A sedated rhino is being prepared before a hole is drilled into its horn and isotopes carefully inserted, at a rhino orphanage in Mokopane, South Africa. AP Photo/Alfonso Nqunjana

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 the Rhisotope Project, injecting rhino horns with harmless radioactive isotopes to thwart poachers via customs detection.