In new revelations in Germany, it has been revealed that the old East German Secret Police (Stasi) used radioactive materials to mark their suspects, their clothing or money in order to keep track on them.
They could then track those people by geiger counter detectors hidden in their armpits. The spray scandium-46 was used, and often whole meeting rooms were sprayed which would lead to identification of many people.
The problem was that too often radioactive bank notes were left in circulation among people. One expert has said they would now have the same effect on fertility for males as castration.