At what distance must the perimeter of the Restricted Area be posted when using an unshielded 20 Cis Cobalt 60 source?

The correct response indicates that the perimeter of the Restricted Area must be posted at a distance of 15.3 feet when using an unshielded 20 Curies (Cis) Cobalt-60 source. This distance is determined by evaluating the radiation exposure limits for personnel and members of the public to ensure safety and compliance with regulatory requirements.

Cobalt-60 is a gamma radiation source, which has a significant penetrating power. The specified distance (15.3 feet) is based on the dose rate at which access to the area should be restricted to prevent individuals from receiving radiation doses exceeding permissible levels. By posting the perimeter of the Restricted Area at this calculated distance, it effectively reduces the potential risk of exposure to workers and the public, aligning with safety protocols and guidelines established in radiography practices.

This specific measurement reflects the importance of adhering to regulatory safety thresholds, ensuring that the radiological environment is managed correctly to protect all individuals potentially affected by the radiation source.