Final answer:
Phenidone and hydroquinone are photographic developers that produce optical density on a radiograph. Phenidone works rapidly to reduce exposed silver halide grains to metallic silver while hydroquinone enhances image density and contrast. The film darkening reflects the amount of exposure and the type of radiation used.
Step-by-step explanation:
The action of phenidone and hydroquinone in producing optical density on a radiograph is central to photographic development. Phenidone is known as a developing agent that works rapidly to reduce silver halide grains within the film's emulsion, which are exposed to radiation, into metallic silver. Hydroquinone, on the other hand, contributes to image density and contrast by working more slowly compared to phenidone but producing more intense darkening in the areas where it acts. During radiographic processing, the exposed silver halide grains absorb photons and ionize, initiating the chemical change within the film. However, the process is not flawless, as not all incident radiation interacts with the film, and not all interactions lead to the desired chemical change.
The resulting optical density on the radiograph relates to the amount of exposure and the type of radiation used. The darkening, or film darkening, also depends on such factors. As x-rays penetrate different densities of material, they produce varying degrees of ionization and therefore differing levels of darkening on the radiograph, which helps in detecting physiological structures like bone fractures or tumors with distinct density from their surroundings. Phenidone and hydroquinone work in conjunction to develop these varying shades of gray that comprise the final radiographic image.