Suppose someone were able to split the atom nuclei of a small chunk of nitrogen, sodium, iron, gold or oxygen (don’t ask how; let’s just suppose it happened) - would it lead to a nuclear explosion just like a normal uranium/plutonium atomic weapon?
(by split, I mean every atom being split, such that we don’t have to worry about the chain-reaction part of it - just asking about the sheer energy released)
Any atom more massive than Iron, yes.
Any less massive would take energy to split, so you would have to add an a-bomb’s worth of energy to split them.
Binding energy:
The idea is to fuse light elements, not split them apart. Cf. hydrogen bombs.
I don’t think this is strictly true. Iron is the minimum of the curve, but something only a little larger than iron, if split in half, would lead to something significantly smaller than iron (or rather, to two somethings).
Also note, of course, that not everything releases the same amount of energy when it splits. Something with an atomic mass of 100ish that split into two ironish nuclei wouldn’t release as much energy as something with an atomic mass of 200ish splitting into two 100ish nuclei.
Also remember what causes a nuclear explosion is chain reaction - splitting a uranium atom yield two atoms of a lighter element (i.e. xenon and strontium) and several free neutrons and energy (which expresses itself as heat and light). Certain isotopes of uranium (esp. U235) are unstable enough that if hit by these neutrons, they too will split - so 3 neutrons becomes 9, then 27, then 81, then 243, then 729, etc. this is a chain reaction… Whether all 3 neutrons can hit U235 and produce 3 x 3 neutrons depends on how pure and dense the starter kit of U235 is. This is why a nuclear bomb consists of 2 or more small pieces (where the odds all 3 neutrons hit another U235 before the exit the piece is low) and setting off the bomb involves setting off explosions around these pieces to slam them together very fast to make a very dense “critical mass”. then the chain reaction happens in a flash - a really really big flash.
The thing is, most elements - especially less dense elements with smaller nuclei, are not sufficiently unstable that a knock by a neutron will split them, and many don’t produce extra neutrons to carry on the process if they can be split. A neutron needs to be released with enough energy to hit the next nucleus hard enough to split it. Most neutrons don’t have that energy. Scientists, and the Military-Industrial Complex, are just lucky that elements like uranium and plutonium do work that way.
You’re asking if you could wave a magic wand and make a whole pile of atoms split up, if I understand. the question. Look at the nuclei binding energy chart in the linked Wiki article. What you want to do is split a nucleus into two smaller pieces and release energy. However, the energy peaks at about nickel or iron. Splitting a nucleus smaller than that does not produce nuclei with less energy, it takes more energy to make 2 out of 1. So your magic wand would work with any element heavier, depending on what you split it into. Just, your wand would have to do all the work, because those elements aren’t necessarily producing enough fast/energetic neutrons to cause the split.
(fusion is the opposite - take 2 light elements, slam them together hard enough, and they form a heavier element and release energy in the process. This the left half of the nuclei binding energy chart, working your way up the periodic table to iron.)
It’s a little more complicated than that. A neutron with too little energy is unlikely to cause a nucleus to split, but so is a neutron with too much energy. There’s some energy that’s optimal. In fact, the neutrons produced by fission of U-235 are actually more energetic than that optimum, and so you can make a reactor run more effectively by slowing down the neutrons. That’s the purpose of the water or graphite moderator in a reactor (aside: Don’t use graphite): To slow down the neutrons to optimal energy.
IANA Physicist but our Chem teacher taught us some nuclear chemistry. I hope this is mostly correct but trust that other dopers will enlighten me where I go astray.
I’m operating from this model:
The particles marked + are protons, are positively charged, and they reside in the nucleus. The particles marked – are electrons; they’re negatively charged and they orbit the nucleus. The red ones (sometimes marked 0) are neutrons. They’re neutrally charged and they reside in the nucleus.
Back in the day, many of us had some sort of magnet experiment for science. We learned that if you put the two + ends of magnets together, they repel. Take a + end to a – end and they attract. With that in mind, how do you explain the nucleus in the atom? Shouldn’t they be repelling each other? Same thing with the electrons in orbits…hey, why aren’t the electrons falling into the nucleus and glomming on to protons?
Answer: there are forces that preclude that from happening. I don’t know much about them but here they are. Forces within the Atom
Imagine a very heavy element, like Uranium. 92 protons and electrons—a lot of forces are applied to keep it together. But a hydrogen atom, with only 2? I wonder if it’s a log scale. IIRC some uranium naturally decays—you don’t need to do anything to it because it’s already too unstable to keep itself together. Unstable, tremendous amount of energy that you can release.
