Which of the following factors is NOT relevant to the exposure rate of gamma radiation?

The exposure rate of gamma radiation is influenced by several critical factors, specifically those that can alter the intensity of the radiation reaching an individual or a detector. Among the choices provided, the type of developing solution used is not relevant to the exposure rate.

Distance from the source plays a significant role based on the inverse square law, which states that as the distance from a radiation source increases, the exposure rate decreases exponentially. This is a foundational concept in radiation safety.

Shielding material is also highly relevant; different materials absorb or block gamma radiation to varying degrees. The effectiveness of shielding is a key aspect of radiation protection planning.

Source activity relates to the amount of radiation produced by the source over time. The higher the activity, the more radiation is emitted, thereby increasing the exposure rate experienced.

In contrast, the type of developing solution used pertains to the processing of radiographic films, not to the exposure rate of gamma radiation itself. This means it does not influence how much gamma radiation is present or the potential exposure to it. Hence, the correct response identifies that developing solution has no impact on the exposure rate of gamma radiation.