CS243547B1 - Electrophotographic plate - Google Patents

Abstract

An electrophotographic plate comprising at least one As2S3 layer and a selenium layer comprises between each As2S3 layer and the selenium layer an intermediate layer of the composition /As2S3/xSe3_x, where x is 0 to 1. The intermediate layer may comprise doping elements with which the selenium layer is doped in the same atomic ratio to selenium as in the selenium layer.

Description

The invention relates to a radlographic plate for clinical and flaw detection purposes.

Films containing silver halogens are most often used to record X-rays transmitted through the studied object. Their advantage is good sensitivity and easy processing. The disadvantage, however, is the low resolution, which makes it difficult to distinguish areas that differ only by very little absorption, eg cancerous tumors in the soft parts of the body at an early stage.

It is known that a radiographic process based on exposure of X-rays to the surface of a charged selenium layer exhibits a much better resolution. By the interaction of X-rays with the selenium layer, the resulting charges neutralize the charge on the surface of the selenium layer, thereby creating an image which is visible by the powder lamp.

The basic requirements for a radiographic plate are:

1 / high sensitivity to X-rays,

2 / the ability of the selenium layer to maintain a high potential for a sufficiently long time (greater than 15 minutes) without a significant decrease.

For example, arsenic (US Patent Nos. 2,803,542 and 2,822,300) or sulfur (US Patent No. 2,662,832) are added to the selenium layer to improve the durability of the selenium layer and crystallization resistance. It is also known that the addition of ASjSj to Se decreases the sensitivity to visible light while maintaining the sensitivity to X-rays (U.S. Pat. No. 2,863,768).

The As ₂ S ₃ layer vapor deposited on an aluminum support also contributes to improving the properties of radiographic plates (U.S. Patent No. 2,901,349). Selenium is deposited on this layer by vacuum evaporation.

The selenium surface can be protected by a layer with high electrical resistance and a higher abrasion resistance than the selenium resistance. For example, polyvinylcarbazole, which also exhibits photosensitivity (U.S. Pat. No. 3,037,861) and other organic materials, is used for this purpose.

A significant improvement in the properties of the radlographic plate achieved by vapor deposition of the As ₂ S ₃ layer between the aluminum substrate and selenium is that it prevents injection of charge carriers from the metal substrate, thereby contributing to the reduction of spontaneous discharge in the dark. This is particularly important in the clinical use of radiographic plates where the time between plate loading and exposure can reach 15 minutes.

The formation of this layer with ₂ with ₃ between the aluminum substrate and the selenium layer, or other layers on the selenium surface, also automatically creates the interface between environments of different permittivity, different equilibrium charge concentrations and different mobility leads to the formation of narrow transition areas manifest when transporting the generated charge carriers.

These disadvantages are overcome by the electrophotographic plate according to the invention, which comprises an intermediate layer between the As ₂ S ₃ 'layer and the selenium layer, in which the composition changes continuously from As ₂ S ₃ to selenium, respectively. from As ₂ with ₃ to selenium doped with other elements such as tellurium, arsenic, sulfur etc.

Assuming that the base photoconductive material is pure selenium without impurities, the intermediate layer has the general composition / As ₂ ^s 3 / x ^Se ix ' ^{where x} changes gradually from 1 to 0. If the base photo conductive selenium layer is doped with impurities, when the interlayer is formed, these dopants together with selenium and their content also increase in proportion to the selenium content with increasing selenium content in the interlayer.

According to another finding, it is suitable to form an intermediate layer of composition / As ₂ ^s 3 / _x Se _{1 x} , where x varies gradually from 0 to 1 when the layer of composition As ₂ s _{3 is} used as the top layer. If the selenium layer is doped with other elements, these elements are also incorporated in the interlayer, and their content decreases with decreasing selenium content in the interlayer. The thickness of both said interlayers is chosen from 0.1 µm to 5 µm.

The arrangement of the individual layers is apparent from the drawing. On the aluminum pad £ is a layer 2 of aluminum oxide on it is applied to the lower layer 3 As ₂ S _3, interlayer £ the composition / As ₂ S ₃ / _{X 1} _ _x, where x varies from 1 to 0, a selenium layer £ and another interlayer £ of composition / As ₂ S ₃ / _x Se _{1 x} , where x varies from 0 to 1, the top layer £ As ₂ S ₃ ·

If selenium is enriched with M to contain p atomic% of this dopant, then the composition of the interlayer can be written in the form / As ₂ S ₃ / / Se + p atomic% M / j, where x varies from 1 to 0 in if the interlayer is vapor deposited on the As ₂ S ₃ layer and from 0 to 1 if the interlayer is vapor deposited on the Se layer.

The formation of the interlayer reduces the fatigue sensitivity of the plate and increases the spontaneous discharge resistance.

The formation of the / ^As 2 ^S 3 / x ^Se i x x composition where x varies from 1 to 0, which is part of the radiographic plate, will be explained in Example 1.

Example 1

TO. two independent heater boats were inserted both Se and As ₂ s ₃ · On the aluminum pad containing the alumina layer, the 2 ^As 2 ^S 3 'layer was first steamed. When its thickness reached 2.5 µm, the glow current was a boat containing As ₂ S ₃ gradually decreased while increasing the current by the selenium-containing boat.

In this way, an intermediate layer 6 was formed where the composition changed continuously during a thickness of 1 (µm to As ₂ S ₃ to Se.) The study of radiographic properties showed that the radiographic plate produced in this way showed very good sensitivity and fatigue resistance.

The use of this type of radiographic plate construction allows the production of plates with low fatigue sensitivity while maintaining all the benefits of using the As ₂ S ₃ layer.

The construction of a plate comprising a composite layer 5 of / As ₂ S ₃ / _x Se _{1 x} , where x varies from 1 to 0, and an interlayer 6 of composition / As ₂ S ₃ / _x Se _{1 x} , where x varies from 1 to 0 0 to 1 will be explained in Example 2.

Example 2

As ₂ S ₃ and Se were inserted into two independent heating boats. As ₂ S ₃ was deposited on the aluminum substrate (6) with an oxide layer ( ₆ ) to form the bottom layer (As ₂ S ₃ ). When its thickness reached 3.5 µm, the heating current was gradually reduced while increasing the current by the Se-containing boat.

In this way, an intermediate layer 6 was formed where the composition varied continuously from As ₂ S ₃ to Se during the thickness of the intermediate layer 1,5 1.5 µm. Selenium was vaporized on the thus produced intermediate layer 6 to form a selenium layer 6 having a thickness of 160 µm.

Upon reaching this thickness, the heating current through the selenium-containing boat was gradually reduced, while increasing the current through the boat with As ₂ s ₃ - In this way, an intermediate layer 6 of the composition / As ₂ S ₃ / _x Se _{3 x} was formed. 0 to 1 during 1 µm thickness.

The top layer As ₂ S ₃ ař was deposited onto the intermediate layer 8 thus produced. ^To stabilize the properties of the radiographic plate, the plate was exposed to radiation without shading by the object before use.

The plate thus prepared exhibited excellent resolution, low fatigue sensitivity and low potential drop in the dark.

Claims (2)

SUBJECT OF THE INVENTION An electrophotographic plate comprising at least one layer AS 1 S 1 and a selenium layer, characterized in that between each layer (3 AS ₂ S ₁ ) and the selenium layer 5 is formed between a layer (4) of composition (As ₂ S ₃ ) _x With _{1, x} , de x is 0 to 1. An electrophotographic plate according to claim 1, characterized in that the interlayers (4) comprise doping elements which dope the selenium layer (5) in the same atomic ratio to selenium as in the selenium layer.