Cameron and Fowler 1971
Cameron, A.G.W., and W.A. Fowler, 1971: Lithium and the s-process in red-giant stars. Astrophys. J., 164, 111-114, doi:10.1086/150821.
Some consequences are discussed of the possibility that helium-burning shell flashes in advanced stages of stellar evolution occasionally induce complete convection of the outer envelope down to the helium-burning shell. If the hydrogen mixing is relatively small for the first 107 seconds, the result may be the production of large amounts of heavy elements by the s-process. When complete mixing commences, the 3Re in the envelope will be converted to 7Be, and the subsequent delayed electron capture to form 7Li may allow enough lithium to remain near the surface to account for the very large lithium abundances in some S and carbon red-giant stars. On this basis the 7Li/6Li ratio in these stars should be quite large (>100).