1. Radiographic processing
Principles

2. Introduction
A latent image is formed in the film emulsion when exposed to different intensities of radiation passed through an object.
Chemical processing of the film is necessary to make the latent image visible and permanent
Film processing involves a number of complex chemical reactions whose activity and efficiency are influenced by various factors such as;
Temperature
Acidity or alkalinity (pH)
of the chemicals used

3. Processing cycle
Dev.
Rinse
Fix
Wash
Dryer

4. Processing stages Manual processing Automatic processing Development
Rinsing
Fixing
Washing
Drying
Automatic processing
Development
Fixing
Washing
Drying

5. Development
Primary purpose is to convert into visible form the invisible latent image
The silver halide grains affected by exposure are reduced to metallic silver
Silver halide grains unaffected by exposure remains largely unchanged

6. Chemical action of developer
The emulsion becomes wet
Chemicals penetrate in to the emulsion
A process of chemical reduction takes place
Developer donates electrons to the silver ions in the exposed silver bromide grains
Silver ions by obtaining electrons converted into metallic silver
(The mode of action is not fully known but explained as follows)

7. Result of exposure on silver halide
Unexposed AgBr grain
Exposed AgBr grain
Br -
Br -
Br -
Br -
Br -
Ag+
Ag+ Br
Ag+
Ag+
Ag+
Ag+ Br
Br -
Ag+
Ag+ Ag
Ag+
Br - Ag Ag
Sensitivity Spec e
Br -
Br - Br
Br -
X ray photon
Sensitivity specs are deliberately formed during film emulsion production
When exposed to radiation The bromine ion release electrons which lodge in the sensitivity area resulting attracting and neutralizing silver ions

8. Mode of action of Developer
Unexposed AgBr grain
Exposed AgBr grain
Br -
Br -
Br -
Br -
Br -
Ag+
Ag+ Br
Ag+
Ag+
Ag+
Ag+
Ag+ Br
Ag+
Ag+ Ag
Br - Ag Ag
Sensitivity Spec
Br -
Br -
Br - Br
Br - e e Ag Br

9. Mode of action
AgBr grains are surrounded by a negative barrier of Br ions
The charge barriers protect the silver ions from attack by electrons
Exposed AgBr grains possess a weakness in the charge barrier caused by the presence of neutral silver atoms at the sensitivity specs (development centre)
The development centre enables electrons from the developer to penetrate grain and reduce all its silver into metallic silver

10. Result of over development
If a film spends too long a time in the developer, or if the develop is hyperactive the charge barrier around unexposed grains may be unable to prevent electron penetration, and unexposed grains will be reduced to metallic silver
Chemical fogging is the result

11. Effects of the by-products of development
With continuous use, the developer becomes depleted of electrons and it is said to be oxidized and reduced in activity
The remaining negative Br ions react with positive hydrogen ions in the solution to form hydrobromic acid.
This causes the pH to fall and reduces the developer activity
The atmospheric oxygen also cause developer oxidation and reduce activity

12. Constitution of developer solution
The developer in automatic processing and manual processing are different in several aspects
In automatic processing the solution added to the working developer in the tank is called developer replenisher
When the developer tank is emptied and fresh solution is added the activity of the replenisher is modified by adding a chemical called the starter solution

13. Developer replenisher+
Starter =
Working developer

14. Constituents of developer replenisher solution
Solvent
Developing agent
Accelerator
Buffers
Restrainers
Preservative
Hardener
Sequestering agents

15. Solvent – water Functions
Acts as the carrying medium in which the developer constituents are dissolved.
Provides a means of controlling the developer activity by diluting its effects.
Has a softening effect on film emulsion to allow the chemicals to penetrate into the emulsion and reach AgBr grains
(The water should be clean enough not to have any chemical reaction with the developer constituents
It should not contain mud & dirt or particles which may cause damage to the delicate film emulsion)

16. Developing agents Are reducing agents which supply electrons
Should exhibit the following properties
Must be selective and distinguish between exposed and unexposed grains
Sufficiently high activity
As resistant as possible to the presence of bromine ions in the solution
No Single reducing agent which satisfies all of these requirements
Therefore combinations are used

17. Phenidone = 1-pheyl-3-pyrazolidone
Metol & Hydroquinone (MQ) were use in early manual developers
Phenidone & Hydroquinone (PQ) are used in modern automatic processing
Phenidone = 1-pheyl-3-pyrazolidone
Quick acting
Selectivity low
Mildly sensitive to bromine ion in concentration
Produces low contrast characteristics

18. Hydroquinone
Requires a strongly alkaline medium in which to act
More selective than phenidone
Slow to start the development action
But once started acts rapidly on exposed AgBr grains
Does not affect lightly exposed or unexposed grains
Produces high contrast characteristics

19. Advantages of PQ developer
When phenidone and hydroquinone are together in one developer their characteristics complement each other
Therefore PQ developers have the following advantages over the other developers

20. Tolerance of increase in bromine ion concentration
High selectivity and low chemical fog
Adequate activity even in low concentration
Available in liquid concentration form
Fast acting permitting complete development in seconds
Adequate contrast characteristics
Super-additive effect (the reducing effect of combination is much greater than the sum of the effects they produce when used separately)

