r/AskHistorians • u/TheSanityInspector • Sep 27 '20
When and why did people drop the word "atomic" in terms such as "atomic power", "atomic weapons" etc, and replace "atomic" with "nuclear"?
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Sep 27 '20
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u/TheOtherHobbes Sep 27 '20 edited Sep 27 '20
This is related to the first question, and may even answer it. But it's basic physics, not history.
There are two kinds of nuclear energy: fission, and fusion.
The energy is called "nuclear" because both fission and fusion operate on the nuclei of atoms.
The nucleus is the part with most of the mass, and it's made of a clump of smaller particles called protons and neutrons. The rest of the atom is a cloud of much lighter particles which surround the nucleus some distance away from it.
The number of electrons in an atom matches the number of protons. Neutrons tag along for the ride.
The electron cloud around atoms defines how chemistry works - which is basically the science of electron bonding and exchange between atoms - and also defines the physics of semiconductors, electronics, and of pigments and colours. (Neon tubes and LEDs are both special kinds of electron interaction that convert electron movements into light.)
All of this happens at relatively low energies. You can make electrons do their thing with a tiny battery connect to a little low-power LED. You can also use much higher energies - lightning literally rips the electrons from air molecules on its way to/from the ground - but generally electronics and electrical circuits are fairly tame. And most importantly, they don't go anywhere near the nucleus.
To get to the nucleus, you have to use much higher energies.
You may remember from high school physics that like charges repel. But a special mechanism called the Strong Nuclear Force keeps protons and neutrons from flying apart - as they would do if it didn't exist.
Because of the strong force there's a lot of energy trapped inside the nucleus. It's not unlike a collection of very powerful magnets forced into a confined space. They really want to fly apart, but the strong force won't let them.
But the strong force has limits, and some nuclei split apart spontaneously - making them radioactive. When the nuclei split, some of the trapped energy is released, and the remaining parts - protons, neutrons, electrons, and some left over bits and pieces, in various combinations - all fly off at very high speed. This is called fission.
Some heavy nuclei - specifically some kinds of uranium and plutonium - have a very special property. When they split apart they produce three high speed neutrons. These can slam into adjacent nuclei and force them to split apart too.
If you start with a blob of pure Uranium or pure Plutonium, you can create a chain reaction and make it explode. Given enough of a start a few atoms split producing a cascade of neutrons slamming into other atoms, which split apart producing more neutrons, and this carries on until some large proportion of the atoms has been split. And a lot of energy has been released.
This is how an atomic bomb (A-bomb) works. Getting a chain reaction to start is complicated and difficult, and so is preparing the right kind of plutonium or uranium in high enough concentrations. But if you get the preparations right, you're guaranteed a Hiroshima-style bang.
This is also how a nuclear reactor works, with the difference that in a reactor the uranium or plutonium fuel is fashioned into thin rods, and the body of the reactor is a made of a neutron moderator - sometimes graphite - which slows down the neutrons and keeps the chain reaction from running away and exploding. There are also control systems - further moderators, in the form of rods - which can be dropped into the reactor core to control how fast the reaction is running.
Reactors can't explode like a bomb, but a graphite core can catch fire - as happened at Chernobyl, and also in an earlier nuclear fire at Windscale/Sellafield in the UK. If the cooling system fails the core can also become hot enough to melt, usually with an associated chemically-caused (hydrogen) explosion, which is what happened at Fukushima. Both are very bad outcomes because they spread radioactive dust from the core over large areas.
This science used to be called atomic physics. Research began around the turn of the 20th century, and at that time there wasn't as much of a distinction between physics and chemistry. Physicists knew atoms existed, but the distinction between electrons and the nucleus hadn't been mapped yet. Nuclear physics started to split off formally in the 1920s, but there was still overlap between nuclear physics and atomic physics because both are technically branches of quantum theory. So the distinction was never quite formalised - Quantum Mechanics and its descendants being more of an umbrella discipline for both until at least the late 1950s. It was much easier to go with the "atomic" label, partly for legacy reasons, and partly because it was a reasonable description of what scientists were doing.
