Processing Chemicals

PROCESSING CHEMICALS

PROCESSING CHEMICALS

The primary purpose of a radiographic processing is to deposit enough black metallic silver at the latent image sites to permit a permanent visible image to form The development of latent image can be accomplished manually or with automatic processing equipment.The development and fixing are accomplished in a solution of numerous chemicals

LATENT IMAGE

The silver bromide crystals consist of positive silver and negative ions arranged in geometrical pattern known as a crystal lattice When silver bromide grain is exposed to light or x-ray some of the bromide ions in the lattice emit electrons Electrons are trapped in the electron- trap in the crystal An electron trap is a region of low energy called a sensitivity speck producing during manufacture Electrons tend to collect at sensitivity speck and they confer on speck a negative charge

A crystal lattice

LATENT IMAGE CONT.

Silver ions in the crystal have a positive charge, the silver which are free to move are attracted to the negative charge electrons in a sensitivity speck The negative charge on the electrons neutralises the positive charge on the silver ions; hence forming silver atoms

LATENT IMAGE FORMATION

How the film works

Latent: Hidden – as the silver halide crystals are exposed to electromagnetic radiation, they are ionized and conversion to metallic silver is begun. This is completed in the processor

LATENT IMAGE CONT.

HOW THE FILM WORKS CONT.

• Sensitization speck
• Impurities/imperfections intentionally introduced to crystals during manufacturing.
• Found on surface of crystal
• Acts as electron trap, trapping electrons released during ionization of crystals.
• Essential for development of black metallic silver

LATENT IMAGE FORMATION

The latent image is theorized as being formed in the following manner:

• Radiant energy (x-ray photon or light photon from screen) strike the crystal & liberates an electron from the valence shell of a bromide ion.

This electron is then free to move about in the crystal. If it strikes a sensitivity speck, it may be trapped giving the speck a negative charge.

When a positive silver ion comes within the negative field of the speck, it may be attracted to the speck & take on an electron thus forming an atom of metallic silver

LATENT IMAGE FORMATION cont.

Occurs many times within the same crystal when struck by radiant energy.

Once the film has been exposed to radiant energy & a latent image has been formed, the film is capable of developing a radiographic image.

Chemicals in the processor greatly enhance this chemical reaction converting a latent image to a visible image

LATENT IMAGE FORMATION cont.

IN SUMMARY

Electrons (released by light from bromine ions) are trapped Positive silver ions are trapped at the sensitivity speck by the negative charges on the electrons Positive charges on the silver ions are neutralized by negative charges on the electrons and silver atoms form

Processing Chemicals

Film Processing is a predetermined sequence of chemical treatment of the exposed film whereby the latent image is transformed into a visible image in a dry film.

CHEMICALS IN AUTOMATIC PROCESSOR

Four stages in Automatic processing namely Development, Fixing, Washing and Drying Developing:- it is the first step in processing film, at this stage silver is deposited at the latent image site and an image becomes visible.

Processing Chemicals

The deposition of silver amplifies the density of the image, a modern x-ray developers are capable of amplifying the image by a factor of 108 to 10 9 within 3-4 mins .

Its primary purpose is convert latent image into visible image

During development the exposed silver halide grains are reduced to metallic silver while unexposed remain unchanged A chemical fog is produced by poor developer acting on unexposed grains

CHEMICAL ACTION OF DEVELOPER

Development is a process of chemical reduction; this reduction is achieved by developer donating electrons to silver ions in the grains, thus neutralizing their positive charge and converting them to metallic silver Both exposed and unexposed silver bromide grains are surrounded by –ve charge barrier of bromine ions employed during emulsion manufacture.

Chemical Action of Developer cont..

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 chemical used

Chemical Action of Developer cont..

• 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

Chemical Action of Developer cont..

