Uranium miners. And workers are #1 and #2. Airplane crews are #3. But no, safeguards put in place over the last 100 years have limited exposure to far below cancer-causing levels. Only an employer who was in blatant violation of international standards for safety (as established by iaea) would submit a worker to unsafe levels. Sadly, such employers do exist in the third world.
Uranium miners. And workers are #1 and #2. Third place are aircrews (pilots and flight attendants) because they are exposed to more cosmic rays way up high in the atmosphere! More info: http://www. Iaea. Org/publications/booklets/radpeopleenv/pdf/chapter_9.Pdf.