The anniversaries of the Hiroshima and Nagasaki bombings mark 77 years since the only wartime uses of nuclear weapons. We should be profoundly grateful that such weapons have never been used again in this way to date. Yet our increasing distance from the bombings carries a risk with it.
As the nuclear bombings move further into the past, awareness of the colossal threat posed by nuclear weapons may also become more distant. Complacency or ignorance about the threat hanging over the world since 1945 may become common. The result might be people ignoring the nuclear danger until it’s too late.
The nuclear bombing anniversaries are an appropriate time to address this problem. Reviewing basic facts about the nature and effects of nuclear weapons may help revive the awareness and concern necessary to counter their threat.
Mechanisms of Nuclear Weapons
Nuclear weapons generally work through either nuclear fission or some combination of fission with nuclear fusion. Nuclear fission occurs when the nucleus of an atom splits into smaller nuclei; under the right conditions, splitting an atom nucleus causes other nuclei to split in the same way, leading to a chain reaction. Nuclear fusion occurs when atom nuclei fuse with other nuclei, forming heavier nuclei. Both processes can release enormous amounts energy that can be weaponized.
Nuclear weapons’ destructive power, or yield, is measured in equivalents to tons of dynamite: the “Little Boy” bomb dropped on Hiroshima had a yield of 15 kilotons, or the equivalent of 15,000 tons of dynamite. The “Fat Man” bomb dropped on Nagasaki had a yield of 21 kilotons, or 21,000 tons of dynamite.
Fission is generally achieved using the elements uranium or plutonium. The Little Boy bomb used conventional explosives to forcibly combine two pieces of uranium to cause a fission chain reaction. The Fat Man bomb used explosives to implode a sphere (or “pit”) of plutonium in such a way as to cause a fission chain reaction. More contemporary nuclear fission weapons also typically implode uranium or plutonium.
Fusion is generally achieved using deuterium and tritium, both isotopes (variants) of hydrogen. In a fusion nuclear bomb, also known as a hydrogen bomb or a thermonuclear bomb, a fission chain reaction is used to produce sufficient energy to cause the deuterium and tritium atoms to fuse. The energy from the fusion also accelerates the accompanying fission, in a kind of vicious circle. The result is a massively more destructive release of energy than in a fission nuclear bomb.
Effects of Nuclear Weapons
When a nuclear weapon is detonated, it produces several immediate destructive effects, which all occur within about a minute:
Direct radiation. A nuclear detonation first emits a brief (less than a second) but intense burst of radiation. Such radiation is lethal to those close to the explosion. For a nuclear bomb with a 10 kiloton yield, direct radiation would be lethal within a 1-mile radius. Other, more wide-ranging, effects quickly become more important, though.
Thermal flash. A detonating nuclear weapon radiates energy that heats the surrounding air, creating a vast fireball. This thermal flash lasts several seconds. A 1 megaton nuclear weapon (yield equivalent to 1 million tons of dynamite) creates a fireball that is ultimately 1 mile in diameter and that is brighter than the sun for up to 50 miles away. Depending on the weapon’s power, a thermal flash can severely burn people 20 miles away.
Blast wave. The expanding fireball causes a rapid jump in the surrounding air pressure, creating a blast wave that radiates out from the explosion. Initially moving at thousands of miles per hour, the blast wave causes most of the destruction to buildings that results from a nuclear detonation.
The scope of death caused by these immediate effects of a nuclear weapon depends on the weapon’s destructive power, or yield. To give rough estimates, a 100 kiloton nuclear weapon would kill everyone within a 2-mile radius; a 1 megaton weapon would kill everyone within about 4 miles; and a 10 megaton weapon would kill everyone within almost 10 miles.
Beyond these immediate effects, nuclear weapons cause further damage in the short- and long-term. Fires caused by the thermal flash or blast wave will continue to burn and may even combine into a firestorm; this occurred at Hiroshima. Nuclear detonations also spread harmful radioactive materials, known as a “fallout,” which are mainly created by fission.