Silver ions by obtaining electrons converted into metallic silver The charge silver bromide protects silver bromide from attack by electrons in developing solution Exposed silver bromide grains possess a weakness in the charge barrier caused by the presence of neutral silver atoms which have collected at the sensitivity speck

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 Bromine 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

CONSTITUTION OF DEVELOPER SOLUTION

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 The developer in automatic processing and manual processing are different in several aspects Developer replenisher

• +
• Starter
• =

Working developer

CONSTITUENTS OF DEVELOPER REPLENISHER SOLUTION

• Solvent
• Developing agent
• Accelerator
• Buffers
• Restrainers
• Preservative
• Hardener

Sequestering agents

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)

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

DEVELOPING AGENTS

• No Single reducing agent which satisfies all of these requirements
• Therefore combinations are used
• METOL & HYDROQUINONE (MQ) were use in early manual developers

PHENIDONE & HYDROQUINONE (PQ) are used in modern automatic processing

DEVELOPING AGENTS Cont ..

• PHENIDONE = 1-pheyl-3-pyrazolidone
• Quick acting
• Selectivity low
• Mildly sensitive to bromine ion in concentration

Produces low contrast characteristics

DEVELOPING AGENTS Cont ..

• HYDROQUINONE =benzene–1, 4-diol
• 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

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 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 20-30 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

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 Tolerance of increase in bromine ion concentration High selectivity and low chemical fog Adequate activity even in low concentration

Advantages of PQ Developer cont…

• Available in liquid concentration form
• Fast acting permitting complete development in 20-30 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

SUPER-ADDITIVE EFFECT

The shape of the characteristic curve is controlled by the two developing agents

• Hydroquinone only
• Phenidone only
• Combine effect
• Optical density

Exposure

developer…. ACCELERATORS

• PQ developers need an alkaline medium to operate (pH between 9.8- 11.4)
• 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

developer…. Accelerators cont…

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

developer…. 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

developer…. RESTRAINERS

• Restrainer

Modifies the behavior 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 antifogging

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

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

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

OTHER CONSTITUENTS

Bactericides & Fungicides – These inhibit the growth of organisms in the solution and in containing vessels.

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

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

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 Therefore the developer has to be replenished continuously if the activity is to be maintained

EFFICIENCY OF DEVELOPMENT & FACTORS AFFECTING DEVELOPMENT

• 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
• Evaporation
• Gelatin of emulsion absorption
• Developer adhering to the film surface

The replenishment compensates for this too

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

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

EFFECT OF INCREASE OF TEMPERATURE

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

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

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 ——– 130 s
• 3 ½ m ——- 68 s
• 110 s ——— 30 s

90 s ———- 26 s

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

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
• Constant temperature

Constant time

KEY POINTS

DEVELOPER CHEMISTRY FOR AUTOMATIC PROCESSOR

Provides required alkalinity for reducing agents

KEY POINTS

• DEVELOPER CHEMISTRY FOR AUTOMATIC PROCESSOR. Cont…

FIXING (FIXATION)

• It has four major functions

To stop further development

To fix the image i.e. Render it chemically stable so that it does not undergo further changes and no longer photosensitive To complete the process of hardening of the film emulsion To clear the image by removing the remaining silver halide from the emulsion

Fixing (fixation), cont…

STOPPING FURTHER DEVELOPMENT

Achieved by making the fixing solution acidic (pH between 4.0-4.5) Phenidone hydroquinone developing agents only operate in an alkaline environment; thus any further development is inhibited as film enters the fixing solution Intermediate rinsing stage between developing and fixing fulfils this function in manual processing

Fixing (fixation), cont…

FIXING THE IMAGE:- Process of clearing is also the process of fixing the image HARDENING THE EMULSION:-Ensures the gelatine does not absorb too much water and thus minimizes drying time.

Also toughness emulsion and protect it from chemical damage during washing & drying stages of processing.

Fixing (fixation), cont…

CLEANING THE IMAGE:- Only about 40% of silver halide in the film emulsion is converted to silver during development During process of fixation the undeveloped halide grains 60% are converted into soluble compounds which then dissolved out of the emulsion into fixing solution. Thus the unexposed parts of the image become transparent and milky appearance is lost Clearing time is the time taken for the image to lose its milky appearance

CONSTITUENTS OF FIXING SOLUTION

• Solvent
• Fixing agents
• Acid
• Hardener
• Buffer
• Preservative

Anti- sluing agent

Constituents of Fixing Solution cont…

• SOLVENT :- Water is the solvent and diluents used in fixing solution
• Acts as a carrying medium for the active constituent in fixer

Provides a means of controlling the activity by diluting its effects FIXING AGENTS:- Are chemical which combine with insoluble halide in the film emulsion to form solution compounds which diffuse and can be washed out of the emulsion Ammonium thiosulphate is supplied in liquid concentration while Sodium thiosulphate is in powder form and used in manual processing

Constituents of Fixing Solution cont…

CHEMICAL REACTION THAT OCCURS IN FIXER

Silver bromide + Ammonium thiosulphate > Ammonium salt of monogento- dithio- sulphuric acid + Ammonium bromide = Compounds formed are soluble in water and be removed by washing.

