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Thread: Mass Energy Equivalence Nuclear Chemistry

  1. #1 Mass Energy Equivalence Nuclear Chemistry 
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    This question probably shows my obvious ignorance in this topic. Huzzah for asking questions!
    When a radioactive isotope decays, part of it's mass is converted into energy. (It emits alpha particles, beta particles, or gamma rays). If a radioactive isotope (lets call it X) emits, say, an alpha particle, then the total mass of the system is represented by:
    Mass of X=Mass of Y + Mass Alpha Particle,
    where Y is the next element in the decay series, with mass equal to Mass X minus Mass Alpha particle.
    According to my understanding of the concept, when this occurs a portion of the mass is converted into energy, and this is where the energy for nuclear reactors and nuclear devices is derived from. Where does the mass come from? According to the probably over-simplified equation above, all the mass is conserved, unless somehow Mass X > Mass Y + Mass Alpha Particle.


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    Ophiolater Nehushtan's Avatar
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    Quote Originally Posted by s. soloyov View Post
    Where does the mass come from?
    Umm from ?


    Last edited by Nehushtan; March 1st, 2013 at 01:51 AM.
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    Brassica oleracea Strange's Avatar
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    A slightly more accurate description would be:
    Mass of X=Mass of Y + Mass Alpha Particle - Kinetic energy of X - kinetic energy of Y - kinetic -energy of alpha particle.

    This says that, yes: Mass X > Mass Y + Mass Alpha Particle

    The difference is the energy released. This energy came from the binding energy holding X together. Or, rather, the difference between the binding energy of X and the binding energy of Y.
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    Quote Originally Posted by Strange View Post
    A slightly more accurate description would be:
    Mass of X=Mass of Y + Mass Alpha Particle - Kinetic energy of X - kinetic energy of Y - kinetic -energy of alpha particle.

    This says that, yes: Mass X > Mass Y + Mass Alpha Particle
    So if Mass X > Mass Y + Alpha Particle, does that mean that the particles in Y and the alpha particle have less mass than the corresponding particles in X? Meaning that a neutron from Y would have less mass than a neutron from X?

    Quote Originally Posted by Strange View Post
    The difference is the energy released. This energy came from the binding energy holding X together. Or, rather, the difference between the binding energy of X and the binding energy of Y.


    Does this mean that the binding energy has mass?
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    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by s. soloyov View Post
    So if Mass X > Mass Y + Alpha Particle, does that mean that the particles in Y and the alpha particle have less mass than the corresponding particles in X? Meaning that a neutron from Y would have less mass than a neutron from X?
    No, the individual particles all have the same mass. The combined mass may be slightly more because of the energy holding them together.

    Does this mean that the binding energy has mass?
    Yes, mass and energy are equivalent (E = mc2 as Nehushtan noted earlier). If you add energy to something you effectively increase its mass.
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