Can we produce tritium from helium 3? If yes how?

I want to know the best and economic way of the manufacture of tritium from helium-3




From my knowledge, helium-3 is actually a by-product of tritium decaying. Tritium is usually manufactured industrially by bombarding lithium-6 nuclei with neutrons in a nuclear reactor, and is currently the cheapest way to manufacture tritium.


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In fact, producing T from 3He is straightforward. A visit to the [National Nuclear Data Files](https://www.nndc.bnl.gov/exfor/endf00.jsp) site gets you cross sections for the various reactions. 


The He3(n,p)T reaction has a cross section in excess of $10^{5}$ barns at low (thermal) neutron energies.


The Li6(n,T)He4 reaction mentioned in another answer has a smaller cross section, in excess of $10^{4}$ barns at low neutron energies, so it is about 10x less efficient to make tritium this way (not even counting enriching to get Li6 instead of Li7). 


Yet, tritium is indeed bred from Li6 in reactors. This is beacuse they use solid lithium compounds in the reactor. Trying to stuff as much He3 into the same volume would require high pressures, and you still would not get the same amount in a given reactor volume. So, they use Li6 and wait longer.


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