# Nuclear fission / fusion? **URL:** \ **Category:** Factual Questions\ **Tags:** science-math\ **Created:** [January 13, 2024, 5:06pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046 "2024-01-13T17:06:15Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 14, 2024, 12:36am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/21 "2024-01-14T00:36:52Z")
> [@HoneyBadgerDC](#): > > Did scientists have a rough idea of how much energy would be produced when the theory was developed? > [@Chronos](#): > > Sure. They knew the masses of the raw materials and the products, and they knew E = mc^2. > [@Chronos](#): > > The uncertainty there wasn’t in how much energy would be released per reaction, but in how much of the fuel would react before the rest was blown all to smithereens. A fairly common failure mode for nuclear bombs is that it starts off by producing just enough of a bang that it blows apart the critical mass, and doesn’t react further. It’s not real clear what the OP meant. First is he asking about theory or engineering? And if we’re engineering, are we engineering an explosive weapon, or a long-running not-self-damaging powerplant? But IMO @Chronos pretty well nailed it as I snipped it. E=MC^2 defines the upper limit of what energy could be produced by fission or fusion _if_ every bit of mass was converted to energy. Whether quickly or slowly. The problem is we aren’t going to invent a machine that can convert every single subatomic particle of the “fuel” into energy. So efficiency matters hugely, like multiple orders of magnitude hugely. One hell of a lot of engineering has gone into weapons. And lots into powerplants. Each still have really shitty efficiencies albeit in very different ways for very different reasons. The shitty efficiency percentages are tolerable only because E=MC^2 gives a _very_ big number for total potential conversion, so even grabbing a couple percent of that is still a big number. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 14, 2024, 12:44am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/22 "2024-01-14T00:44:16Z")
> [@LSLGuy](#): > > The problem is we aren’t going to invent a machine that can convert every single subatomic particle of the “fuel” into energy. So efficiency matters hugely, like multiple orders of magnitude hugely. Well, that depends on what you mean by “efficiency”. Is a fully-efficient nuclear reaction one where every uranium atom splits? Even if you do that, you lose only a small fraction of the mass of the uranium: The products have well over 99% of the mass of the original. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 14, 2024, 3:03am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/23 "2024-01-14T03:03:34Z")
Good question. My point only was that E=mc^2 is a **very** loose upper bound for any practical bomb/reactor. Precisely because, as you say, even reacting 100% of the uranium atoms once each is still only converting a trivial fraction of the available _m_ into _E_. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [January 14, 2024, 3:09am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/24 "2024-01-14T03:09:56Z")
I think you need an antimatter reaction to pull off 100% conversion. We have some antimatter on earth but not a lot. Often cited as the most expensive “thing” measured by mass on earth…by a long shot. We won’t be making antimatter bombs any time soon (thankfully). ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 14, 2024, 3:14am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/25 "2024-01-14T03:14:49Z")
> [@Whack-a-Mole](#): > > I think you need an antimatter reaction to pull off 100% conversion. Even at that, ~50% is lost to neutrinos. Even by the standards of sci-fi engineering magic, that energy is lost for good. It wouldn’t meaningfully add to a bomb’s explosive power, let alone a reactor’s efficiency. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [January 14, 2024, 3:23am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/26 "2024-01-14T03:23:22Z")
I thought the “advantage” of an antimatter bomb is you could fit a Hiroshima nuke inside a pen (10,000 pound nuke you can carry in your pocket). ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [January 14, 2024, 3:27am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/27 "2024-01-14T03:27:24Z")
Oh, it’s still a lot of energy, no doubt. It just means that you need perhaps a gram of antimatter to equal Hiroshima rather than half a gram. Gamma rays carry away a significant amount of energy as well, but I don’t know how well their spectrum gets absorbed by typical matter. Probably some is lost to space or heats things deep underground. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 14, 2024, 3:30am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/28 "2024-01-14T03:30:12Z")
> [@Dr.Strangelove](#): > > > [@Whack-a-Mole](#): > > > > I think you need an antimatter reaction to pull off 100% conversion. > > Even at that, ~50% is lost to neutrinos. Even by the standards of sci-fi engineering magic, that energy is lost for good. I’m reminded of this handy little calculation: **[Lethal Neutrinos (xkcd.com)](https://what-if.xkcd.com/73/)**. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 14, 2024, 10:26am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/29 "2024-01-14T10:26:48Z")
> [@Whack-a-Mole](#): > > I thought the “advantage” of an antimatter bomb is you could fit a Hiroshima nuke inside a pen (10,000 pound nuke you can carry in your pocket). Don’t you need _two_ pockets? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 14, 2024, 2:10pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/30 "2024-01-14T14:10:06Z")
And a small older sports car to carry the flux capacitor (and its cooling system) that provides the containment for that gram of antimatter inside the pen. ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [January 14, 2024, 4:33pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/31 "2024-01-14T16:33:57Z")
