Why Does Fission of U235 Release More Energy Than Calculated?

  • Thread starter bphiz
  • Start date
  • Tags
    Fission
In summary, the conversation discusses the fission of U235 into Barium 144 and Krypton 89 and the resulting energy released. The missing mass on the products side is converted to 173MeV, which agrees with various sources on the difference in binding energy. However, there is confusion about why most sources state that more than 200MeV is released per fission reaction, when the calculations only result in 173MeV. The concept of binding energy and its relation to the release of energy in fission reactions is also discussed. It is explained that binding energy is not something that needs to be added to hold the constituents together, but rather a measure of the energy required to pull them apart. The difference between the binding
  • #1
bphiz
2
0
Hi all

I am struggling with the fission of U235 into Barium 144 and Krypton 89.

U= 235.044u +(1.0087 mass of neutron)=236.053

Ba=(143.923) + (Kr=88.917) +3(1.0087u)

This leaves 0.186u missing on the products side.

If this is converted to MeV I gain the value, 173MeV. This agrees with various sources on the difference in binding energy of the different isotopes.

HOWEVER most sources then go onto say that in a single fission reaction more than 200 MeV is released per fission reaction. I can not reach this number at all. Even accounting for neutrino's making some of that energy inaccessible.My second problem is I can not really wrap my head around the concept this releasing energy...

With fusion, the mass of the products and the binding energy required is less than that of the constituent particles, therefore the missing mass manifests itself as energy, easy.

However even though the binding energy per nucleon is less for Uranium:

Binding energy for an entire uranium atom 1783MeV,
Krypton 766.909MeV
Barium 1190MeV

(I looked up those binding energies and they came out slightly differently to how I calculated them using (no of protonsx1.0073)+(no of neutrons) - mass of nuclues)

The binding energy required to hold the products together is HIGHER, than the energy required to hold uranium together.

Somebody please help explain this to me:(
 
Physics news on Phys.org
  • #2
Binding energies are negative, so the higher binding energies of the products mean that energy is released.

Binding energy is not something you have to put into 'glue' the constituents together, it is actually a measure of the energy you would have to put into drag them apart. The (strong) nucelar force is sufficient to overcome the electrostatic force with a little bit to spare; that difference is what constitutes the binding energy.
 
Last edited:
  • #3
Thankyou

So why the MeV different then? 173 produced to upwards of 200?
 

1. What is nuclear fission?

Nuclear fission is a process in which the nucleus of an atom splits into two or more smaller nuclei, releasing a large amount of energy.

2. How does fission occur?

Fission occurs when a large, unstable nucleus of an atom absorbs a neutron, causing it to split into two smaller nuclei, releasing more neutrons and energy.

3. What is the purpose of fission reactors?

Fission reactors are used to generate electricity by harnessing the energy released from the splitting of atoms. This energy is then used to heat water and produce steam, which in turn powers turbines to generate electricity.

4. What are the risks associated with fission?

The main risks associated with fission are the potential for nuclear accidents and the disposal of radioactive waste. If not properly managed, nuclear reactors can release harmful radiation into the environment. Additionally, the disposal of radioactive waste can pose long-term health and environmental risks.

5. How is fission being used in nuclear weapons?

Fission is used in nuclear weapons by triggering a chain reaction of nuclear fission. This causes a massive release of energy, resulting in an explosion. The destructive power of nuclear weapons comes from the rapid and uncontrolled release of energy through fission reactions.

Similar threads

B How energy is released during nuclear fission?
    • High Energy, Nuclear, Particle Physics
Replies
4
Views
2K
I Questions about the energy released by nuclear fission
    • High Energy, Nuclear, Particle Physics
Replies
4
Views
1K
  • Poll
Source of Energy in a Fission Reaction
    • High Energy, Nuclear, Particle Physics
Replies
6
Views
4K
I Q: Binding energy per nucleon & energy released in reaction
    • High Energy, Nuclear, Particle Physics
Replies
2
Views
9K
Nuclear fission calculation of energy released
    • Introductory Physics Homework Help
Replies
9
Views
2K
Why does U235 fission to U236 18% of the time
    • High Energy, Nuclear, Particle Physics
Replies
5
Views
3K
What is the energy released from a complete fission of 1kg of 235U (in joules)?
    • High Energy, Nuclear, Particle Physics
Replies
7
Views
3K
Energy dissipated by a nuclear fission
    • High Energy, Nuclear, Particle Physics
Replies
1
Views
2K
I Why does a Mass Defect Exist if |PE| Increases?
    • High Energy, Nuclear, Particle Physics
Replies
7
Views
2K
Where does the energy from Nuclear Fission comes from?
    • High Energy, Nuclear, Particle Physics
Replies
2
Views
3K

Hot Threads

Recent Insights

Back
Top