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| Fig. 1: The aftermath of the dropping of a 15 kiloton atomic bomb over Hiroshima in August 1945. (Courtesy of the U.S. Air Force. Source: Wikimedia Commons) |
Nuclear bombs can be deployed via airdrop from an aircraft or delivered from the ground as an intercontinental ballistic missile (ICBM). The difference in choice of delivery is due to strategy and effectiveness, but perhaps a more impactful choice to be made is when to actually detonate the nuclear bomb. When a bomb is detonated below 100,000 feet but high enough that the fireball of the detonation does not actually touch the Earth's surface, it is considered an air blast. [1] Conversely, when a nuclear bomb is detonated at or slightly above the surface of land or water, it is deemed a surface blast. Both types of blasts yield different destructive outcomes to the surrounding areas.
When a nuclear bomb is detonated close or on the ground, it produces radioactive fallout. Upon explosion radioactive particles such as fission products, radiated soil and weapon waste are sent into varying levels of the atmosphere. Depending on the direction and power of the wind, radioactive fallout can travel extremely long distances. [1] Surface burst detonations are most effective in creating high amounts of concentrated damage to the area close to the ground zero of the bomb detonation. [1] Tactically, surface detonations can be seen as an effective means to obliterate a specific target and surrounding ground forces.
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| Fig. 2: The resulting "mushroom" cloud formed above Hiroshima after being bombed. (Courtesy of NARA. Source: Wikimedia Commons) |
Unlike surface blasts, air blasts produce almost no local fallout upon detonation. Instead, air blasts are more effective in producing high levels of overpressure over larger areas and increased yields of thermal radiation. In the case of the bombing of Hiroshima, about 192,000 total people died. [2] (See Fig. 1.) The toppled buildings and vast desolate landscape pictured shows the undeniable force of overpressure and thermal energy that buildings and people close to ground zero are subject to. Upon the aerial detonation of the 15 kiloton bomb in Hiroshima, a large cloud formed over the bomb site as seen in Fig. 2. This white colored mushroom cloud is characteristic of an air blast due to the condensation of water droplets in the atmosphere. [3]
© Esteban Abbate. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] NATO Handbook on the Medical Aspects of NBC Defensive Operations, "U.S. Department of Defense, Army Field Manual FM 8-9," February 1996.
[2] K. Page, "US Nuclear Weapon Decision-Making Framework in the 1950s," Physics 241, Stanford University, Spring 2018.
[3] B. Lutnick, "The Mushroom Cloud," Physics 241, Stanford University, Winter 2019.
