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copnonymous t1_iu3qvyj wrote

Yes a nuclear detonation makes other things radioactive. The process is called "neutron activation". Essentially all the high energy particles being flung out from the explosion slam into atoms. The neutrons can be captures in the heavier atoms, mainly in the soil. This creates internal instability in the atom and causes it to become radioactive.

That is what fallout largely is. While most nuclear blasts don't consume all the nuclear material, there really isn't enough to form the dust we get from fallout. That's why if we detonate a bomb high enough over a population there will be little to no radiation damage. A lot of the radiation and danger afterwards come from the neutron activated soils flung into the sky by the blast.

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restricteddata t1_iu4aves wrote

> That is what fallout largely is.

Most of what you've said is right, but this part is not. The most radioactive parts of fallout are fission products, the split "halves" of atoms reacted during the nuclear fission part of the explosion. The reason surface bursts are more dangerous from fallout is not because the dirt itself became neutron activated, but because the fission products mix into the dirt, which makes them fall out of the cloud much sooner than they would otherwise. The mushroom cloud from an air burst is still highly radioactive, it just doesn't (usually) send its products back to the ground very quickly (though there are circumstances in which it could, like if it started raining), and so by the time the radioactive byproducts come back down, they have had some time for the shortest half-lives to burn out, and they are diffused over a larger area (so no single spot on the ground gets too much).

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johnnymacmax t1_iu3sv09 wrote

Do you mean the neutrons get conveniently stuck in a heavy atom’s nucleus or do you mean they knock out other neutrons?

Follow-up, if neutrons lack charge then how do neutrons effect how radioactive an atom is?

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copnonymous t1_iu3u49q wrote

There's nothing convenient about it. In a nuclear explosion there are trillions of neutrons flying outwards from the epicenter. Through simple statistical probability some will collide with something. Only other radioactive elements would be unstable enough to be fully destroyed by the energy of being slammed into by a neutron. Thus neutrons get stuck inside the nucleus of the atom.

However, without more protons to keep the forces inside the atom balanced it must be released. So the atoms themselves will become radioactive just naturally trying to relieve that imbalance.

Here are some of the radionuclides (atomic isotopes) made by a nuclear explosion.

https://en.m.wikipedia.org/wiki/Activation_product

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Yancy_Farnesworth t1_iu4q3pv wrote

Neutrons attach to atomic nuclei and transform them into other elements by literally slamming into the nucleus. It's not really about convenience, even a 0.00001% chance of a neutron hitting an atom just right to transform it is inevitable when we talk about the number of atoms in a given volume. The molar mass for atmospheric oxygen (2 oxygen atoms) is about 32 grams. 6 x 10^23 molecules of O2 weighs 32 grams. There's a lot of atoms around a nuclear explosion taking place on earth.

Any atom can be radioactive, they do not need to be heavy. Tritium for example is a radioactive form of hydrogen with 2 neutrons. Hydrogen is stable and not radioactive with 1 or 2 neutrons. There's generally a ratio between neutrons and protons (really simplifying this) where elements tend to be stable. Go outside of that ratio and the element tends to be unstable and will decay into something else. The why is related to quantum mechanics.

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BillWoods6 t1_iu5640k wrote

> Hydrogen is stable and not radioactive with 1 or 2 neutrons.

You meant 0 or 1 neutrons.

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Sklifosovsky20 OP t1_iu5l2jp wrote

Why would a neutron get stuck in the nucleus instead of bouncing off?

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SchiferlED t1_iu6cjvs wrote

Neutrons don't have an electric charge, so they are not repelled by the negative electrons around the atom, or the positive protons in the nucleus. The strong nuclear force (which is much stronger than other forces, hence the name) holds protons and neutrons together in the nucleus, and keeps the new neutron there instead of it "bouncing" off.

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