Unidentified thieves who stole a radiographic device containing a highly radioactive isotope of iridium from a gas pipe-laying work crew in Larissa on Friday have been warned that opening the box containing the isotope will place at risk their lives and those near them. The National Commission for Nuclear Energy said on Saturday that the device posed a major health risk to whoever had taken it. The device – which uses radiography to create images for engineers laying down natural gas pipelines in subterranean darkness – was stolen at 6.50 p.m. on Friday from the junction of Farsalon and Theofrastou roads in the north-central city of Larissa, the commission said. The isotope – encased in a steel-plated case bearing a radioactive warning sign – must not be tampered with, the commission said on Saturday, appealing to whoever has the device not to touch or open it but to contact either the Thessaly Police Headquarters on 0410. 683.103 or the commission on 010.650.3540. No questions will be asked, officials said.