Silver bromide + sodium thisulphate > sodium salt of monoargento- diothio- sulphuric acid + sodium bromide = Compound formed is soluble in water and can be removed by washing

Constituents of Fixing Solution, Chemical reaction cont…

ADVANTAGES OF AMMONIUM THIOSULPHATE OVER THE SODIUM THIOSULPHATE

• Highly soluble, thus its available in liquid concentration
• Highly active , thus fixing can be done rapidly e.g. 15sec in 90 sec processing cycle

Its by-products are highly soluble hence readily washed out of the film emulsion

Constituents of Fixing Solution cont…ACID

ACID :- Stops development as soon as film enters the fixer Avoid staining of the image dichronic fog –which give yellow green blue tinged stain when the image is viewed by reflecting light and tinged pink when view by transmitted light.

• Also provide suitable environment for the hardening agent to fixer.

Acetic acid is used; pH 4.0-4.5

Constituents of Fixing Solution cont…HARDENER

HARDENER

• Limit water uptake by emulsion layer: hence
• reduces drying time

prevents physical damage to the emulsion surface

Constituents of Fixing Solution, Hardener cont…

THREE HARDENING AGENTS USED FOR FIXING

Chrome alum (chrome potassium alum)

• Its efficiency last for few days; whether in use or not. Therefore it’s suitable be used soon after preparation
• Works better in pH range of 3.5- 4.7 low pH cause sulphurization- process of sulphur

Constituents of Fixing Solution, Hardener cont…

• It retains its hardening properties well with time
• Works well at higher pH from 4.5-4.9
• pH beyond 5.5 causes precipitate of aluminium hydroxide with potassium alum hardener ( a white bloom) may appear on film

Constituents of Fixing Solution, Hardener cont…

• Used with rapid ammonium thiousulphate fixers and allows hardening to be completed in very short time

-The optimum pH for hardening action is 4.1 to 4.4

Constituents of Fixing Solution, BUFFER

• Buffer prevents sulphurization
• ii) Ensure neutralization of developer

iii) Maintain optimum hardener activity Fixing solution should be buffered against neutralization effect of alkaline developing solution carried by films from the developing tank Chemical used is Sodium acetate with Acetic acid Manual processing rinse reduces developer carry-over into fixing solution.

Constituents of Fixing Solution, PRESERVATIVE

Preservative slows down the decomposition of thiosulphate delays the onset of sulphurization Chemical in use is Sodium sulphite

Constituents of Fixing Solution, ANTI-SLUDGING AGENT

Aluminium salts used as a hardener have tendency to produce insoluble aluminium compound, which precipitate out of solution and form sludge which adhere to the films & to the side of the fixing tank To reduce the formation of sludge BORIC ACID is included as an anti sludging agent

Fixing, cont… FACTORS AFFECTING FIXATION

• The process of fixing a film material occurs in three stages
• The fixing solution diffuses into the film emulsion

The fixing agent reacts chemically with the silver halides in the emulsion The resulting soluble silver complexes and halide dissolve and begin to diffuse out of the emulsion

Fixing, cont… FACTORS INFLUENCING QUANTITY & QUALITY OF FIXING

• Constitution of fixing solution
• Fixer temperature

Fixing time

Fixing…Factors Influencing Quantity & Quality of Fixing: 1.FIXER CONSTITUTION

• CONSTITUTION OF FIXING SOLUTION

The activity of fixer at a given temperature depends on a number of aspects relating the chemical composition of the fixing solution Choice of fixing agents:- Ammonium thiosulphate gives a rapid acting higher energy fixer

Fixing… Factors Influencing Quantity & Quality of Fixing…1.Constitution cont…

• Concentration of fixing agent in solution:- Activity

increases with concentration

As film pass through fixing tank fixing agent is used up in the reaction with silver halides Fixing agent is also lost due to carry over of fixing solution during the transfer of films to wash tank.

