Hanoi - More than 400 workers on an oil rig off Vietnam were evacuated after a small amount of radioactive material went missing, authorities said Sunday.
Workers later found the piece of iridium-192, which was used to power equipment used to check for flaws in welding on the oil rig off of the southern port city of Vung Tau, 100 kilometers east of Ho Chi Minh Ciy.
The iridium had apparently dislodged from the equipment and was discovered missing on Friday and relocated the same day, local media said.
'No one has fallen ill since then, but all the workers at the site have been taken to hospital for health check,' said Nguyen Van Thuong, a Vung Tau police official.
At least 28 workers who had come in close contact with the iridium were sent to Vietnam's Institute for Nuclear Energy in Dalat for observation, he said.
Vietnam is working to build a nuclear power plant by 2020 with the blessing of the International Atomic Energy Agency.
The country is also working to improve safety procedures for the small amounts of industrial and commercial radioactive materials found in hospital and other equipment.
'We don't know yet how the iridium source was dislodged and we are trying to find out if the iridium source had been properly used,' Thuong said.
On Saturday, several dozen of the oil rig workers reported to the local hospital complaining of headaches and dizziness, according to Tuoi Tre newspaper.
However, the director of Le Loi Hospital in Vung Tau declined to connect the patients' complaints with the small amounts of radiation that the iridium source would have emitted.
'Most of them have been released,' Tran Van Bay, the hospital director, said of the patients from the oil rig.
© 2007 dpa - Deutsche Presse-Agentur 
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