According to NRC regulations, what sign should be posted if radiation levels are measured at 7.5 mR/hr?

The correct signage for radiation levels measured at 7.5 mR/hr is "Caution: Radiation Area." According to the Nuclear Regulatory Commission (NRC) regulations, a radiation area is defined as a location where radiation levels are higher than 0.005 mSv/hr (or 0.5 mRem/hr), which is significantly below the level of 7.5 mR/hr. This means that appropriate caution is necessary to inform individuals entering the area about the potential radiation exposure.

In this context, the sign serves as a warning to ensure that people are aware of the radiation hazards and can take the necessary precautions to minimize exposure. On the other hand, a sign indicating "Caution: High Radiation Area" would apply when radiation levels exceed 100 mR/hr, which is not the case here, and thus it's inappropriate. The "Caution: Radioactive Materials" sign is generally used when there are materials that are radioactive present, but it does not pertain to exposure rates. Lastly, stating that "No posting is required" does not comply with the NRC regulations since the identified radiation levels necessitate a warning to maintain safety and health standards.