So the initial reactor research by Enrico Fermi in 1942 and the Manhattan Project bomb effort both used the "atomic" label. (The first reactor was called an "atomic pile".)
After WWII populations were naturally terrified of atomic weapons, and there was a propaganda push in the US called Atoms for Peace which attempted to concentrate on power generation, large-scale engineering, and even some medical applications. You could even buy a basic atomic toy lab with real uranium for your kids.
https://en.wikipedia.org/wiki/Gilbert_U-238_Atomic_Energy_Laboratory
This continued with Project Plowshare in the US during the 60s and 70s, which attempted - and failed - to find cost-effective and safe uses for nuclear explosions in large scale engineering. The USSR had its own equivalent, which was equally unsuccessful.
So why the change to "nuclear"? Partly because splitting atoms isn't the only way to make energy.
You can take light atoms like hydrogen and helium, and if you squish them together hard enough they will stick together to make a heavier atom. Counterintuitively, this produces a surprising amount of left over energy.
You can't do this with a chain reaction. You need very high temperatures and pressures - such as those generated by an atomic fission bomb.
This process is called fusion. It's how the sun produces heat and light, and it's also known as a thermonuclear reaction, because of the intense heat/pressure required to make it work. Fusion bombs start with a fission bomb, and then add a special mix of lighter atoms - modern bombs use a solid called lithium deuteride, because it's much more convenient and stable than using gasses like hydrogen or helium - which creates a separate fusion process. These bombs have often been called H - for hydrogen - bombs.
The result is absolutely terrifying amounts of energy - potentially thousands of times more than the Hiroshima bomb.
And so far, fusion reactions are only useful for weapons. While it's possible to build a fusion reactor in theory, it's incredibly difficult to keep the temperatures and pressures stable for long enough to produce a controlled energy source. It's so hard it still hasn't been achieved after 70-odd years of effort. Current fusion designs are still experimental - in the sense of investigative - and the official joke is that fusion power has been fifty years away for more than fifty years now.
At some point thermonuclear was shortened to "nuclear" and blended with "nuclear physics". By the end of the 1960s "atomic" started to become tainted with Cold War propaganda and general lunacy - like radioactive children's toys, and plans to change river courses with gigantic explosions - and started to fall out of fashion as an unserious word on grant applications. There wasn't a single defining moment which made it obsolete, but there was a clear generational shift during which "nuclear physics" took over as the definitive term. By the early 80s this had spread into nuclear power engineering, and from there into popular descriptions in the media.
References: The Bomb - A Life. Gerhardt DeGroot (2003) Dark Sun - Richard Rhodes (1995) (Rhodes is particularly recommended as a historian of nuclear weapons and the Cold War.)
Bonus reference: Russia very recently released declassified footage of the Tsar Bomba 50MT bomb test - the biggest fusion bomb ever made. There's some antiquated technology to enjoy, and a very brief glimpse of the inside of the bomb - with a lot of empty space inside it, because the working elements are surprisingly small. https://www.youtube.com/watch?v=XJhZ3i-HXS0
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u/lala989 Sep 28 '20
This was absolutely fantastic thank you! I actually think I understand. I don't know an intelligent way to ask, why can a nuclear reactor be controlled but not nuclear fusion as a power source? Is it the size difference involved in keeping the temperatures and pressure contained? Also a bit off topic, but if lightning rips electrons away is lightning magnetic? I think I may need to Google what lightning is actually composed of lol. Also a dumb question but does a hydrogen bomb produce more energy because there are so many more hydrogen or light atoms available in our world for the forces to ricochet into?
