Nuclear Fission, Mass Defect, and Electricity Generation.

Discussion in 'Physics & Math' started by Captain Covalency, May 16, 2015.

  1. Captain Covalency Registered Member

    Messages:
    15
    When an induced Nuclear Fission reaction occurs, mass is 'lost', and by 'lost' I of course mean converted into energy, via Einstein's equation E=mc^2 (Proving matter and energy are relative). However, it just makes one wonder, why is that mass lost? Why are the products (daughter isotopes) lower in mass than the reactant (parent isotope)? It suggests that mass was converted into energy, but for what purpose?

    Apparently, different isotopes have different levels of binding energy (The more binding energy per nucleus, the more stable the isotope), and the most stable isotope is iron-56, so, as expected, the products of a nuclear fission reaction are closer in mass to 56, than the reactant was (To become more stable). Now, since the closer an isotope is in mass to Iron-56, the more binding energy it has, it would make sense that the products would have less mass, losing it due to it being converted to the extra binding energy needed to hold the new nucleons together.

    Now that, fellows, is where my problem comes in. When we want to find out the energy yield of a Fission reaction, we take the Mass Defect (Difference in mass) from the Reactant to the Product, and input that mass difference into the equation E=mc^2, to give us the amount of energy that would be created from that amount of mass. However, if I am not mistaken, would the energy value we get, merely be the amount of binding energy produced by transforming the mass into energy? Why do we act like that value is the value we yield or receive? We don't harness that binding energy and use it to transform into thermal energy, to eventually generate electrical energy, do we?

    That's my question. When we calculate the energy value from a given mass defect after a nuclear reaction, is all that energy just binding energy, that was created from the mass, or is some of it different types of energy, such as thermal, used to generate electricity (by boiling water and turning a turbine which is connected to a magnet and a metal coil, for those of you that are wondering how the thermal energy produces electrical energy)? I know it's a lot, but two more questions arise from the last one, depending on the answer; If all the energy is simply just binding energy, then how do we harness it to create thermal energy for electricity production (If we took some of that energy for transformation, would the nucleus of the isotope not begin to dis-incorporate, not having enough binding energy to keep itself together)? However, if the energy is, in fact, multiple forms of energy (binding, thermal, electromagnetic, etc), when why did the atom lose mass to create the unnecessary forms (it should only need the binding energy), and why do we use the same mass defect value (which gives us the total energy produced) and say that we yield or harness all of that energy into the thermal energy we need, when realistically, we are only actually using a fraction of that energy value that we calculated?
     
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  3. Layman Totally Internally Reflected Valued Senior Member

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    From what I have hear, in a nuclear fission reaction the amount of energy produced is always calculated to be slightly less that what would be expected to come from the equation E = mc^2. It is not known really why it comes out to be less, but it is suspected to be from loses of energy that cannot be accounted for. That is actually a problem that needs to be worked on and explained in physics or discovered.

    I am not exactly sure about the specifics of the rest of the question, but I would think it is just calculated from the loss of mass from the reaction. Some of the protons or neutrons may be lost, and the energy would just come from that portion of mass that was changed to energy or destroyed in the process. "Binding energy" as you say, sounds more like the strong force, and the strong force is a fundamental force of nature. Then the fundamental forces of nature are thought to not be able to be a source of energy in itself. Then I would have to say, no, none of the energy would come from the binding force of the atom.

    The mass itself would be lost, because protons and neutron would be destroyed. They would then be converted to other particles considered to be forms of energy, because the new particles do not have mass. Then it could also lose a number of electrons that would also have mass.
     
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  5. Captain Covalency Registered Member

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    That does make logical sense, not being able to harness the energy responsible for the four fundamental forces. However, if all that energy received from the transformation of mass (the energy we calculate from the mass defect) is solely other forms of energy (such as thermal, kinetic, etc.), and not binding energy, then why would the atom have lost mass to create those forms of energy in the first place? What would be the point in doing so? I'm wondering, since the products are smaller in mass, closer to a mass of 56 amu, and therefore need more binding energy to keep their nuclei together, then where would they get the extra energy to accommodate for the extra needed binding energy, if not from the loss of their own mass?
     
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  7. mathman Valued Senior Member

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    The energy from nuclear fission result from the energy equivalence of the masses of starting particles (U235 + neutron) and the masses of the products. Some of the energy is in the kinetic energy of the products, but most of it is gamma rays, etc.
     
