What will happen if I fire a proton beam at a Lithium-6 nucleus? What products will it produce? Is it exothermic and if so, how much energy is released? How would you calculate it?
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$\begingroup$ Well, fission is very unlikely to occur with such small masses $\endgroup$– Orion 73Commented Apr 23, 2020 at 12:42
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1$\begingroup$ @Orion73 - and yet, when you hit $^{7}$Li with a proton you get 2 $\alpha$ particles... $\endgroup$– Jon CusterCommented Apr 23, 2020 at 13:46
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3 Answers
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As with many nuclear physics questions, a good first place to look is your local Evaluated Nuclear Structure Data File source (I generally use the mirror at Brookhaven.
Adding a proton to Lithium-6 makes a compound nucleus with mass 7, so enter 7 in the search box and hit Search. Look down the list until you get to $^{7}$Be. There you will see an entry for "6LI(P,P),(P,2P),(P,PA)" - those are the reactions that have been found and used for mapping the $^{7}$Be energy levels.
Another good resource is the Nuclear Data Evaluation Project at the Triangle Universities Nuclear Laboratory. There you can search by mass, and in particular pay attention to the Energy Isobar diagrams. There you will see that $^{6}$Li+p comes in some 5.6MeV above the $^{7}$Be ground state, and not near any excited nuclear states.
So, you have a variety of reactions that are possible.
answered Apr 23, 2020 at 13:45
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In addition to the reactions explained in the other answers, there are several other processes that can happen:
Elastic scattering, in which the proton scatters off of the whole nucleus at once without producing anything new;
Quasielastic scattering, in which the proton scatters off of a single proton or neutron inside the nucleus without producing any new matter;
Coulomb excitation, in which the proton inelastically scatters off of the nucleus, exciting it to a higher energy level; and
Resonance production, in which the proton inelastically scatters off of a nucleon, converting it to a higher-mass baryon.
These are arranged roughly in order of increasing momentum transfer; elastic scattering happens at low momentum transfer, and resonance production happens at higher momentum transfer.
At even higher momentum transfer (above a few proton masses), nucleon-nucleon interactions give way to interactions between quarks and/or gluons, and the collisions begin to look more like proton-proton collisions in the LHC (modified to account for all of the "spectator" nuclear matter surrounding the collision area), in which all manner of exotic matter can be produced.
answered Apr 23, 2020 at 16:01
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Wikipedia gives the following sequence of reactions for lithium burning, but unfortunately it does not mention how much energy it produces. This sequence is often classed as a fusion reaction, although the last step does involve fission. Many writers prefer to just call it lithium burning.
$$\begin{align}\\ \mathrm p+{}^6_3\mathrm{Li}&\longrightarrow{}^7_4\mathrm{Be}\ \text{(unstable)}\\ ^7_4\mathrm{Be}+\mathrm e^-&\longrightarrow{}^7_3\mathrm{Li}+\nu\\ \mathrm p+{}^7_3\mathrm{Li}&\longrightarrow{}^8_4\mathrm{Be}\ \text{(unstable)}\\ ^8_4\mathrm{Be}&\longrightarrow{}2\ ^4_4\mathrm{He}+\ \text{energy}\\ \end{align}$$
These reactions can occur at a lower temperature than the standard proton-proton chain, which is the dominant family of fusion reaction in stars less than 1.3 solar masses. (The CNO cycle is more important in larger stars).
Lithium burning is important in T Tauri pre-main sequence stars.
