Binding energy or Kinetic energy?

AI Thread Summary
The discussion clarifies the relationship between binding energy, mass defect, and kinetic energy in nuclear fusion, specifically in the Deuterium-Tritium fusion process. It explains that the mass defect results from the difference in binding energies before and after the reaction, leading to the release of energy, which is emitted as kinetic energy or radiation. The confusion arises from the misconception that mass defect is directly spent on changing binding energy; instead, it is the difference in binding energy that accounts for the energy released. The conversation also touches on the binding energy changes in nuclear reactors and emphasizes that more tightly bound nuclei are less massive. Overall, the key takeaway is that the energy released in fusion reactions stems from the difference in binding energies, not a direct conversion of mass defect.
A M
Messages
83
Reaction score
16
Summary: I always confuse Binding Energy with Released Energy in such processes. Which one comes from mass defect?
For example in a Deuterium-Tritium fusion two nuclei with lower binding energy converse to He-4 with much higher binding energy (and a neutron). The released energy is 17.6 MeV.
What exactly happens to mass defect?
Is it conversed to the higher binding energy of ∝-particle
or the released kinetic energy of the products?

Anyone could help me with this problem?

1565138815307.png
Fusion of deuterium with tritium creating helium-4, freeing a neutron, and releasing 17.59 MeV as kinetic energy of the products while a corresponding amount of mass disappears, in agreement with kinetic E = Δmc2, where Δm is the decrease in the total rest mass of particles....This difference in mass arises due to the difference in atomic "binding energy" between the atomic nuclei before and after the reaction.

Isn't it a contrast?!:confused:
https://en.wikipedia.org/wiki/Nuclear_fusion
 
Last edited:
Physics news on Phys.org
Concrete has high chemical binding energy. Uranium has low binding energy, it's actually negative. When an atom bomb explodes above a city, the end result is that the uranium has gained more binding energy while the concrete has lost binding energy. The concrete gained mass, the bomb lost mass.

An asteroid can do the same thing as an atom bomb, because it has lot of kinetic energy.

What can we conclude now? Well, it seems that kinetic energy is negative binding energy. Or those two things are the same thing.

(Maybe I made a little bit too strong claim there, negative binding energy is potential energy, kinetic energy and potential energy are both energy, but different types of energy. )
For uranium: nuclear binding energy + electrostatic binding energy < 0

For concrete: total binding energy < 0 , but chemical binding energy is the only binding energy that changes in this particular scenario.

Questions:

A) What binding energy changes are occurring inside a BWR nuclear power plant? BWR = Boiling Water Reactor.

B) What binding energy changes are occurring inside a dedicated district heating reactor?
 
Last edited:
A M said:
What exactly happens to mass defect?
Is it conversed to the higher binding energy of ∝-particle
or the released kinetic energy of the products?
You're confused because you're double counting. It's not that mass defect is spent on changing the binding energy - it is the difference in binding energy. More tightly bound means less massive. That difference is then emitted as kinetic energy or radiation.

So, let's say we have the reaction shown in the picture:
##m_d, m_t, m_h, m_p, m_n## - rest masses of deuterium, tritium, helium, isolated proton, and isolated neutron respectively.
##E## - released energy
##B## - binding energy

now:
##m_d=m_p+m_n-B_d##
##m_t=m_p+2m_n-B_t##
##m_h=2m_p+2m_n-B_h##

and the fusion reaction is:
##m_d+m_t=m_h+m_n+E##

here we could write:
##m_d+m_t-m_h-m_n=E##
##\Delta m=E## (*using natural units)
and conclude that all the energy comes from the difference in initial and final masses (mass defect),

or write:
##(m_p+m_n-B_d)+(m_p+2m_n-B_t)=(2m_p+2m_n-B_h)+m_n+E##
cancelling out all the rest masses of isolated nucleons we get
##-B_d-B_t=-B_h+E##
##-B_d-B_t+B_h=E##
##\Delta B=E##

So we can see that all the released energy comes from the difference between initial and final binding energies. It's the same thing, just more deeply understood.
 
  • Like
Likes A M
Bandersnatch said:
You're confused because you're double counting. It's not that mass defect is spent on changing the binding energy - it is the difference in binding energy. More tightly bound means less massive. That difference is then emitted as kinetic energy or radiation.

So, let's say we have the reaction shown in the picture:
##m_d, m_t, m_h, m_p, m_n## - rest masses of deuterium, tritium, helium, isolated proton, and isolated neutron respectively.
##E## - released energy
##B## - binding energy

now:
##m_d=m_p+m_n-B_d##
##m_t=m_p+2m_n-B_t##
##m_h=2m_p+2m_n-B_h##

and the fusion reaction is:
##m_d+m_t=m_h+m_n+E##

here we could write:
##m_d+m_t-m_h-m_n=E##
##\Delta m=E## (*using natural units)
and conclude that all the energy comes from the difference in initial and final masses (mass defect),

or write:
##(m_p+m_n-B_d)+(m_p+2m_n-B_t)=(2m_p+2m_n-B_h)+m_n+E##
cancelling out all the rest masses of isolated nucleons we get
##-B_d-B_t=-B_h+E##
##-B_d-B_t+B_h=E##
##\Delta B=E##

So we can see that all the released energy comes from the difference between initial and final binding energies. It's the same thing, just more deeply understood.
Thank you very much!
 
Hi there, im studying nanoscience at the university in Basel. Today I looked at the topic of intertial and non-inertial reference frames and the existence of fictitious forces. I understand that you call forces real in physics if they appear in interplay. Meaning that a force is real when there is the "actio" partner to the "reactio" partner. If this condition is not satisfied the force is not real. I also understand that if you specifically look at non-inertial reference frames you can...
I have recently been really interested in the derivation of Hamiltons Principle. On my research I found that with the term ##m \cdot \frac{d}{dt} (\frac{dr}{dt} \cdot \delta r) = 0## (1) one may derivate ##\delta \int (T - V) dt = 0## (2). The derivation itself I understood quiet good, but what I don't understand is where the equation (1) came from, because in my research it was just given and not derived from anywhere. Does anybody know where (1) comes from or why from it the...
Back
Top