Nuclear fallout

Nuclear fallout is the radioactive material that falls to earth after a nuclear explosion. It is created when the explosion vaporizes soil and other materials, which then mix with radioactive fission products. The amount and spread of fallout depends on the size of the weapon and the altitude at which it is detonated. Fallout can be carried by winds for long distances, contaminating areas far from the explosion site. The Fallout series takes its name from this debris.

Mechanics[]

Radioactive fallout is the primary long-term effect of nuclear weapons. This radioactive particulate comes from debris leftover from the fission and fusion reactions and non-radioactive isotopes that become radioactive due to neutron capture. Atoms can split during fission in over forty different ways, producing a mix of eighty different isotopes, whose half-lives range from fractions of a second to decades and centuries. As these decay they may form more or less stable child isotopes, creating a complex mixture of radioactive isotopes. Over 300 different isotopes of 36 elements have been identified in nuclear fission products.^{[Non-game 1]}

Short-lived isotopes release their energy rapidly, resulting in intense, but short-lived radiation fields. Long-lived isotopes release their energy slowly over a much longer time, resulting in persistent, but much less intense levels of radiation. As a general rule, radiation decays according to the rule of sevens: For every seven-fold increase in time following a fission detonation (starting at or after 1 hour), the radiation intensity decreases by a factor of 10 (an approximate t^-1.2 scaling relationship).^{[Non-game 1]}

For example: After 7 hours, radiation declines by 90%. After two days or 49 hours (7*7 hours), the remaining radiation declines again by 90%. After 2 weeks (7*2 days), it once again drops by 90%, and so on and so forth. The rule is accurate to 25% for the first two weeks, factor of two for the first six months, and the rate of decline accelerates even further after six months.^{[Non-game 1]}

The term fallout typically refers to these products that settle down to the ground after a nuclear explosion. The precise amount depends on the altitude of the detonation and the size of the explosion. Airburst detonations result in vaporized radioactive products entering the atmosphere. Explosions with yields of 100 kilotons or less remain within the troposphere and all of the fallout will be deposited to the ground by weather processes. As the yield increases, the nuclear fireball will rise higher, eventually entering the stratosphere near megaton ranges, resulting in an ever increasing amount of fallout injected into the stratosphere. The fallout deposited on the ground will be distributed on a global scale and only descend after months or even years.^{[Non-game 1]}

On the other hand, groundbursts or explosions closer to the ground will disturb large amounts of soil and suck it into the fireball. The radioactive isotopes mix with the debris, which is heavier than air and quickly falls to the ground, within minutes or days. This results in intense downwind contamination that can reach thousands of kilometers away. Rainfall can quickly wash out the fallout to the ground, reducing its reach, but increasing intensity, creating local pockets of intense radiation. Even apparent airbursts can still cause significant fallout, due to neutron activation.^{[Non-game 1]}

Modern strategic warheads used by the United States and China largely rely on 200-750 kiloton warheads, with few exceptions. This switch has resulted in a significantly increased fallout risk, and long-term consequences for the wasteland.^{[Non-game 1]}

Effects[]

The Great War resulted in vast quantities of fallout being deposited all over the world, though it took time for it to settle down. What would become New California appears to have suffered limited exposure despite the devastation,^[1] and Roger Maxson's exodus to Lost Hills had to contend with next to no fallout while traveling down the Central Valley.^[2] Across the United States, ghouls emerged as a result of exposure to nuclear fallout,^[3] with the background radiation severely increasing.^[4]

By the 22nd century, long-lived nuclear fallout remained a significant problem in various parts of the country, particularly in the mountains, as significant amounts of fallout were deposited at higher elevations, at least in California.^[5] Hot spots, isolated pockets of intense radiation due to fallout, like The Glow, remained^[6] making the wasteland hostile and dangerous.^[7]

The elevated background radiation forced humans as a species to adapt, triggering subtle changes in the DNA that persisted through the generations. These genetic changes made them indistinguishable from pre-War humans, but were enough for the Enclave to declare all humans exposed to radiation as mutants and pursue a course of extermination, without any understanding what the ramifications of the changes were or what they meant.^[8] In other words, normal evolutionary processes and change became a mortal threat to mankind insofar as the Enclave was concerned, permitting genocide.^[9]

References[]

Non-game