Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
2001-09-19
2003-03-04
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S396000, C430S440000, C430S567000, C430S606000, C430S942000, C430S966000, C430S967000
Reexamination Certificate
active
06528227
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system suitable for use in direct X-ray applications as industrial non-destructive testing applications and personal monitoring, said system being comprised of a radiation-sensitive black-and-white silver halide photographic material in contact with screen sheets having been designed in order to emit electrons when exposed to X- or •-rays with an energy greater than or equal to 10 kVp.
BACKGROUND OF THE INVENTION
Industrial radiography is a non-destructive technique for testing and analyzing defects in components such as glass, paper, wood or metal parts, etc. This technique is widely used in aeronautics, the nuclear industry or the petroleum industry since it makes it possible to detect welding defects or defects in the texture of materials in aircraft components, nuclear reactors or pipelines. This technique consists of exposing a component to be analyzed to an ionizing radiation, in general X- or gamma rays having an energy between 10.000 and 15.000 kVp, either directly or by means of an intensifying screen. It is therefore necessary with this technique to use specific radiographic elements which are highly sensitive to this ionizing radiation. The major part of the ionizing radiation however passes through the silver halide grains without being absorbed and only a very small part of the incident radiation (less than 1%) is really absorbed and contributes to the formation of a developable latent image.
In order to really achieve high film sensitivity, also called “speed”, which is an indispensible asset especially for direct-röntgen applications, efficient absorption of the exposure radiation is a prime condition. It has been shown empirically that for X-rays the mass absorption coefficient is proportional to a power of the atomic number Z as has been described in the “Encyclopaedic Dictionary of Physics” vol. 7, p. 787, eq. 10, Ed. J.Thewlis, Pergamom Press, Oxford 1957. This strongly favours the use of iodide(Z=54), more than bromide (Z=35) and further more than chloride (Z=17).
As a consequence silver bromo(chloro)iodide crystals have preferably been used hitherto. Absorption of the ionizing radiation can further be enhanced by increasing the silver content and/or the thickness of the emulsion layers. Moreover it is known to provide double-side coated materials in favour of absorption of high energy radiation.
Cubic silver bromoiodide grains have until now preferably been used in non-destructive testing applications for the reason set out above, preferably coated in high amounts of more than 20 g/m2, expressed as equivalent amounts of silver nitrate. Lowering of coated amounts of silver thus results in a reduction of sensitivity for direct-Röngten rays and further leads to a lowering in contrast, which may be in favour of image quality (especially graininess) as desired for some well-designed applications, but makes maximum density decrease to an unacceptable level. When in such case only use can be made of radiation sources for X-rays having a lower energy output (exposure energies of about 100 kVp instead of the normally used 220 kVp) besides undesired higher contrasts a reduced speed can be expected. Although said reduced speed can be compensated in industrial radiographic exposure techniques by application of intensifying screens in contact with industrial non-destructive test film materials, thereby taking profit of the combined effect of direct-Röntgen exposure and exposure by light emitted from light-emitting phosphors present in the intensifying screens, the problem of too high contrasts remains in that case.
A suitable solution therefor has been presented in EP-A 0 890 875 and the corresponding U.S. Pat. No. 6,030,757 wherein a multilayer arrangement has been disclosed for a material suitable for e.g. concrete testing and wherein use was made, besides the well-known cubic grain emulsions, from tabular grain emulsions. Applicability of tabular grains in nondestructive testing applications had already been proposed before in EP-A 0 757 286 and the corresponding U.S. Pat. No. 5,965,337, moreover providing an improved speed.
As had indeed been made clear in the earliest patents about practical materials coated from tabular grain emulsions, such as in U.S. Pat. No. 4,414,304 with tabular grains having an aspect ratio of at least 5:1 and, more particularly, an average grain thickness of less than 0.20 &mgr;m, a high covering power can be provided, even when the gelatinous coating layers of the material have been strongly prehardened. An increase in covering power in the presence of such tabular grains, if compared with more compact grains such as cubic grains having the same volume, can be translated into a decrease in coated amounts of silver halide, in order to reach the same maximum density. One of the disadvantages reflected by the presence of thin tabular grains however, when present in an industrial photographic material for nondestructive testing, which is often manipulated without taking precautions as has been described in Example 4 of EP-A 0 757 286, is its pressure sensitivity (also called “kink” therein). When the emulsions comprised AgBr(I) tabular grains with an iodide peak, the kink was improved as set forth. Example 4.2 e.g. comprises bromoiodide (1% iodide) tabular grains prepared according to the above described preparation process (iodide was added in one step after having added 64% of the total silver amount).
Presence of iodide in higher concentrations in the outermost layers of silver halide emulsion grains may however lay burden on the developability of the grains and also fixation times may increase, which results in a longer processing time or in a decrease in image quality if processing times are left unchanged.
OBJECTS OF THE INVENTION
It has been an object of the present invention to provide a direct X-ray system having silver halide photographic film materials for industrial non-destructive testing applications and personal monitoring, said system offering high speed after rapid processing of said film materials, being exposed to high-energy radiation exposure by X-ray of •-ray sources, as e.g. from a Co-60 source, and a method in order to provide images having high image quality, with a high diagnostic value, i.a., without disturbing kinks due to pressure sensitization.
Other objects will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
In order to reach the objects as set forth, a direct X-ray system has been provided, said system being comprised of
(1) a black-and-white negative-working radiographic film material, more particularly used as non-destructive testing material, comprised of a transparent support coated on at least one side thereof with a tabular grain emulsion layer, substantially free from spectrally sensitizing dyes, in which at least 50 percent of total grain projected area of all grains is accounted for by silver bromoiodide tabular grains having an iodide content of less than 5 mole %, based on silver, further having an average aspect ratio of at least 2, and having a volume greater than 0.03 &mgr;m
3
, characterized in that said tabular grain emulsion layer(s) comprise(s), in an amount of from 5 mg up to 100 mg per mole of coated silver bromoiodide at least one desensitizing agent having a hetero-aromatic part and an electron-withdrawing group;
(2) disposed on opposite sides of the radiographic element, two intensifying screen sheets selected from the group consisting of lead, lead oxide, copper and steel, said screen sheets being designed to emit electrons when exposed to X- or &ggr;-rays with an energy greater than or equal to 10 kVp.
An image-forming method in order to form an industrial radiographic image has also been claimed, said method comprising the steps of exposing a system as set forth hereinbefore to X- or &ggr;-rays with an energy greater than or equal to 10 kVp in order to form a latent image in radiation-sensitive layers of the film material, and developing the said latent image.
A persona
De Vester Marleen
den Zegel Marc Van
Agfa-Gevaert
Guy Joseph T.
Nexsen Pruet Jacobs & Pollard LLC
Schilling Richard L.
LandOfFree
Film/screen system and image-forming system for use in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Film/screen system and image-forming system for use in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Film/screen system and image-forming system for use in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3068724