Latent image formation l defects in crystal l Radiographic film part-2 lRadiography Simplified l

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Radiographic film part - 1

   • Radiographic / x- Ray films l construction...  


I am posting a video on latent images formation and crystal defects.

emulsion is a homogenous mixture of gelatin and silver halide crystal.

It is light sensitive material.

Silver halide crystal contain 90 99% silver bromide and 1 10% silver iodide.

it is formed from the ions silver, ion of bromine & ions of iodine arrange in cubic lattice

crystal defects-: variation in regular arrangement of atom and molecules of a crystal.

1) point defects-: if a silver ion move out of its normal position in the crystal lattice it create point defect these interstitial silver ions may move in the crystal.

2) linear defects -: it cause when crystal contain misaligned planes of atoms they are referred as dislocation . since atom are dislocated from their normal position in the lattice .
Dislocation is line imperfection in the crystal.
iodine ions strain the crystal in this way.

3) chemical sensitization-: allylthiourea is a sulphur containing compound when mixed with emulsion it produces chemical sensitization.

Which react with silver halide to form silver sulphide.

silver sulphide is usually located on the surface of crystal and is called sensitivity centre.

this sensitivity centre trap the electron and begin the formation of latent image.

Latent image :- when x-ray film is exposed from the light Photon from intensifying screen it creates and invisible image on the radiographic film called latent image.

In this process the light from the intensifying screen strike the crystal and bromine iron absorb the photon and release electron and converted into bromine atom and moves to gelatin/ emulsion.these liberated electron trapped at the the sensitivity centre and sensitivity centre acquired negative charge the negative charge.
sensitivity centre start attracting free silver iron and convert them into neutral metallic silver atom and this process is repeated many time and more and more silver ion is converted into metallic silver atom.

Accumulation of these metallic silver atom result in the formation of invisible image called latent image.

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