Day 3 Film Construction & Processing Flashcards
A film is basically made up of two (2) parts. They are?
The Base & The Emulsion
The Base is made of polyester to resist warping with age. Provides structure for the emulsion that is unbreakable, fairly rigid, and will not changed size or shape, this causing distortion.
The Emulsion is a homogeneous mixture of gelatin and silver halide crystals. The gelatin is porous to allow the chemicals in and out.
The grouping or “clumping” together of the crystals constitutes a grain.
What are some factors that contribute to the type of film chosen?
The Part: density, shape, thickness.
Type of Radiation used: X-Ray or Gamma.
The Energy of the radiation
The Intensity of the radiation
The Level of Inspection required
Also,
Speed, Contrast, Latitude, Graininess
Type/Class 1 Film Characteristics
Speed: Very Slow
Grain: Extra Fine
Contrast: High
Latitude: Low/Little
For critical inspection, higher voltages and radiography of light metals and their alloys.
Type/Class 2 Film Characteristics
Speed: Slow
Grain: Fine
Contrast: High
Latitude: Low/Little
For radiography of light metals at lower voltages, and heavier steel parts at 1000 to 2000Kv
Type 3 Film Characteristics
Speed: Medium
Grain: Medium
Contrast: Medium
Latitude: Medium
Highest available speed when gamma or high voltage x-rays are used directly with lead foil screens
Type/Class 4 Film Characteristics
Speed: Fast
Grain: Large
Contrast: Low
Latitude: High/Wide
Highest available speed and high contrast when used with fluorescent screens. Lower contrast when used direct or with lead foil screens.
Film Processing:
What are the Six (6) steps in converting the invisible image (latent image) on the exposed film to permanent visible image?
1) Developer
2) Stop
3) Fix
4) Wash
5) Wetting Agent
6) Drying
Film Processing:
What are the seven main step before starting manual processing?
1) Check levels of all solution.
2) Check temperature of developer. 20c (68f)
3) Stir solutions.
4) Ensure ample flow of water for washing.
5) Set timer in conjunction with temperature.
6) Clean all work surfaces and hands!
7) Turn off the lights.
What is Developer?
Is an alkaline solution with the main purpose of:
1) Soften the coating so that the chemicals can get in and do their job
2) To change (reduce) the exposed silver halides to black metallic silver. It does not act on the unexposed silver halides.
The Developer causes the latent image formed on the film to become visible. Normal developing time is five (5) minutes at 20c (68f)
Stop Bath Process
This is an acidic solution of acetic acid and water.
1) It immediately stops the action of the developer solution.
2) It prevents contamination of fixer bath by the developing solution, thus prolonging the life of the fixer. The fixer solution is acidic and will be neutralized by the alkaline developer solution.
Either Glacial (pure) or 28% acetic acid
Film should be agitated while in the Stop Bath. Temp 20c (68f)
Leave film in bath 30sec to 1min (approx).
If an acidic stop bath is not available, then developed film can be immersed in running water for 2-3min
Fix(er) Bath process
This also a acidic solution which has three (3) functions:
1) Removes the unexposed, undeveloped silver halides from the emulsion.
2) Hardens the emulsion.
3) Ensures that ALL the development has stopped
What are the two different phases of fixing radiographic film?
1) Clearing time - this is the time it takes to remove the unexposed silver halides from the emulsion. Visually, it is the time it takes for the yellow milk cloudiness to disappear from the film
2) Fixing time - this should be 3 times the clearing time. Again, the film must be agitated to ensure all areas are covered and all development stopped. Temp 20c (68f)
Note: Fixer should be replaced when the total fixing time reaches 15 min (clearing time - 5 min). Insufficient fixing results in yellow/brown stains. This can also exhausted fixer. Improper fixing may also cause the film image to fade over a period of time.
The Wash process:
This ensures that the film remains in good condition during long term storage, proper washing is crucial.
Film should be washed in clean running water, with a flow rate of 4-8 tank volumes/hour.
Total wash time for be twice the fixing time, but not less than 10 min or more than 30min.
Temp should be 20c (68f) no more than 24c (75f) or less than 16c (60f)
Film should be immersed in a wetting agent. This overcomes surface tension of the water preventing formation of water marks/streaks. Decreases drying time.
The Drying Process
Drying temperature should not be over 49C (120f), in a steady volume of air which can circulate freely between films to eliminate curling and distortion.
Cabinet should be free and dust or lint .
After the exposed film is dry, trim corners in order to remove the sharp projections caused by hanger clips to prevent scratching
How to store Unexposed Radiographic Film?
Storage area should dry.
Free from contaminating chemicals and free ionizing radiation.
Temperature on the cool side.
Boxes should be stored on side, not stacked.
