Under what circumstances should a collimator be used during radiographic operations?

The use of a collimator in radiographic operations is essential for directing the radiation beam precisely to the area of interest while limiting exposure to surrounding areas. This is crucial for both radiographic quality and minimizing unnecessary radiation dose to personnel and the public. Option B, indicating that a collimator should be used at all times except when physically impossible, reflects best practices in radiation safety and operational efficiency.

A collimator allows for better image quality by reducing scatter radiation and enhancing contrast in the radiographic image. Using a collimator contributes to safety protocols by ensuring that only the necessary area is irradiated, thus protecting more significant portions of the environment and any individuals who may be nearby.

The other options are not aligned with best safety practices. While audits may prompt scrutiny over safety measures, the necessity of a collimator extends beyond just compliance during audits. The statement concerning cobalt and iridium sources inaccurately suggests that the use of collimators is limited to specific types of radioactive sources—this is not the case, as all radiographic operations can benefit safely from collimation regardless of the source in use.