Devastation Caused by the Atomic Bombs: Hiroshima and Nagasaki

Abstract

Now, let’s go back to the atomic bombs dropped on Japan. The following is a summary of the features of the atomic bomb (“Little Boy”) dropped on Hiroshima. It has been estimated that it was equivalent to 16 KT of TNT (trinitrotoluene, explosive). Only about 860 g of the 70 kg of U-235 contained in the bomb was thought to have exploded. The energy released was 6.3 × 10¹³ J (63 TJ) (Little Boy, Wikipedia; Los Alamos Report (1985)). About 50 % of it caused the windblast, 35 % turned into heat, and 15 % was released as radiation. The temperature just below the epicenter is believed to have reached as high as 6,000 °C. Many charred bodies were scattered around there. The high temperature caused fires. The pressure created by the wind was about 35 atm at the epicenter, and 5 atm even 2 km away from it. This caused a very strong wind (shockwave) that destroyed most buildings and killed many people by the flying debris. Just as a comparison, a hurricane or typhoon’s very strong wind is caused by a pressure difference of only about 0.1 atm. These two factors, blast and heat, caused the devastating visible effects of the atomic bomb.