1. ## Plutonic Fusion detected

I recently watched MIB and have found myself wondering:
1: What would it take to force plutonium to undergo nuclear fusion (not fission, fusion)?
2: Can anyone guesstimate the potential energy output?
I'm assuming any numerical answers would boil down to theoretical math, and I suspect both answers would be ridiculous, but I can't help but be curious.

2. ## Re: Plutonic Fusion detected

Originally Posted by Avigor
I recently watched MIB and have found myself wondering:
1: What would it take to force plutonium to undergo nuclear fusion (not fission, fusion)?
2: Can anyone guesstimate the potential energy output?
I'm assuming any numerical answers would boil down to theoretical math, and I suspect both answers would be ridiculous, but I can't help but be curious.
Plutonium has a heavier atomic nucleus than iron-56, and thus it requires energy input to cause it to undergo nuclear fusion.

Assuming you could successfully fuse two plutonium nuclei (rather than just fusing on smaller nuclei, which is a simplified explanation of how research labs today synthesize elements like Oganesson (née Ununoctium)), you'd have some kind of hideously unwieldy element (element 188, or unoctoctium) whose properties (besides extreme instability) would be purely theoretical.

3. ## Re: Plutonic Fusion detected

What he said. You would no doubt get energy released as whatever super-massive element you just created decayed back into sensible territory in a matter of picoseconds, but that energy release would not be greater than the amount you had to put in there in the first place in order to fuse the plutonium.

4. ## Re: Plutonic Fusion detected

The energy from fusion is not from the product decaying back into "sensible" matter. It comes from the handful of neutrons that are converted from matter to energy via e = mc2. I would argue that if you did manage to fuse two plutonium atoms together, you would get back the same amount of energy you put in when it decayed. Minus losses due to entropy and for energy already released from the conversion of neutrons of course.

Also, not being an expert on nuclear fusion nor plutonium, I'm probably spouting off from the top of Stupidity Hill. Keep that in mind as you consider my argument.

Edit: First sentence in this post is poorly worded. I meant that Fusion power doesn't come from forcing the two nuclei together; it comes from the conversion of some of the neutrons involved into energy

5. ## Re: Plutonic Fusion detected

Originally Posted by Lord Torath
The energy from fusion is not from the product decaying back into "sensible" matter.
Er, but when a product decays, that's nuclear *fission*, not fusion? And it most definitely releases energy, that's how every nuclear reactor on this planet works! We've already said that actually getting the fusion to happen in the first place would require an energy input with elements this size.

6. ## Re: Plutonic Fusion detected

Originally Posted by factotum
Er, but when a product decays, that's nuclear *fission*, not fusion? And it most definitely releases energy, that's how every nuclear reactor on this planet works! We've already said that actually getting the fusion to happen in the first place would require an energy input with elements this size.
Yes, but it takes an energy input with Hydrogen as well. It's only that Hydrogen has a greater output than input, and Plutonium would have a greater input than output. As I understand - which could be totally wrong - you would have to use an enormous amount of energy - even in terms of nuclear power - to fuse Plutonium. The fusion process, however, would also release energy, albeit less than you put in. That amount seems to be what the original question was asking about.

The nuclear fission that would immediately follow is something that could be considered, and is worth mentioning, but is not actually what the question was. As far as I can tell, there are three pieces of information that have been established.

1) You would lose energy if we're only taking fusion into account. There would be an output, but it would be less than the input, like using a light bulb to activate a solar panel.
2) The resulting atoms would very, very quickly decay or undergo fission, which would produce extra energy.
3) The total energy gain would probably be negative, even taking 2 into account. If it is positive, it would certainly be less than could be gained by simply using Plutonium in fission.

Is that a reasonable assessment?

7. ## Re: Plutonic Fusion detected

Presumably you slam an alpha particle into it with the right energy and see what happens. *Uranium* fusion is well known, and is how a breeder reactor works. And that's the whole point of a weapons producing breeder reactor (creating Plutonium from Uranium [I'm assuming there are intermediaries, but U goes in and Pu comes out]).

The big difference here is that Uranium (and presumably Plutonium) fusion *loses* energy (at least until the produced element/isotope falls apart) and weapons plants aren't supposed to make energy efficiently. The traditional point of hydrogen fusion is to gain energy.

