Conservation scientists in South Africa are injecting rhino horns with radioactive isotopes. The doses are too weak to harm the animals, but strong enough to set off nuclear security system alarms at international border crossings.

South African scientists have launched an anti-poaching campaign in which rhino's horns will be injected with a radioactive material. The group, from the University of the Witwatersrand, said the process is harmless to rhinos but will allow customs officers to detect smuggled horns as they're transported across the world.