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Why do both nuclear fission and fusion produce energy?

It seems a little odd that both would produce energy. One would think that it uses up energy to do one thing, and it releases energy to do the other. Why does it go either way?

Update:

Edit: To clarify: I understand that when you fuse two nuclei together, there is energy given off because of the nuclear binding energy, but wouldn't this be less than the energy required to actually get the two nuclei to fuse?

I could say the same thing in the other direction: why isn't the energy in the neutron that is used to split an atom in fission greater than the energy released when it splits?

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  • Talasi
    Lv 4
    10 years ago
    Favorite Answer

    You are actually right in your assumption, to a degree. There is a certain point in fusion where you don't get any energy. Once you hit iron, suddenly doing any more "fusing" is going to require energy input.

    The same with fission. If you drop down to that point, you won't be getting any energy out of the process.

    So fusion with uranium would get you nowhere. It'll only be productive with fission. And you couldn't actually perform fission on hydrogen, but the point is the same. Fusion, yay. Fission, nay.

  • Anonymous
    5 years ago

    Actually, this is not exactly that fusion and fission release energy. It is the fusion of *light* nucleus and fission of *heavy* nucleus release energy. If you try to fuse uranium, of fission helium, you will have to provide energy. The point is that the static nuclear energy is at lowest for a specific nickel isotope, but for all practical purpose, this is about the same as for the most common iron isotope, so this is usually what is being quoted as the most stable nucleon. Everything lighter would release energy when fusing, everything heavier would release energy when fissioned. Of course, there is a problem with fission, as breaking a nucleus in 2 means having two pieces that are about 1/2 the mass of the original. And each piece cannot be lighter than iron, or else the fission would absorb a bit of energy instead of liberating energy. This has interesting implication. Any element heavier than iron that exists around us thus required energy to be provided, hence could only be made in a process where lots of energy forces light elements to fuse despite them absorbign energy while doing so. This occurs naturally only in supernova. That is where gold, lead, uranium, etc. originates from.

  • 10 years ago

    Sorry, why would it use up energy for one and release energy for the other?

    Obviously nuclear fission has been used for many years without 'using up' energy - just creating pollution and a dangerous and relatively inefficient method.

    One produces energy by splitting an atom, the other by fusing or compressing it (as the sun does).

    Until fossil fuels like oil stop funding our politicians and our politicians are less concerned with money, alternative fuels will never be relevant until they replace oil.

  • 10 years ago

    Both fission and fusion create new isotopes that have less total mass than the original atoms. The mass is converted to energy (E = mc^2).

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  • 10 years ago

    both processes release binding energy that holds the nucleus together.

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