Final answer:
Radiographic density decreases as intensifying screen speed decreases because slower screens convert less radiation into light photons needed to expose the film.
Step-by-step explanation:
With a given exposure, as intensifying screen speed decreases, radiographic density decreases. Intensifying screens are used in radiography to enhance the effect of X-ray photons by converting them into a larger number of light photons, which in turn expose the radiographic film. A faster screen requires less radiation to produce an image, thus when a screen with a slower speed is used, it requires more radiation to achieve the same density on the film.
As a result, with a given fixed exposure, using a slower screen speed means fewer light photons are created, leading to a lower density on the film. This is because the density of the radiograph is directly related to the amount of radiation that reaches the film, and a slower screen converts less radiation into light photons needed to expose the film.