RAJAHMUNDRY: A container carrying radioactive substance Caesium-137 CS-137 ) is missing from a lorry that transported the material to the ONGC site at Rajahmundry in Andhra Pradesh's Krishna district. However, ONGC on Friday described the isotopes as of "mild radioactive" source.According to an official EU website, CS-137 is radioactive with a long 'half-life' of 30.15 years - the time required for the substance to become half of its original weight.It is suspected that the radioactive source may have gone missing between January 14 and 16 from the logging shed of the ONGC complex. The quantity of the missing substance is not yet known.After efforts to trace the container proved futile, the radiation safety division of Atomic Energy Regulatory Board, Mumbai, was informed as the missing item was a radioactive source and, if mishandled, could cause serious public health hazard.The authorities have complained to police, who have formed four special teams to trace the missing substance. ONGC authorities said CS-137 is used in oil and gas exploration. They said it is not an explosive. The cost of the missing material, which was purchased in 2013, was Rs 27 lakh and not Rs 100 crore as reported by the media, they clarified. CS-137 is an isotope of the element Caesium. It was one of the radioactive substances emitted during the Chernobyl nuclear mishap. It can enter soil and food sources.As per the police complaint, CS-137 was being carried in a container lorry along with another radioactive isotope AmBe-241(Americ um-241) on January 14. The container was kept in the logging shed on the same day. When the shutters were opened on January 16, it was noticed that the container was missing. However, the AmBe-241 radioactive source was present in the shed.