Is this the reason why the obviously wrong calculation that fusion ends with iron is hammered into everyone?
You can overshoot iron, but you'll decay back to it.
If you fused into something bigger, it would still be more efficient to split that atom and fuse it's nucleons into more Iron.
Atoms are mostly empty space - chemical lattices are mostly empty space - so in something like a star you can make super-dense iron and turn anything else kicking around into more iron.
EDIT: I feel like the problem here if you're assuming that the size of an atomic nucleus is anything other then negligible compared to it's electron shells. There's no situation under which a non-neutron star will "fit" more of a heavier nucleus in, compared to just densifying iron.
Of course, but that doesn't easily happen, as the nucleons are already bound together into heavier nuclides. In fact I guess that might happen in supernovas: The main sequence burns into lead, which is then reconstituted into the iron-nickel mixture that we know from iron meteorites, which also releases energy due to the higher average binding energy per nucleon, but needs extreme conditions to occur.
So in a star creating regular fusion events, even an errant heavier nuclei is going to eventually be decayed down to Fe (or head off to become a heavy element in the upper crust).
Below iron fusing nucleons gives you energy; above iron it takes energy. If binding energy increased all the way up you wouldn't be able to have nuclear fission.
You would, because the smaller nuclides have higher total binding energy than the large nuclides. That doesn't contradict every step inbetween being favorable. You are adding hydrogen with zero binding energy.
i.e. total binding energy literally goes down as you get to larger nuclides.
> That doesn't contradict every step inbetween being favorable.
Yes, it does. Energy is strictly additive.
> You are adding hydrogen with zero binding energy.
Exactly. You are taking a bare nucleon, with zero binding energy, adding it to a system, and reducing the total binding energy (i.e. increasing the potential energy of the system). By conservation of mass-energy, this requires you to put in energy, and increases the total mass of the system.
No, it goes up. Iron-56: 492.26 MeV Uranium-238: 1801.7 MeV
Binding energy is a negative energy value; iron having a high binding energy means it is a low energy state, so adding zero-binding-energy hydrogen to that system and decreasing the binding energy increases the potential energy of the system from the low value of iron.
While fusion does not end at iron 56 (whose nucleus has the lowest mass per nucleon), the quantities of heavier nuclei produced by fusion decrease very steeply with increasing atomic mass, becoming low beyond the isotopes of nickel, very low beyond the isotopes of zinc and negligible beyond the isotopes of germanium.
The elements heavier than zinc are produced mostly or completely by other kinds of reactions, e.g. neutron capture.
The nuclei you're producing needs to have a higher binding energy than the nuclei you're fusing do on their own. There is nothing you can fuse with iron, or any heavier nucleus, that will produce a stable element with greater binding energy than its components. Nickel-62 is actually the most stable nucleus, with the most binding energy per nucleon, but stellar nucleosynthesis ends with Nickel-56 which decays into Iron-56, which has the lowest mass per nucleon. All nuclei heavier than Nickel-62 are produced endothermically.
62Ni(p,2n)61Cu
Copper-63 has spin of 3/2 while nickel-62 has a spin of 0, so you can't simply add a proton (whose spin is 1/2), you need at least 3 fermions to participate in the reaction.
The Copper-61 and two neutrons of course have a higher mass than the Nickel-62 and the proton.
> That doesn't make any sense, the difference between nickel-62 and copper-63 is one extra proton. It's also bullshit, since the differences in spin get equalized by neutrinos.
First, nuclei are not simply the sum of their protons and neutrons. They have structure. While copper-63 happens to have 1 more proton than Nickel-62, in its stable, lowest-energy form it also has 2 neutrons that are in a different configuration. This is why it's spin is not simply the sum of Nickel-62's spin and a proton's spin. Spin needs to be preserved. Producing neutrinos to carry off spin would violate conservation of lepton number. You need to create a lepton pair, which is exactly how Nickel-63, produced by neutron capture, is able to beta decay into Copper-63.
> Also note that this closely corresponds to what we see: A star would be expected to burn by fusing hydrogen into heavier nuclei, which shed helium as alpha particles once they get too heavy, eventually ending up with mostly lead and helium.
