Jeudi 8 juillet, à 14h00
This talk will present an overview on isotopic signatures in presolar grains found in meteorites, with emphasis on noble gases in silicon carbide and nanodiamond grains. Most of the SiC grains originate from carbon stars and in the heavy elements show the signature of the s-process (slow neutron capture). Data for krypton, among others, constrain the neutron capture timescale. Cosmogenic neon in SiC offers the possibility to determine the transport time from stellar source to the early solar system, but a reliable correction for recoil loss is required. Noble gas, tellurium and (new) platinum data suggest a relation of the diamonds to supernovae (r-process, i.e. rapid neutron capture ?). One of the models suggested for explaining the Xe isotopic pattern involves a “rapid” separation between unstable precursors and stable endproducts of the r-process. A speculative interpretation for apparent 3He overabundances in nanodiamonds involves the trapping of cosmic ray 3He (rather than its production within the grains).