In addition to a weapon’s yield, the location of a nuclear detonation influences the harm caused. If a weapon detonates in the air (an “air burst”), the resulting blast wave reflects off the ground and causes more extensive destruction. If a weapon detonates on the ground (a “ground burst”), the blast wave destruction is more limited. Much of the fallout from an air burst rises into the stratosphere and may not reach the earth for months or even years. Fallout from a ground burst becomes attached to the immense amount of soil, rock, and other materials consumed in the explosion and returns to earth relatively quickly. Depending on weather conditions, fallout with high or even lethal radioactivity may descend to earth quite far from the detonation.
Consequences of Nuclear Weapons
To put all these destructive effects into specific terms that American readers might find meaningful, consider the calculations made by historian Alex Wellerstein. Wellerstein simulated the effects of using nuclear weapons with yields equivalent to the Little Boy bomb against several American cities.
Used against New York City, such a nuclear weapon would kill an estimated 264,000 people, while injuring 512,000 people. Against Los Angeles, such a weapon would kill 100,000 people and injure about 151,000. Against Chicago, the toll would be 151,000 killed, 209,000 injured. Against Washington, DC, 120,000 killed, 169,000 injured.
Even these estimates don’t provide a full sense of the nuclear threat, however. The bomb used against Hiroshima has limited value as a model for future nuclear destructiveness. In a nuclear war between the United States and Russia or some other nuclear-armed nation, the bombs used would be much more powerful than the Little Boy bomb and far more of them would be used. We happily have no past model for such a situation, but we have a general idea of what would happen.
A 1979 US government study of nuclear war’s effects explained matters clearly:
The destruction resulting from an all-out nuclear attack would probably be far greater [than US policymakers anticipate]. In addition to the tens of millions of deaths during the days and weeks after the attack, there would probably be further millions (perhaps further tens of millions) of deaths in the ensuing months or years. In addition to the enormous economic destruction caused by the actual nuclear explosions, there would be some years during which the residual economy would decline further, as stocks were consumed and machines wore out faster than recovered production could replace them. Nobody knows how to estimate the likelihood that industrial civilization might collapse in the areas attacked; additionally, the possibility of significant long-term ecological damage cannot be excluded.
More recent assessments of ecological damage from nuclear war paint a similarly bleak portrait.
The bombings of Hiroshima and Nagasaki are growing more distant in time but sadly the threat to humanity from nuclear weapons is not becoming more distant. We need persistently to educate ourselves about the devastation nuclear weapons can wreak, remember that danger, and resolve never to allow nuclear weapons to be used again.
A version of this essay originally appeared on the Consistent Life Network blog.
 “How Do Nuclear Weapons Work?” Union of Concerned Scientists, September 29, 2016, https://bit.ly/3F0mtbt.
 “Little Boy and Fat Man,” Atomic Heritage Foundation, accessed July 31, 2022, https://bit.ly/3F4weFw.
 “How Do Nuclear Weapons Work?”; “Types of Nuclear Weapons [archived webpage],” Comprehensive Nuclear-Test-Ban Treaty Organization, accessed October 21, 2022, https://bit.ly/3CTlc3a.
 “How Do Nuclear Weapons Work?”; “Types of Nuclear Weapons.”
 Richard Wolfson and Ferenc Dalnoki-Veress, “The Devastating Effects of Nuclear Weapons,” MIT Press Reader, accessed July 29, 2022, https://bit.ly/3ePEIWr.
 Aria Bendix, “A Nuclear Attack Would Most Likely Target One of 6 US Cities. Simulated Images Show How a Hiroshima-Like Explosion Would Affect Each,” Business Insider, December 23, 2019, https://bit.ly/3guUA0J.
 US Office of Technology Assessment, The Effects of Nuclear War (Washington, DC: Government Printing Office, 1979), 4, available at https://bit.ly/3ePuKEk.
 “Nuclear Winter Would Threaten Nearly Everyone on Earth,” Science Daily, August 28, 2019, https://bit.ly/3MU6FZJ. © 2022 John Whitehead. All rights reserved.
© 2022 John Whitehead. All rights reserved.
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