Fixing… Factors Influencing Quantity & Quality of Fixing…1.Constitution cont…

Presence of hardener:- Slows down the fixing process but speeds up the drying process Presence of soluble silver complexes:- As films are fixed ammonium argento-thiosulphite (silver complexes) accumulate in the fixing solution. They release silver ions into the solution which slow action of fixing agents. This can be corrected by replenishment

Fixing… Factors Influencing Quantity & Quality of Fixing…1. Constitution cont…

Presence of soluble halides:- Soluble ammonium halides accumulate in the fixing solution; their presence slow down the action of fixing agents.

Controlled by replenishment of fixer, hence maintaining fixer activity

Fixing… Factors Influencing Quantity & Quality of Fixing…1.Constitution cont…

pH of fixing solution:- carry over of alkaline developing solution tend to neutralize the acid fixer, causing pH to rise Buffering chemicals resist this tendency.

Fixer replenishment ensures that lost chemicals are replaced and contaminated removed hence optimum quality films are produced

Fixing… Factors Influencing Quantity & Quality of Fixing…2. FIXER TEMPERATURE

• FIXER TEMPERATURE

Activity of fixing agents increase with temperature and at higher temperatures diffusion processes are more rapid Too great difference in temperature between developer and fixer results in film reticulation (cracking of film)

Fixing… Factors Influencing Quantity & Quality of Fixing…3. FIXING TIME

• FIXING TIME

During passage of film through fixing solution, developer must diffuse out of the film whilst the fixer must diffuse into the film and processes of clearing and hardening must be completed In a 90s automatic processing cycle, 15s are for the fixing stage.

In manual processing, fixing time is as long as 5 minutes

Fixing… Factors Influencing Quantity & Quality of Fixing…3. Fixing Time cont…

FACTORS DETERMINING FIXING TIME

Fixer activity:- the higher the fixer activity is the required fixing time Type of film emulsion:- rapid process film incorporate thin emulsion which can be penetrated rapidly by processing chemicals

Fixing… Factors Influencing Quantity & Quality of Fixing…3. Fixing Time , Determining Factors cont…

Agitation of film:- Vigorous agitation accelerates fixation by speeding the removal of by-products from the film emulsion and their replacement with fresh fixer

Fixing… MAINTENANCE OF FIXER VOLUME

Loss and gain of volume of fixing solution:

When film leaves fixing tank small volume is lost due to carry over and similar volume of solution is gained due to carry over on film entering tank from developer.

Net change in volume of fixer solution is not significant Other fluid losses are from evaporation and deliberate bleeding off of solution to remove contaminants.

Fixer Replenishment must make good these losses.

Fixing… FACTORS AFFECTING FIXER REPLENISHMENT RATE

Volume of replenisher required to maintain fixer activity depends upon number of factors:

AREA OF FILM PROCESSED:- The volume of replenishment required is proportional to the area of film & also the size and number of films processed

Fixing… FACTORS AFFECTING FIXER REPLENISHMENT RATE

TYPE OF EMULSION:- More fixing agent is needed to process direct exposure x ray film than screen type because the emulsion has a higher coating weight TYPE OF IMAGE:- A lightly exposed film contain more unexposed silver halide grains than a similar film which has received greater exposure.

Thus after development there is more silver halide to be cleared , more fixing agent is used and more fixer replenisher is necessary.

KEY POINTS

FIXER CHEMISTRY FOR AN AUTOMATIC PROCESSOR

RINSING, WASHING & DRYING

Film leaving fixer is contaminated with Silver Complexes and Ammonium halides. If not removed:

• Chemicals acquire yellowish-brown sulphur stain during storage.
• Dissolved salts may crystallize out onto film surface.

Tap water is satisfactory for soluble chemicals to dissolve out of emulsion.

RINSING, WASHING & DRYING: 1. RINSING

Stage in the processing cycle which is between development and fixing in manual processing is called Rinzing or Intermediate Stop Bath.

