Is there a connection between mass defect and bound energy?

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Discussion Overview

The discussion revolves around the relationship between mass defect and binding energy in atomic nuclei, particularly in the context of nuclear reactions such as fission. Participants explore the implications of mass defect when nucleons are bound within a nucleus and the energy dynamics involved in breaking these bonds.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that the mass defect indicates that the sum of the masses of protons and neutrons exceeds the measured mass of the nucleus, suggesting a conversion of mass into binding energy.
  • Others argue that to split off a nucleon, one must input energy equal to the binding energy, as the mass defect reflects energy that was dissipated during the formation of the nucleus.
  • A participant questions how mass defect appears if energy was initially invested to form the nucleus, seeking clarification on the process.
  • It is noted that energy is released when nucleons bind together, but energy must be supplied to break these bonds, contradicting the initial assumption that energy is released during the breaking process.
  • Fission is discussed as a process where a nucleus with lower binding energy per nucleon splits into daughter nuclei with higher binding energy per nucleon, resulting in a net release of energy, although activation energy is required to initiate the process.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and confusion regarding the concepts of mass defect and binding energy. There is no consensus on the initial assumptions about energy dynamics in nuclear reactions, indicating that multiple competing views remain.

Contextual Notes

Some misunderstandings about the relationship between binding energy and mass defect are evident, particularly regarding the energy required to break nucleon bonds versus the energy released during binding. The discussion highlights the complexity of these concepts without resolving the uncertainties expressed by participants.

Bassalisk
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Simple question:

We have defect of mass delta(m) in some nucleus. This simply means that sum of all protons and neutrons is larger than the measured mass of the nucleus.

When I break this bound energy, that mass defect that is turned into bound energy, I have fission? Assuming that I do this with a neutron(most easily approaches nucleus). Energy will be released equal to this bound energy?

Shouldn't then those protons and neutrons, that were scattered, be "defected"?
 
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Bassalisk said:
Simple question:

We have defect of mass delta(m) in some nucleus. This simply means that sum of all protons and neutrons is larger than the measured mass of the nucleus.

When I break this bound energy, that mass defect that is turned into bound energy, I have fission? Assuming that I do this with a neutron(most easily approaches nucleus). Energy will be released equal to this bound energy?

No .. you have that backwards .. in order to split off a nucleon, you would need to put in excitation equal to at least the binding energy. The mass defect reflects binding energy that was *dissipated* when the nucleus was formed ... therefore you need to put it back in in order to reverse the process.
 
SpectraCat said:
No .. you have that backwards .. in order to split off a nucleon, you would need to put in excitation equal to at least the binding energy. The mass defect reflects binding energy that was *dissipated* when the nucleus was formed ... therefore you need to put it back in in order to reverse the process.

So... When I invest energy into reaction, e.g. sending neutron towards some nucleus, It will have to be at least the energy of the binding. Well, when the nucleus was formed, if I invested energy, why does mass defect show up? How does this work exactly?

Can you clear these misunderstandings I have?


Thanks
 
Bassalisk said:
So... When I invest energy into reaction, e.g. sending neutron towards some nucleus, It will have to be at least the energy of the binding. Well, when the nucleus was formed, if I invested energy, why does mass defect show up? How does this work exactly?

Can you clear these misunderstandings I have?Thanks

The mass defect shows up because a certain amount of mass was converted into energy when the nucleus was formed. This energy is radiated away (typically as gammas). Basically it is nothing more complicated than E=mc2 ... it's just that the energy involved from binding of nucleons due to the strong force is so large that it makes sense to measure it as mass.

Note that there is nothing special about this ... there is a mass defect associated with the binding of electrons to atoms as well. It's just very very small compared to the mass defects due to nucleons in the nucleus. However it can still be measured .. I don't have a reference handy but I believe that this mass defect for electron binding has been measured by very high-precision mass spectrometry.
 
I am beginning to form a slight picture. If I want to expel one nucleon from the core, I have to hit it with at least binding energy. When hit it, energy is released? What happens then? What happens to that defect of mass, that binding energy?
 
Bassalisk said:
I am beginning to form a slight picture. If I want to expel one nucleon from the core, I have to hit it with at least binding energy. When hit it, energy is released? What happens then? What happens to that defect of mass, that binding energy?

No .. energy is released on *binding*. If you want to *break* the binding, you have to put energy back in. There is no energy released by the breaking of the bond.
 
Ahaaaaaaaaaaaaaaaaaaaaaaaaa :D I had it confused with a fission, nuclear explosion etc.
 
Bassalisk said:
Ahaaaaaaaaaaaaaaaaaaaaaaaaa :D I had it confused with a fission, nuclear explosion etc.

Fission is different .. in such a case, a nucleus with a *lower* binding energy per nucleon splits, resulting in two daughter nuclei with *higher* binding energy per nucleon. So the overall process releases energy. However, fission often (always?) has an activation energy associated with it, so you need to put a little energy in (e.g. with a neutron collision) so that you can get a LOT of energy out.

That last point may have been what was confusing you ... yes, you do have to do something to start the process, which then releases energy. It's similar to lighting a fire with a match .. you put in a little energy to start the combustion process, but the overall process releases far more energy that you put in initially.
 
Last edited:
Thank you for your help Cat <3
 

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