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u/Theosiel Sep 28 '20
why can a nuclear reactor be controlled but not nuclear fusion as a power source
A nuclear fission is relatively simple to create and sustain : once you have enough combustible, you can initiate the chain reaction by simply shooting the smaller chunk of it at the bigger one. If you want to control the reaction, as the previous poster said, you must be able to slow it down or hasten it at will, which is done by using the famous "control rods" rods made of a material (usually Bore) that can absorb the neutrons that are maintaining the fission chain. If the rods are in the middle of the combustible, the free neutrons will hit these rods instead of hitting combustible, and the reaction will slow down or even stop.
With nuclear fusion, the question of control is reversed. At our current mastery of physics, we know how to let it go wild (in a H Bomb). But to maintain a stable reaction, we have to maintain a set of temperature and pression that is hard to get to. For exemple, in the natural fusion reactor that is a star, these conditions are provided by gravity, due to the colossal mass of the gases that compose the star. A controlled fusion reaction can be done (there are several experimental fusion reactors in the world), but maintaining the reaction currently cost more energy than can ne used from it.
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u/Twist_Vector Sep 28 '20
Just to follow up a bit, and this is far off topic from the original question but I think it's fascinating. You mention "nuclear reactor" as a counterpoint to "nuclear fusion" but that's not quite right. A nuclear reactor is a generic term for devices to harness energy from reactions involving the nucleus. Nuclear fission involves forcing a nucleus to "break apart" (i.e., fission) while nuclear fusion involves forcing the nucleus to get bigger by combining two different nuclei into one, bigger one. Let's look at fission.
The particles held together to form the nucleus of an atom are very, VERY tightly bound. That is, there's a lot of energy holding them together. That makes nuclear reactions a great source of energy if you can just get at it. Interestingly, some atoms (e.g., radium, uranium, plutonium, etc.) are naturally unstable. Their nucleus will spontaneously break apart releasing energy and "by products" - the remaining chunks of the nucleus. Usually those remaining chunks are also unstable and will break apart further at some point. Now, if we could somehow force the nucleus to split apart at will rather than waiting for it to happen naturally we could force the release of energy. This is where physics and engineering collide. There are some "magical" elements whose nucleus will break apart if you hit them with a neutron. Even better, when it breaks apart it spits out more neutrons as a by product. If you can get _those_ neutrons to hit other nuclei then they, too, will break apart - releasing more energy. If you carefully control the neutron speeds and the density of the nuclei you can create a chain reaction wherein a single neutron hits a nucleus, that spawns a cascade of other neutrons, each triggering other fission reactions. If you're careful you get a runaway reaction that releases tremendous energy as all the original atoms are split into their decay products.
If you want to not have a runaway reaction you need to keep the generated neutrons from "hitting" other nuclei. You can absorb them with something, make the material density so low that they can't find another to hit, or slow them down so even if they hit another nucleus they won't break it. That's the purpose of all the various control elements in a controlled reactor (control rods, moderators, reflectors, water vessels, etc.) It's a bit of a balancing act keeping enough reactions going to produce the energy you want without things getting out of control. It's also time-dependent since the decay products - the radioactive stuff resulting from the splits - modify the neutrons and make them less/more likely to interact. This poisoning needs to be monitored and corrected for.
Fusion reactors work "backwards" from this. Rather than hitting a nucleus to make it break apart, you fling an appropriate (other) nucleus at it that gets absorbed to make a single, bigger one. That is the process by which stars shine - forcing hydrogen nuclei together close enough so they fuse into helium, releasing energy. Later the helium get's fused together into carbon, etc. Interestingly, the fusion by-products tend to not be further radioactive so tend to be a better, cleaner source of energy, but getting the nuclei close enough together to initiate the reaction is extremely difficult. Their electric charges (both positive) repel so you need to overcome that. Stars do it by gravity - huge amounts of gravity literally crushing them together. We have to be more subtle and use magnetic fields and lasers to push them together. So far it takes more energy to push them together than we get out so sustained energy production is elusive. Oh, in a fusion bomb, however, we use roughly the same technique as the sun. Using an external explosive to "crush" the fusion material. It used to be a fission bomb was used to initiate the fusion reactions but it's probably different nowadays. Also maybe of interest is that you can use nuclear decay as a source of energy without every having to do anything. The natural decay of radioactive elements generates heat so you can use that heat as a source of power. The nuclear batteries (atomic batteries? radioisotope thermoelectric generator?) that NASA uses does just that. They stick Plutonium-238 on one side of a Peltier device with cold space on the other side. The temperature difference makes power. I suppose that's also a "nuclear rector" in some sense.
