Final answer:
The interaction of radioactive particles with photographic emulsion results in tiny black silver grains in the emulsion after development, which form images as dark spots corresponding to the radiation exposure.
Step-by-step explanation:
When a photographic emulsion is brought into close contact with a radioactive source in a specimen, the particles emitted by the source interact with the emulsion. This interaction involves a quantum of energy from a radioactive particle which chemically alters the emulsion, leading to the development of the film. Specifically, the correct answer to what happens is option B) The particles emitted by the source leave tiny, black silver grains in the emulsion after photographic development. Silver is reduced from radiation-sensitive silver compounds in the emulsion to create images in the form of dark spots. This process was first observed by Henri Becquerel in 1896 and is the basis for the use of photographic film as a detector of ionizing radiation.