If in nuclear fission, the sum of the masses of the resulting atoms is the same as the parent ($\text{U}_{236}$, after fission is $\text{Cs}_{93}$ + $\text{Rb}_{140}$ + 2 neutrons), where does the concept that mass is lost in favor of energy come from? Keeping in mind the formula: $$E=mc^2$$ Are some electrons and protons of the progenitor disappearing in favor of energy?
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The nuclear reaction that you have written is incorrect. The product should have 3 neutrons. – Mechanic Sep 29 '21 at 16:33
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From my knowledge, I believe that one of the neutrons is the one who caused the reaction, correct me if I am wrong. In that case, I may need to reformulate the question. – PhysicccM Sep 29 '21 at 16:36
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The one neutron reacts with the $U_{235}$ nucleus to produce $U_{236}$, which undergoes nuclear fission to produce the products. – Mechanic Sep 29 '21 at 16:41
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Totally fine, then my reasoning was kind of wrong (I have edited the question). Anyways, in that case, what is the portion of mass that is really transformed into energy? – PhysicccM Sep 29 '21 at 16:45
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Try this https://physics.stackexchange.com/a/667132/313823 This confusion seems to come up a lot. – RC_23 Sep 30 '21 at 00:51
2 Answers
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The total number of nucleons (protons and neutrons) is the same after nuclear fission as it was before. The energy released in fission comes from the difference in binding energy between the fissile material and its fission products.
gandalf61
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The atomic number is not the same as the atomic mass. The number is just the sum of the counts of protons and neutrons in a nucleus. That number is conserved during fission (be sure to include the escaping neutrons). The mass is an actual measurement and accounts for the masses of the protons and neutrons and the energy content of the nucleus. Therefore your assertion that the masses before and after fission are the same is wrong.
niels nielsen
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