What element is typically associated with human-made radiation sources?

Cesium is typically associated with human-made radiation sources due to its usage in various applications, especially in the medical field and industry. For example, cesium-137, a radioactive isotope of cesium, is used in radiation therapy for cancer treatments and in certain types of industrial gauges and equipment. This makes cesium a significant element in contexts where human intervention has led to the exposure of radiation.

In contrast, uranium and radon are more naturally occurring elements. Uranium is primarily found in geological formations and is not considered a purely human-made source of radiation, despite its use in nuclear power and weaponry. Radon, meanwhile, emanates from the decay of uranium in the soil and can accumulate in homes but is not a product of human activity. Coal is also a naturally occurring substance and doesn't produce radiation in the same manner as cesium, although it can contain trace amounts of radioactive elements. Thus, cesium stands out as the element commonly linked to deliberate, human-made radiation sources.