How is fusion a viable energy source if fission, the opposite, also functions as an energy source?


Fission is what is currently used in nuclear reactors today, and it basically consists of atoms breaking apart and releasing energy due to their bonds being broken.

How is fusion such an efficient energy source? I would imagine that to create atoms, large amounts of energy would have to be pumped in to make bonds.

In: Physics

To create large atom, large amount of energy have been pumped in to make the bons, this was done by supernova that created those heavy elements.

Fusion of light element create energy, only up to Iron. Anything equal or bigger than Iron will absorb energy as it fuse. This is why a star will have fusion until Iron pile up in its core (if it’s massive enough to get there) and then the fusion of Iron will suck up a lot of energy, which make the star collapse on itself. This is a supernova.

It’s similar with fission. We can create excess energy only with fission of heavy element, not lighter one.

There’s an interesting curve called the [nuclear binding energy curve](; it shows the relationship between the mass of an atom and how much binding energy it has per nucleon (proton or neutron). It shows that lights atoms, smashed together, have more binding energy per nucleon that the parent atoms; this energy difference is released. Conversely, if a very heavy atom is split, its daughters will also have more binding energy per nucleon. This is because nuclear binding energy rises as you get more nucleons, but it has an extremely short range and is “saturable” (each nucleon can only pull on a finite number of others). If you start with a few nucleons, adding more has them all pulling on each other, and they’re more tightly held. But as an atom gets bigger past about 56, the nucleons on one side of the nucleus are too far from the ones on the other side to pull on them as hard. Once you get to big atoms, 100 and 200 nucleons big and bigger, some of the nucleons are barely being held in at all.

Because those are different atoms being used. In a fission reactor, you would have a large aton like uranium splitting apart. In a fusion reactor, you would have hydrogen atoms combining into helium. In both cases, your final product has lower potential energy than what you started with, and the leftover energy is what you use.

Different atoms. Elements heavier than iron release energy if they are split. Elements lighter than iron release energy if they are fused.

If you fuse two atoms of hydrogen together, you generate helium and you eject a neutron. That ejection creates a LOT of energy because you are tapping into the strong nuclear attraction. Since I am not breaking the atom down, I am not creating a radioactive byproduct.

To put it more simply, there are left over ‘parts’ of the atom’s nucleus that result from the fusion process. Regardless of fission or fusion, those leftover parts expend energy that was bottled up by the atom’s atomic force. It is relatively easy to fuse hydrogen together, we have done it many times, but it is inefficient. For fusion into metallic atoms, you need the energy of an exploding star. So…nothing we can yet do. A star is the one real alchemist in our universe. That might be old information, but it is what I remember from a while back.