PRESENCE OF DEVELOPING AGENTS IN FIXING BATH RESULTS IN:-

• Dichroic fog
• Increased alkalinity of the fixing bath

Brown stain which result from oxidized developer

Rinsing, Washing & Drying: Rinsing cont…

PURPOSE OF INTERMEDIATE STAGE IN MANUAL PROCESSING ARE

• Slow action and remove developer from surface of film
• Stop action of the developer by neutralizing effect (Achieved by putting film in an acid solution e.g. Acid stop bath

Rinsing, Washing & Drying: Rinsing cont…

PLAIN RINSE CAN BE:

• A static bath- Just tank full of water

A spray rinse –Fresh water provided by a number of jet directed on the film Running rinse- Flow of water through tank, water entering at lower level and leaving at top

Rinsing, Washing & Drying: 2. WASHING

WASHING

• In automatic processing, the film out of fixing bath carries in its emulsion layer
• Argento- thiosulphate which has been formed in the chemical action of the fixer
• Residual fixing agent

Remaining salts which are other constituents of fixing bath

Rinsing, Washing & Drying: 2. WASHING

Without washing:

Colourless argento-thiosulphate decomposes after a while to forms silver sulphide which produces yellow brown stain Residual fixing agent decomposes and produces substances which attack silver image and form silver sulphide results in yellow brown stain and loss of image Residual salts crystallizes on film surface making interpretation difficult.

N/B Tap water wash controls Yellow brown sulphur stain

RINSING, WASHING & DRYING

DIFFUSION Transfer by diffusion of chemical from the emulsion gelatin to wash water occur in the concentration gradient WASHING EFFICIENCY:-The level of contamination should be reduced to the point where no image staining occur.

In 90 sec cycle processing, about 15 sec is allowed for washing stage while in manual processing 10 min

Rinsing, Washing & Drying: 2. Washing: FACTORS AFFECTING WASHING EFFICIENCY

Film emulsion:- Thick emulsion takes longer to wash than thin one Hardening of emulsion inhibit diffusion but also shortens diffusion path by reducing emulsion thickness

• Condition of fixing solution :- To avoid inadequate washing it is important to maintain fixer in optimum condition by correct replenishment
• Condition of washing water:- Wash water should be replaced frequently with fresh water

Rinsing, Washing & Drying: 2. Washing: FACTORS AFFECTING WASHING EFFICIENCY

• Agitation:- Ensure fresh water is being forced against the emulsion surface and contaminated water carried away.

This maintain concentration gradient needed and its efficient diffusion

• Washing time:- Duration taken for level of residual contaminants in a film emulsion to be reduced to acceptable level
• Temperature of wash water:- washing efficiency increases with temperature because surface tension of water is reduced and its penetration into emulsion is accelerated

Rinsing, Washing & Drying: 3. DRYING

DRYING is the final stage in processing of radiograph during which all water surface and most of that retained in the emulsion is reduced to 10-15% In automatic processing surface water is removed by squeegee rollers while evaporation removes water from emulsion In 90sec processing cycle 25sec is allowed for drying stage

Rinsing, Washing & Drying: 3. Drying, cont…

• Three important feature in drying photographic film
• The temperature of the air
• The humidity of the air

The flow of air past the emulsion

Raising temperature of the air increases the rate at which moisture evaporates from gelatin and thus shortens drying time Drying temperature is governed by:-

• amount of drying to be done
• length of drying time

Rinsing, Washing & Drying: 3. Drying, FACTORS ON DRYING TIME

FACTORS AFFECTING DRYING TIME: Wetness of Emulsion and Drying conditions The wetness of the emulsion:- Volume of water retained in the emulsion per unit area of its surface depends on:

• Hardness of emulsion – hardened emulsion retains less water than a soft emulsion and therefore can be dried quickly
• Emulsion thickness- thin emulsion retain less water than thick one. Direct exposure x-ray film takes longer to dry than screen type of x-ray film

Rinsing, Washing & Drying: 3. Drying… Factors on Drying Time cont…

The drying medium is air.

The speed at which air can evaporate moisture from the emulsion depends upon: Humidity, Temperature and Circulation.

