Nuclear Fallout

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Nuclear Fallout Definition

Nuclear fallout is a destructive, long-term consequence following large-scale releases of radioactivity into the environment. Radioactivity is the transfer of energy through waves or particles, and is common in the world. Light, for instance, can have a radioactive source and is not harmful by itself. However, human created scenarios in which the nuclei of atoms are ripped apart release large amounts of radioactive particles and energy. These events, like nuclear bombs and nuclear reactor meltdowns, pour radioactive substances into the air and water.

Radiation causes a number of chemical reactions, changing elements and creating dangerously reactive charged particles, or ions. Further, X-rays and gamma rays can be released by the splitting particles. These waves carry tremendous energy and can easily disrupt living systems and mutate DNA. As particle and waves are release into the air, they can travel long distances before finally settling back to the Earth. The nuclear fallout, with its devastating effects, happens in the area where the particle reach. Some nuclear fallouts reach a global scale, while others are limited to a localized area.

Nuclear Fallout Radius

The size of the area affected by nuclear fallout is entirely dependent on the type and quantity of radiation exposure. While many nuclear isotopes are handled and produced every day for commercial and medical applications, these industries rarely operate on the scale or with reactive enough isotopes to cause a nuclear fallout. Two human activities have been responsible for large-scale nuclear fallout events throughout history. Nuclear weapons were the first human invention to cause fallout.

A nuclear blast will create nuclear fallout in an area proportionate to the size and quality of the bomb, and adjusted for where the bomb is detonated. Two main types of nuclear weapons exist: fission bombs and fusion bombs. Fission bombs release energy by smashing two pieces of uranium together, causing individual atoms to fuse together. This releases a lot of energy. The first atomic bomb dropped in wartime, a bomb named “Little Boy” dropped by the United States on Japan, was a fission bomb. The bomb produced a blast equivalent to 15 thousand tons of TNT. Below is an image of the initial blast radius, and the fires it produced. The bomb exploded in the air, before reaching the ground. This is known as an “air blast”, and sends radiation into the atmosphere and into the surroundings as nuclear fallout. This small, preliminary bomb had a blast radius of about a mile. Measurements of the fallout were not accurately obtained, but it is assumed that the radioactivity travels tens or hundreds of miles in the surrounding air.

Hiroshima Damage Map

The largest nuclear bomb to be set off was the “Tsar Bomba” or “King of Bombs”, detonated by the Soviet Union in 1961. The bomb was a fusion bomb, which relies on the energy created in a fission reaction to spark a much more powerful fusion reaction between atoms of hydrogen. Bombs in this class are therefore called hydrogen bombs, H-bombs, or thermonuclear weapons. The Tsar Bomba was the largest ever built in this class. The mushroom cloud created by the explosion could be seen for hundreds of miles. The resulting nuclear fallout from the explosion was condemned by the United States and led to escalations in the Cold War. It is believed that nuclear fallout from this, and hundreds of other nuclear weapons tests, can carry nuclear fallout around the globe, as the explosion reaches straight into the upper atmosphere. It can take weeks or months for the radioactive materials to make their way to ground, and they can travel thousands of miles. This nuclear fallout causes an increase in chemically reactive ions, radioactive isotopes, and causes mutation and even death in living organisms.

The true threat of a nuclear war is not in the localized effects of the bomb, or even the leveling of entire cities, but of the possibility of a global nuclear fallout. If multiple weapons of this size and quality were detonated around the same time, radioactive isotopes would descend on all parts of the globe. Global food and water supplies would quickly become tainted and most people would starve to death or die from radiation poisoning within a few years.

The second invention of humanity to cause nuclear fallout was based on the theory of nuclear weapons, but meant to aid humanity. Nuclear power uses the energy from splitting atoms and converts it to electrical energy. Today, nearly 20% of the United States energy is produced using nuclear. Many countries have turned to this method as a high-yield energy source. However, there have also been many disasters caused by the nuclear energy industry. One of the most significant, the leak at the plant in Chernobyl, Russia, caused a nuclear fallout which has lasted decades and caused significant health effects for citizens of surrounding countries. Cancers have been found which can be specifically linked to the radioactive isotopes released by the plant. More recently, the reactor core at the Fukushima Daiichi Nuclear Power Plant in Japan was severely damaged by an earthquake and tsunami.

