Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
2001-09-19
2003-10-07
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S567000, C430S569000, C430S966000, C430S967000, C430S603000, C430S605000, C250S370090, C250S370100
Reexamination Certificate
active
06630278
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system for direct X-ray detection and image-formation suitable for use in radiographic industrial non-destructive testing materials and personal monitoring.
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 bromoiodide crystals have preferably been used hitherto. Absorption of the ionizing radiation can futher be enhanced by increasing the silver content and/or the thickness of the emulsion layers. Moreover it is common knowledge 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 25 g/m2, expressed as equivalent amounts of silver nitrate, particularly when a higher speed is envisaged, as for those materials having grains with an average equivalent crystal diameter of at least 0.4 &mgr;m or an average equivalent volume of at least 0.034 &mgr;m
3
. Lowering of coated amounts of silver thus results in a reduction of speed (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.
An indication of the applicability of tabular grain emulsions grains, known for practical applications in photography since the eighties, was already given before in dental X-ray applications in EP-A 0 653 670 and the corresponding U.S. Pat. No. 5,370,977.
Said tabular have however already been proposed in EP-A 0 757 286 and the corresponding U.S. Pat. No. 5,965,337 as effectively suitable for use in industrial non-destructive testing applications, moreover providing an improved speed. In the Examples of said EP-A 0 757 286 it has been established that high speed for such tabular grains is obtained after chemical sensitization thereof with sulphur and gold, the quantity of sulphur being between 30000 and 50000 atoms per &mgr;m
2
and of gold between 15000 and 50000 atoms per &mgr;m
2
.
Apart from attaining the desired speed it is an indispensable asset to maintain a good developablity of the emulsion crystals present in the materials after exposure, even when the developer gets exhausted as commonly appears in the field after some working time. Within this aspect cubic grains offer a more expressed advantage over tabular grains. As developability, even under bare circumstances as exhaustion of processing solutions, is important with respect to consistency of the resulting diagnostic image, obtained after processing, it is of utmost importance to provide means in order to take away this disavantageous aspect which is related with the use of tabular grains, particularly in critical applications as in radiographic industrial non-destructive testing.
OBJECTS OF THE INVENTION
It has been an object of the present invention to provide a system for industrial non-destructive testing applications and personal monitoring, making use therefor of silver halide photographic film materials coated with tabular grain emulsions, offering high speed and minimum variation thereof, even after processing of said materials in exhausted processing solutions.
Other objects will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
The above mentioned objects have been realized by providing a system for direct X-ray radiography comprised of (1) a silver halide photographic element or material free from dyes spectrally sensitizing radiation sensitive emulsion grains coated in radiation sensitive layers thereof, said emulsion grains being tabular silver brom(oiod)ide grains with {111} major faces, an average equivalent circular diameter of at least 0.5 &mgr;m and an average thickness of less than 0.30 &mgr;m, accounting for at least 50% of the total projective area of all grains, said grains further having been chemically sensitized by the steps of
adding at least a gold salt in order to provide the surface of said tabular grains with at least 6000 atoms of gold per &mgr;m
2
of its grain surface and en per (0.1 &mgr;m of thickness)
2
; and
adding at least a sulfite salt in such an amount that the ratio of the number of gold atoms per &mgr;m
2
and per (concentration of said sulfite salt, expressed in mmole per mole of silver)
2
is at least 200000;
and wherein said emulsion has been coated symmetrically in same emulsion layers at both sides of a double-side coated support, said element having, per side, an amount of silver, expressed as an equivalent amount of silver nitrate, in the range of from 5 up to 25 g/m
2
;
said system further having,
(2) disposed on opposite sides of said element, two intensifying screens designed to emit electrons when exposed to X- or &ggr;-rays with an energy greater than or equal to 10 kVp.
It is however required to have a gold salt and a sulfite salt present in amounts of at least 0.010 mmole and 0.05 mmole per mole of silver (nitrate), respectively.
In a preferred embodiment according to the present invention said material is an industrial non-destructive testing material. In another preferred embodiment according to the present invention said element is a material for personal monitoring.
A personal electromagnetic radiation monitor wearable by a person in order to warn the person of a radiation hazard condition caused by electromagnetic rad
De Vester Marleen
den Zegel Marc Van
AGFA-Gevaert
Baxter Janet
Guy Joseph T.
Nexsen Pruet Jacobs & Pollard LLC
Walke Amanda C.
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