what is it called when an unwanted material that contains radioactive atoms is present on another material?

When an unwanted material containing radioactive atoms is present on another material, it is called "contamination." This term specifically refers to the presence or deposition of radioactive substances on surfaces or within materials where their presence is unintended or undesirable. The contamination poses a radiation hazard because the radioactive material emits ionizing radiation, and unlike irradiation, the contaminated object itself becomes a source of radiation as long as the contamination remains.