21. Super-additive effect

22. The shape of the characteristic curve is controlled by the two developing agents
Optical density
Combine effect
Hydroquinone only
Phenidone only
Exposure

23. Accelerators PQ developers need an alkaline medium to operate
It is established by adding a strong alkali
Usually Potassium carbonate or Potassium hydroxide is used
The alkali is known as accelerator since its function is to accelerate the developing process

24. PH and development
The pH of the developer has a marked effect on its activity and on image contrast:
Low pH – low activity and development sluggish
High pH – high activity and chemical fog
The range of pH values for different developers will vary from 9.8 to 11.4
However for a particular developer the pH should not vary.

25. Buffers
A buffer is a chemical compound which has the effect of maintaining the pH of a solution within close limits
Potassium sulphite used as the preservative and the potassium carbonate used as accelerator provides an adequate buffering action

26. Restrainers
Modifies the behaviour of developing agents so that they become more selective
That is to reduce the tendency to convert unexposed silver halide grains to metallic silver and therefore to prevent chemical fogging
KBr-The developer by product will act as a restrainer
In PQ developer benzotriazole is used as a restrainer and an antifoggant.

27. Preservatives
To check oxidation of developing agents by the action of atmospheric oxygen
Additionally it permits more efficient regeneration of Phenidone by hydroquinone
Potassium sulphite is commonly used

28. Hardeners
To prevent excessive swelling of the emulsion by the absorption of water which is pronounced in the alkaline developer
Powerful hardeners like glutaraldehyde may employed – they are more effective in alkaline developer
But manufacturers use alternatives because of its undesirable allergenic effects
Manual processing does not need hardeners

29. Sequestering agents
These are chemicals which prevent precipitation of insoluble mineral salts which tends to occur in hard water
They act by combining with the minerals to form soluble compounds which do not react with the developer chemicals
Compounds based on EDTA are commonly used

30. Other constituents
Bactericides
Fungicides

31. Starter solution
The starter solution is added to the fresh solution in the developer tank at the start
To reduce the initial activity of the developer to the safe working level by bringing down the pH to the correct value
It is an acidic restrainer which provides KBr until the development process produce its self restraining effect
Developer replenisher + starter = working developer
Manual processing does not use starter solution

32. Efficiency of development & Factors affecting development
How is the efficiency of development measured? Or assessed?
Assessing the optical density
Assessing the contrast
Factors influence the quantity and quality of development are
Constitution of the developer
Temperature of the developer
Development time

33. How Constitution of the developer affect development?
The activity of the developer depends on
Type of developer
Concentration pH
Concentration of restrainer & anti-foggant
The developer activity reduces with use because,
The concentration of developing agent and pH drops, while the concentration of restrainer increases

34. The replenishment compensates for this too
Therefore the developer has to be replenished continuously if the activity is to be maintained.
The rate of replenishment depends on
The area of film processed
Type of emulsion
Type of image
Aerial oxidation
Not only the activity but the volume of developer also is reduced with use because of
The developer carry over by the films
Evaporation
The replenishment compensates for this too

35. How does developer temperature affect development?
The developer activity increases with temperature
The temperature has to be controlled and maintained if development is to be standardized
Methods used – temperature & cycle times
High temperature development ; 38 – 42 0 C , 90S
Low temperature development : 20 – 30 0 C, 7m -90s
Medium temperature development ; 37 – 33 0 C, 90s-160s

36. Effect of increase of temperature
A slightly increased temperature (0.5 0C) without compensating reduction of development time results in:
Increased image density for the same exposure
Slightly increased chemical fog
Increased image contrast
A more severe rise in temperature (several degrees) initially leads to
Gross increase in density
Unacceptably increase in chemical fog
Reduction in contrast

37. Effect of increase of temperature

38. Effect of decrease of temperature
A slightly lowered temperature will result in:
Decreased image density for the same exposure
Slightly reduced chemical fog
Reduced image contrast
A more severe fall in temperature will result in:
Gross overall reduction in density
Loss of contrast and reduced D-max

39. Effect of decrease of temperature

40. Developer temperature in manual processing
Manufacturers of manual processing recommend a temperature of 20 0 C for optimum result. But they provide acceptable results two or three degrees high or low provided the developing time is adjusted accordingly

41. Development time This is the time the film is kept in the developer
In automatic processing it may be defined as the time interval which elapses between the entry of a specified part of a film (e.g. leading edge) into the developing solution and the exit from the developing solution of the same part of the film.
It varies with the full cycle time of the processor
7 m s
3 ½ m s
110 s s
90 s s

42. Development time is determined by:
Developer concentration
Developer temperature
Film type
Agitation of developer solution
Agitation of solution in automatic processing is achieved by
Film motion
Rotation of rollers
Circulation of developer

43. Summary Development is the most important part of processing
The quality of the recorded image greatly depend on development
To maintain standard development following has to be maintained as constant as possible
Developer concentration by constant replenishment
Constant temperature
Constant time