What has kept the world safe from the bomb since 1945 has not been deterrence, in the sense of fear of specific weapons, so much as it`s been memory. The memory of what happened at Hiroshima.
The third stage was the reaction that came when the body struggled to compensate for its ills - when, for instance, the white count not only returned to normal but increased to much higher than normal levels.
The second stage set in ten or fifteen days after the bombing. Its first symptom was falling hair. Diarrhea and fever, which in some cases went as high as 106, came next.
The first stage had been all over before the doctors even knew they were dealing with a new sickness; it was the direct reaction to the bombardment of the body, at the moment when the bomb went off, by neutrons, beta particles, and gamma rays.