Asymmetrical radiographic elements, assemblies and packages

Abstract

An asymmetric radiographic element is disclosed comprised of a transparent film support, silver halide emulsion layer units of differing sensitometric characteristics coated on opposite sides of the film support, and a processing solution decolorizable means for reducing crossover to less than 10 percent. The radiographic element is positioned between intensifying screens and mounted in a cassette for exposure to X-radiation. A feature is included for ascertaining which of the emulsion layer units is positioned nearest a source of X-radiation during exposure.

What is claimed is: 
     
       1. A radiographic element comprised of a transparent film support,   first and second silver halide emulsion layer units coated on opposite sides of the film support, and   means for reducing to less than 10 percent crossover of electromagnetic radiation of wavelengths longer than 300 nm capable of forming a latent image in the silver halide emulsion layer units, said crossover reducing means being decolorized in less than 90 seconds during processing of said emulsion layer units,   characterized in that said first and second silver halide emulsion layer units exhibit significantly different sensitometric characteristics and   means are provided for ascertaining which of said first and second emulsion layer units are positioned nearest a source of X-radiation during exposure.     
     
     
       2. A radiographic element according to claim 1 further characterized in that said first silver halide emulsion layer unit exhibits a speed at 1.0 above minimum density which is at least twice that of the second silver halide emulsion layer unit, the speed of the first silver halide emulsion layer unit being determined with the first silver halide emulsion unit replacing the second silver halide emulsion unit to provide an arrangement with the first silver halide emulsion unit present on both sides of the transparent support and   the speed of the second silver halide emulsion layer unit being determined with the second silver halide emulsion unit replacing the first silver halide emulsion unit to provide an arrangement with the second silver halide emulsion unit present on both sides of the transparent support.   
     
     
       3. A radiographic element according to claim 2 further characterized in that the first silver halide emulsion layer unit is from 2 to 10 times faster than the second silver halide emulsion layer unit. 
     
     
       4. A radiographic element according to claim 3 further characterized in that the first silver halide emulsion layer unit is from 2 to 4 times faster than the second silver halide emulsion layer unit. 
     
     
       5. A radiographic element according to claim 1 further characterized in that said first silver halide emulsion layer unit exhibits an average contrast of less than 2.0, based on density measurements at 0.25 and 2.0 above minimum density and   said second silver halide emulsion layer unit exhibits an average contrast of at least 2.5, based on density measurements at 0.25 and 2.0 above minimum density,   the contrast of the first silver halide emulsion layer unit being determined with the first silver halide emulsion unit replacing the second silver halide emulsion unit to provide an arrangement with the first silver halide emulsion unit present on both sides of the transparent support and   the contrast of the second silver halide emulsion layer unit being determined with the second silver halide emulsion unit replacing the first silver halide emulsion unit to provide an arrangement with the second silver halide emulsion layer unit present on both sides of the transparent support.   
     
     
       6. A radiographic element according to claim 5 further characterized in that the first silver halide emulsion layer unit exhibits an average contrast that differs by 0.5 to 3.5 from that of the second silver halide emulsion layer unit. 
     
     
       7. A radiographic element according to claim 6 further characterized in that the first silver halide emulsion layer unit exhibits an average contrast that differs by 1.0 to 2.5 from that of the second silver halide emulsion layer unit. 
     
     
       8. A radiographic element according to claim 1 further characterized in that the crossover reducing means decreases crossover to less than 5 percent. 
     
     
       9. A radiographic element according to claim 8 further characterized in that the crossover reducing means decreases crossover to less than 3 percent. 
     
     
       10. A radiographic element according to claim 1 further characterized in that the crossover reducing means is comprised of a hydrophilic colloid layer interposed between at least one of said silver halide emulsion layer units and said support containing a dye capable of absorbing electromagnetic radiation to which said silver halide emulsion layer unit on the opposite side of the support is responsive. 
     
     
       11. A radiographic element according to claim 10 further characterized in that the dye in said interposed layer is, prior to processing, in the form of particles and is capable of being decolorized during processing. 
     
     
       12. A radiographic element according to claim 1 further characterized in said silver halide emulsion layer unites are comprised of emulsions in which tabular silver halide grains having a thickness of less than 0.3 μm exhibit an average aspect ratio of greater than 5:1 and account for greater than 50 percent of the total grain projected area. 
     
     
       13. A radiographic element according to claim 12 further characterized in that said silver halide emulsion layer units are spectrally sensitized to at least 60 percent of their highest attainable sensitivities. 
     
     
       14. A radiographic element according to claim 13 further characterized in said silver halide emulsion layer units are comprised of emulsions in which tabular silver halide grains having a thickness of less than 0.2 μm exhibit an average aspect ratio of greater than 8:1 and account for greater than 70 percent of the total grain projected area. 
     
