RT5FIAPIA-LECTURE-3-PRELIM.pdf

RT5FIAPIA: Film-Screen Acquisition, Processing and Image Analysis Spectral Matching The most important consideration in selecting screen film is spectral absorption matching. For the screen to work at maximum efficiency, the light absorption characteristic of the film must match to the light...

RT5FIAPIA: Film-Screen Acquisition, Processing and Image Analysis Spectral Matching The most important consideration in selecting screen film is spectral absorption matching. For the screen to work at maximum efficiency, the light absorption characteristic of the film must match to the light from the screens Calcium Tungstate Screen – emit blue and blue violet light Rare-earth elements – ultraviolet, blue, green and red. NOTE: All silver halide film respond to violet and blue but not to green, yellow and red unless they are spectrally sensitized with dyes. Type of Films according to its sensitivity: Panchromatic film – Orthochromatic film sensitive to the – green sensitive film entire visible light spectrum In Safelight to Film: blue-sensitive film, an green-sensitive and amber filter is blue sensitive film, a used (550 nm red filter is used. wavelength) (600 nm wavelength) Film Humidity – 40-60% >60% - < 40% - increase the static fog artifacts MANUAL PROCESSING UNIT PROCESSING TANKS MASTER INSERT TANK TANKS MASTER TANK This tank serves as a water jacket to hold the insert tanks and is usually large enough to provide space between insert tanks for rinsing and washing of films. INSERT TANKS These are removable containers for the individual processing solutions (developer and fixer), and are spaced in the master tanks PROCESSING CHEMICALS DEVELOPER FIXER FILM PROCESSING The term applied to the chemical reactions that transform the latent image into a manifest image. Wetting Wetting agent - water During wetting, it penetrates the gelatin of the emulsion, causing it to swell. NOTE: In automatic processor, the wetting agent is in the developer. 1. Development The primary function of development is to convert the latent image into a visible image. A very short and critical stage where the latent image is converted to manifest image Principal action of the developer is to change the silver ions of exposed crystals into metallic silver. PROCESSING CHEMICALS DEVELOPER FIXER DEVELOPING FIXING DEVELOPER COMPONENTS: Component Chemical Function 1.Developing Phenidone / Metol Reducing agent; Agent (2) produces shades of gray rapidly Hydroquinone (1) Reducing agent; produces black tones slowly 2. Activator Sodium carbonate helps swell gelatin; produces alkalin ity; controls pH 3. Restrainer Potassium Bromide Antifog agent; protects unexposed crystals from chemical "attack". (also potassium iodide) DEVELOPER COMPONENTS: Component Chemical Function 4. Preservative Sodium Sulfite controls oxidation; maintains balance among developer components 5. Hardener Glutaraldehyde controls emulsion swelling and enhances archival quality. 6. Sequestering Chelates Removes metallic agent impurities ; stabilizes developin g agent DEVELOPER COMPONENTS: Component Chemical Function 7. Solvent Water Dissolves chemicals for use. The Developer contains alkali components or buffering agents: Sodium carbonate Sodium Hydroxide – aka lye, strongest alkali Purpose: enhance the action of the developing agent and controlling the concentration of hydrogen ions (pH)  DEVELOPING STAGE Reduction – neutralize positive ion EUR / OPE Oxidation – opposite of Electrons Oxidation reduction; reaction that Used Produces produces electron Reduction Electrons Redox reaction – reduction and oxidation work simultaneously. 2. FIXING When development is complete, the film must be treated so that the image will not fade. This stage of processing is fixing. The image is said to be fixed on the film, and this produces film of archival quality. FIXER COMPONENTS: Component Chemical Function 1. Activator Acetic Acid Neutralize developer and stop its action 2. Fixing Agent / Ammonium removes Clearing Agent / Thiosulfate undeveloped silver Hypo / Thiosulfate bromine from the emulsion. 3. Hardener Potassium Alum stiffens and shrinks emulsion. 4. Preservative Sodium Sulfite Maintains chemical balance Hypo rentention - is the term used to describe the undesirable retention of the fixer in the emulsion Excess hypo slowly oxidizes and causes the image to discolor to brown over a long time. FIXER COMPONENTS: Component Chemical Function 5. Buffer Acetate Maintains proper pH 6. Sequestering Boric Acids/salts Remove agent aluminum ions 7.Solvent Water Dissolves other components 3. WASHING This stage in processing is to wash away any residual chemicals remaining in the emulsion, particularly hypo that clings to the surface of the film. Note: Wash water should be maintained at approximately 3°C (5°F) below the developer temperature.  Inadequate washing leads to excessive hypo retention Wash bath also serves to and the production of an stabilize developer image that will fade, turn temperature. brown with time, and be of generally poor archival quality. 4. DRYING Final step of film processing Manual Processing – takes longer than 1 hour to be completed. Automatic Processing - the dry-to-drop time is 90 seconds AUTOMATIC PROCESSING UNIT PRINCIPAL COMPONENTS OF AUTOMATIC PROCESSOR a. TRANSPORT SYSTEM b.TEMPERATURE SYSTEM c. CIRCULATION SYSTEM d.REPLENISHMENT SYSTEM e. DRYER SYSTEM A. TRANSPORT SYSTEM Transports film throughout various stages at precise intervals I. Feed Tray – where film to be processed in inserted into the processor II. Entrance Rollers - grip the film to begin its trip through the processor. III. Microswitch is engaged to control the replenishment rate of the processing chemicals. Transport System consist I. Rollers of 3 principal II.Transport Racks subsystems: III.Drive Motor  3 types of Rollers 1. Transport Rollers – with a 1 diameter of 1 inch, convey the film along its path. They are positioned opposite one another in pairs or are offset from one another.  3 types of Rollers 2. Crossover racks - smaller rack assembly that is composed of rollers and guide shoes. - Guide to transport the film to the next assembly a. Master roller – with a diameter of 3 inches, is used in when the film makes a turn in the processor. b. Planetary roller – 1 inch in diameter (25mm) c. Guide shoe – curved metal lip, smoothly guides the film around the bend  3 types of Rollers 3. Drive Motor – provides the fractional horsepower B. TEMPERATURE CONTROL SYSTEM Developer temperature is most critical, and it is usually maintained at 35°C (95°F). Wash water is maintained at 3°C (5°F) lower. Thermocouple/thermistor - monitors the temperature C. CIRCULATION SYSTEM Agitationis necessary to: ✓ continually mix the processing chemicals, ✓ maintain a constant temperature throughout the processing tank, and: ✓ aid exposure of the emulsion to the chemicals.  In automatic Developer – processing, a continuously mixes circulation system continuously pumps the Fixer – continuously developer and the mixes fixer, thus maintain ing constant agitation within Wash – Single pass each tank. water flows at constant rate D. REPLENISHMENT SYSTEM meters the proper quantities of chemicals into each tank to maintain volume and chemical activity ▪ Microswitch – turns on the replenishment for as long as a film travels through the microswitch. Replenishment Rates: Developer – 60-70 ml Fixer – 100-110 ml (for every 35 cm or 14 inch of film) E. DRYER SYSTEM The dryer system extracts all residual moisture from the processed radiograph, so it drops into the receiving bin dry The system consists of: a. Blower b. Ventilation ducts c. drying tubes, and; d. exhaust system.