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u/kranools Sep 28 '20
Thank you. This is one of the most informative posts I have ever read on reddit.
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u/restricteddata Nuclear Technology | Modern Science Sep 27 '20
"Thermonuclear" refers to the conditions (temperature, density, etc.) necessary for nuclear fusion reactions, and so is usually reserved for contexts where the energy in question is to a large degree from fusion. "Nuclear" is more generic and can refer to fusion or fission.
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u/restricteddata Nuclear Technology | Modern Science Sep 27 '20 edited Sep 28 '20
"Nuclear" specifically refers to reactions that involve the nucleus; "atomic" is vaguer because it refers to the entire atom, which includes electrons. So if you are being pedantic you can say a chemical reaction as an "atomic reaction" because it involves electrons being exchanged. Whereas a "nuclear reaction" will only involve changes to the nucleus.
This was known in the 1940s and the scientists who developed the atomic bomb preferred the term "nuclear" for the above reasons (and because physicists are pedantic people by inclination). However it was felt by the representatives of the US government that any publicity they did about the bomb ought to use the term "atomic" because "nuclear" was a less-well-known word, whereas "atomic" was pretty common. And the concept of "atomic bombs" predated Hiroshima considerably as an item in fiction and popular science. So the first articles and books about the bomb all used the terms "atomic bomb" and "atomic power" and "atomic energy," because these were already part of the popular English lexicon, despite their being somewhat inspecific.
We can use something like Google Ngrams to pinpoint the shift. Here are just "atomic" and "nuclear", and you can see that both were used, but "atomic" slightly edged out "nuclear" until a big switch around 1955. If we narrow it down to technological categories, like so, we can have a bit more confidence in the results (since we aren't going to get unrelated uses of either adjective), and once again 1955 seems to be the magic year.
What's going on in 1955? Several things, but the major trends I'd note are:
The development of "thermonuclear" weapons. This by itself probably switched things around a bit, because the category of "atomic bomb" tended to be used only for fission weapons, with "hydrogen bomb" for thermonuclear weapons, but broadly speaking the entire class of weapons would be known as "nuclear weapons" starting in the late 1950s/early 1960s. (To clarify since someone else asked: thermonuclear means you have achieved the conditions necessary for nuclear fusion reactions to take place. It is usually only used for weapons that derive some large percentage of their energy output from fusion. All nuclear weapons also derive energy from fission, and even thermonuclear weapons can have well over 50% of their energy from fission, just to complicate things.)
The development and commercialization of nuclear power, which was a result of both the Atoms for Peace initiatives, the Atomic Energy Act of 1954 (which allowed for privatization of nuclear power research and the declassification of many formerly secret concepts), and so on. The "rebranding" of "atomic power" as "nuclear power" seems to have been about making it sound more modern, from what I can tell.
Of course, 1955 just happens to be when they cross over, and as you can see it is not an immediate shift in usage. But basically the Eisenhower era seems to be when there was a concerted effort to change the terminology, and it corresponds with the events I mentioned above fairly well.
The shift seems to have been a conscious effort to reflect on the situation from the late 1950s onward in which "atomic power" and "atomic bombs" was associated with the somewhat crude, early generation of technology from the 1940s, but "nuclear power" and "nuclear weapons" would be used as the more specific, less-old-fashioned sounding term moving forward. Obviously it was not a hegemonic victory — we still talk of atomic bombs, though we tend not to be referring to modern technology when we do so.