The amount of that three of 14 workers irradiated in a nuclear accident at uranium-processing firm JCO Co. were exposed to is estimated to have been at least eight sievert, doctors said Thursday evening.

This is equivalent to the amount of gamma rays measured 700-800 meters from ground zero when an atomic bomb was dropped on Hiroshima in 1945.

About half of all people exposed to radiation of 4 sievert or higher face the possibility of death within 30 days.