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LATENT IMAGE FORMATION

LATENT IMAGE FORMATION. by: Prof. Susan A. Olavidez. Last Revised: June 2004. LATENT IMAGE. Invisible image produced on the film after exposure prior to development. Latent image can only be visible through the development process.

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LATENT IMAGE FORMATION

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  1. LATENT IMAGE FORMATION by: Prof. Susan A. Olavidez Last Revised: June 2004

  2. LATENT IMAGE • Invisible image produced on the film after exposure prior to development. • Latent image can only be visible through the development process. • The production of latent image is the first step of the photochemical process.

  3. REVIEW OF EMULSION AND SILVER BROMIDE AgNO3 + KBr = AgBr + KNO3

  4. REVIEW OF EMULSION AND SILVER BROMIDE • Emulsion is a suspension of silver bromide and certain impurities in gelatin. • AgBr is formed by reacting AgNO3 and KBr. • During manufacturing process, the silver and the bromide becomes an ion. • ION - an atom that has either many or few electrons than the protons. • The unlike charges of the two ions causes the formation of what is known as the univalent ionic cubical lattice.

  5. REVIEW OF EMULSION AND SILVER BROMIDE • In unexposed silver halide crystal the bromine ions usually occupy the surface of the crystal and the silver ions the center of the crystal. And somewhere in the crystal there are electrons traps (sensitivity speck) caused by gelatin.

  6. MECHANISMS OF LATENT IMAGE FORMATION • Effects of Exposure • photoelectric effect • Compton effect • Nucleation Process • Gurney Mott Theory • Mitchell Theory • Growth Process

  7. EFFECTS OF EXPOSURE • Photons interact through photoelectric and Compton interaction. • Interactions usually occur at the bromine ions since they are located at the surface of the crystal.

  8. EFFECTS OF EXPOSURE • Photons interact through photoelectric and Compton interaction. • Interactions usually occur at the bromine ions since they are located at the surface of the crystal. • Both interaction releases high energy electrons.

  9. EFFECTS OF EXPOSURE • Photons interact through photoelectric and Compton interaction. • Interactions usually occur at the bromine ions since they are located at the surface of the crystal. • Both interaction releases high energy electrons. • Bromine ions becomes neutral and they migrate out of the crystal into the gelatin.

  10. EFFECTS OF EXPOSURE • The process disrupted the crystal lattice formation. • Ions in the crystal are now free to migrate and move around. • Bromide migrate out of the crystal leaving the silver ion, free electron and electron trap in the crystal Unexposed Crystal Exposed Crystal

  11. NUCLEATION PROCESSGurney Mott Theory • An electron that has been released by exposure is captured by a trapping center and temporarily localized.

  12. NUCLEATION PROCESSGurney Mott Theory • A mobile positively charge silver ion may migrate to this center and form a silver atom when combined with the electron.

  13. NUCLEATION PROCESSGurney Mott Theory • Unfortunately, a single silver atom is unstable, separation occurs and stage one and two happen again.

  14. NUCLEATION PROCESSGurney Mott Theory • Fortunately, during its short life the single silver atom can act as a trap for another electron, and if another silver ion is attracted to this site ...

  15. NUCLEATION PROCESSGurney Mott Theory • A stable-atom speck is formed and is called a latent sub-image center.

  16. NUCLEATION PROCESSMitchell Theory • A free silver ion comes near to a shallow electron trap and deepens it.

  17. NUCLEATION PROCESSMitchell Theory • A free electron, released by exposure, and a silver ion approach the trap together and immediately form a silver atom. This is called a pre-image center

  18. NUCLEATION PROCESSMitchell Theory • Unfortunately, as in Gurney-Mott theory, the single silver atom is unstable, and it dissociates into a silver ion and electron.

  19. NUCLEATION PROCESSMitchell Theory • Fortunately, the single silver atom acquire a second silver ion. And a free electron arrives before the escape of this second silver ion, thus ...

  20. NUCLEATION PROCESSMitchell Theory • A stable-atom speck is formed and is called a latent sub-image center.

  21. GROWTH PROCESS • Growth is the enlargement of sub-image center until it becomes development centers (at least 10 silver atoms).

  22. THANK YOU 

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