The puzzle of the synthesis of the rare nuclide La

Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium

Corresponding author: S. Goriely, sgoriely@astro.ulb.ac.be

Received: 27 June 2001
Accepted: 3 July 2001

Abstract

The calculations of the p-process in the O/Ne layers of Type II supernovae are quite successful in reproducing the solar system content of p-nuclides. They predict, however, a significant underproduction of the rare odd-odd nuclide ¹³⁸La. A model for the explosion of a 25 star with solar metallicity is used to suggest that -captures on ¹³⁸Ba may well be its most efficient production mechanism. The responsibility of an inadequate prediction of the 138La and ¹³⁹La photodisintegration rates in the too low production of ¹³⁸La 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 ¹³⁸La production.