in said deep local capture centers.

The method according to the invention makes it possible to obtain an electroradiogram even on those materials which do not generate free charge carriers upon exposure to the radiation. This new method of generating latent electrostatic imaging in the field of shortwave and corpuscular radiation exploits the fact that radiation forms a wide range of charge carriers for charge carriers in a variety of organic and inorganic substances by locally changing the physical structure at the radiation impact site.

The latent electrostatic image can be produced by charge carriers captured in the deep centers thus formed.

It is known that radioactive, ionizing, X-ray, short-wave ultraviolet, or other radiation, hereinafter referred to as "radiation", generates a number of disorders in both organic and inorganic materials, the emergence of which is usually accompanied by the formation of charge carrier capture centers.

Some of these centers may have a considerable energy depth, which is manifested by the fact that the charge carriers retained in these centers remain there for a considerable period of time, creating a high concentration of spatial charge. The end result is the polarization manifestations of the sensitive medium.

• Examples of the effects of “radiation” on a substance can be the formation of radicals, tearing of chemical bonds, color centers, dislocations, clusters, catalysis, etc. Charge carriers captured in deep capture centers can be detected by conventional thermostimulated techniques: thermostimulated currents, thermoluminescence, limited currents spatial charge, thermopolarization and thermodepolarization currents, change of electric permittivity etc.

Obviously, in conventional electrophotographs, the capture of charge carriers in deep capture centers is undesirable. The charge retained during corona charging releases reluctantly from the deep centers due to long relaxation after light exposure. time and represents actually the "permanent" undesirable electrification of the sensitive medium.

Toner particles adhering to charged parts reduce image contrast, increasing optical noise (forming a veil). Conversely, in the present novel technique of the invention, we use this spatial charge to construct a latent image.

Recording can be performed on conventional electrophotographic imaging media prepared in the form of thin films by vapor deposition, electric discharge, spillage from solution, etc., subject to the formation of deep capture conditions when exposed to "radiation". It is also possible to use materials in which the generation yield of the free charge / / quantum of radiation is small or even zero. The photoconductive media layer, which must have the ability to form a barrier against the injection of surface charge into the volume after being corona charged, is in contact with the conductive pad, which is a cartridge for charge carriers.

The interlayer, at the interface between the layer itself and the substrate, must create a barrier for charge carriers of the opposite sign to the surface charge. If the surface charge is positive, the interlayer must prevent electron injection.

In the case of a negative surface charge of the interlayer, it must prevent the injection of holes, while in the actual volume of the layer the hole capture centers have to be replaced by electron centers. Such an arrangement will allow a perfect discharge of the layer by light (in the following we will distinguish between the light used to discharge the corona-charged layer and the radiation used to create deep capture states), but also create a high surface potential affecting the image contrast.

The intermediate layer between the substrate and the photosensitive medium layer itself, which in fact constitutes a field-controlled charge injection barrier, may be replaced by a spontaneous layer of space charge trapped in the local centers of the intermediate layer.

The formation of a blocking layer results in a decrease in the rate of discharge of the layer in the dark, i.e. a reduction in the change in surface potential over time.

If the barrier-forming charge is trapped in very deep local centers, it can also greatly affect the rate of change of the surface potential under illumination, which is also influenced in particular by: the amount of light absorbed in the photosensitive layer; the quantum efficiency of the primary generation process, ie the number of free electron pairs — the hole produced by light absorption; the rate of electron and hole recombination; the rate at which charge carriers are captured and their lifetime trapped; and finally the mobility of the carriers in the photosensitive layer.

Based on this theoretical analysis, we can now propose a procedure for generating a latent electrostatic image formed by a charge trapped in deep traps resulting from exposure of a photosensitive medium to radiation:

a) The image of the original (original) is projected onto the photoconductive imaging medium. This creates a system of deep capture centers both in the volume of the photosensitive medium and in the interlayer at the interface of the photoconductive medium and the conductive substrate in the medium due to the occurrence of disturbances, radicals or color centers, tearing of the chemical bond, catalysis etc.

(b) The medium shall be charged with a corona discharge of positive or negative polarity, depending on whether the radiation forms deep capture centers for holes or electrons. The charge on the surface indicates the formation of spatial charge in volume due to the entrapment of charge carriers in deep centers as well as at the interface of the photoconductive medium and the conductive pad.

c) The medium is exposed to light evenly over the entire area. A conventional electro-photographic discharge process will take place in places that have not been exposed to radiation before and the charge is transferred to the substrate. Irradiated areas with a high concentration of deep capture states will lose their charge considerably more slowly. This creates a charge gradient at the irradiated and non-irradiated areas.

d) Charge carriers trapped in deep traps create a latent image that can be generated by conventional electrostatic techniques.

For application, it is advantageous to use a photosensitive medium in the form of a thin film obtained by evaporation in a vacuum, prepared in an electric discharge or deposited from solution, or by other techniques, both in the form of amorphous or polycrystalline phase inorganic and organic, low molecular weight and polymeric materials, including crosslinked. as a dispersion of a crystalline low molecular weight substance in a polymeric binder. The erasure of the information may be accomplished by removing deep capture centers from the material, for example, preferably for polymeric materials, by heating above the glass transition temperature.

Next, the use of this recording technique for a one-time recording will be exemplified. The example serves to illustrate the applicability of the invention and is not intended to limit the scope of the invention in any way.

Example

The polycrystalline iodoform layer as the medium for recording the x-ray information of iodoform is the UV-sensitive photoconductor itself. The spectral characteristic shows a slightly wavy plateau for light wavelengths shorter than 300 nm. The quantum yield of charge carrier photogeneration is nízká ^-3 —10 ^-2 of charge carriers per photon for low electric fields; for high electric fields (of the order of 10 ⁸ V m ^-1 ) it is close to one. The sensitive recording medium can be prepared as a thin polycrystalline layer by vacuum vapor deposition.

X-ray irradiation leads to catalytic formation of deep capture centers, mainly for electrons. By charging the negative corona and then exposing it to ultraviolet light, it is possible to produce a latent image using charge carriers captured in deep catalytic centers. The latent image can also be constructed using a positive corona and subsequent exposure to ultraviolet light, but at the expense of image quality and contrast. The recording system is suitable for single use.

Claims (1)

OBJECT OF THE INVENTION An electrostatic imaging method in the field of X-ray, ionizing and radioactive radiation, characterized in that a layer of material in which, after irradiation with actinic radiation, preferably X-rays, deep local capture centers are formed, OF THE INVENTION by exposing the actinic radiation to the image, then the layer of material is homogeneously charged with a terminal discharge and then is homogeneously illuminated to discharge a charge not present in said deep local capture centers.