In fusion , I have understood so far that two light nuclei fuse to form a heavy nucleus. The nucleons in the light nuclei experience lesser binding energy as compared to the nucleons in heavy nucleus which experience higher binding energy. The mass of the reactants is more than the mass of the product hence energy is released. Since the nucleons experience a change in binding energy, they lose mass. This mass turns into the extra binding energy required to bind the nucleons into place. But where does the mass defect originate from?
The helium nucleus (for instance) has 2 protons and no neutrons-the mass remains the same, so why did the mass defect occur? Also, if the mass converts to binding energy then why is energy released in the fusion. It should remain the same or should in fact, absorb energy. Please correct my understanding if wrong or, please answer the two questions above. I have been thinking about this for a month now.... :(