Binding energy after fission and fusion

In summary, the total binding energy decreases after fission and fusion. However, the binding energy per nucleon increases.
  • #1
v_pino
169
0
I've read the following:

The total binding energy after fission and fusion decreases.

Does that sound right to you? Can you please give me some explanation also? Or direct me to webpages for further understanding of binding energy in the context of fusion and fission.

Thanks
 
Physics news on Phys.org
  • #2
Hi there,

That sounds right to me. Meaning that each nucleons is less glued after the fission of the heavy nucleus. This is precisely this "excess" energy that is release in the nuclear process (fission or fusion).

I will spare you the whole theory behind binding energy of nucleons. Instead, let's take an example to illustrate the idea. Take the nucleus U-235, which is used in the nuclear fission process. Go on your periodic table of elements, and check the atomic weight of this element. This element, once bombarded with a neutron, will fission into something like Kr-94 and Ba-141, plus a few neutrons. Check again the atomic weight of these two elements, add three neutrons to it. The weight result is not the same as originally.

There was some energy (E=mc²) lost/gain in the process. This energy is precisely the energy carried away by the different elements of the fission.

Hope this helps a bit.

Cheers
 
  • #3
Hmm... I was having a look at the 'binding energy per nucleon versus nucleon number' curve. I've been told that a large nucleus goes through fission to form smaller daughter nuclei and that small nuclei go through fusion to form a large nucleus.

This means that fission is moving from the very right of the curve to the left of the curve (not going beyond the peak); fusion is mvoing from the very left of the curve to the right of the curve (not going beyond the peak).

Doesn't this mean that, for both fission and fusion, binding energy increase?

Thanks for the previous reply. But hope my explanation makes sense and please help again. x
 
  • #4
No, the whole point of "fusion" and "fission" is that they release energy. Energy is removed from the nuceus. Binding energy in the products of both fusion and fission is less than in the inputs, accounting for the energy released.

Yes, fission "moves to the left" and fusion "moves to the right" and both are moving toward minimum binding energy in the periodic table (which is, I think, at lead).
 
  • #5
Thanks a lot - I understand that the total binding energy decrease.

But what about the binding energy per nucleon?
 
  • #6
There may be an issue of semantics here. Usually "binding energy" of a bound system is defined as a positive quantity. So something that is more tightly bound is said to have a larger binding energy, whereas the total energy of the bound system is smaller.

Therefore, when a system spontaneously splits or fuses into a lower energy state, you would say the binding energy has increased.

See, for example, the standard plot for the binding energy per nucleon:

http://en.wikipedia.org/wiki/Nuclear_binding_energy#Fission_and_fusion

where Iron (not lead) has the maximum binding energy per nucleon.

So, at least according to my understanding, the original sentence "the total binding energy after fission and fusion decreases" seems to be backwards from the standard terminology.

Edit: It would, however be correct if you just remove the word "binding". The total energy of the system decreases.
 

1. What is binding energy?

Binding energy is the amount of energy required to hold a nucleus together. It is the difference between the mass of a nucleus and the sum of the masses of its individual protons and neutrons.

2. What is binding energy after fission?

Binding energy after fission refers to the energy released when a large nucleus, such as uranium, splits into two smaller nuclei. This energy is a result of the strong nuclear force, which is responsible for holding the nucleus together. The binding energy after fission is calculated by subtracting the total mass of the products from the mass of the original nucleus.

3. How is binding energy after fusion calculated?

Binding energy after fusion is calculated by subtracting the mass of the reactants, or the nuclei that are fusing together, from the mass of the resulting nucleus. The difference in mass is converted into energy according to Einstein's famous equation E=mc^2.

4. What is the significance of binding energy in nuclear reactions?

Binding energy plays a crucial role in nuclear reactions, as it determines the stability of a nucleus and the amount of energy released during a reaction. Higher binding energy means a more stable nucleus and a greater amount of energy released during fission or fusion.

5. How does the binding energy change during fission and fusion reactions?

In fission reactions, the binding energy decreases as the nucleus splits into smaller fragments. This decrease in binding energy is responsible for the release of large amounts of energy. In fusion reactions, the binding energy increases as smaller nuclei combine to form a larger, more stable nucleus. This increase in binding energy is also responsible for the release of energy.

Similar threads

  • Introductory Physics Homework Help
Replies
1
Views
404
  • Other Physics Topics
Replies
12
Views
3K
  • High Energy, Nuclear, Particle Physics
Replies
3
Views
2K
  • Introductory Physics Homework Help
Replies
4
Views
516
  • High Energy, Nuclear, Particle Physics
Replies
11
Views
1K
Replies
2
Views
4K
  • Introductory Physics Homework Help
Replies
4
Views
757
  • High Energy, Nuclear, Particle Physics
Replies
4
Views
1K
  • Introductory Physics Homework Help
Replies
11
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
3
Views
2K
Back
Top