• Air humidity:- Dry air accelerates the evaporation process and reduces drying time. Relative humidity should not be greater than 60%

Rinsing, Washing & Drying: 3. Drying… Factors on Drying Time cont…

• Air temperature:- Heated air can retain more moisture than cold air and therefore more effective drying medium. Air temperature should be between 40 & 60%
• Air circulation:- As moisture evaporates from the emulsion air around the emulsion becomes more humid; this humid air should be replaced with drier air by using an air circulation system.

PROCESSING STAGES

• Manual
• processing
• Development
• Rinsing
• Fixing
• Washing
• Drying
• Automatic
• Processing
• Development
• Fixing
• Washing

Drying

MANUAL FILM PROCESSING

The processing of radiographs involves a number of chemical reactions and changes, which must take place under carefully controlled conditions if a satisfactory radiograph is to be produced.

Such factors as location and construction of the processing room, good organization of the materials to be used, efficient use of the room and the x-ray specialist's skills, and satisfactory adjustment to adverse environmental conditions enter into the efficient production of satisfactory radiographs

Manual Film Processing, cont….

Manual procedure of processing a radiograph:

Refers to the processing time, the period during which one film passes through the processor This period begins with insertion of film to the processor as unprocessed film and complete when dry processed film.

Manual Film Processing…THE CYCLE

Development is usually 4min at 20ºc variation are determined by a time temperature graph and the optimum temperature depends upon type of developer used Above 24ºc, reduction in radiographic contrast reaches unacceptable limits with uneven development and emulsion damage.

Manual Film Processing…The Cycle cont…

Film should be Drained for some few seconds before using spray rinse. This avoids an excessive carrying rate A Spray Rinse is used for 5-6 seconds with film immersed in spray, this removes surface developer from film before being immersed in fixer.

Manual Film Processing…The Cycle cont…

Film is then Fixed for 10 min immersed in fixing bath, but variation of time depends upon factors such as fixer type, concentration, agitation , degree of exhaustion and temperature Film should be drained for some few seconds, to avoids an excessive carrying rate

Manual Film Processing…The Cycle cont…

Film is the Washed in running water for 10-30mins. The length of time depends upon water flow rate and temperature.

Finally film is Dried in cabinet for about 20min. This can be shortened by use of wetting agent.

Wetting agent reduces fluid on the film surface hence reducing drying time

FILM DEVELOPMENT IN MANUAL PROCESSING CONT.

Manual Film Processing…STOP BATH/RINSING

• From the developer the film is placed in an acid stop bath and then rinsed in water.

Stop bath 0.04 % acid ( weak acid).

When the film is removed from the developer the gelatin emulsion is soft and swollen and contains chemicals which are removed by placing the film in a water bath.

Manual Film Processing…Rinsing/Stop Bath, cont…

By rinsing the film in the water the soluble chemicals are removed, the development reaction is stopped, and the alkalinity of the residual developer is reduced.

The unexposed silver halide crystals are not water soluble and will not be washed away.

Manual Film Processing…Rinsing/Stop Bath, cont…

The film should be rinsed for 10-15 seconds in a bath of fresh, running water.

The temperature of the water must be as close as possible to the temperature of the developer and fixer to avoid reticulation – uneven expansion and contractions of the emulsion layer.

Manual Film Processing…Rinsing/Stop Bath, cont…

If this step were omitted, the alkaline developer retained by the film would soon neutralize the acid of the fixer.

The fixing and hardening action of the fixer would be impaired and as a result, brown stains will be produced on the radiograph within a few weeks.

Manual Film Processing…Rinsing/Stop Bath, cont…

Because the emulsion layer (gelatin) is soft when wet, the film scratches easily.

Safe-light conditions must be maintained when transferring the film from the developer to the wash tank and then to the fixing tank to avoid fogging

Manual Film Processing…REPLENISHMENT

Replenishment is used in photographic film and paper processing, where fresh chemistry is used to replace exhausted chemistry in a continuous or per-batch fashion.

Replenishment rates are calculated by the quantity of film processed in each individual bath; and additionally by the amount of film push-processed

Manual Film Processing…REPLENISHMENT

KEY POINTS

• Manual processing

Should contain developing agents with high concentration.

Developer replenisher should contain a high concentration of alkali, so the need of adding sodium hydroxide, extra sulphite (preservative) and also carbonate (hardener)