8. ## Re: Plutonic Fusion detected

Originally Posted by Strigon
Yes, but it takes an energy input with Hydrogen as well. It's only that Hydrogen has a greater output than input, and Plutonium would have a greater input than output. As I understand - which could be totally wrong - you would have to use an enormous amount of energy - even in terms of nuclear power - to fuse Plutonium. The fusion process, however, would also release energy, albeit less than you put in. That amount seems to be what the original question was asking about.

The nuclear fission that would immediately follow is something that could be considered, and is worth mentioning, but is not actually what the question was. As far as I can tell, there are three pieces of information that have been established.

1) You would lose energy if we're only taking fusion into account. There would be an output, but it would be less than the input, like using a light bulb to activate a solar panel.
2) The resulting atoms would very, very quickly decay or undergo fission, which would produce extra energy.
3) The total energy gain would probably be negative, even taking 2 into account. If it is positive, it would certainly be less than could be gained by simply using Plutonium in fission.

Is that a reasonable assessment?
That's about how I see it. I would expect the energy gained from 2 would be roughly equivalent to the power required to fuse the two nuclei in 1. Same order of magnitude, anyway. But again, not an expert. Also we're dealing with an imaginary super-heavy product of fusion - what properties would Unoctoctium possess, other than a half-life even shorter than Astatine's?

Related question: How many Hydrogen atoms get fused into each Helium atom? A Helium atom has roughly 4 times the mass of a Hydrogen atom (two protons and two neutrons), so I would tend to guess four. What happens to the excess charge, though?

9. ## Re: Plutonic Fusion detected

Charge balance in such nuclear reactions is often maintained by emission of positrons or electrons, as needed. (Lepton number is maintained by corresponding emission of neutrinos or anti-neutrinos). For fusion of Hydrogen-1 to Helium-4, two positrons and two neutrinos are produced.

10. ## Re: Plutonic Fusion detected

Originally Posted by Lord Torath
Related question: How many Hydrogen atoms get fused into each Helium atom? A Helium atom has roughly 4 times the mass of a Hydrogen atom (two protons and two neutrons), so I would tend to guess four. What happens to the excess charge, though?
In the process which happens in our Sun, you start with two hydrogen nuclei fusing into deuterium, emitting a positron and a neutrino--the positron carries away the positive charge from the proton that turns into a neutron. Deuterium then fuses into Helium-3 with the addition of another hydrogen nucleus, and two He-3 nuclei fuse into He-4 and two H. Note that the initial part here (hydrogen nuclei fusing into deuterium) is a horribly inefficient process which rarely happens--it only manages to yield such a high output in the Sun because it's so huge.

Higher mass stars than the Sun use the CNO cycle, which uses atoms of carbon, nitrogen and oxygen to catalyse the process, but I'm really not sure how that works.

11. ## Re: Plutonic Fusion detected

And I thought Plutonic Fusion was a geological term referring to melting of subsurface rocks.

12. ## Re: Plutonic Fusion detected

You would be able to fuse Plutonium with lots of gravity and pressure as in the inner crust of a neutron star. You would likely end up with a lot of electron captures in the process, resulting in proton clusters somewhat larger than Plutonium, with electrons orbiting them, floating in a soup of free "dripped" neutrons.

13. ## Re: Plutonic Fusion detected

Assuming you could use alien tech magic to put them together without requiring such a massive energy investment to begin with, my only-a-layman's-grasp-of-nuclear-alchemy self assumes that the energy released in the subsequent decay would be at least ballpark what you'd need to put them together in the first place, and would be massively radioactive to anyone around.

But this is again a good reason not to expect much more from soft sci-fi than "shiny alien tech magic".

14. ## Re: Plutonic Fusion detected

Originally Posted by Anymage
Assuming you could use alien tech magic to put them together without requiring such a massive energy investment to begin with, my only-a-layman's-grasp-of-nuclear-alchemy self assumes that the energy released in the subsequent decay would be at least ballpark what you'd need to put them together in the first place, and would be massively radioactive to anyone around.

But this is again a good reason not to expect much more from soft sci-fi than "shiny alien tech magic".
You don't need alien technology, just particle accelerators. Sure you're more likely to break the plutonium atoms apart by shooting alpha particles at it, but some should stick. You end up with curium (which is entirely synthetic and decays into plutonium)

15. ## Re: Plutonic Fusion detected

Originally Posted by Anymage
Assuming you could use alien tech magic to put them together without requiring such a massive energy investment to begin with, my only-a-layman's-grasp-of-nuclear-alchemy self assumes that the energy released in the subsequent decay would be at least ballpark what you'd need to put them together in the first place, and would be massively radioactive to anyone around.

