出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：The s-process reaction path in the vicinity of 176Lu has attracted considerable interest for a long
time. Initially, 176Lu was considered as a potential s-process chronometer due to its long half life
of 36 Gyr. However, it turned out that the hot photon bath at typical s-process temperatures leads
to thermally induced transitions between the long-lived ground state and the short-lived isomer
(3.68 h), which are otherwise strictly forbidden. In this way the effective half life can be reduced
to a few days. Accordingly, the final abundance ratio 176Hf/176Lu becomes a sensitive function of
temperature and neutron density, which turns 176Lu into an s-process thermometer. In this context,
the isomeric ratio has to be known at the temperatures of the two neutron sources of the main sprocess
component, i.e. at 9107 K (kT = 8 keV) and 2:7108 K (kT = 23 keV), respectively.
The stellar cross section feeding the isomeric state in 176Lu has been measured at kT = 5 keV
and 25 keV at the Karlsruhe 3.7 MV Van de Graaff accelerator via the activation technique. With
these results and recent TOF data for the total capture cross section, the isomeric ratio was found
to be constant in the relevant thermal energy range, in good agreement with a statistical model
calculation. In the light of the improved cross section information, the branching at 176Lu was
analyzed with respect to the temperature conditions during He shell flashes in thermally pulsing
low mass asymptotic giant branch stars.
