Distribution of released energy in nuclear fusion

In summary, on Wikipedia, we can find various channels of nuclear fusion reactions, including combinations of hydrogen isotopes that result in the production of helium and energy release. The released energy is usually in the form of kinetic energy of the products, but there is a possibility of gamma ray emission. However, the total energy must be conserved and in cases where only one nuclide is produced, the entire energy cannot be transferred to that product. The CNO cycle, a type of fusion reaction, also involves the emission of gamma rays and positrons.
  • #1
Toreno
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Hi,

On Wikipedia (here), we can find that in following channels of nuclear fusion reactions:
H-2 + H-3 -> He-4 (3.5 MeV) + n (14.1 Mev)
H-2 + H-2 -> H-3 (1.01 MeV) + H-1 (3.02 MeV)
H-2 + H-2 -> He-3 (0.82 MeV) + n (2.45 MeV)
H-2 + He-3 -> He-4 (3.6 MeV) + H-1 (14.7 MeV)
The released energy is always distributed between products.
But I have a few questions regarding above and other reaction channels:

1) Does this energy always manifests as kinetic energy of products?
2) If no, does the product nuclide can be created in excited state (and consume some of kinetic energy)?
3) or may a gamma photon be emitted consuming some the energy?
4) and finally, if only one nuclide is produced (e.g. He-4), does whole energy is transferred to that product?

Oh, I am talking about reactions in low energies, up to ± 30 MeV.

Many Thanks,
Toreno
 
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  • #2
Toreno said:
1) Does this energy always manifests as kinetic energy of products?
Most of the time. All those reactions can happen with the emission of gamma rays (directly), but that is a rare process. I don't think there are nuclear excitations that don't decay via proton or neutron emission (which effectively looks like a different reaction then).
Toreno said:
4) and finally, if only one nuclide is produced (e.g. He-4), does whole energy is transferred to that product?
That would violate energy-momentum conservation.
 
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  • #3
Hi,

Thank you for fast response.
Could you please expand a little more that energy-momentum violation?

Thanks,
Toreno
 
  • #4
Toreno said:
Could you please expand a little more that energy-momentum violation?

Suppose for the sake of discussion that the fusion reaction X + Y --> 4He exists, and that there are no other products (e.g. gammas).

Recall that in a fusion reaction that releases energy, the sum of the masses of the reactants must be greater than the sum of the masses of the products. In this case, we must have

m(X) + m(Y) > m(4He).

Consider this reaction in the reference frame in which the final 4He is at rest. That is, its kinetic energy K(4He) = 0. The total energy must be conserved. Therefore we must have

m(X)c2 + K(X) + m(Y)c2 + K(Y) = m(4He)c2

The previous condition then implies that either K(X) or K(Y) or both must be negative. But kinetic energy can't be negative!
 
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  • #5
Ok, I got this now. Thank you for. Thank you for explanation!
 
  • #6
The CNO cycle emits 3 gamma rays in each turn of the cycle, and 2 positrons, which, upon annihilation, generate 4 additional gamma rays, bringing the total to 7.
 

1. What is nuclear fusion?

Nuclear fusion is a process in which two or more atomic nuclei fuse together to form a heavier nucleus, releasing a large amount of energy in the process. This is the same process that powers the sun and other stars.

2. How does energy released in nuclear fusion compare to other energy sources?

The amount of energy released in nuclear fusion is significantly greater than other energy sources, such as fossil fuels or nuclear fission. In fact, one kilogram of fusion fuel can produce as much energy as 10 million kilograms of coal.

3. How is the released energy distributed in nuclear fusion?

The released energy in nuclear fusion is distributed in the form of high-energy particles, such as photons and neutrons. These particles are emitted in all directions, creating a large amount of heat and light.

4. What are the challenges in harnessing the released energy from nuclear fusion?

One of the main challenges in harnessing the released energy from nuclear fusion is containing and controlling the extremely high temperatures and pressures required for the fusion reaction to occur. Additionally, finding materials that can withstand these conditions and developing efficient methods for extracting and utilizing the energy are also major challenges.

5. Can nuclear fusion be used as a source of renewable energy?

Yes, nuclear fusion can be considered a source of renewable energy as it uses abundant resources, such as hydrogen isotopes found in water, and does not produce carbon emissions or long-lived radioactive waste. However, it is still a developing technology and has not yet been successfully implemented on a large scale for energy production.

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