> [@xtenkfarpl](#): > > This is a bit of a hijack, but is there any possibility that a fusion reaction could be ignited without a fission starter? > > Maybe a really energetic chemical explosive where all the hydrogen atoms have been replaced by deuterium, or even tritium? Mix in some lithium and… ?? Answering myself: none at all. Now I remember that particle energy is linearly related to absolute temperature by Bolzmann’s constant, we see that even at 10,000K we get only on the order of 10 electronvolts for each particle. At least 3 orders of magnitude below the energy needed to overcome the coulomb repulsion between charged nucleons. And even considering that this is an average & there is a small tail of energies at the high end, there would not possibly be enough high energy ones to cause any significant fusion. So, no low-tech H-bombs for the terrorists! It was just an anxiety thought I had during a sleepless night… 😉 ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [January 14, 2024, 5:00pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/32 "2024-01-14T17:00:19Z")
> [@xtenkfarpl](#): > > none at all. Nah, it works fine, except it is not exactly “low-tech”, which is why to achieve those temperatures they utilise those neutral-beam accelerators and cyclotron heating. ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [January 14, 2024, 5:09pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/33 "2024-01-14T17:09:48Z")
I was thinking of purely chemical methods. Given the heroic measures heavily funded experimentalists have to resort to in order to generate even a bit of fusion, I don’t think we need to worry about home-made H-bombs soon. Unless of course some demented genius comes up with something that knocks a lot of current physics into a cocked hat…? 😉 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 14, 2024, 5:18pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/34 "2024-01-14T17:18:17Z")
Again, if you don’t care about sustaining the reaction, it’s easy, as with a Farnsworth fusor (the same inventor as the television tube, and after whom the Futurama character is named). > **[Fusor](https://en.wikipedia.org/wiki/Fusor)** > > A fusor is a device that uses an electric field to heat ions to a temperature in which they undergo nuclear fusion. The machine induces a potential difference between two metal cages, inside a vacuum. Positive ions fall down this voltage drop, building up speed. If they collide in the center, they can fuse. This is one kind of an inertial electrostatic confinement device – a branch of fusion research. > A Farnsworth–Hirsch fusor is the most common type of fusor. This design came from work by Philo... ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [January 14, 2024, 5:40pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/35 "2024-01-14T17:40:46Z")
Right, these have been round for a while. Interesting as a research tool for generating neutrons perhaps, and as a high-end hobbyist project. But of course the energy ratio (energy generated by fusion vs total energy used by the apparatus) is vanishingly small. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [January 15, 2024, 4:07am UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/36 "2024-01-15T04:07:05Z")
[Muon catalyzed fusion](https://en.wikipedia.org/wiki/Muon-catalyzed_fusion) is another long known method of inducing nuclear fusion, the idea originating in the 1950s. The problem isn’t _doing_ it, the problem is figuring out a way to do so that exceeds breakeven. You certainly aren’t getting a bomb out of it, though. > [@Whack-a-Mole](#): > > I think you need an antimatter reaction to pull off 100% conversion. Or a micro black hole undergoing evaporation via Hawking radiation. Of course much like antimatter first you need to somehow make it, then somehow survive being near it…and by “near it”, I mean “being in the same solar system”. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 15, 2024, 2:49pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/37 "2024-01-15T14:49:02Z")
Black hole evaporation has an even higher loss to neutrinos than antimatter does. ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [January 15, 2024, 4:39pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/38 "2024-01-15T16:39:37Z")
Damn, we really need to find a way to harvest the energy from all those wasteful neutrinos. Some material which will stop them. Where is scrith when we need it? Paging the protectors… I wonder what the neutrino energy flux from the sun is at earth orbit radius (I recall the electromagnetic energy flux is on the order of 1 KW per square meter)… OK, I could probably look up the data and calculate it myself but I’m lazy… 🙂 ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 15, 2024, 4:42pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/39 "2024-01-15T16:42:57Z")
> [@xtenkfarpl](#): > > Damn, we really need to find a way to harvest the energy from all those wasteful neutrinos. Where you see only problems, perhaps there is opportunity. Can we design a “neutrino diet” weight loss program around this, where most of the energy goes to neutrinos rather than your belly and thighs? ---
**Author:** ![xtenkfarpl](https://avatars.discourse-cdn.com/v4/letter/x/c2a13f/32.png) [@xtenkfarpl](https://boards.straightdope.com/u/xtenkfarpl)\ **Post date:** [January 15, 2024, 4:49pm UTC](https://boards.straightdope.com/t/nuclear-fission-fusion/996046/40 "2024-01-15T16:49:16Z")
We’d have to retrain our metabolism to run on nuclear rather than chemical reactions, I think? Probably vaporize ourselves in the process. Of course there are theoretical aliens who run on nuclear energy… Robert Forward’s Cheelas in Dragon’s Egg, for example… [Previous page](https://boards.straightdope.com/t/nuclear-fission-fusion/996046.md?page=1) [Next page](https://boards.straightdope.com/t/nuclear-fission-fusion/996046.md?page=3)