Hello. My teacher and I have had this very intense debate for quite some time now and we need your opinion on this issue. This question is, where does the energy released in a nuclear fission reaction come from? (Please use the terms "nuclear binding energy" and "mass defect") My take on this issue is that when Uranium 236 splits into Krypton, Barium and 3 neutrons, the nuclear binding energy on a per nucleon basis increases for this fission event. This is because Krypton and Barium have higher nuclear binding energy than Uranium, per nucleon. This, in turn, means that the products of the fission reaction (Krypton, Barium and 3 neutrons) have a smaller mass than Uranium does. This missing mass is converted to energy. In short, my belief is that the products of a fission reaction has more nuclear binding energy than the reactants does, therefore the products experience greater mass defect and thus possess less mass. This mass is converted to energy via E=mc^2. My teacher, however, has a different opinion. My teacher believes that although nuclear binding energy increases on a per nucleon basis in a fission reaction, the fact is that 3 neutrons have been released. This means that overall nuclear binding energy has decreased during the fission reaction. In short, my teacher's opinion is that the source of energy in a fission reaction is the nuclear binding energy that has been holding the 3 neutrons. Please indicate which theory is more correct and why. Thank you!