  A thermal pulse during the post-AGB phase of stellar evolution may lead to a
unique mode of light element nucleosynthesis. The stage is set by the ingestion
of the unprocessed envelope material into the hot He-flash convection zone
below. If the temperature is sufficiently large and the C12 abundance high
enough (e.g. T_8 > 0.8, X(C12) ~ 0.4 and X(H) ~ 1E-3) protons react faster with
C12 and form C13 than destroying Be7 The latter forms by alpha-capture of He3
after an initial reduction of the He3 abundance to about 3E-5 X(He4) by the ppI
reaction He3(He3,2p)He4 (for T_8 ~ 1). All He3 is burned within minutes to
weeks depending on the temperature. Be7 is now present at about the previously
mentioned level of He3. Its further fate is determined by the reactions
Be7(e-,nu)Li7 and the alpha-capture reactions of Be7 and Li7. These captures
lead to the production of Be11 which in turn is finally destroyed by
Be11(alpha,n)N14$. The details of this mechanism of light element production in
real stars is expected to be fairly dependent on the description of mixing.
