Proton–lithium-7 fusion - energy of the two He nuclei?

In summary, the kinetic energy of the 2 helium nuclei is 17.2 MeV. Gamma rays are also negligible in this reaction.
  • #1
Sven Andersson
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In articles on aneutronic fusion, the reaction Proton–lithium-7 is mentioned as a possibility. Now I wonder; what is the kinetic energy of the 2 He nuclei? How much is gamma rays?

Proton–lithium-7 fusion p + 7Li → 4He + 4He + 17.2 MeV
 
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  • #2
I can't quickly find a cross section for that proton lithium7 reaction, but I believe its not feasible because of very low cross section compared to the more likely fast neutron fusion with lithium 7, which produces yet another neutron: n+7Li -> 3T + 4He + n - 2.5MeV.

As far as gammas go, in the light element fusion reactions in which they occur (e.g. p+D->3He+gamma), their energy is a small minority of the total energy which is dominated by the kinetic energy of the products.
 
  • #3
There will be very little in gamma rays. The energy will go into the alphas, shared equally in the center of mass frame. In the lab frame, there will be a distribution of energies with angles. It's fairly trivial to calculate this - just use energy/momentum conservation.
 
  • #4
mheslep said:
As far as gammas go, in the light element fusion reactions in which they occur (e.g. p+D->3He+gamma), their energy is a small minority of the total energy which is dominated by the kinetic energy of the products.
If the reaction produces only one nucleus, nearly the whole energy goes to the photon. The nucleus just takes the recoil, but it does not get much energy as it is heavy.
 
  • #5
mfb said:
If the reaction produces only one nucleus, nearly the whole energy goes to the photon. The nucleus just takes the recoil, but it does not get much energy as it is heavy.
Why no gamma photon then with D+T to alpha + n, with all the energy (17mev) in the KE of the products?
 
  • #6
Two nuclei (a neutron counts as nucleus here) that can both take kinetic energy and fly off in different directions to conserve momentum. The neutron will get most of the energy as it is lighter.
The larger the mass difference, the more pronounced the energy difference gets. And photons are massless.
 
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  • #7
According to the paper published by Japanese, 7Li-p fusion has high neutron yield, 2.94*10^-2 vs. much lower ~7*10^-4 neutron yields for other reactions. So, having higher neutron yield and lower cross-section, 7Li-p reaction is less attractive vs. the alternatives.

http://ci.nii.ac.jp/els/110003827252.pdf?id=ART0005015547&type=pdf&lang=en&host=cinii&order_no=&ppv_type=0&lang_sw=&no=1433835136&cp=
 

1. What is proton-lithium-7 fusion?

Proton-lithium-7 fusion is a nuclear reaction in which a proton and a lithium-7 atom combine to form a helium-3 atom and a gamma ray. This process releases a large amount of energy.

2. How is energy produced in proton-lithium-7 fusion?

Energy is produced in proton-lithium-7 fusion through the conversion of mass into energy. When the proton and lithium-7 atom fuse, their combined mass is slightly less than the mass of the resulting helium-3 atom and gamma ray. This missing mass is converted into energy according to Einstein's famous equation, E=mc^2.

3. What are the advantages of proton-lithium-7 fusion as an energy source?

Proton-lithium-7 fusion has several advantages as an energy source. It produces a large amount of energy, is relatively clean and safe, and uses readily available materials. Additionally, the by-products of this fusion reaction are non-toxic and do not contribute to air pollution or climate change.

4. What are the challenges of achieving proton-lithium-7 fusion as a viable energy source?

One of the main challenges in achieving proton-lithium-7 fusion as a viable energy source is the extremely high temperatures and pressures required for the reaction to occur. This requires sophisticated and expensive equipment, as well as advanced materials that can withstand the extreme conditions. Another challenge is the containment of the plasma, which is necessary for sustaining the fusion reaction.

5. How close are we to using proton-lithium-7 fusion as a practical energy source?

Currently, we are still in the early stages of developing and testing proton-lithium-7 fusion as a practical energy source. While there have been successful demonstrations of the fusion reaction, there are still many technical challenges that need to be overcome before it can be used on a large scale. However, with continued research and advancements in technology, it is possible that proton-lithium-7 fusion could become a viable energy source in the future.

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