Answers to revision questions

Chapter 9: Radiographic Film

1. Draw a diagram of a duplitised film.

This should be similar to Figure 9.1.

2. What are the structural differences between duplitised and single-sided film?

Duplitised film has two emulsion layers and supercoat layers, one on each side of the base.

The single-sided film has emulsion and supercoat on one side and an anti-halation and anti-curl layer on the other.

3. Why is gelatine used as the support for the silver halide crystals in the emulsion?

Gelatine is a liquid allowing, it to be spread evenly over the base during manufacture. It will absorb water allowing the chemicals to penetrate during processing and can then be dried to give a protective layer after processing.

4. How is the emulsion of a film sensitised?

The x-ray beam or light from the intensifying screens strike the film. This causes the silver and bromine to react forming a latent image.

5. What is halation?

Halation is the back scatter of light after it has passed through the film. This can have a detrimental effect on image quality.

6. Why should an animal be anaesthetised when using a non-screen film?

Non-screen film relies on x-rays alone to form an image. This requires a longer exposure time. This increase in exposure time gives a longer period of time for movement to occur. The film needs to be placed in the mouth and to ensure the patient does not bite through the envelope they should be fully anaesthatised.

7. What other types of film are available beyond conventional duplitised film?

Single-sided, dental film, non-screen film, film monitoring, Polaroid film, duplication film.

8. How should radiographic film be stored?

In the box, upright, cool, dark storage away from chemicals and radiation.

9. Outline the four stages of the silver halide reaction.

  • The interaction of light or x-rays with the crystal will result in the release of electrons.
  • The electron will migrate to the sensitivity speck within the crystal. This will allow the formation of metallic silver at the sensitivity speck with negative bromine atoms being released. The will be repeated every time the crystal is exposed to light. Eventually the negative surface charge of the bromine will disappear and the amount of silver in the crystal will increase.
  • This collection of silver atoms is the latent image.
  • The remaining silver halide will be converted during processing to a visible image.

12. What is film speed?

The sensitivity of film to light or radiation.

Fast films require less exposure to give a similar film using a slow film.