This is not what we see. Stars burn hydrogen by two different methods into helium via the pp process and the CNO cycle. Carbon is formed in the triple-alpha process where three alpha particles fuse. Heavier elements are formed along the alpha ladder by adding alpha particles, a process that stops at iron-56. There are some other side processes like Carbon, Oxygen, Neon, and Silicon burning which also end at iron-56. Heavier elements like lead are not produced during the star's lifetime, but rather during events like supernovae and neutron star collisions by neutron capture in the s and r processes.
> No need for "exotic" physics. And it also explains the persistent failure of fusion energy
Fusion reactors fail because of plasma instabilities which have nothing to do with nuclear reactions.
> as it tries to build upon nonexistent mechanisms made up to confuse people trying to build nuclear weapons.
Basic principles like conservation of spin are not exotic physics nor are they a conspiracy. If the American government did sabotage fusion research to preserve nuclear secrets, why don't any of those powers who discovered those nuclear secrets anyways like Russia or North Korea have working fusion reactors?
Please take the time to read up on nuclear physics, it's a fascinating topic and very enlightening about why many things in the universe are the way they are.
Yes you need a neutrino/antineutrino pair. I don't see what is being violated.
>This is not what we see. Stars burn hydrogen by two different methods
No such observation has been made.
>why don't any of those powers who discovered those nuclear secrets anyways like Russia or North Korea have working fusion reactors?
They also don't want to reveal how these weapons work.
The observation has been made. We can use emission spectra to look at the composition of stars, we can detect neutrinos given off by the stellar fusion processes and measure their energies. Do not mistake ignorance of the data for lack of data.
So if everyone from Washington to Pyongyang is in on the conspiracy, exactly who are they trying to keep these details a secret from?
>exactly who are they trying to keep these details a secret from?
Pretty much everyone. There are not that many countries with thermonuclear weapons (Pyongyang doesn't have one) and you don't want e.g. ISIS make a clandestine 10Mt bomb.
The most lead rich stars ever detected are less than 0.000000000000005% lead by mass. Stars are formed from stellar nebulae which are the remnants of supernovae that create heavy elements - except for the very first stars in the universe all of them contain heavy elements. As a star ages and its temperature changes, it can bleed off some material, which will preferentially remove lighter elements (because it takes less energy for them to escape), leaving behind an increased concentration of the heavy elements.
Anyone who conducted even rudimentary nuclear experiments would be able to identify if the most basic tenets of quantum mechanics were a lie. Maintaining the ruse would require pretty much all the physicists in the world to be in on it. And if all the physicists are in on it, who exactly that is not in on it would be building these thermonuclear weapons? No, the basic physics of thermonuclear weapons are well known, but the engineering is incredibly difficult and resource intensive.
You get a nickel-63 if a nickel-62 captures a neutron. You can't get a positron/neutrino pair directly, you get a w+ boson which will decay into a positron/neutrino pair, but that w+ boson, like the z0 boson in the other case, is prohibitively heavy so this reaction doesn't take place. If you want, you can think of the 62Ni(p,2n)61Cu as a Nickel-62 fusing with a hydrogen to produce an excited state of Copper-63 which then immediately decays by double neutron emission to Copper-61, but the fact is the end product being Copper-61 is observed reality, and any model that doesn't predict its production is at best an elegant fiction.
Good. So you agree that p+p fusion into deuterium cannot occur?
>Maintaining the ruse would require pretty much all the physicists in the world to be in on it.
Any time anyone figures out they get shut down as described in the article.
>the basic physics of thermonuclear weapons are well known, but the engineering is incredibly difficult and resource intensive.
They figured making false principles well known would make keeping the real mechanism secret easier.
Until the iron 56 isotope, the average mass per nucleon decreases quickly, then it increases slowly with increasing atomic mass.
For reactants heavier than iron 56, fusion is not possible, but for some reactants lighter than iron 56 it is possible to fuse into nuclei a little heavier than iron 56, belonging to the few elements placed immediately after iron, where the average mass per nucleon has not increased much yet, so it is still lower than that of many of the lighter elements.
That doesn't equal to the binding energy per nucleon though, as you add a nucleon.
And since most of the results of hydrogen hitting something are unstable, this happens almost immediately, leaving the total process looking more like fission (a proton hitting a nucleus, and producing two nuclei of smaller mass than the original). Which is, in fact, how uranium fission works, only with neutrons rather than protons.