- #1
eroxore
- 23
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Hello forum.
So the other day I was pondering properties of atomic nucleus, in particular the property of binding energy (mass defect). Whenever a nucleus -- through a nuclear reaction of some sort -- is split or joined into a more stable nucleus, energy is released. However the newly formed nucleus which is more stable has more binding energy than the nucleus from which it formed. How can we then say that energy is released? Is it not rather contradictory? The binding energy grew post-reaction, but should it not have decreased since energy was released?
(Maybe I am just interpreting binding energy incorrectly, since it essentially just measures the change in mass in nucleons in a free versus bounded state and therefore does not necessarily have anything to do with the pre-reaction nucleus).
If we look at masses-per-nucleon, this problem can be intuitively explained: The newly formed and more stable nucleus has less mass-per-nucleon than the nucleus from which it formed. According to E = mc^2, that means that the new nucleus cumulatively has less energy than the pre-reaction nucleus in terms of the masses of the elementary particles. Thus one realizes the nucleons lost energy during the reaction and one can reasonably conclude that lost energy was the energy released in the reaction.
Another perspective on the same problem is that "less stable" can be interpreted as "more/highly energized". So if a nucleus joins/splits into a more stable one, we can conclude that this "excess" (if you will) energy prior to the reaction has been released throughout the reaction. So this is why for example iron will not spontaneously join/split into any other nucleus. It is because iron is as stable is at gets (for all intents and purposes) and in order for iron to form a less-stable nucleus (i.e. more energized nucleus), energy must be inserted externally into the system.
Much appreciated if anyone could help me understand how the increasing of binding energy despite releasing energy throughout the reaction is true.
So the other day I was pondering properties of atomic nucleus, in particular the property of binding energy (mass defect). Whenever a nucleus -- through a nuclear reaction of some sort -- is split or joined into a more stable nucleus, energy is released. However the newly formed nucleus which is more stable has more binding energy than the nucleus from which it formed. How can we then say that energy is released? Is it not rather contradictory? The binding energy grew post-reaction, but should it not have decreased since energy was released?
(Maybe I am just interpreting binding energy incorrectly, since it essentially just measures the change in mass in nucleons in a free versus bounded state and therefore does not necessarily have anything to do with the pre-reaction nucleus).
If we look at masses-per-nucleon, this problem can be intuitively explained: The newly formed and more stable nucleus has less mass-per-nucleon than the nucleus from which it formed. According to E = mc^2, that means that the new nucleus cumulatively has less energy than the pre-reaction nucleus in terms of the masses of the elementary particles. Thus one realizes the nucleons lost energy during the reaction and one can reasonably conclude that lost energy was the energy released in the reaction.
Another perspective on the same problem is that "less stable" can be interpreted as "more/highly energized". So if a nucleus joins/splits into a more stable one, we can conclude that this "excess" (if you will) energy prior to the reaction has been released throughout the reaction. So this is why for example iron will not spontaneously join/split into any other nucleus. It is because iron is as stable is at gets (for all intents and purposes) and in order for iron to form a less-stable nucleus (i.e. more energized nucleus), energy must be inserted externally into the system.
Much appreciated if anyone could help me understand how the increasing of binding energy despite releasing energy throughout the reaction is true.