What is the minimum gamma and/or neutron radiation dose rate that requires posting a radioactive sign?

The correct choice indicates the minimum gamma and/or neutron radiation dose rate that necessitates the posting of a radioactive sign as per regulatory standards. A dose rate of 2.5 mrem at 30 cm is significant because it represents a threshold established to protect individuals from potential radiation exposure. Regulatory agencies set these thresholds based on studies that assess the risk of radiation exposure to workers and the public.

At this level, the radiation exposure is acknowledged to be sufficiently above background levels, warranting a cautionary approach that includes signage to inform individuals of the elevated radiation presence. This serves both a safety and regulatory compliance purpose, ensuring those in the vicinity are made aware of potential hazards.

The other dose rates provided do not meet the threshold established by regulations for mandatory signage. A lower dose rate may not adequately inform individuals about the potential risks associated with exposure. By establishing a requirement at 2.5 mrem, regulatory bodies ensure that adequate precautionary measures are taken to protect individuals from unnecessary exposure to radiation in environments where it is present.