     
       15. A radiographic element according to claim 1 further characterized in that said emulsion layer units and crossover reducing means are each comprised of processing solution permeable hardenable hydrophilic colloid layers,   said crossover reducing means includes a hydrophilic colloid layer interposed between one of said emulsion layer units and said support containing a particulate dye capable of absorbing radiation to which said emulsion layer unit coated on the opposite side of the support is responsive and at least 10 mg/dm 2  of said hardenable hydrophilic colloid,   said emulsion layer units contain a combined silver coating coverage sufficient to produce a maximum density on processing the range of from 3 to 4,   a total of from 35 to 65 mg/dm 2  of processing solution permeable hardenable hydrophilic colloid is coated on each of said opposed major surfaces of said support, and   said processing solution permeable hydrophilic colloid layers are forehardened in an amount sufficient to reduce swelling of said layers to less than 300 percent, percent swelling being determined by (a) incubating said radiographic element at 38° C. for 3 days at 50 percent relative humidity, (b) measuring layer thickness, (c) immersing said radiographic element in distilled water at 21° C. for 3 minutes, and (d) determining the percent change in layer thickness as compared to the layer thickness measured in step (b),   whereby said radiographic element exhibits high covering power, reduced crossover without emulsion desensitization, reduced wet pressure sensitivity, and can be developed, fixed, washed, and emerge dry to the touch in a 90 second 35° C. process cycle consisting of   ______________________________________                                    
development      24 seconds at 40° C.,                             
fixing           20 seconds at 40° C.,                             
washing          10 seconds at 40° C., and                         
drying           20 seconds at 65° C.,                             
______________________________________                                    
        where the remaining time is transport between processing steps, the development step employs the following developer:   ______________________________________                                    
Hydroquinone            30     g                                          
1-Phenyl-3-pyrazolidone 1.5    g                                          
KOH                     21     g                                          
NaHCO.sub.3             7.5    g                                          
K.sub.2 SO.sub.3        44.2   g                                          
Na.sub.2 S.sub.2 O.sub.5                                                  
                        12.6   g                                          
NaBr                    35     g                                          
5-Methylbenzotriazole   0.06   g                                          
Glutaraldehyde          4.9    g                                          
Water to 1 liter at pH 10.0, and                                          
______________________________________                                    
        the fixing step employs the following fixing composition:   ______________________________________                                    
Ammonium thiosulfate, 60%                                                 
                        260.0  g                                          
Sodium bisulfite        180.0  g                                          
Boric acid              25.0   g                                          
Acetic acid             10.0   g                                          
Aluminum sulfate        8.0    g                                          
Water to 1 liter at pH 3.9 to                                             
                        4.5.                                              
______________________________________                                    
       
     
     
       16. A radiographic element according to claim 1 further characterized in that said means for ascertaining which of said first and second emulsion layer units are positioned nearest a source of X-radiation during exposure is comprised of a mark capable of being seen under safe-light conditions. 
     
     
       17. A radiographic element according to claim 1 further characterized in that said means for ascertaining which of said first and second emulsion layer units are positioned nearest a source of X-radiation during exposure is comprised of means for permitting tactile discrimination between said first and second emulsion layer units. 
     
     
       18. A radiographic element according to claim 17 further characterized in that said means for permitting tacile discrimination is a boundary rendering said support asymmetrical. 
     
     
       19. A radiographic element according to claim 18 further characterized in that said support is rendered asymmetrical by an aperture or edge notch. 
     
     
       20. An imaging assembly comprised of a radiographic element and   a front and back pair of intensifying screens characterized in that said radiographic element is that recited in any one of claims 1 to 19 inclusive.   
     
     
       21. An imaging assembly according to claim 20 further characterized in that at least one of said front and back intensifying screens includes means for referencing its orientation to that of said radiographic element. 
     
     
       22. An imaging assembly according to claim 21 further characterized in that said orientation referencing means is comprised of a visual indicator capable of being seen under safe-light conditions. 
     
     
       23. An imaging assembly according to claim 21 further characterized in that said radiographic element and said front and back intensifying screens each include means for permitting tactile identification of their orientation. 
     
     
       24. An imaging assembly according to claim 23 further characterized in that said means for permitting tactile identification of the orientation of said radiographic elements and said first and second screens is comprised of a boundary rendering each of said radiographic element and said first and second screens asymmetrical. 
     
     
       25. An imaging assembly according to claim 24 further characterized in that said radiographic element and said front and back screens are each rendered asymmetrical by an aperture or edge notch. 
     
     
       26. An exposure package comprised of an assembly and   means forming a cassette housing for said assembly,   characterized in that said assembly is constructed according to claim 20.   
     
     
       27. An exposure package according to claim 26 further characterized in that said assembly includes at least one boundary for imparting asymmetry and said cassette housing includes means for limiting said asymmetry imparting boundary to a single orientation. 
     
     
       28. An exposure package according to claim 27 further characterized in that said cassette housing includes means peripherally defining a seating area for said assembly and means for rendering said seating area asymmetrical. 
     
     
       29. An exposure package according to claim 28 further characterized in that said means for rendering said seating area asymmetrical includes a pin. 
     
     
       30. An exposure package according to claim 28 further characterized in that said means for rendering said seating area asymmetrical includes an edge for cooperating with an asymmetrical edge of said assembly. 
     
     
       31. An exposure package according to claim 26 further characterized in that an exposure step tablet is located on said cassette housing.