One question I have for those in the know: how are neutrons formed? It seems like an obvious combination of proton and electron, given the respective weights, but it seemed like science teachers didn’t want to go there. I’ll guess it does happen but under rare circumstances.
You can make a neutron from a proton and an electron (with a neutrino produced as a by-product), but it’s not made of a proton and a neutron. That is to say, there isn’t a proton and an electron inside of a neutron. What both protons and neutrons are made of (electrons, so far as we can tell, are fundamental, and not made of anything smaller) is smaller particles called quarks, three each. Quarks come in multiple varieties, but the two relevant ones here are called the “up quark” and the “down quark”: An up quark has a charge of +2/3, and a down quark has a charge of -1/3 (yes, fractional charges, which would be a bit awkward if it were ever possible to get a quark by itself, but so far as we can tell, that can never happen). A proton consists of two ups and a down (for a total charge of +1), and a neutron consists of an up and two downs (for a total charge of -1). (And yes, it’s possible to have a particle made of three ups, for +2, or three downs, for -1, and they’re produced in particle accelerators sometimes, but they’re unstable).
So when you get, say, beta decay (where a neutron turns into a proton, an electron, and an antineutrino), what’s actually happening is that a down quark is turning into an up quark, an electron, and an antineutrino. Or to look at it in more detail, typically the down turns into an up and a particle called a W-, and then the W- turns into the electron and antineutrino.
Incidentally, the mass of a proton or neutron is much more than the sums of the masses of the three quarks, and the mass of a W particle is much more than the mass of a proton or neutron. So you certainly can’t say that the down is “made of” an up and a W- (besides, it’s also possible, under the right circumstances, for it to go the other way, for an up to turn into a down and a W+).
Much of your description is over my head, but thanks. I kind of figured it would combine into a new form, stop being its components, but can see where that might not be a given. So that isn’t a typical path for making a neutron and that’s why they skipped it.
One thing I learned recently is that exposure to certain elements is known as ionizing radiation. I’ve also heard of free radicals. Essentially these mean that you might have a stable molecule in your body, like H20 (water). After exposure to radiation, it might lose an electron and become H20 +. Left to its own devices, some of those radicals become harmful to the body.
But I also thought, hey, where did that electron go? Is it hooking up with a proton to form a neutron? It isn’t that simple, as you say.
@Velocity, I meant to include this. Things like legos that work well on small scale start to fall apart on a larger one.
Some of the superheavy elements are so unstable their half lives are measured in minutes.
Minutes, nothing. There are some elements with half lives so short, you need to use yoctoseconds to express them properly.
By way of analogy: A leather jacket is made out of cowhide. It’s processed, of course, but the material is still identifiably a cow’s skin, and if you look close, you can see things like pores. It’s mostly still held together the way it was when it was coating the cow.
By contrast, gelatin is often made from cowhide, but by the time it’s gelatin, it’s not cowhide any more. You could make almost the exact same product (and often do) from horse hooves, or pig bones.
Sot of, yes.
The key is this graph in the article -
If the products of the split have (net) more energy than the atom you are splitting (i.e. are higher on the curve) then there’s energy released. If they are lower, it takes energy for your magic wand to split them. So uranium splits into 2 atoms (often, xenon and strontium) that are higher on the curve. With iron, for example, and split produces other atoms lower on the curve. They absorb energy to split.
The graph isn’t smooth, though. Li6 and Li7 have a lower binding energy than He4, so splitting them should release energy. Li7 was actually the first atom to be split experimentally, and the helium nuclei produced had more energy than the original lithium and hydrogen nuclei:
Wikipedia has that reaction (1p + 7Li → 2 4He + 17.2 MeV) listed under “fusion” 
I suppose you could also call it “total alpha decay”.
Really, that’s mostly just because helium has an extraordinarily stable nucleus. Ultimately, for the same reason that it’s stable chemically, though the nice simple correspondence breaks down after that.
Well now I feel funny about wearing anything made from leather.
That summary neglects a step: 1p + 7Li → 8Be → 2 4He + 17.2 MeV
The actual fusion product is Beryllium-8, which is unstable and immediately decays into 2 normal Helium nuclei. So it’s fusion then fission.
Yes, if you wave that magic wand to make a certain fission happen (instead of what happens in the real world) perhaps you can construct different fissions that yield energy. But real-world, fission below iron usually(!) absorbs energy. Hence, no explosion.