A South African university has launched an anti-poaching campaign to inject the horns of rhinoceroses with radioactive isotopes that it says are harmless for the animals but can be detected by customs agents.

Under the collaborative project involving the University of the Witwatersrand, nuclear energy officials and conservationists, five rhinos were injected in what the university hopes will be the start of a mass injection of the declining rhino population, which they are calling the Rhisotope Project.

Last year, about 20 rhinos at a sanctuary were injected with isotopes in trials that paved the way for Thursday’s launch. The radioactive isotopes even at low levels can be recognised by radiation detectors at airports and borders, leading to the arrest of poachers and traffickers.