The five workers exposed to airborne plutonium at the Oarai Research & Development Center in Ibaraki Prefecture were quarantined for about three hours in the room where the accident occurred, a Japan Atomic Energy Agency official said Friday.
Although this action was taken to prevent the plutonium and other radioactive contaminants from spreading to other parts of the nuclear research facility, it probably worsened their internal exposure as they breathed the tainted air.
Internal radiation exposure has been confirmed in four of the five men.