What does contamination refer to in nuclear terms?

In nuclear terms, contamination refers specifically to the situation where radioactive materials are present in places where they are not supposed to be, which aligns with the definition provided in the correct choice. This includes scenarios where radioactive particles are found on surfaces, in air, or even in the body that should otherwise be clean and free from such materials. Contamination can pose significant health risks to workers and the environment, which is why protocols for handling, storing, and disposing of radioactive materials are critically important in nuclear facilities.

The other choices do not accurately define contamination. Safe handling of radioactive materials emphasizes proper procedures and safety measures rather than the presence of material in unintended areas. The natural decay of radioactive substances refers to the process by which these substances lose their radioactivity over time, and excessive monitoring of radiation levels pertains to the observation of radiation, not the presence of unwanted radioactive material. Understanding these distinctions is crucial for maintaining safety and compliance in nuclear operations.