But this is again a good reason not to expect much more from soft sci-fi than "shiny alien tech magic".
You need 1940s tech for this, no more (for values of producing elements roughly on the current periodic table). If you want to insist that "unobtanium" is a stable element of atomic number ~200, then "shiny alien tech magic" is needed to produce it. This might even qualify as "hard SF", at least for traditional definitions (there seems to be a large gulf between pre-sputnik tech readers and current STEM types. Don't expect to read "hard SF" without spotting errors outside the author's field).

Just understand that doing fusion with plutonium is well known for fusing small nuclei to it (typically alpha particles). This causes a loss of energy but might supply nuclear fuel (or radioactive material for other reasons).

16. ## Re: Plutonic Fusion detected

Originally Posted by DavidSh
And I thought Plutonic Fusion was a geological term referring to melting of subsurface rocks.
That is a possibility, and one that I hadn't thought of... it's just more fun to speculate about the other way of interpreting the term. Granted, google fails to find the exact phrase in a geological context, but "plutonic" does seem to refer to certain kinds of rock so it could easily be they meant some sort of either "nuclear fusion beam" effecting the elements in the rocks, or something intended to melt the crust and fuse separate tectonic plates together or something, which I suspect would cause catastrophic damage if someone tried to fuse all of Earth's tectonic plates together - I wouldn't be surprised if the crust tried to tear itself apart afterwards if that were attempted.

I forgot to list the potential energy output of the rapid decay any resulting new element would undergo; not too surprising that it is most likely that the final total would be less than what went in.

17. ## Re: Plutonic Fusion detected

Whether you get net energy output or energy input is, in general, very simple: is the output element closer to iron than the input element is? Moving towards iron on the periodic table produces energy, moving away from iron absorbs energy.

Fusion with Plutonium is taking an element that's already very far away from iron, and then moving even further away. That will cost you a lot of energy.

18. ## Re: Plutonic Fusion detected

First things first - here's a graph that shows basically everything I'll be talking about in this post, as visual reference:

The sign convention is a bit weird, but essentially the higher up that graph you are the lower energy state you're in.

Originally Posted by Lord Torath
The energy from fusion is not from the product decaying back into "sensible" matter. It comes from the handful of neutrons that are converted from matter to energy via e = mc2. I would argue that if you did manage to fuse two plutonium atoms together, you would get back the same amount of energy you put in when it decayed. Minus losses due to entropy and for energy already released from the conversion of neutrons of course.
This is largely wrong. The total number of nucleons doesn't change in either nuclear fission or nuclear fusion, every nucleon in the reactant ends up somewhere in the product. This can be as a stray alpha particle, emitted neutron, or other such thing, and nucleons can be converted from protons to neutrons and vice versa via decays, but you don't lose entire nucleons to energy.

The mass comes from a different, subtler place. As has been mentioned E=mc^2, and as c is a constant you can use this pretty directly for change in energy and mass. On top of that a free proton on its own and a free neutron on its own do not have the same mass as a proton or neutron in a chemical nuclei. More than that, the mass of a proton or neutron is different in different atoms. That subtle change in mass is where the energy comes from.

Originally Posted by Strigon
Yes, but it takes an energy input with Hydrogen as well. It's only that Hydrogen has a greater output than input, and Plutonium would have a greater input than output. As I understand - which could be totally wrong - you would have to use an enormous amount of energy - even in terms of nuclear power - to fuse Plutonium. The fusion process, however, would also release energy, albeit less than you put in. That amount seems to be what the original question was asking about.
Not so much. As I mentioned above the mass of individual nucleons in an atomic nucleus varies by element. A fusion or fission process that releases energy does so by changing higher mass nucleons into lower mass nucleons. That curve is centered around iron, which is the minimum on a curve with nucleon mass on the y axis and atomic number on the x axis that looks a lot like the picture above, reversed and flattened. For heavy elements (e.g. plutonium) you approach iron by breaking them into lighter elements, releasing energy. For light elements (e.g. hydrogen) you approach iron by fusing them into heavier elements. There's also some variation between isotopes; most of it is pretty negligible but there's a substantial difference between hydrogen isotopes.

The amount of mass is a state function, and can be easily related to energy (again, E=mc^2). This also makes the change in energy for given reactions a state function. For a hypothetical plutonium fusion reaction, the product is in a higher energy state than the reactants, and thus energy is lost. In addition to that actually performing the reaction involves an activation energy, much like in chemical reactions. In some cases this is basically free, such as in stellar fusion, where the energy comes out much the same way it went in and it's largely the change in energy between states that gets released as heat.

