The calculations of the p-process in the O/Ne layers of Type II supernovae are quite successful in reproducung the solar system content of p-nuclides .
They predict , however , a significant underproduction of the rare odd-odd nuclide { } ^ { 138 } \kern - 0.8 ptLa .
A model for the explosion of a 25 M _ { \odot } star with solar metallicity is used to suggest that \nu _ { e } -captures on { } ^ { 138 } \kern - 0.8 ptBa may well be its most efficient production mechanism .
The responsibility of an inadequate prediction of the { } ^ { 138 } \kern - 0.8 ptLa and { } ^ { 139 } \kern - 0.8 ptLa photodisintegration rates in the too low production of { } ^ { 138 } \kern - 0.8 ptLa is also examined quantitatively .
A detailed discussion of the theoretical uncertainties in these rates suggest that the required rate changes are probably too high to be fully plausible .
Their measurement would be most welcome .
They would help disentangling the relative contributions of thermonuclear and neutrino processes to the { } ^ { 138 } \kern - 0.8 ptLa production .