Sometimes, the unexpected happens, and radioactive materials appear in places they should not be. Radioisotopes might be disposed of improperly, for instance. Or industrial imaging equipment could be recycled before the radioactive sources have been removed.
Not all radiation exposure is dangerous, and some radiation doses are unavoidable. High doses of radiation, particularly during a short period of time, can cause adverse health effects, from burns and radiation sickness to an increased risk of cancer and even death in some cases. Chronic doses of radiation, doses received regularly over a long period of time, can also increase your risk of cancer.