The initial radiation leakage in these events was not known. In the case of Fukushima, it was assumed that the radioactivity was sealed off, until explorations by radioactively-shielded robots revealed groundwater seeping into the facility. While very few deaths have been directly reported from the incident, it is still unknown how far reaching the nuclear fallout is, and who will be affected. Initial reports warned of the radioactivity leaking into the sea, which could carry it worldwide. As advanced instrumentation is required to detect and classify nuclear radiation, the best bet for avoiding nuclear fallout is to get as far away from the source as possible, as quickly as possible.

How Long Does Nuclear Fallout Last?

As with the size of the area affected by nuclear fallout, the length of time an area will remain affected is determined by the amount of radioactivity release. Radioactive isotopes have a specific rate at which they decay. This is known as the half-life of a radioactive material, as half of the material will decay in that amount of time. Some radioactive chemicals are present in nature, from the forming of the stars and planets. We can use these isotopes, like Carbon-14, to date ancient objects by measuring the amount of Carbon-14 they have compared to their surroundings. Other radioactive isotopes are produced by the human inventions discussed above, and can produce toxic and long-lasting isotopes. Plutonium-239, for instance, has a half-life of 24,600 years. This means that leftover plutonium from nukes and nuclear energy production will give off radiation for hundreds of thousands of years to come.

That being said, the radiation levels in a fallout area after a nuclear blast tend to subside quickly. Weather events like rain can help to wash away the radiation and ions created by the blast. Some blasts have been found with lower levels of radiation after only a few weeks, while other events leave radiation for many years. The Fukushima disaster, for instance, will take 30 to 40 years to clean up entirely. However, the surrounding areas will be free of radiation long before that. Further, while nuclear fallout can last weeks to months, the health effects from it will be seen for many decades after. Many health effects of radioactivity are seen as cancers which develop after the energy from radiation has mutated DNA. The more immediate effects of radiation poisoning and contaminated food and water supplies can be replaced and replenished more quickly.

How to Survive Nuclear Fallout

The best way to survive a nuclear fallout is to leave. The area affected by a nuclear fallout will likely not be safe anywhere. Dust and particles carried in the air will be radioactive, and contaminate anything they touch. Local water supplies will become radioactive and should be avoided, as drinking from them or using them to bathe will result in radiation poisoning. Considering that all historical nuclear fallout events have been mostly localized, traveling only a few hundred miles is usually sufficient to protect yourself from radiation.

However, in the event of a global nuclear fallout, the option to flee is no longer viable. In this case, you must obtain enough food, water, and energy to survive several months or even years before the radiation subsides. During the Cold War, a large business sprang up installing nuclear fallout shelters. The basics of a shelter are simple: put as much dense material between you and the radiation as possible. Several simple designs consist of digging a hole in the ground, and covering it with a thick material. Supplying oneself with enough food and water in this case is difficult, which is why worried homeowners often turned to underground bunkers, complete with years of food and water. The walls were often lined with lead, tungsten, or other dense metals to block radiation.

While this scenario was hyped during the Cold War and many retreats were created, the feasibility of surviving a nuclear fallout is unknown. Critics contend that radiation would still get in through the air ducts or water supply, and that no one can be truly safe. This has led some to say that the best way to survive nuclear fallout is to avoid it altogether, and put bans on nuclear weapons and energy.


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  • Williams, D. (2002). Cancer after nuclear fallout: lessons from the Chernobyl accident. Nature Reviews Cancer, 543-549.

Cite This Article

MLAAPAChicago Editors. "Nuclear Fallout." Biology Dictionary,, 12 Feb. 2018, Editors. (2018, February 12). Nuclear Fallout. Retrieved from Editors. "Nuclear Fallout." Biology Dictionary., February 12, 2018.

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