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Stet radiation was a type of radiation that did not exist until around the year 100,000,000,000,000. The radiation was deadly to humans and could easily vaporise them, however it had no effect on clothing. The Tenth Doctor was not aware of its existence until Professor Yana informed him that the couplings room in Silo 16 was flooded with it and they needed to go in there to set off the gravity footprint required to launch the Utopia Project Rocket. Jack Harkness, who could never die, was the one for the job, and soon after the rocket was successfully launched. (TV: Utopia)