Fusion Questions: How Does Fusing Nuclei Produce Energy?

[ParticalMan28]

Hi everyone, Name's Mike.

I have a few questions regarding the fusion of atomic nuclei:

One of the basic laws of matter is that if you loose mass you release energy, and if you absorb energy efficiently, you'll gain mass respectively.


I understaind that during fission, when heavy atomic nuclei are split and energy is released from the force that once held the nuclei together ( I think that's the weak force...right? or was that the strong force?) is now force apart. So there was a lose in mass for heavy nuclei and neutron, and there was a gain in energy from fission fragments, electrons, and nuetrinos.

but..in fussion such as the one in the sun fuses lighter nuclei to form heavier nuclei. but that you're creating a more massive object, but you still release more energy from the reaction (even more from the fission reaction).

So, I now I'm missing out on something in the prosses, so how can this be?

 

[Meir Achuz]

In fusion deuteron+triton-->He+n.
Since d+t is more massive than He+n, energy is released.

In fission, the force holding the nucleus together is the "strong" force, but the energy release arises mostly from the difference in the Coulomb energies of the nuclei.

 

[Norman]

Take a look at (aka google) "Binding energy per nucleon."

Basically, for the lighter nuclei, the binding energy per nucleon increases with mass (up to Iron). This makes fusion a reaction that releases energy for nuclei lighter than Iron. For heavier nuclei you do not.

After about Iron on the "binding energy per nucleon" vs mass number graphs, you see that the slope become negative. This means that fission is a process that will release energy.

 

[malawi_glenn]

And here is the "binding energy per nucleon" vs mass number graph:

http://en.wikipedia.org/wiki/Binding_energy