A package containing radioactive materials produces 12 mR/hr at the surface. What DOT label must be affixed to the outside of the package?

The correct label affixed to a package containing radioactive materials is based on the radiation level at the surface of the package. In this case, the package produces 12 mR/hr, which falls within a specific range defined by the Department of Transportation (DOT) for the categorization of radioactive materials.

According to DOT regulations, packages that have a radiation dose rate at the surface between 0.01 mR/hr and 0.1 mR/hr are classified as "Category I," while those that have a surface dose rate between 0.1 mR/hr and 1.0 mR/hr fall into "Category II."

However, when the dose rate exceeds that which is typical for the lower categories, it moves into "Category III" and "Category IV," which correspond to higher radiation levels. Given that 12 mR/hr is significantly greater than the maximum limit for "Category II," one can determine that a "Category III" label is appropriate for dose rates at the surface up to 10 mR/hr to 100 mR/hr, aligning precisely with the question's parameters.

Thus, this package should be marked with "Category II," as it matches the range correctly for its measured radiation output.