Energy of fission reaction

It is like you go to the store, see that apples cost 30 Cents, but then you buy them for 50 Cents each because you assume they are bananas.
  • #1
bs vasanth
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The binding energy (BE) per nucleon for 235U is 7.6 Mev. The 235U undergoes a nuclear fission to produce two fragments both having a BE of 8.5Mev. What is the energy released from a complete fission of 1kg of 235U (joules)?

Here I assumed that it breaks into two 118X element. Therefore
BE(product) per atom is 2*118*8.5=2006
BE(reactant) per atom is 236*7.6=1793.6
Energy released per atom= 212.4 Mev
Number of atoms in 1 kg U=1/.235*6.022*[itex]10^{23}[/itex] = 2.5625*[itex]10^{24}[/itex]
Total energy = 2.5625*[itex]10^{24}[/itex] *212.4
= 5.4428*[itex]10^{26}[/itex] Mev
= 8.7*[itex]10^{13}[/itex] joules
I want know if my answer is correct ?
 
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  • #2
Seems about right (up to two sig. figs.)
 
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  • #3
Here I assumed that it breaks into two 118X element. Therefore
BE(product) per atom is 2*118*8.5=2006
BE(reactant) per atom is 236*7.6=1793.6
You have U235, not 236. You don't have to (and you should not) assume specific decay products, as you know the total number of nucleons both in the initial nucleus (235) and as the sum of all decay products (has to be the same).
 
  • #4
mfb said:
You have U235, not 236. You don't have to (and you should not) assume specific decay products, as you know the total number of nucleons both in the initial nucleus (235) and as the sum of all decay products (has to be the same).

Yes but U235 is stable and usual fission occurs only by bombarding with a neutron , thus making it U236 which is unstable.Also the question says it breaks up into two same products which means they should have the same number of nucleons. Therefore having an even number of nucleons is the only way it can happen which supports the stability argument .
 
  • #5
Fission does not fragment into two equal parts, you get one heavy and one light fission product and 2-3 free neutrons, e.g. I-135 + Tc99 + 2n.
 
  • #6
bs vasanth said:
Yes but U235 is stable and usual fission occurs only by bombarding with a neutron , thus making it U236 which is unstable.
U235 is not stable. While fission reactions in commercial applications are usual induced by other neutrons, this is not always the case (and the problem statement, as you wrote it, does not mention that). If you want to consider induced fission, you have to take the energy released in the U236 formation into account.

Also the question says it breaks up into two same products
Where? I just see that their binding energies per nucleon can be assumed to be the same (a reasonable approximation for typical fission products).
 
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  • #7
mfb said:
U235 is not stable. While fission reactions in commercial applications are usual induced by other neutrons, this is not always the case (and the problem statement, as you wrote it, does not mention that). If you want to consider induced fission, you have to take the energy released in the U236 formation into account.

Where? I just see that their binding energies per nucleon can be assumed to be the same (a reasonable approximation for typical fission products).

If I can't make the assumption that they are the same product how else can I solve it, and I have taken U236 for calculating the energy.
 
  • #8
bs vasanth said:
If I can't make the assumption that they are the same product how else can I solve it
You know the binding energy per nucleon, and you know the total number of nucleons.

If an apple costs 30 Cents and you have to buy 100 apples by going to the shop 2 times, it does not matter how many apples you buy each time (like 50+50 or 20+80 or whatever), the total cost is independent of that.

and I have taken U236 for calculating the energy.
Which is wrong.
 
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1. What is the energy of fission reaction?

The energy of fission reaction refers to the amount of energy released when an atom splits into two or more smaller nuclei. This process releases a large amount of energy in the form of heat and radiation.

2. How is the energy of fission reaction measured?

The energy of fission reaction is measured in units of energy, such as joules or electron volts. The total energy released in a fission reaction is typically calculated by subtracting the mass of the resulting nuclei from the mass of the original atom and then converting this mass difference into energy using Einstein's famous equation, E=mc².

3. What causes the energy of fission reaction?

The energy of fission reaction is caused by the breaking apart of atomic nuclei due to the absorption of a neutron. When a neutron is absorbed by a heavy atom, such as uranium, it becomes unstable and splits into two smaller nuclei. This splitting releases a large amount of energy.

4. How is the energy of fission reaction used?

The energy of fission reaction is used in nuclear power plants to generate electricity. The heat produced by the fission reaction is used to create steam, which then turns turbines to generate electricity. Fission energy is also used in nuclear weapons to create powerful explosions.

5. What are the potential risks associated with the energy of fission reaction?

The energy of fission reaction can have serious risks if not properly controlled. The radioactive materials produced during fission can have harmful effects on living organisms and the environment. Additionally, the potential for nuclear accidents, such as a meltdown, can have catastrophic consequences. Proper safety protocols and regulations are necessary for the safe use of fission energy.

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