In conditions that don't involve massive gravities and stupidly high temperatures, that's not the case with fusion, or even with fission. Energy has to be put in to clear the activation energy, and that energy put in is put in at fairly low efficiencies.

19. ## Re: Plutonic Fusion detected

Originally Posted by Knaight
Originally Posted by Lord Torath
The energy from fusion is not from the product decaying back into "sensible" matter. It comes from the handful of neutrons that are converted from matter to energy via e = mc2. I would argue that if you did manage to fuse two plutonium atoms together, you would get back the same amount of energy you put in when it decayed. Minus losses due to entropy and for energy already released from the conversion of neutrons of course.

Also, not being an expert on nuclear fusion nor plutonium, I'm probably spouting off from the top of Stupidity Hill. Keep that in mind as you consider my argument.

Edit: First sentence in this post is poorly worded. I meant that Fusion power doesn't come from forcing the two nuclei together; it comes from the conversion of some of the neutrons involved into energy
This is largely wrong. The total number of nucleons doesn't change in either nuclear fission or nuclear fusion, every nucleon in the reactant ends up somewhere in the product. This can be as a stray alpha particle, emitted neutron, or other such thing, and nucleons can be converted from protons to neutrons and vice versa via decays, but you don't lose entire nucleons to energy.

The mass comes from a different, subtler place. As has been mentioned E=mc^2, and as c is a constant you can use this pretty directly for change in energy and mass. On top of that a free proton on its own and a free neutron on its own do not have the same mass as a proton or neutron in a chemical nuclei. More than that, the mass of a proton or neutron is different in different atoms. That subtle change in mass is where the energy comes from.
Sweet! I learned something new today! Thanks, for setting me straight, Knaight!

20. ## Wait, what?

Originally Posted by Knaight
and nucleons can be converted from protons to neutrons and vice versa via decays, but you don't lose entire nucleons to energy.
Charge isn't conserved in nuclear decay? That's downright weird.

I seem to recall an experiment (with huge pools of underground water) waiting to observe proton decay. According to google, they never saw it. I suppose if things decayed from positive to neutral as often as vice versa, it wouldn't be all that different from assumptions based on enthropy (nothing forces entropy to always increase, just like nothing forces a casino to continue running a net profit (at least just on the tables, covering payroll and the rent is another story)).

21. ## Re: Wait, what?

Originally Posted by wumpus
Charge isn't conserved in nuclear decay? That's downright weird.
No, charge is conserved, but there may be particles involved that are not part of the nucleus. The change in charge can be accounted for by emitting or absorbing an electron or positron.

The actual specific subatomic reactions involved are more restricted than that, and also involve neutrinos, anti-neutrinos, muons, photons, and other such things that I don't know much about, but the point is that charge is conserved for the total of the nucleus and the surrounding environment, and a change in charge in the nucleus can be balanced by an opposite change in charge of the environment.

22. ## Re: Plutonic Fusion detected

Originally Posted by wumpus
Charge isn't conserved in nuclear decay? That's downright weird.
Charge is conserved, individual nucleon types aren't. A neutron splitting into a proton and an electron conserves charge, a proton emitting a positron and becoming a neutron conserves charge, etc.

Originally Posted by wumpus
I seem to recall an experiment (with huge pools of underground water) waiting to observe proton decay. According to google, they never saw it. I suppose if things decayed from positive to neutral as often as vice versa, it wouldn't be all that different from assumptions based on enthropy (nothing forces entropy to always increase, just like nothing forces a casino to continue running a net profit (at least just on the tables, covering payroll and the rent is another story)).
This is another difference between particles on their own and particles in a nucleus. A free neutron will decay into a proton and a free electron pretty quickly (I want to say that the half life is about 15 minutes, but that's from memory); they're much more stable in most nuclei. Similarly a free proton is all sorts of stable, but if they're in a nucleus outside the band of stability (essentially a set of proton-neutron ratios stable at given atomic numbers) that can be pushed into the band by proton decay it's generally going to be fairly radioactive as a result, usually with positron radiation.

Of course, there's exceptions there, which is all but inevitable when making broad generalizations for a bunch of different elements. Plus there's electron capture, which is also fairly major.

23. ## Re: Wait, what?

Originally Posted by wumpus
I seem to recall an experiment (with huge pools of underground water) waiting to observe proton decay. According to google, they never saw it..
Isn't that what they do to detect neutrinos? How would you tell the difference?

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•