Image Receptors 2 Flashcards
what is the purpose of the films outer plastic?
keeps film dry, saliva free
protects film from light damage and fogging
ensures orientation is correct
what is the purpose of the film black paper?
protects film from light leakage
stiffens and supports film
prevents crimp and pressure mark
what is the purpose of the lead foil?
composed of mixture of lead/aluminium
readily absorbs xrays
prevents back scatter
has distinct pattern embossed in lead
film components?
base - plastic - polyester blue antiglare tint adhesive layer double emulsion protective gelatin layer
what is in the emulsion?
silver halide crystals in gelatin
silver bromide/silver iodide/combo of two
gelatin allows even distribution
gelatin absorbs liquid readily allowing processing
what is the purpose of the adhesive layer?
sticks emulsion to base
what does the super coat provide?
additional gelatin protective layer
how is an image produced on film?
xrays hit silver halide crystals in emulsion
silver halide crystal becomes sensitised
latent image produced
what is a latent image?
a pattern produced in the emusion by the sensitising of the crystals by xrays
not visible to the naked eye but becomes visible by chemical reactions during processing
what is the main reaction during processing?
the reduction of silver bromide crystals to black metallic silver
what is the film speed?
the sensitivity of the film to the xrays
larger crystals = larger speed
what would the dose be like for a fast film?
lower amount of xrays required to produce the film
what size of crystals give reduced detail?
large crystals/ fast film
what are the layers of an intensifying screen?
base, reflective layer, phosphor layer, supercoat
what is the base layer made from?
polyester
what happens in the phosphor layer?
fluorescent phopshors emit light when excited by xrays
what is the purpose of the supercoat?
protects phosphor layer from damage
what is the consequence of the reduced dose used?
less detail
sequence of image production in indirect film?
xray hits phosphor crystal in intensifying screen and gives off light
light hits silver halide crystals in film emulstion
silver halide crystals are sensitised
latent image
what is the light produced from the intensifying screen in proportion to?
directly proportional to the energy in the xray phtoton
how to store film?
how to prevent use of old film?
cool dry place away from radiation
stockroom rotation
3 methods of film processing?
automatic, manual, instant
steps of processing?
develop - make latent image vis. wash - remove developer from film fix - make image permanent wash - stop fix and remove residual layer dry - easier handled, prevent damage
stages in a automatic processor?
feed in rollers developer rack fixer rack wash rack dryer
what stages in the automatic processor uses squeeze rollers?
developer rack, fixer rack, wash rack
what happens during developing?
sensitised halide crystals are acted upon by developing agents, phenidore and hydroquinone
reduction of silver bromide to silver +bromide
what are the activator agents?
calcium carbonate - controls activity of developing agents
what is the restrainer agent?
potassium bromide - stops development of unexposed crystals
preservative agent?
sodium sulphite- slows down oxidation
solvent?
water
what is the temp of a developer?
each developer has its own optimum working temperature
too long in developer?
too short in developer?
dark
light
too hot in developer?
too cold in developer?
dark
light
concentration too strong?
too weak?
dark
light
what does the fixing agent do?
fixing agents change unexposed silver halide to soluble compound so they can washed away
acid maintains the pH and neutralises the developer
what is the cleaning agent?
ammonium thiosulphate
what is the acidifier?
acetic acid - maintains pH
what is the hardener?
aluminium chloride
what is the preservative?
sodium sulphite
an over fixed image?
image is removed from the film
an under fixed image?
green tinge- does not archive
when does wash happen in a manual processer?
automatic processer?
dev/fix, fix/dry
between fix and dry
what does wash do?
stops action of developer, reduces carry over of material
removes unexposed crystals once made soluble by the fixer
what happens when there’s insufficient washing?
film will feel tacky
green/silver appearance
dont archive well - image deteriorates
drying film reduces possibility of what?
damage to emulsion
why is an automatic processor good?
its consistent
less operator dependent
temp controlled, time controlled
less damage to film
why is a manual process good
downsides?
done well = as good as automatic
very operator dependent, time needs to be accurate
advantages of instant processor?
disadvantages of instant processor?
quick, convenient
large amount of chemicals to be disposed of, films dont archive well
what is COSHH?
control of substances hazardous to health regulation
danger with fixer?
corrosive and can release sulphur dioxide/ammonia on contact with strong acid/alkali
make sure what is in place when using a processor?
ventilation - 10 room volumes/hour
