The effects following the nuclear bomb that was dropped on Hiroshima by the U.S. killed 90,000 to 146,000 people. The initial blast wasn't the thing that killed everyone, it was the aftermath of the bomb. When a Nuke explodes it gives off radiation from all of the Uranium inside of it, which causes cancer and defects. Uranium is a radioactive material used in nuclear weapons that cause it to detonate.