  8. Russ_Watters Not a Trump supporter... Valued Senior Member

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    5,051
    Yes, we do. Why do you think otherwise?
    I'm not sure you are recognizing what happens to the binding energy when it is released: it is released as EM and particle radiation. Light and heat.
     
  9. Layman Totally Internally Reflected Valued Senior Member

    Messages:
    1,001
    It sounds like your looking for deeper answers that the standard model does not have, but for the most part, it is what Russ Watters said, particle radiation. The standard model doesn't have a theory of gravity, or in other words, it doesn't explain why gravity works. Then the answer is nobody really knows, but some people have ideas about it, like quantum loop gravity.

    Then I think only a handful of people in the world actually understand quantum loop gravity or what it says about exactly what is going on. I haven't had much luck finding good layman descriptions of it, so I never really fancied the idea. Then some people think that it is caused by quantum waves or undiscovered component particles. Then it could also be explained by a theory that goes beyond the standard model that describes hidden variables. The problem is that we don't have the technology to test gravity at the quantum level. It is the weakest force of nature, so it makes it the hardest to detect in small quantities. The only reason why it feels strong to us is because the Earth is so big. Then a magnet that can fit in the palm of your hand can easily overcome the force of gravity.

    I would think that it most likely comes from overlapping waves of component particles or virtual particles that make up higher order particles. Then when these particles break apart from each other, their waves no longer affect each other. Then that is just a hunch at best. People have already been working on theories like that since the inception of the standard model with little to no success. There is a small possibility that a particle from one of these theories actually shows up in the creation of a Higgs Boson, but it doesn't mathematically affect anything or any of the other particles. Then they cannot prove it actually exist. The only function of it, if it is actually there, is allow photons to be generated from the Higgs. Then, in my opinion, it could just also mean that a part of the standard model is just wrong...
     
  10. origin In a democracy you deserve the leaders you elect. Valued Senior Member

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    11,049
    Yes, that is exactly what happens.
    When fission occurs the U235 atom produces 2 fission products (usually 2 nuclei that have a mass of about 95 and 135), between 2 and 3 neutrons and gamma rays. The overwhelming majority of the thermal energy produced results from the kinetic energy of the 2 FP. These completely ionized heavy nuclei blast through the matric of the fuel causing secondary ionization and raising the temperature of the matrix.
     
  11. exchemist Valued Senior Member

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    9,539
    Previous answers may have already given you what are looking for, but I'll focus on one aspect, which is what is meant by "binding energy" and what "sign" we should think of it as having. It is a mistake to think that the stronger the binding the more energy there is in the bond. I may be wrong but I have the feeling from what you have written that you may be thinking this way.

    It is the other way round. The stronger the bond the lower the energy of the bound system, compared to the unbound one. When a strong bond is formed, energy is released. This happens in exothermic chemical reactions: weaker bonds are replaced by stronger bonds and energy is thereby released.

    The converse also applies. It takes energy to break bonds. Think of a rocket bound to the Earth by gravitation, or an electron bound to the nucleus of an atom by electrostatic attraction. In both cases you have to put energy in to separate them - by doing work against the force of attraction that binds them. The more strongly they are bound, the more work has to be done, i.e. the lower the energy state of the bound system, compared to the unbound one.

    So "binding energy" is something of a contradiction in terms. The energy release comes from replacing weaker binding with stronger binding, so that the system moves to a more stable, lower energy, state.

    To recap: the stronger the binding the lower the energy.
     
  12. Aqueous Id flat Earth skeptic Valued Senior Member

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    6,152
    Good answers Russ, Origin and exchem.

    I too wondered what "why don't we harness the binding energy" even meant, given that nukes are now some 50 years old, and for all of that time ''we" have been harnessing the heat to generate electricity.

    That being said, I suppose we could entertain blue-sky schemes to directly induce electric currents at the site of each fission reaction. For example, suppose the energy of reaction ("just before" launching as radiation) is magically coupled into a macromolecule that resembles those that do photosynthesis (e.g. the photosystem II protein complex). And here "magically" allows for such efficiency that negligible excess heat is dissipated, so that the proteins remain cool and intact. Secondly, the perfectly coupled structure would ideally remain devoid of contamination by radiation, thus pure stable oxygen and hydrogen (for example) could be created (from a water supply) and used as fuel, and/ or to power attached fuel cells, etc.

    Not to take this too far into left field but maybe someone can propose a "macromolecular" "gamma ray powered electric generating" "nanocell".

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