South African scientists have begun injecting radioactive isotopes into rhino horns, not to hurt them but to protect them from poachers. The isotopes are harmless to the rhinos, but if smugglers try to transport the horns, radiation detectors at airports and borders will pick up the signal and alert authorities.
Nuclear defense for rhinos? Radioactive horns launched to fight illegal hunting
https://interestingengineering.com/science/radioactive-horns-combat-rhino-poaching
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